# Chapter 13: Initiation Systems

Initiation systems have been developed to control the release of explosive energy in a productive and safe sequence. They time the sequence of detonation of multiple explosive charges in a blast to control breakage, rock movement, and adverse environmental effects of the blast. These environmental effects include vibration, noise, and flyrock. The good results of any blasting operation will be achieved only when the initiation system has been carefully chosen and utilized.

The various systems available transmit a signal from borehole-to-borehole or charge-to-charge with varying timing accuracy in short time intervals. These intervals can vary from microseconds to seconds. This chapter describes the systems used and the technical aspects of their design, construction, and general use techniques.

Good results from any blasting operation can be achieved only when the initiation devices used to detonate the explosive charge are carefully chosen and properly utilized. Initiation devices discussed in this chapter include detonators and blasting caps as elements of systems (electronic, nonelectric, electric, detonating cord, and fuse), and the devices for assembling and initiating these systems. It will also discuss the systems of hardware and in some cases software required to utilize the various systems. Because all initiating devices are made to explode, they should be handled and used with the same care and caution used with all high explosives. They should not be physically abused, tampered with or altered in any manner or exposed to sources of extraneous electricity that may be hazardous. Such treatment can result in premature detonation and serious injury. These small and brightly colored initiating devices attract a child's attention and must be closely inventoried and locked up when not in use. Initiating devices fall into two broad groups: electric and nonelectric, depending on their primary source of initiation energy.

Each initiation system has unique physical properties, performance characteristics, and application uses. They all can be the potential causes of a misfire or blast malfunction. It is important that the blaster review and understand all manufacturers' recommendations prior to use. The manufacturer's technical literature and training must be thoroughly consulted and utilized. All questions about function, construction, quality, or application must be referred to the manufacturer of the system.

Initiation systems and delay detonators allow the blaster to separate detonations by their charge weight when required. This is often considered to be 8 milliseconds (ms). It is important that detonation events occur within an accuracy standard that is shaped by the separation distance of the charges, the physical characteristics of the rock and the timing effects desired. Proper breakage and control of muckpile shape and flyrock are dependent on accurate blast timing.

## General Timing Performance Characteristics

The importance of timing cannot be overemphasized. Detonators and initiation systems provide the timing necessary to separate charge detonations for optimum fragmentation and minimum impact on the surrounding environment. The accuracy and precision of these units is critical to their performance.

### Timing Function

The blaster has a great many timing choices available including both instantaneous and delay intervals. These choices offer the blaster a wide variety of options for the varying blasting needs. Detonator manufacturers have long produced two basic series of delay detonators, the millisecond or short-period (MS) delays, and the long-period (LP) delays, also sometimes called "mine" or "tunnel" delays. The MS series progresses in intervals of tens of milliseconds, and the LP series may have intervals of hundreds of milliseconds in the faster end of the series, up to seconds in the higher end of the series. These two series of delay detonators vary in the number of available delay periods and at times the two series are combined to extend the total blast function time. These are concepts of delay detonators embrace a multitude of industry or applications requirements with the LP delays being used primarily in underground mining.

### Timing Accuracy and Precision

Three statistical factors (mean, distribution, and standard deviation (SD)) define the timing accuracy of delay detonators and the probability of overlap between the detonations of adjacent delay periods. These factors summarize performance of groups of detonators manufactured in batches or lots. All advertised detonator firing times represent design or nominal values, and may not accurately represent the precise time of detonation. Firing times, when evaluated statistically from a normal distribution, Figure 13.1 shows how the distribution of firing times varies from tight or "A", (desirable) to wide or "C", (undesirable).

![Figure 13.1 - Firing time distributions. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 12.4)](images/222.png)

The mean or average firing time for any group of detonators typically as slightly offset from the nominal firing time. This shift of the mean from the nominal is the first timing accuracy factor. The second factor is the distribution of the firing times around the mean or nominal firing time.

A tight distribution of the firing times and a small displacement of the mean firing time from the nominal indicate a precise and accurate delay detonator. In electric and nonelectric delay detonators the timing function is controlled by a delay element that has a bead, core, stack, plastic, or other cylindrical casing and a pyrotechnic (dry chemical mixture of burning compounds) core. To illustrate distinct features see the construction section of each detonator type in this chapter. This core will be initiated by the energy from electrical source wiring a match head, the shell explosion of shock tube, or electric discharge of a capacitor igniting a fuse head. The delay core burn rate is a rate that is primarily controlled by its length. The quality of manufacture, temperature, humidity, internal pressure of the detonator during burning time, and also have an affect on the actual burn time of the delay element. All delay detonators, depending on the reactive ingredients, slow down to some extent as they age.

Using delay detonators of approximately the same manufacturing date will reduce timing errors caused by these characteristics. In the case of ms delay detonators where the interval between delays is 25 milliseconds, if the total deviation from nominal is less than 12.5 milliseconds, no overlap will occur. Expression 13.1 describes a timing standard for 25 millisecond detonators whose probability of overlapping is 0.0% or at 1 time in 1,000 events.

<!-- VERIFIED -->
$$12.5 \text{ ms} \leq 1.5\sigma$$

**Expression 13.1 (for 25 millisecond detonator)**

Where:
- $\sigma$ = Standard deviation of firing times
- Average (mean) of firing time
- is equal to or less than

In situations where the time intervals between electric detonators are to be reduced by the use of the sequential timer, the timing accuracy required of delay detonators is considerably increased. Not only must there simply be no overlap between detonation events, but a high probability must be assured that the required minimum interval can consistently be achieved.

Standard statistical analysis states that any manufactured lot of detonators has 68.8% of its values fall within 1 standard deviation either side of the mean (average) value, 95.5% within 2 standard deviations either side of the average, and 99.7% within 3 standard deviations either side of the average. This means that 99.7% of the firing time of a lot of detonators will fire within 3 sigma or (6) standard deviations, 3 standard deviations either side of the mean. The widely accepted value for 1 standard deviations in modern pyrotechnic delays is approximately 1.5% of the nominal time. If we take a 350 millisecond detonator with a 3 (of 1.5% (5.25 milliseconds), the 6 SD range is 31.5 milliseconds. This range of times can be magnified when using different lots of detonators within the same blast, or different lengths of shock tube or legwire. Different shock (tube or legwire length) products are potentially of different manufacturing lots of delay component.

Detonator accuracy is evaluated by how close the average firing time occurs to the design or advertised time. Detonator precision is a measure of how tight all of the firing times come to the average for the lot. This average may or may not be close to the nominal. Figures 13.2a and 13.2b illustrate the difference between timing accuracy and precision. Good accuracy with precision is illustrated in figure 13.2c.

![Figure 13.2a - Timing accuracy. (Courtesy: Dyno Nobel)](images/223.png)

![Figure 13.2b - Timing precision (Courtesy: Dyno Nobel)](images/223.png)

![Figure 13.2c - Timing accuracy with precision.](images/223.png)

### Activation Energy

The signal that triggers detonator functioning can be (1) an electric current, (2) an encoded signal, (3) the shock and heat from a dust explosion, (4) a detonating cord or another initiator, or (5) the spit from safety fuse. All detonators are designed to reliably initiate when subjected to an energy input above a designed minimum threshold level (activation energy). All contain an explosive train that, once initiated, transitions to detonation.

The explosive energy yield of these devices is designed to efficiently initiate detonator sensitive explosives. In situations where very low ambient temperatures or insensitive explosives are to be detonated, increased output energy initiator products should be used.

### Output Energy

The output energy of detonators is rated on an historic equivalency scale to the output of specific charge loads of mercury fulminate. Currently most commercial detonators are made with strengths at or higher than the No. 6 strength level (equivalent to the energy output of one gram of a mixture of 80% mercury fulminate and 20% potassium chlorate). Some detonators designed specifically to initiate shock tube (starter units) are also available, and their strength is often well below the No. 6 level. Caution must be taken not to confuse these with "high strength" detonators.

### Test Detonators

Output energy is particularly important in the determination of an explosives safety UN shipping classification and ATF storage requirements. An explosive material will detonate with an IME No. 8 TEST DETONATOR when the material is unconditioned (IME: SLP 12, 2010) is normally classified as Explosives 1.1. The No. 8 test detonator in the U.S. is defined to have the output energy of 0.40 grams (400 milligrams) to 0.45 grams (450 milligrams) of PETN, whereas outside the U.S. it is generally defined as having the output energy of 0.75 grams(750 milligrams).

### High Strength Detonators

High-strength detonators have become the norm in North America in order to assure reliable initiation of the newer, more insensitive explosives products. These new explosives are especially susceptible to becoming less sensitive at colder temperatures and the stronger detonators serve to overcome this problem. "High-strength" detonators may contain nearly 1 gram (15.4 grains) of pentaerythritol tetranitrate (PETN) or cyclotrimethylenetrinitramine (RDX) in the base charge.

In the U.S. these detonators have not been tested by accepted scientific procedures to determine where they fit into the historic mercury fulminate rating system of number 1 through number 8, thus no specific "strength" number can be assigned to them but are certainly of greater strength than the number 8 designation. Where explosive energy outputs in excess of those available from the basic charges are required, small boosters containing from 1 gram to 10 grams (0.035 ounces to 0.35 ounces ) or more of explosives are available that may be used in conjunction with the detonator.

### Redundancy

This is a feature of some initiation systems that provides a second surface path for down-the-hole initiation if the desired path is interrupted by ground movement, or it fails to initiate for some other reason. The benefits of a second path of initiation are somewhat offset by the possibility of shot timing being adversely altered and boreholes detonating out of sequence resulting in noise, vibration or flyrock. This can be applied to both electric and nonelectric systems, but is most often thought of with regard to nonelectric systems due to the lack of circuit test capability with that type of initiation.

## Detonator Categories

Detonator categories are based on whether or not they initiate instantaneously or provide timing intervals. If they provide intervals they are categorized as either MS or LP. There is a category of millisecond detonators designed specifically for use in underground permissible atmospheres.

### Instantaneous Detonators

Instantaneous (zero delay) detonators are manufactured in all output strengths and may be either electric or nonelectric. The nomenclature "instantaneous" is somewhat misleading as the function times can be as long as 5 milliseconds or as fast as 0.250 milliseconds (250 microseconds), after the application of the initiating energy. The function times of zero delay electric detonators depend to some extent on the level of initiating current supplied, with faster detonation times resulting from the application of higher electrical current. The function time of zero delay nonelectric detonators must include the travel time of the initiating signal through the cord or shock tubing, and the speed of reaction of the electric match head in electric or electronic detonators. This absolute function time can be very important in seismic applications.

### Millisecond Delays

The application of millisecond (MS) delay blasting techniques has long been proven to improve rock fragmentation and displacement; provide greater control of blasting vibrations, decrease blast hole sand rock throw, reduce powder factors, and reduce blasting costs. The most common selection of delay intervals for the millisecond delay detonator is 25 milliseconds. This sequence of delays is numbered starting at zero or one (1) and may be found with 35 or more delay periods. The initial group of 25 millisecond intervals between delays is typically followed by a short group of 50 millisecond intervals with some manufacturers offering a continuing group of 100 millisecond intervals. Nonelectric millisecond delays may have similar intervals as noted above, but are also available in a series specifically designed for nonelectric applications. Delays such as 9, 17, 25, 35, 50, 65, and 100 milliseconds might be found for in-hole delays, and they are readily available in nonelectric surface delays.

The use of sequential blasting machines with electric detonators has made these newer delay values available for offsetting the in-hole detonators at more useful times. The sequential times may also be electronic in construction and accuracy and this will improve overall accuracy of the timing in a blast. Chapter 14 discusses the importance of proper timing for rock movement and the creation of relief. Chapters in part III of this book show some uses of these delay series. Refer to manufacturers' technical information literature for specific product information.

Millisecond delays are the most widely used delay detonators for quarrying, open pit, and construction projects. They are also used in underground mines for multiple row slabbing blasts, stope blasts, and other production blasting where zones of delay are breaking to a free face. They can be used in the burn or "cut out" when the spacing and timing have been designed to produce adequate rock movement.

Typically, millisecond delay blasts will move rock farther away from the face than the long period (LP) delay detonator series because they permit interaction between adjacent boreholes. Short millisecond delays, however may increase flyrock and airblast potential, so caution and good blast design practices are necessary for optimal performance. A different colored leg is used for each delay period, attached at the mid of the shock tubing or on one legwire, to show both the delay sequence number, i.e., No. 9, and the millisecond timing, i.e. 225 milliseconds.

### Long Period Delays

Long period (LP) delay detonators are used principally in underground mining operations for driving drifts and tunnels, blasting raises, and sinking shafts. In many cases they also find use in sloping in metal mines, on certain utility projects, and other work which requires longer time intervals between borehole detonations. Delay intervals in this series number in the 100 millisecond to 1 second range and many manufacturers offer fractional delay periods such as ½, ¼, ½, etc. to supplement the series in the early firing time range. Shock tube delays for tunneling may follow the same patterns as electric or sonic product lines, but some lines are in use which have both in-hole and surface times so that a blast pattern may be entirely hooked up using a single in-hole delay number.

### Coal Mine Delays

Coal mine delays are electric detonators designed for use in permissible (gasseous) applications, primarily in underground coal mines. Nonelectric systems are not "permitted" in underground coal mines in the United States. Recommendations of the U.S. Mine Safety and Health Administration (MSHA) for short-period delay blasting in underground coal mines specify delays periods between 25 ms to 500 ms are accepted to fire short delay detonators up to 1,000 ms, instantaneous detonators and long period delay detonators for anthracite mines. The detonator shells cannot be made of aluminum. Coal mine detonators are normally supplied only with iron or copper-clad iron legwires to allow for magnetic removal from the coal. The legwire insulation and identifying bands are color-coded for identification of each delay period. Coal mine delays are clearly marked on detonators and their cartons as shown in **figure 13.3**.

![Figure 13.3 - Coal mine delay electric detonators. (Courtesy: Austin Powder Company)](images/226.png)

## Electronic Systems

The electronic detonator is the most recent development in blasting initiation technology. One of these benefits is very precise and accurate timing. Each electronic detonator contains an integrated circuit chip and a capacitor to control the initiation time and provide voltage to fire the bridgewire (match head). Because of this electronic timing control, the concerns of accuracy and precision previously discussed are now negligible. Uniquely designed control equipment (blasting machines) and communication devices are also used in conjunction with these detonators. The ability of using very long program times (up to 20,000 milliseconds) with electronic systems is also a new and very useful feature.

Manufacturers have developed several types of system and control equipment (See figure 13.4) to utilize the nearly absolute accuracy and precise timing available with a microchip-timing device. These systems utilize varying methods to identify and communicate with the detonators for testing, addressing, and firing time assignment. In addition, manufacturers have developed different combinations of communication, voltage, and coding to operate the systems during communication, arming, and firing.

![Figure 13.4 - Typical electronic system components. (Courtesy: Orica USA)](images/226.png)

In the past decade electronic detonator systems have proven their use and performance in all blasting applications. Surface, underground, demolition, and specialty blasting projects have been successfully implemented using these systems. Their use to improve fragmentation and equipment productivity, and to reduce vibration, overbreak, airblast, and flyrock risk has been well proven. Methods for their efficient utilization have been developed and extensively documented.

### Use Benefits

As discussed, accuracy and precision are no longer a significant concern with electronic detonators. The near absolute timing of electronics has allowed significant improvement in blasting results of fragmentation, vibration control, and air blast control. The signature hole analysis technique has also proved its validity through the use of electronic detonators. Blasters throughout the world have now proven time and again the value of the proper use of electronic detonators and their utilization techniques.

The ability to accurately and precisely program electronic detonators now permits the simultaneous initiation of two or more primers in a single column. Blasters have long speculated the effect from this simultaneous initiation, and they have now realized improved vibration and fragmentation from this simultaneous initiation. Some experts contend that the results are from colliding shock waves at a point half way between the initiation points, and others claim it is due to the release of the explosive energy in half the time versus single priming. In either case, the benefits have proven real in many case studies.

### Use Limitations

With all the apparent benefits listed above, the blaster must realize the limits and potential hazards of using an electronic detonator system. Communications within the wired systems are very critical and specific. Disruptions due to stray current, static electricity, or direct electrical current is their primary limiting use factor. Intended blasting areas must be checked for these electrical hazards and any that are present must be brought within manageable ranges before any loading begins. Caution must also be taken to prevent any lead-in-lines or connecting wire from contacting overhead power lines as a result of ground movement during the blast. There have been many instances of injury and death of blasters at the blasting machine being shocked by circuit line-wires that contacted the lead-in-line or connecting wire that was contacted overhead power lines.

Currently the cost of electronic detonator systems has been much higher than electric or nonelectric. It is expected that these cost differences will decrease as they become more widely used. Many blasters have concluded that the total cost of the operation has been reduced, fragmentation improved, and vibration and airblast reduced with the proper applications of electronic detonators.

Some systems require special configurations and wire metals for proper signal transmission. These special wires can be for connections within the blast and lead line to the blasting control equipment. Check the manufacturer's technical literature or support for these requirements.

Due to the sensitive nature of electronic circuits wires in robust protective delay construction, shock and pressure sensitivity may be an issue. The internal construction, mounting, and protection of the electronic circuit determine the detonators' resistance to shock and pressure. Caution should be used in tight underground or surface blasting (parallel borehole rounds, ditching, or pressure sensitive rock formations) unless the electronic detonators are durably constructed or protected by external means. Some manufacturers make outer sleeves or lined cast boosters available with electronic detonators.

### Characteristics

All electronic systems share three characteristics that have to be met before they can detonate. As they all have an "intelligent" integrated circuit chip that controls the function of the detonator, they must be assigned a firing time as the detonator memory for the clock to count (programmed). Second, they must then be given an electrical charge that will power the circuitry, and provide enough voltage to fire the fuse head. Third, they have to be given the command to fire. This is a chain of events that if one step is interrupted or eliminated, then the result will be a no fire.

Today's wired electronic systems normally have two separate components. These are the detonators themselves; and the control systems and hardware needed to test, communicate, program, arm, and fire the detonators. In the case of the detonator, each system has a logic chip to control timing and communications, and an internal capacitor that must be charged to program arm and fire the detonator. This capacitor is a device that will store enough energy to fire the fuse head in the detonator, which will initiate the fuse charge once the timing clock has counted down to the assigned firing time. Blasters must consider this internal power source at all times when selecting and using an electronic detonator. The procedures, protocols, voltage levels of the system must be understood; therefore extensive training by a manufacturer's representative is a must.

### Construction

Virtually all electronic detonators appear to be similar or identical to conventional electric detonators. The only exception is a nonelectric, shock tube product not presently in wide use, and this looks exactly like a conventional nonelectric detonator. In each case, the difference in the detonator is internal. The operation of the electronic detonator obeys an external controller that will energize the electronics and capacitor to provide power to operate the internal clock and provide enough power to fire the electric match and initiate the base charge. Figure 13.5 shows the internal construction detail of an electronic detonator.

1. Base charge
2. Ignition charge
3. Fuse head (specific design promotes accuracy and precision)
4. Integrated circuit chip
5. Capacitor (energy storage device)
6. Filtering safety device (excludes non-specific energy inputs and overloads
7. Housing legwires
8. Seal

![Figure 13.5 - Electronic detonator construction (Dyno Nobel: Persson, 1992, Humistal, 1999).](images/228.png)

These are the internal components of every electronic detonator using wires as an energy input path. The nonelectric electronic detonator mentioned above will have elements 6 and 7 replaced with an energy conversion unit to change the shock wave reaction of the tube to electrical energy for the circuit chip and capacitor, and an incoming shock tube.

### Performance Features

The accuracy and precision of electronic detonators is nearly total. Nearly all present electronic detonator manufacturers supply products that can supply an accuracy of +1 milliseconds across the range of delay intervals their units have. These delay ranges can be up to 20,000 milliseconds (20 seconds) and can usually be established at 1 millisecond increments. This nearly no range of error delays allows greatly expanded possibilities for timing and creative blast designs. Caution should be used to stay within conventional industry practice unless good practices or experience allow otherwise.

Electronic accuracy enables the blaster to create delay time intervals that may be outside recommended or regulatory design interval (+5milliseconds). These short times should be used with caution, and only with experience or recommendations of blast design tools such as signature hole analysis. The large number of available times allows the complete arming of all detonators in very large blasts. And these long times using electronic detonators permit the firing of a signature hole with or as part of a full production blast and allow the arming of all boreholes in the blast. The time between the signature hole and the rest of the blast can be long enough to allow the recording instruments to reset for the second record.

The integrity and functionality of the wiring harness and detonator electronics can also be tested in the wired systems. In addition, routines to test the functionality and power levels of any control equipment are also available.

### Safety Features

Due to the communications, voltage, and frequency protocols used in the individual systems, they are generally believed to be less susceptible to stray current or static electricity premature detonation. Very specific commands at specific voltages and frequencies are needed to begin and sustain any communication with the detonator or its electronics. These electronic features can make the products more secure from accidental detonation by unauthorized personnel by readily available electrical sources. Some systems have imprinted or stored identification features, that make inventory and usage records very accurate.

> **Caution**
>
> In the presence of lightning, operations involving the handling and loading of explosives should be immediately suspended and the areas secured until the threat is gone. In the United States federal regulatory authorities forbid the handling and loading of explosives upon the approach of a storm.

### Accessories and Tools

As described above, all wired electronic systems must have in addition to the detonators themselves, various pieces of communication and control equipment. This hardware facilitates the testing, addressing, programming, arming, and firing of the electronic detonator circuit. The testing and control equipment usually consists of two separate components. One is used normally for testing, programming (when necessary) and communicating with individual detonators or groups of detonators and is normally used at the blast bench or face. These pieces of hardware are normally voltage and software limited so they cannot create some or all of the three steps needed to fire the detonator. The second component is a blasting machine or control device that will perform the final stages of blast preparation. These are only used after the blast area and safety perimeter have been cleared of all personnel and equipment. The blasting machine has the voltage levels, software, and communications capability to integrate the three steps needed to fire the detonators.

Some manufacturers have created software that allow design and timing of the blast on a computer. These programs can plot by hand or import hole collar coordinates, create and save various timings for a blast, and output a printed or electronic copy of the blast tie-in and timing. In addition, some may be able to simulate the blast detonation and calculate direction of movement and timing per ms of burden. Some systems allow downloading of firing times to on the bench devices or blast machines for assigning firing times (programming). Recent refinements have added remote firing capability to these very valuable tools.

### General Use Techniques

The delay pattern design method of an electronic blast is nearly identical to that done with conventional electric or nonelectric initiation systems. A diagram with borehole location and firing times should be created before loading begins.

> **Manufacturer's Recommendations**
>
> Electronic initiation systems are available from a number of manufacturers. Many electronic system products made by different manufacturers look alike but should not be mixed within a blast. The manufacturer's recommendations must be followed and training by their representatives is important for proper and reliable operation of these systems.
>
> Each electronic initiation system may have a unique method or device for connecting downhole connections to trunklines or firing lines, and blast arrays to lead-in-lines. Connections on the bench or to blast machines may also be different. The manufacturer will specify these methods and devices in their training and technical literature.

As the previous discussion clearly indicates, wired electronic systems can be very complicated and require hardware and software to operate properly. It is a necessity that the blasters' have extensive training; and operating and troubleshooting support from the manufacturer. All manufacturers' training and recommendations should be strictly followed.

## Shock Tube Systems

Shock tube nonelectric systems have come to dominate the initiating system market in the past several decades. Their ease of use, durable construction, intuitive layout, and electrical insensitivity has made them one of the most widely used systems in the world.

This classification includes those activated by detonating cord, and shock tubing. In the past, a gas activated system was in wide use, but it is obsolete in North America, and its use is not presently known outside North America. It will not be discussed in this handbook.

The advantages of nonelectric versus electric initiation systems are perceived to principally be their lack of susceptibility to premature activation by extraneous electrical energy. Additional advantages are the ease of hookup and the relatively simple activation devices that most systems use. The principal shortcoming of most nonelectric systems is the lack of a circuit testing capability.

Shock tube initiation systems have proven their dependability and flexibility in most blasting applications. From small-scale quarry and construction blasts to very large and complicated surface and underground blasts. Many configurations and applications have developed since their inception, and they have become very flexible.

### Use Benefits

Electrical insensitivity is the main benefit of using shock tube systems. Their proven ability to be safely loaded and fired in high-static, high-stray current environments has been a great improvement in blasting safety for all users. The often simple and intuitive (logical) tie-in process has also made more effective blast timing and control available to blasting personnel worldwide. Nonelectric shock tube systems can replicate timing patterns once only possible by using electric detonators with sequential timers.

### Use Limitations

The primary objection to nonelectric shock tube systems has been the inability to check the circuit for continuity and condition. The blaster is totally dependent on the manufacturers to have effective quality control processes in place to ensure proper and complete filling of the shock tube, and the error proof assembly of the shock tube to detonator connections. The use of double or redundant nuts in the borehole and on the surface greatly increases the reliability of shock tube systems. Redundancy also reduces the firing time scatter of the system.

### Characteristics

Shock tube systems may be found with a great many varieties of fittings and configurations, depending on the application and the particular manufacturer's product in use. These systems are the most common initiation system used today and are continuing to replace both electric detonator and detonating cord downline systems. In general, the products discussed in this chapter are manufactured by most initiation system component.

In normal practice the tubing remains intact after activation, and except for the disappearance or discoloration of the internal coating, appears as it did prior to activation. Under certain circumstances, however, tubing may rupture and vent hot gases through the opening. For this reason is it never advisable to hold the tubing in the hand during initiation. A variety of shock tube system configurations are available for specific applications. Millisecond trunkline delay assemblies are used for surface blasting. Also available under a variety of trade names are assemblies with a delay unit attached to one end of the shock tube and a conventional shock tube delay detonator to the other. These directional devices are used to generate individual borehole delays in a modified series hookup. These shock tube initiation systems are very application flexible with the hookups and timing configurations easy to design and execute. For specific information the various manufacturers should be consulted.

### Construction

Nonelectric shock tube is a plastic tube coated with a thin layer of reactive material on the inside. The plastic shock tube is composed of one or more layers of plastic which are designed to enhance the physical properties (tensile strength, flexibility, and abrasion resistance). The thin interior coating of reactive dust (HMX and aluminum) is bound to the inner wall of the tube. The inner tube wall may be coated with other materials to provide additional water and abrasion resistance. Figure 13.6 is a cross section of the construction of standard shock tube and figure 13.7 illustrates the cross section of a shock tube detonator.

![Figure 13.6 - Shock tube construction (Dyno Nobel).](images/231.png)

![Figure 13.7 - Shock tube detonator construction (Source: ISEE Blasters Handbook™ 17th Edition, figure 12.3).](images/231.png)

### Performance Features

The shock tube is very insensitive to initiation by ordinary heat or impact and requires an intense high impulse shock to be energized. The most commonly used initiation sources are various forms of mechanical devices that utilize a short shell primer activated by a firing pin. Also used is a handheld initiation device, which generates energy by using a piezoelectric crystal. Tight connections to appropriate strength detonating cords or starters also serve as means of initiation.

The reactive material is composed of the high explosive octogen (HMX) mixed with aluminum, and is held on the inside wall of the tubing by a static charge. When sufficient shock is delivered to the tubing the reactive components are shaken loose from the wall and the ignition propagates similar to that in a cool dust explosion as an undergrounded mode. This reaction continues, generating a shock wave within the tube as shown in figure 13.8 that travels at a rate of approximately 6,500 feet/second (1,981 meters/second). Nonelectric shock tubing has no adverse effects on the explosive in the borehole.

![Figure 13.8 - Shock tube functioning mechanism (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.1)](images/232.png)

### Safety Features

Three important features create the electrical safety of the system. The high-resistivity of the plastic tube is the first feature, although the tube will conduct static, and stray or other electrical currents. This conductivity is much lower than electrical legwires. The second feature is an electrostatic bleeder feature incorporated into the sealer element to dissipate any static electricity or electrical current that has traveled down the tube.

The third and most important safety feature is the "Isolation Cup" shown in figure 13.7, this is a conductive plastic that provides a path for any electrical current coming down the tube to be dissipated to the detonator shell.

> **Caution**
>
> In the presence of lightning, operations involving the handling and loading of explosives should be immediately suspended and the areas secured until the threat is gone. In the United States federal regulatory authorities forbid the handling and loading of explosives upon the approach of a storm.

### Accessories and Tools

Software is available to plan and report blast designs with shock tube blasts. These software products often calculate holes per delay period, direction of movement, ms per meter (foot) of burden, and quantities of product needed for specific designs. These are valuable tools in the design, layout, and tie-in of shock tube blasts. They also provide for the important documentation program of a good blasting operation.

### General Use Techniques

Shock tube initiation systems are composed of various components and factory manufactured units. They allow much flexibility in delay pattern designs. The various products are discussed here.

> **Manufacturer's Recommendations**
>
> Shock tube initiation systems are available from a number of manufacturers. Many shock tube products made by different manufacturers look alike but should not be mixed within a blast. The manufacturer's recommendations must be followed and training by their representatives is important for proper and reliable operation of these systems.
>
> Each shock tube initiation system supplier may have developed and tested component combinations to ensure the signal is transferred from component to component.

### Shock Tube Lead-in-Line Detonators

Shock tube lead-in detonators can be used when nonelectric blast patterns require nonelectric initiation at a safe distance from the blast site. These units are factory assembled precot in lengths varying 22 meters to 300 meters (75 feet to 1000 feet) or longer. Figure 13.9 is an example of a basic line detonator assembly. Shock tube lead-in-line is also available in very long length spools with no detonator attached. This shock tube can be spliced to other shock tube assemblies and then used to connect to a loaded blast pattern. This is often used when there is a need for a greater distance from the blast to the blaster. It must be emphasized that this is the only case where splicing shock tube is recommended. The manufacturer's accessories and techniques for splicing must be used.

![Figure 13.9 - Shock tube lead-in-line with detonator. (Courtesy: Austin Powder Company)](images/233.png)

### Millisecond and Long Period Shock Tube Detonators

These detonators resemble electric detonator units in appearance except that the two electric wires are replaced by a single shock tube as shown in figure 13.10. They may be used as either an in-hole detonating unit or as a delay unit between boreholes in a row or rows in a blast. Factory assembled shock tube units should never be cut and field-spliced when used in the borehole or in a surface connector. Water can enter the shock tube through the cut and make the unit nonfunctional.

![Figure 13.10 - Shock tube detonator with "J-connector". (Courtesy: Austin Powder Company)](images/233.png)

For underground development and face production blasts using MS and LP shock tube detonators, multiple periods are normally used to achieve the desired delay design. Detonating cord is used to connect the shock tube units using plastic detonating cord connectors (J-connectors) as shown in figure 13.10 that are attached to the collar ends of the shock tube units. All connections of shock tube to detonating cord must be tight and at right angles. Field connections are illustrated in figures 13.16 and fit are again tight and at right angles (Se figure 13.17).

In millisecond delay nonelectric detonators the additional factor of shock tube tubing may or may not be taken into account during manufacture. Timing from hole-to-hole in a blast may be shortened by utilizing detonator of the surface tube from connector to trunkline the burn of the tube. The shock tube and the shock tube trunkline are connected to the start borehole as shown in figure 13.14.

To connect the boreholes, the shock tube detonator, and trunkline to the next hole, are placed in the plastic connector block on the surface trunkline delay unit. Close the door (hinged flap) on the surface delay block, ensuring the tubes extend straight from the plastic block for at least 150 millimeters (6 inches) before making a turn in any direction. Cover the connection with dirt or stemming material to reduce the possibility of "snapped cutoffs" as shown in figure 13.14. New designs of shock tube accessories alleviate the necessity of covering the delay unit to prevent snapped cutoffs. The plastic block is constructed in a clip configuration as shown in figure 13.15. The shock tubes clip into the plastic block. The construction of the block ensures initiation of the shock tube in both directions. These detonators have 5-meter input strength, thus reducing the possibility of snapped cutoffs. The tubes should be snapped into the plastic block and then laid in the collar of the borehole as shown in figure 13.16 to avoid twisting of the tubes in the block. The right angle J-connector to detonating cord connections in underground blasting is illustrated in figures 13.12, 13.13 and 13.17.

![Figure 13.11 - Shock tube trunkline-delay block. (Courtesy Austin Powder Company)](images/234.png)

![Figure 13.12 - Shock tube detonator with detonating cord trunkline to prime a column of cartridged explosives in underground blasting. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.5).](images/234.png)

![Figure 13.13 - Shock tube detonator with detonating cord trunkline to prime ANFO column in underground blasting. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.1).](images/235.png)

![Figure 13.14 - Covered surface connector to contain shrapnel and reduce noise. (Courtesy: Dyno Nobel).](images/235.png)

![Figure 13.15 - No cover plastic block. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.7)](images/235.png)

![Figure 13.16 - Surface shock tube connections with plastic blocks. (Source: ISEE Blasters' Handbook, 17th Ed. figure 19.7)](images/235.png)

## In-Hole Shock Tube Delays With Detonating Cord Trunklines

Shock tube units that are factory assembled in desired lengths can be purchased from all nonelectric initiation system manufacturers. These units are available in timing sequences commonly used for surface and underground applications. Millisecond (MS) and long period (LP) delays are used in the same way with detonating cord. The boreholes are charged with the desired explosive for the application and the main explosive charge is introduced. Then the detonating cord trunkline and the surface connectors are placed as needed for the blast. The detonating cord snaps onto the detonator tube-in-hole cord (LP or MS) via a detonating cord connector ("J-Connector") as shown in figure 13.17. This connector replaces the knot method of detonating cord downlines had been employed. However, 90° angles must be used to avoid "angle cutoffs". The shock tube must remain perpendicular to the detonating cord trunk-line as shown in figure 13.17.

![Figure 13.17 - Right angle connection with "J-Connector". (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.9)](images/236.png)

## In-Hole Delays With Detonating Cord Downlines

Short lead units are the most common product of this type used in the commercial market today. Short load delays have approximately 76 centimeters (30 inches) or more of shock tube crimped to the detonator. The often end of the shock tube has a loop to facilitate tying it to the detonating cord downline as shown in figure 13.18. A square knot or double wrap square knot, depending on the detonating cord strength, is recommended for securing the shock tube to the cord. Different timings of in-hole shock tube delays exist for use in the borehole with detonating cord downlines. These units ensure bottom hole initiation and have the added advantage of downhole delays.

![Figure 13.18 - Short load shock tube delays. (Courtesy Dyno Nobel)](images/236.png)

Short load downhole delay units can also be used for "multiple-priming" and/or decking applications. The short load is threaded through a specially made cast booster. These boosters have a tunnel attached to the caskell. The detonating cord passes through this tunnel and through the loop on top of the tube. The short load stays in proximity to contain the detonating cord on the side of the tube. This configuration facilitates sliding primer units to the desired position in the borehole. Thus, they are referred to as slider primers and are shown in figure 13.19. When using this type of system, the blaster must ensure that the detonating cord downline has sufficient energy to initiate the shock tube, but not so much that it will initiate the booster unintentionally or damage the explosive in the borehole.

![Figure 13.19 - Slider primer with downhole delay. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.11)](images/237.png)

## Dual Delay Detonators

Dual delay detonators are the newest type of shock tube detonator and are rapidly replacing other shock tube systems in many applications. They combine nonelectric in-hole and surface initiation in one product. The units are factory assembled at preset lengths. They have an in-hole standard or high-strength MS or LP delay detonator attached to one end. Attached to the other (surface) end is a low-strength MS-delay initiator. This surface delay is housed in a clip block made of plastic as seen in figure 13.20. Connect boreholes by clipping the surface connector to the shock tube of the next borehole in the blast pattern. All of the holes are loaded with the same in-hole delay detonator as shown in figure 13.21. The surface delay and all will have the same delay. The pattern timing is acquired by tying the holes together in the sequence that is needed for detonation. In multiple row blasts, trunk line delays with bunch blocks or surface connectors are used to tie in the rows together and are shown in figure 13.21.

![Figure 13.20 - Nonelectric delay shock tube detonator. (Courtesy: Dyno Nobel)](images/238.png)

![Figure 13.21 - Multi-row shock tube hookup. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 18.17)](images/238.png)

## Shock Tube Initiation Methods

Nonelectric shock tube systems must be initiated with a high-energy shock or detonation. Fuse cap or electric detonator to shock tube, or detonator to detonating cord to shock tube were the first methods of initiating a shock tube blast. Slat shell primer devices in combination with a length of shock tube crimped to a nonelectric detonator were later developed to initiate blasts. Capacitor discharge devices have also been developed to generate a spark in the cut off shock tube end to initiate the reaction in the shock tube. The most recent development has been the use of bulk shock tube spliced to a short length shock tube unit with the burn head and cut off. These splicers have proved very reliable, but must be made up clean and dry.

In the case of all initiation methods for shock tube, care and training is important. The detonator to shock tube connections are electrical and sensitive to shrapnel from the detonator to the shock tube, or rock fragments blown by the detonator. Shock tube is very sensitive to the "fast ball" effect around exploding detonating cord. It can generate premature wees, lants, and rock fragments that will damage and shut down the outgoing shock tube. Slat shell primer devices and capacitor discharge starters must be cleaned and dried regularly to prevent contamination from being blown into the shock tube and shutting down the reaction.

## Electric Systems

Electric blasting systems use an electrical power source to initiate detonators. Electric detonators are connected in circuits to provide electric current to them. Voltage level must be sufficient to generate ample current to ignite the match head inside each detonator in the circuit. Delay powders inside the detonators control the detonator firing times.

Delay electric detonators have enjoyed widespread use in nearly every blasting application worldwide since their introduction in the 1940s. They became the dominant system until nonelectric shock tube systems were introduced in the 1970s. They have proven their value for surface, underground, and construction blasting where electrical field and extraneous current are not a problem or are controllable. Typical instruments used to test electric circuits are shown in figure 13.22. A variety of Capacitor Discharge (CD) blasting machines are shown in figure 13.23.

A specific line of instantaneous electric detonator is made for use in geophysical surveying applications. These detonators are designed to function in less than one millisecond following application of the recommended level of current and are designed for rugged field usage. They typically incorporate a time-break function in which the circuit is interrupted only at the moment of detonation, providing a highly accurate (zero) time on the seismic recording trace.

![Figure 13.22 - Typical electric initiation system instruments. (Courtesy: Austin Powder Company)](images/239.png)

### Use Benefits

The primary benefit of electric detonators is that they and their circuit can be thoroughly tested to verify circuit continuity and resistance before initiation. This allows the blaster to confirm that the initiating voltage will reach all detonators in the circuit. Careful measurement of wire lengths and gauges and the resulting resistance calculations are key to the confirmation of circuit integrity and that the planned numbers of detonators and connecting wires have been tied-in. Sequential blasting machines used with more precise electric detonators can be used to make larger and more effective blasts.

![Figure 13.23 - Variety of Capacitor Discharge Blasting Machines. (Courtesy: Ideal Supply)](images/240.png)

### Use Limitations

Electric detonators susceptibility to initiation by stray current, static electricity, or direct electrical current is their primary limiting use factor. Intended blasting areas must be checked for these electrical hazards and any that are present must be brought within manageable ranges before any loading begins. Caution must also be taken to prevent any lead-in-lines or connecting wire from contacting overhead power lines as a result of ground movement during the blast. There have been many instances of injury and death of blasters at the blasting machine being shocked by circuit line-wires that contacted the lead-in-line or connecting wire that was contacted overhead power lines.

The normal construction and electrical characteristics of commercial electric detonators may vary considerably among manufacturers. For this reason, electric detonators from different manufacturers are not compatible in the same blasting circuit. Therefore, electric detonators of different manufacturers must never be used in the same blast. Such a practice is almost certain to result in dangerous misfires. Further, in the U.S. this mixing practice is in direct violation of U.S. MSHA regulation. A detailed discussion of blasting circuit design is discussed in appendix F.

### Basic Operating Principle

Electric detonators and initiation systems operate on the basic principle of electric current flow through circuits. This principle is when voltage is applied, the current flows through the circuit and returns to the voltage source through the circuit. When the circuit is broken or an alternative path for the electric problems are explained as listed in **table 13.1**. The following electric circuit laws describe how electric current flows through the circuit. These rules are important to know and apply, since electric detonators initiate with the application of electric current. Current rules must meet the criteria of the detonators and electrical hazards must be accurately determined. Detailed performance concerning current calculations can be found in appendix F.

**Table 13.1 - Non-circuit Paths for Electric Current.**

| Paths | Definition |
|-------|------------|
| Additional conductors insulated from ground, such as electric cables. | |
| Conductors not insulated from ground, such as rails. | |
| Stray currents | |

### Construction

The electric detonator consists of a metal shell containing a high explosive base charge designed to initiate other explosives. Above the base charge is a small charge of primary explosive (primer charge) that converts a burning reaction transmitted from the ignition or pyrotechnic fuse into a detonating reaction. Above the primer charge, in delay detonators, is a pyrotechnic delay element that burns at a known rate and whose length and composition control the transit time of the burning front. Detonators classified as instantaneous or "zero" delay do not contain a delay fuse element. The primary reactive element in the electric detonator is the ignition area where a bridgewire is attached between the legwire pins and is embedded in an ignition mixture. The ignition mixture may be in the form of loose powder, a primer spot, or a match head, depending on the manufacturer's designs. Figure 13.24 is an illustration of the construction features of a delay electric detonator.

![Figure 13.24 - Electric detonator construction (Source: ISEE Blasters' Handbook™, 17th Ed. figure 12.2)](images/241.png)

Detonator legwires are made of solid copper, iron, or copper-clad iron wire in a variety of gauges and lengths. Iron or copper-clad iron legwires are designed for use in operations where it is desirable or necessary to remove the leg wire remnants from the blasted rock by magnetic means. Plastic coating provides insulation, abrasion resistance, and flexibility. The wire insulation is typically color-coded to provide positive identification with maximum visibility and to assist in wiring hookups. Most short-length electric detonator legwires are coded in a figure-8 fold that is secured with a paper band. Longer length detonator wires are usually supplied with either duplex wire with a single color and wound on spools or wide length individually colored wires that are coiled in a figure-8 fold (Se Figure 13.25). Longer legwires are typically heavier gauge to code to provide improved tensile strength and lower resistance per main of length.

![Figure 13.25 - Typical electric detonator with spool and figure-8 folded legwires. (Courtesy: ISEE Blasters' Handbook™, 17th Ed. figure 12.2)](images/241.png)

### Performance Features

When sufficient electrical current passes through the detonator, the bridgewire becomes hot enough to ignite the ignition mixture. The majority of electric detonators removed the ignition area with a plastic ferrule that insulates and protects the ignition mixture from the shell. The legwire pins are embedded in a thermosetting resin plug, and are connected to the detonator's legwires within an elastomer-like material above the resin plug. The elastomer-like material top seal is securely crimped near the open end of the initiator shell forming a water resistant closure that firmly positions and secures the legwires inside the shell.

Successful simultaneous initiation of a large number of electric detonators requires delivery of sufficient current to all devices within a few milliseconds. The time required to heat the bridgewire in an electric detonator to a temperature that causes burning of the ignition charge is a function of the current's intensity. Although manufacturers' specifications may vary, the bridgewire in U.S. domestic commercial detonators is approximately 0.07 millimeters in diameter and requires 1 ampere to 1.5 amperes for reliable initiation. The bridgewire may heat up very quickly and rapidly transfers heat to the bridge post and ignition mix. As a result, energy delivered over a time interval of more than 10 milliseconds is not as efficient in heating the bridge wire as the same amount of energy delivered in a few milliseconds.

Delivery of sufficient current to all detonators in the circuit within a few milliseconds is critical. At marginal low-current levels, slight differences from one device to another can result in large variations in initiation times. In series circuits this can result in one detonator functioning prior to initiation of others in the circuit. This "fast" firing of one detonator cuts off the flow of current before all others have been initiated and results in failure of one or more detonators.

### Safety Features

All modern commercial electric detonators include an internal feature to prevent electrostatic energy from accidentally activating the detonator. There are several designs, some of which provide a bypass path around the bridgewire using a semi-conductive material and others, which utilize a printed circuit, which provides a controlled path to ground. All electric detonators produced in North America have shunts on the free ends of the legwires to provide a low resistance path to prevent current from flowing through the bridgewire to ground. In addition, some designs completely enclose the ends of the wires in order to prevent corrosion and to keep bare wires from contacting extraneous electrical current sources. In one design the shunt consists of aluminum foil with an insulator layer on the outside. Electric detonators are supplied with a distinctive, numbered tag to facilitate easy identification of the delay period.

## Electric Blasting Hazards

This section discusses some of the sources of extraneous electricity and some conditions that could present hazards if precautions are not taken to insure safe usage. Unwanted electrical energy that could potentially enter a blasting circuit must be kept at safe levels or, preferably, excluded altogether. If it is not, such energy has the potential to cause premature detonations or malfunctions. For this reason, if electric detonators are to be used, a thorough evaluation of any extraneous electricity or its potential should be made at the blasting site before any explosives or detonators are brought onto the site. Sources of electric blasting hazards are listed in **table 13.2**. Information concerning tests and measurement of the severity of specific hazards when using electric blasting systems can be found in appendix F.

> **Caution**
>
> In the presence of lightning, operations involving the handling and loading of explosives should be immediately suspended and the areas secured until the threat is gone. In the United States federal regulatory authorities forbid the handling and loading of explosives upon the approach of a storm.

The accepted "safe" level of extraneous electricity for electrical blasting is derived from the current required to detonate the most sensitive commercial electric detonators plus a safety factor. The maximum firing current for commercial electric detonators presently manufactured in the United States is approximately 0.25 amperes (250 milliamperes). The IME has established the maximum "safe" current permitted to flow through an electric detonator without hazard of initiation as one-fifth of the minimum firing current, or 0.05 amperes (50 milliamperes), which provides a current safety factor of five. Therefore, electric blasting must not be conducted in areas where extraneous currents are greater than 0.05 amperes (50 milliamperes).

When blasters using electric detonators are alerted to the presence of extraneous current sources, they should measure for extraneous currents in the blast site area at frequent intervals to assure that all extraneous currents are at a safe level. When extraneous currents exceed 0.05 amperes (50 milliamperes), the source of the current must be traced and eliminated before electric detonators can be safely used. If the source of the current cannot be traced and eliminated, a nonelectric initiating system must be used. It must be remembered however that even nonelectric initiating devices can potentially be initiated by high voltage sources such as lightning.

**Table 13.2 - Electrical blasting hazards.**

| Hazard Type | Source | General Conditions | Blast Precautions |
|-------------|--------|-------------------|-------------------|
| Lightning | Natural | 25 mi (42 km) from blast site | Suspend operations |
| | Lightning | 10 mi (17 km) from blast site | Evacuate from blasting area |
| Atmospheric Conditions | Static charge | Heat and low humidity | Safety ground |
| | | Low humidity and high winds | Safety ground |
| Mechanical-Static Charges | Static charge | Dry powder or contaminated air flowing through hoses, pipes, or ducts | Safety ground |
| Stray Current | Conductors – insulators | Ground currents around substations or transmission lines | Measure and eliminate |
| | Ground – AC or DC | 0.05 ampere or less | Use non-electric |
| Radio Frequency | RF Energy | Blast site within RF/minimum distance for transmitters | Distance and shield |
| Induced Currents | Electromagnetic | Proximity to high-voltage lines | Distance and shield |
| Galvanic Action | Dissimilar metals | Contacts/conducting fluids | Measure and eliminate |
| Power Transmission Lines | Parallel circuit | Long blasting circuit parallel to power lines | Distance, position, and shield |
| Current Leakage | Conductors – insulators | All conductors and insulators should be in good condition | Inspect, test, and repair |

### Lightning

Lightning undoubtedly represents the greatest single hazard to blasting because of its erratic nature and high energy. A lightning strike can have voltage potential exceeding a million volts and discharge currents of over 100,000 amperes. If lightning strikes a blast area the probability is high that all or part of the blast will probably detonate. Because of this extremely high hazard potential even distant lightning strikes can be hazardous to electric initiating systems in both underground and surface operations.

Therefore, whenever lightning storms are in the vicinity of the blast, all blasting operations should be suspended in the interest of safety. All personnel should be immediately evacuated to a safe distance from the blast area. The shortest evacuation of the electric detonation in a blast seems to have little bearing on the susceptibility of detonators to premature detonation from lightning. The danger from lightning is considerably increased if there is a transmission line, water line, compressed air line, fence, stream, or other conductor available to carry the current between the storm and the shot location.

Lightning storms tend to be somewhat seasonal and often occur during the late afternoon and early evening hours. Scheduling blasting to avoid these hours is a common sense option. Lightning detection equipment is commercially available that can warn of the approach of thunderstorms to distances of several tens of kilometers (miles). Such instrumentation can provide warnings of hazardous atmospheric conditions even when they occur in the absence of audible thunder or visible lightning.

Regional tracking services for lightning storms that predict the course and arrival time of such events can warn subscribers well in advance of lightning storms. These services are available in many areas. A less definitive, but occasionally used, field expedient for lightning detection is an AM (not FM) radio tuned to a weak station or (preferably) between stations. Static noises on the radio indicate the presence of static charges in the air. Supplementing all lightning detection equipment should be one or more individuals located so they can spot the approach of thunderstorm activity. A specific procedure alerting all personnel who could be affected by an approaching electrical storm should be maintained.

A common sense rule is to evacuate the shot area when thunderstorm activity occurs within about 8 kilometers (5 miles) of the blast site. U.S. regulations require that electric blasting circuits be shunted at all times unless being tested or tied-in. In wiring situations where some series are complete and shunted and some are incomplete and in the process of being wired and the approach of thunderstorm activity is noted, common sense dictates that the shot wiring activity be abandoned and the area cleared and guarded.

### Atmospheric Conditions

Lightning is not the only hazard associated with the atmospheric generation of electrical energy. The atmosphere can build up dangerous charges of static electricity at distances well removed from the storm center. These static charges can be stored on any insulated and ungrounded conductive body, such as a person or truck, and can be discharged through detonator wires to ground causing premature initiation. The shunt and legwire insulation of electric detonators offer no assured protection under these conditions because the voltages can be sufficient to break down the insulation.

### Mechanical Static Charges

Operating machinery can also generate static electrical charges. This charge potential must be considered if operated in the vicinity of electric blasting circuits. When static electricity is mechanically generated the blaster should take note of the recommended precautions discussed in appendix F.

### Stray Ground Currents

Electric detonators are potentially subject to premature detonation when exposed to extraneous "stray" ground currents. Electric current flowing through power lines to electrical equipment from a battery, a generator, or a transformer will always return to that source by the three available paths listed in table 13.1 (See *Electric Systems* in this chapter).

The preferred method of dealing with stray ground currents in the vicinity of electric blasting operations is to eliminate their source. If the return conductor between the load and the source is interrupted, the current will find another path and potentially result in dangerously high ground currents. This hazard can be minimized if extraneous metal objects are kept away from the immediate vicinity of electric blasting circuits. In addition, measurements for stray ground currents should be conducted before electric detonators are introduced into a particular location. Generally, in homogeneous ground, AC or DC currents sufficient to detonate electric detonators rarely are found. That is because the resistance of the earth is usually high and the potential between two points from ground currents is usually too low.

However, dangerous currents can be found when electric detonator legwires contact separate conductive strata. Hazardous currents, greater than 50 milliamperes, can also result electric detonators if the legwires contact rails, pipelines, or ventilating ducts. The earth offers such a large cross section to impede-able extraneous currents that even high resistance earth draws current out of rails circuits conducted.

The stray current test method and the frequency at which it should be made are discussed in appendix F.

### Radio Frequency (RF) Energy

Intense high frequency radiation can accidentally initiate electric detonators. Therefore, an investigation of any potentially hazardous source of radio frequency (RF) energy near a blasting site should be conducted before any electric detonators are brought into the area. The intensity of RF current induced in a blast circuit depends on radiated power, distance from the transmitting source, transmission frequency, and wiring layout itself.

All available evidence indicates that radio frequency energy is not normally a hazard in the transportation of electric detonators in their original containers. Coiled or folded wires provide effective protection against induced current. Metal truck bodies and freight cars also effectively prevent the penetration of radio frequency energy. If vehicles equipped with radio transmitters are used in transporting electric detonators to or from a job, the precautions listed in **table 13.3** should be observed.

**Table 13.3 - Precautions when transporting electric detonators.**
- Carry the detonators in a closed metal box that complies with the local regulations for transportation of electric detonators.
- Ensure the transmitter is turned off when the detonators are being removed or returned to the box.

### General Precautions To Reduce Radio Frequency Hazards

**Stop Procedure**

1. When blasting electrically at a fixed location, such as a quarry, a mine, or a construction site, make certain that there are no radio frequency transmitting antennas located closer to your blasting site than recommended in IME SLP 20. Be on the lookout for the installation of new antennas and check new installations before they go into service to ensure that they will not pose a hazard to your blasting operation.
2. Keep mobile radios in the "off" position near blasting areas and plan adequate signs to remind operators.
3. Determine if electrical radar antennas, which project powerful beams over large distances, operate near the blast site and, if so, determine if electric blasting can be conducted safely.

**Table 13.4 - General precautions to reduce radio frequency hazards.**

The precautions listed in table 13.4 increase safety and reduce hazards when conducting electric blasting operations near RF energy sources.

### Induced Currents

Alternating electromagnetic fields can induce current flow in nearby conductors. Such electromagnetic fields exist in the vicinity of power lines, transformers, switches, and ground return rails and can induce a current directly in an electric blasting circuit. Electric detonator wires touching extended conductors could either intercept the induced current or physically complete an induction loop. Test methods for induced currents are discussed and illustrated in appendix F.

Induced voltages need a well-defined, closed circuit in order to establish a current flow. Such a circuit can be formed by a series of electric detonators and its connecting lines. Two or more series of electric detonators connected to a set of parallel bus wires can also form a closed circuit or loop, capable of intercepting induced currents, if they are located too close to an overhead power line or other alternating electromagnetic fields.

To reduce the intensity of induced currents, the area enclosed by the loop of connected legwires and lead lines should be minimized. When blasting near high-voltage transmission lines or any other high-voltage source, the public utility company or agency involved with the equipment should be consulted to determine the maximum power surge that can be expected. Measurements should always be made during the peak periods.

### Galvanic Action

Galvanic currents are generated when dissimilar metals are immersed in an electrolyte, such as wet ground or a conductive explosive. For example, an aluminum loading pole, designed to replace the heavier wooden loading pole in seismic shooting, experienced a short career in the field. Not long after adopting the new pole, a seismograph crew had two premature detonations. Both were definitely traced to the battery effect developed by the aluminum loading pole, the steel casing in the shot hole, and the alkaline drilling mud. It is obvious that metallic liners, metal loading poles, or any conductive devices should not be allowed to enter a borehole containing an electric detonator. Underwater blasting operators should be alert to the hazard of dissimilar metals in the borehole when loading, particularly in salt water or if making the loading barge hull part of the blasting circuit.

## High-voltage And Power Transmission Lines

Several potential hazards associated with electric blasting near high-voltage and power transmission lines are summarized in table 13.5.

### High-Voltage Power Line Hazards

Electrocution: Legwire or lead-in wire is thrown by the blast over the low power line. Steps must be taken to insure that electric detonator legwires or lead lines do not contact the power lines. The shot point should never be located inside the drape of the lead-in wire grip line length of lead-in wire to allow it to be thrown over the power line. Steps must also be taken to insure that single conductor wires are not used as lead-in-lines. The length of lead-in-lines should be rolled on a stick, long single conductor. Anchoring the leg and blast wires with a large rock is strongly recommended. If a legwire or a lead-in wire is thrown near a power line, the blasting crew should not attempt removal of the wire.

Stray A current or extraneous current electric transmission lines, other than induced current from the electric (conducted) themselves to a shot layout with the low is static (not) that is present on many transmission lines and is found parallel to and above the transmission or distribution line. More current may be induced by electromagnetic induction along the line at the poles or towers. This line also serves to ground any current induced on the shot line or current from an electronic liability.

It is advisable to contact the power company when the tests are conducted, to determine whether measured voltages and currents may increase at scheduled times (annual or biannual). Tests of this type should not be conducted during a lightning storm since the overhead ground wire prevents lightning from striking the power lines and conducts the energy to ground nearby.

Overhead power lines can induce currents in electric blasting circuits. Because the induced current is proportional to the area enclosed by the blast wiring, the restricted area should be reduced to a minimum. Due the previous section discussing induced currents.

**Table 13.5 - High-voltage power line hazards.**

If hazardous stray and/or induced currents above 50 milliamperes are detected, or if the shot point cannot be relocated to ensure that the blast wiring will not be thrown over power lines, nonelectric initiation systems should be used.

### Current Leakage

Current leakage is the loss of part of the firing current through the ground. This circuit bypasses a portion of the firing circuit. This occurs when the insulation on the detonator wires has been damaged or abraded during loading, when bare connections between holes contact the ground, or when poorly insulated splices are placed in a borehole. Detonator failures are likely to occur unless the condition is recognized and preventive measures are taken. The amount of current loss is determined by many factors, with the conductivity of the rock being the principal one. Leakage can occur in relatively nonconductive formations if the ground is wet. Most ANFO and water gels are conductive and will permit current flow to the rock formations if damaged legwire insulation is present in the borehole.

### Accessories and Tools

The voltage or power level of electric blasting machines (rack bar, twist type, or capacitor discharge) is critical to the correct functioning of all the detonators in the blasting circuit. Low battery level, or insufficient power to handle the number of detonators in the circuit will result in misfires. Without the use of sequential blasting machines, conventional electric blasts are limited by the number of delay periods available. This is usually no more than 20 periods.

### Lead Lines and Wire

Lead lines or firing lines are an essential part of the blasting circuit and must be inspected, tested, and kept in good repair to insure a successful blast. Well-insulated, solid-core copper wire of 10 gauge to 14 gauge is recommended for series and series-in-parallel circuits of normal size. Stranded wire should never be used where the blasting line is rolled on a reel after every blast because individual strands may break due to flexing. This results in a reduced load carrying capacity that is not readily detectable with the instruments normally available in the field. The lead line should be tested with a "blaster's" multimeter for continuity and resistance before every blast. It should be replaced when there is any evidence of physical damage to the insulation. Where lead lines are permanently installed. An electrician should test the lines under load. This test should be carried out on a regular schedule.

Connecting wire is usually 16-gauge to 20-gauge plastic insulated solid-copper wire. It is used to connect between holes or to connect individual series to the lead line.

> **Caution**
>
> Connecting wire is always subjected to damage by the blast and should be considered expendable (i.e. never reuse connecting wire).

Bus wire is usually 10-, 12-, or 14-gauge solid-core uninsulated copper wire used as connecting parallel circuits in tunnel and shaft rounds. Aluminum bus wire is not recommended because oxidation of the aluminum can result in high-resistance connections.

Several tools are needed to prepare and initiate an electric detonator blast. Wire strippers and electrical tape are constantly utilized. A blasting galvanometer is essential for checking individual detonators and groups of detonators for continuity. This continuity check is for the wired connections and match head only and does not confirm the functionality of the other internal workings of the detonator. The blasting galvanometer is a specially constructed instrument that will not generate enough current to fire the match head (at the detonator 0.050 amperes or 50 milliamperes).

> **Caution**
>
> Do not use any ohmmeter, galvanometer or multimeter that is not rated blasters'.

A "blasters'" multimeter will make all voltage and resistance measurements associated with electric blasting. It will perform checks for blasting machine output voltage, AC and DC power-line voltage, electric detonator and blasting circuit resistance, breaks or shorts in the firing line; current leakage; AC and DC stray current; capacitive and inductive coupling near high voltage power; and shorts in rack bar, twist, and capacitor discharge blasting machines. It is a very useful tool for the blaster and should be used.

### Measuring Devices

A "blasters'" multimeter, blasting ohmmeter or blasting galvanometer should be used to test blasting circuits for continuity and resistance. Never use any test instruments not specifically designed for blasting circuits. Before using an instrument, make certain the needle can be adjusted to "zero" when the terminals are shunted. Digital meters should read "zero" in the display when being calibrated. If not, replace the batteries and make the necessary adjustments as recommended in the meter instructions.

Replace the battery with the same type of battery specified by the manufacturer for use in the blasting instrument. If in doubt, contact your supplier's technical representative. Both digital and analog (swing needle) type "blasters'" multimeters are available that can detect extraneous electricity in the AC and DC millivolt and milliampere range as well as resistances from 0.1 ohm to 200 megaohms. A special "stray current test" button is available on some models that place a one ohm resistor across the instrument's input terminals. This simulates the resistance of an electric detonator and represents the lowest resistance and greatest current flow at a given voltage that might be expected as a circuit. The voltage and amperage are then numerically equal when the "stray current test" button is pressed. Consequently, the current can be read directly from the AC or DC millivolt scale. This meter frequently gives similar voltage readings when measuring extraneous currents when the voltage switch is turned through several ranges, because extraneous electricity usually has a very high effective resistance. The current from these high resistance sources can be quite small when the "stray current test" button, placing a one (1) ohm lead in the circuit, is pressed. (Never use a standard electrician's multimeter).

Testing devices for blasting machine condition are also available. Please consult your blasting machine manufacturer for recommendations.

### General Use Techniques

Elimination of electrical hazards must be the first consideration before starting to load any blast. Refer to earlier parts of this chapter to recognize and measure extraneous currents for safety recommendations.

In any blasting operation the blasting machine, or blasting switch, should be directly under the control of the blaster-in-charge. It should be kept locked while not in use with the key in the Blaster's possession. The lead lines should never be laid out until the blast circuit is completely tied and all unnecessary personnel have been removed to a safe location. Check the lead line with a "blaster's" multimeter for continuity after it is laid out. It should also be visually inspected for cuts and serious abrasion to the insulation. The end of a lead line must be shunted before either end of the line is connected to the blasting circuit. After the final connections are completed, the resistance of the entire circuit should be tested with a "blasters'" multimeter or a blasting ohmmeter (blasting galvanometer). The calculated resistance of the entire circuit must always agree with the readings on the meter or no attempt should be made to fire the blast. If proper readings are not obtained, re-check the lead line before returning to the blast site to locate and correct the source of trouble. Do not allow the bare ends of the circuit or the lead line to come in contact with the ground or with any metallic object.

When the instrument readings confirm the calculated resistance, the blasting machine, or blasting switch, can be unlocked and the lead lines can be connected for initiation. After the blast, the blasting machine or blasting switch should be locked before returning to the blast area. Never leave a blasting machine or blasting switch unguarded.

> **Manufacturer's Recommendations**
>
> Electric initiation systems and products are available from a number of manufacturers. Many electric detonator products made by different manufacturers look alike but should not be mixed within a blast. The manufacturer's recommendations must be followed and training by their representatives is important for proper and reliable operation of these systems.
>
> Electric detonators from different manufacturers may look alike but have different electrical characteristics. Each manufacturer has specific current requirements for their products.

### Wire Connections (Splices)

The electrical connections must be tight, clean, and insulated from the ground. Care must be taken to avoid abrading or stripping the legwires either in the borehole or on the surface. Lead lines should be inspected and tested prior to every blast. The resistance of all circuits should be calculated, and a Blasters' Multimeter or Blasting Ohmmeter should be used to verify the calculations. No attempt should be made to initiate the blast until the theoretical calculations and the test readings are the same.

The recommended method of connecting legwires is shown in figure 13.26. The clean, bare wires are held side by side and folded over at half their length to form a loop. The loop is twisted several times to form a tight, low-resistance connection. The proper method of connecting legwires to a bus line for a parallel circuit is shown in figure 13.27. When connecting to the lead line with legwires or connecting wire, the ends of the lead line should be "staggered" approximately 30 centimeters (1 foot) to prevent the bare ends from coming in contact with each other. The smaller gauge wire should be tightly wrapped around the clean, bare wire, and the ends should be twisted back to prevent them from being pulled loose. Bare connections must be kept from touching the ground or any type of conducting material to prevent current leakage.

![Figure 13.26 - Recommended end-to-end wire splice. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 16.1)](images/249.png)

![Figure 13.27 - Recommended legwire to bus wire splice. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 16.2)](images/250.png)

## Basic Circuitry

Electric blasting circuits are described based on whether there is only one or multiple paths available for the current flow. The following information discusses and illustrates the commonly used electric blasting circuits and how they are hooked up. Appendix F contains information for calculating their resistance.

However, where special problems are involved, a computer analysis of a particular blasting circuit can be provided by many detonator manufacturers or blasting consultants to help decide which circuit to use. A sample request for information is provided in figure 13.28. In the interest of clarity and simplicity, metric conversions are not shown in this section providing circuit calculations.

![Figure 13.28 - Sample request for analysis of electric circuit design information. (Source: ISEE Blasters' Handbook™, 17th Ed. table 16.4)](images/250.png)

The three basic circuits used in electric blasting systems are (1) series, (2) parallel, and (3) series-in-parallel circuit. These circuits are used to fire circuits powered by either capacitor-discharge blasting machines or power lines. Their resistance calculations with examples are provided in appendix F. Those calculations are made for the two common initiation methods used—capacitor-discharge blasting machine and power lines.

The series circuit is the simplest of electric blasting circuits (See figure 13.29). In it the current has only one flow path.

![Figure 13.29 - Series circuit's single current flow path. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 16.5)](images/250.png)

The parallel circuit provides multiple flow paths for the current. This is shown in figure 13.30. There are different current and voltage requirements for the parallel circuit than for the series circuit. This is discussed in appendix F.

![Figure 13.30 - Parallel circuit's multiple current flow paths. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 16.10)](images/251.png)

Parallel circuits were used in the past for wiring simplicity in many high-speed tunnel and shaft sinking operations. Today nonelectric systems have taken over most of this type of blasting work. However, in the interest of illustrating circuit calculations, and to adequately cover all wiring situations that may arise, this section should be useful.

The series-in-parallel circuit combines the series and parallel circuits by replacing the single detonators with a series circuit. The main advantage of the series-in-parallel circuit is that a large number of detonators can be fired from a blasting machine without a large input voltage requirement. The simplest series-in-parallel circuit uses splits a series circuit into two series circuits hooked up in parallel (See figure 13.31). This can be expanded to include more series as shown in figure 13.32.

![Figure 13.31 - Simplest series-in-parallel circuits. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 16.6)](images/251.png)

![Figure 13.32 - Five series hooked up in parallel. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 16.7)](images/251.png)

### Electric System Initiation Methods

The blaster must verify that the blasting machine or power source to be used is capable of delivering the correct amount of current to each detonator in the circuit. When steady voltage is delivered by AC and DC power sources into electric circuits the normal rules established by Ohm's Law and Kirchhoff's Law apply (See appendix F).

The use of batteries as a power source for initiation should be discouraged. The energy from most batteries is limited and misfires can occur from insufficient current. In addition the extended terminals are always energized, and are potential causes of premature detonation.

> **Caution**
>
> U.S. Federal regulations forbid the use of batteries as initiation devices.

### Capacitor Discharge Machine Initiation

When used properly capacitor discharge blasting machines are the most dependable means of firing electric detonators. Current flow is more complex with capacitor discharge machines. The discharge current from a capacitor discharge type machine decays exponentially from a high initial value to zero over a short period of time. The decay of steady state-sensing firing currents, as demanded for AC and DC power-line firing, cannot be used. Ohm's and Kirchhoff's laws must be implemented by transient circuit calculations to determine the effective firing current required from a capacitor discharge machine. The initial current from a capacitor discharge blasting machine must be considerably in excess of the minimum DC firing current required for a circuit because of this rapid current decay.

### Power-Line Blasting

Power lines can also be used to fire electric detonators. It is essential that sufficient energy be provided to initiate all detonators in a few milliseconds. When firing from power lines, the calculations required to provide sufficient current to every detonator in the circuit are straightforward by applying the basic principles of Ohm's law and Kirchhoff's law (See Electric Blasting Circuit Design, Calculations, and Hazard Evaluation in the appendix).

Power line blasting is still used in some underground mining operations where initiation is made from a central station. With the availability of capacitor discharge machines, power line firing for surface operations has become obsolete. All comments concerning power line firing are directed primarily to underground operations. Electric detonators can be fired by DC power or AC power line, if they deliver the manufacturer's recommended minimum current to every detonator in the circuit.

### Other Electric Initiating Devices

The exploding bridgewire (EBW) and semi-conductive bridgewire detonator are specialty electric detonators and are briefly explained here. For more detailed information please consult a manufacturer.

#### Exploding Bridgewire (EBW) Detonators

These specialized detonators are used where extreme safety precautions are felt necessary, or where very fast initiation is required after the application of current. Being very insensitive to extraneous current, they principally find application as a primary initiator in central blasting systems and in military applications. A specialized capacitor-discharge power source is required.

#### Semi-Conductive Bridgewire Detonators

In this technology, the bridgewire is replaced by a microchip containing a semi-conductive bridgewire, which flashes upon the application of a low current. This design, when combined with microelectronic circuits, can be used to produce electronic delay detonators.

## Detonating Cord Systems

Detonating cord is a flexible cord containing a center core of a high-velocity, detonator-sensitive explosive, usually PETN that is used to either detonate other high explosives with which it comes in contact or transmit a detonation signal from one detonating cord to another or to a shock tube nonelectric detonator.

Although PETN detonating cords are sensitive enough to be initiated by most strengths of commercial detonators, they are not sensitive to low-strength detonators intended to initiate shock tube. Detonating cord is relatively resistant to accidental detonation from impact, shock, friction, or extraneous electricity. Despite this relative lack of sensitivity, detonating cords are high explosives and on rare occasions have been accidentally detonated prematurely. Consequently, as with all explosives, they must be handled, stored, and transported with respect and common sense, and in accordance with local, state and federal laws. Detonating cord initiation is particularly well suited for any of the reasons listed in table 13.6.

**Table 13.6 - Detonating cord system applications.**

| Application | Comment |
|-------------|---------|
| Hazardous situations | Potentially hazardous stray currents present |
| Simultaneous multiple charge initiation | Seismic operations |
| | Perforator applications |
| | Deep large diameter boreholes fired row by row |
| Fracture line-grain ore bodies | In situ leaching |
| Submarine blasting | Electrical connections difficult to insulate |
| Initiate multiple nonelectric delay detonators | Single downline |
| Coyote blasting | |
| Chute blasting | Underground mines |
| Dimension stone blasting | |

### Use Benefits

Detonating cord has provided a reliable closed loop surface tie-in for detonating cord or shock tube downlines. When used in conjunction with MS connectors to delay between rows and boreholes, it provides a redundant path of initiation. It has been very successfully used in this manner for many years. The ability to fire row-by-row with the boreholes within the row firing very close together has provided excellent movement and muck pile loosening. Large core load detonating cords 25-8.5 grams/meter (40 grains/foot) have repeatedly proven their reliability as downlines, surface connections, and initiators for detonator sensitive explosives in extreme blasting conditions such as instantaneous or short delay trenching, very rough ground and hole condition, and high and low temperature environments.

A disadvantage of detonating cord downlines is that the exploding detonating cord adversely affects the main charge of explosive in the borehole. It can reduce the energy output of the main charge, bypass the delay and result in an instantaneous blast, or dead press the main charge and result in a borehole misfire. In addition, the disruption of the top stemming material can early contribute to boreout and additional flyrock.

### Use Limitations

Noise generation by detonating cord surface tie-in and stemming relief by cord down the borehole has been a limiting factor in its widespread use. In addition to the high frequency, high decibel (dB) noise level of the cord itself, an intensifying or magnifying effect can be generated when the inter-row or inter-hole delay timing closely approximates the speed of sound between rows or boreholes. When the burden or spacing is approximately 5 milliseconds/0.33 meters (1 foot) between rows or boreholes, the velocity of sound travel is nearly matched (340 meters/second (1,100 feet/second)). If this occurs, the sound will intensify row-by-row or hole-by-hole in the direction of firing and magnify the results in that direction. Lower core load detonating cords will reduce the noise effect. Exposed detonating cord creates air blast. Using the lowest detonating cord core load will somewhat reduce this effect.

When using reduced core load detonating cords, the ability of the cord to donate initiation to the same or other cords through a knot can be reduced to the point of failure. The detonator and receptor characteristics are also reduced due to improper or loose knot and connection that create cord-to-cord incompatibility issues.

Detonating cord used to make priming units sometimes cause low-order detonations of ANFO products in small-diameter (holes less than 100 millimeters (4 inches). In single-point bottom hole priming, the cord shoots through the ANFO column before reaching a primer and delivers a sharp blow to the ANFO. In some cases the energy of the cord is sufficient to partially detonate the ANFO. This results in a portion of the cross-sectional area of the borehole being partially detonated at a low-order velocity of detonation (VOD). In other situations the ANFO is dazed and pressed ahead any possibility of initiation in that area of the cord. This is frequently the reason for poor or inconsistent breakage of the rock at upper portions of holes. This effect can be minimized by the use of multiple point priming techniques. Place one primer near the top of the ANFO column and another close to the bottom of the borehole, but never more than 0.1 meters (20 feet) apart. In deep holes several primers spaced 3.0 meters to 4.6 meters (10 feet to 15 feet) apart may be necessary. Wherever possible, detonating cord should not be used in ANFO loaded boreholes smaller than 100 millimeters (4 inches) in diameter. Varieties of detonating cord are illustrated in figure 13.33.

Detonating cord core loads of PETN are susceptible to reduced sensitivity when wet with water or petroleum fluids. Their detonation and receptor abilities through knotted connections may be compromised to the point of failure. Side priming with a detonator or connecting through a knot to the wet end of a length of detonating cord will almost surely result in failure. If wetting is suspected, cut a generous length from the wet end before making the connection. If this is not possible, a tightly taped or secured connection of the detonator base charge to adequately cut explosive core at the cord end will reliably initiate the detonating cord.

![Figure 13.33 - Various detonating cords. (Courtesy: Austin Powder Company)](images/254.png)

### Construction

Detonating cord is a round flexible cord containing a core of high explosive (PETN). It is spooled on nonspurging reels (See figure 13.33), which are shipped in fiberboard boxes. The core load is usually expressed in grams per meter, or grains of explosive per linear foot of cord. The number of grams/grains of explosive per linear meter (foot) and the type and thickness of countering (coverings or wrappings) determine the cord's priming ability. With this product, the term "50 grain" (10.5 grams) used in relation to cord means "50" grains/foot (10.5 gram/meter). The various combinations of textile and plastic wrappings provide the cord's tensile strength, tie-in characteristics, and abrasion and water resistance. The most widely used cords have 1.2 grams/meter to 10.5 grams/meter (5 grains/foot to 50 grains/foot) although cords loads with as little as 1.5 grams/meter (7.05 grains/foot) were recently available, and up to 85 grams/meter (400 grains/foot) are available. The explosive core, usually PETN, is covered with various combinations of materials (See figure 13.34). These include textiles, water-proofing materials, and plastics that protect the detonating cord from damage caused by physical abuse or exposure to water, oil, or other elements, and provide such essential features as tensile strength, flexibility, and other desirable handling characteristics. Figure 13.34 shows the typical construction of detonating cord.

Other core loadings, such as RDX and HMX are used in cords designed for specialized uses, such as in oil wells or other hot environments. If such applications arise, contact the cord manufacturer for recommendations.

Most cords detonate at approximately 7,000 meters/second (23,000 feet/second). Their explosives initiating energy varies with the core load. Recently, low velocity cords with velocities of less than 4,000 meters/second (13,000 feet/second) have been developed to reduce pressure and air-blast on dimension stone blasting. All high-velocity cords will detonate cap-sensitive explosives and many other detonator-sensitive products. Some products may not be initiated, but might be dead pressed or otherwise damaged by the energy output of cord. Consult with the explosives manufacturer as to which products can safely be used with detonating cord.

![Figure 13.34 - Detonating cord construction (Courtesy: Dyno Nobel).](images/255.png)

### Performance Features

Cyclotrimethylenetrinitramine (RDX) core loading is available for situations where high ambient temperature is a concern. Also available are detonating cords for use in situations where the possible setting of undesirable fires is of concern, such as in some seismic work. Detonating cord is typically color-coded by each manufacturer to assist in the easy identification of the product grade. A "Fireline" cord for explosively creating narrow fuel fire lines is manufactured with fire suppression coatings. The table below details the core loads, diameters, and tensile strength of some commercially available cords in North America.

**Table 13.7 - Examples of detonating cords.**

| Core load | Diameter | Tensile strength |
|-----------|----------|------------------|
| 0.5 g/m (2.5 gr/ft) | 2.0 mm | 18 kg |
| 1.05 g/m (5 gr/ft) | 3.0 mm | 23 kg |
| 1.5 g/m (7 gr/ft) | 3.4 mm | 32 kg |
| 2.1 g/m (10 gr/ft) | 4.0 mm | 36 kg |
| 3.15 g/m (15 gr/ft) | 4.5 mm | 45 kg |
| 4.2 g/m (20 gr/ft) | 5.0 mm | 54 kg |
| 5.25 g/m (25 gr/ft) | 5.5 mm | 63 kg |
| 6.3 g/m (30 gr/ft) | 6.0 mm | 72 kg |
| 8.4 g/m (40 gr/ft) | 7.0 mm | 90 kg |
| 10.5 g/m (50 gr/ft) | 7.5 mm | 100 kg |

### Safety Features

The electrical insensitivity of detonating cords is an important safety feature when using detonating cords. Durability of the larger core load products in rough or difficult conditions is a proven safety characteristic.

> **Caution**
>
> In the presence of lightning, operations involving the handling and loading of explosives should be immediately suspended and the areas secured until the threat is gone. In the United States federal regulatory authorities forbid the handling and loading of explosives upon the approach of a storm.

### Accessories and Tools

Nonspurging blanks for cutting lengths of cord are a necessity. Blasters have often made wooden or nonsparking metal reel holders for handling of cord reels and safe transportation. Many detonating cord manufacturers construct the shipping boxes to serve as a reel holder and feed device for range for field deployment.

### General Use Techniques

In some blasting situations, "50 grain" (10.5 grams/meter) detonating cord is preferred as the downline to initiate the high explosive column charge or boosters. It has greater priming reliability and tensile strength than the lighter detonating cord and greater economy than heavier cords. However, the trend in blasting with detonating cord has been to use lower gram detonating cord. The variety of conditions and types of explosive used most often dictate the size of cord to be used. Primer assembly using detonating cord is illustrated in chapter 19. Large-diameter boreholes are often initiated with detonating cord for safety reasons, cutoff prevention, multiple-point priming capability, and multiple decking applications. The detonating cord loading procedure is provided in table 13.8.

Detonating cord is easy to connect for a blast. Most detonating cords will transmit the detonation reactions between sections spliced or joined together securely and tightly with the proper knots. Some of the smaller cords do not unuter through knots or splices reliably. The following recommendations apply for most cords which have core loads of 5.3 grams/meter to 27.5 grams/meter (18 grains/foot- 60 grains/foot). Consult the manufacturer for the recommended way to splice or connect unusually large or small detonating cords.

**Table 13.8 - Detonating cord Loading Procedure.**

| Step | Action | Comment |
|------|--------|---------|
| 1 | Check borehole | Check for debris, contamination, or loose rock |
| 2 | Check for detonation | Use a meter, or other method |
| 3 | Attach a detonating cord to the primer cartridge or booster | |
| 4 | Check primer or booster for secure attachment | |
| 5 | Avoid non-sparking tool or igniter wire to small hole in the | The reel may be handheld or mounted in the top of a box. This allows the cord to run off the spool while the cartridge or primer is being lowered (not dropped) to the bottom of the hole. |
| 6 | Lower cartridge or booster into borehole position | Insure charge is at borehole bottom. If it ledges or comes to rest on a protruding ledge, the lower portion of the hole will be a misfire. |
| 7 | Provide a 2-3 foot loop at the collar | Curl up on top of the collar where delay will be placed. This is the tie-in point and preparation for tying surface connections with the del cord. |
| 8 | Allow 0.3 meters (1 foot) extra length | Extra length compensates for explosives slumping and pulling on the cord. Extra length provides for making inter surface connections. |
| 9 | Grase downline cord | As cord in the stemming (coming from the hole has more time for the next borehole. |
| 10 | | Note: The grease prevents the stemming from binding with the cord. This cord propagation is for other explosives (not other that may blow down, etc.). |
| | | - boreout, or |
| | | - interfere with the subsequent loading operation. |
| 11 | Security fasten cord to top of downline | Tie or secured a rock or some other object heavy enough to present it from being kicked, or pulled into the borehole by slumping product. The detonating cord should be secured with sufficient slack to accommodate stemming operations |

In general, when connecting sections of detonating cord together the blaster must assure the factors as table 13.9 to ensure quality.

**Table 13.9 - Steps to Maintain Detonating Cord Connection Quality.**

| Step Action | Comment |
|-------------|---------|
| 1 | Ensure cut ends are free of contamination. |
| 2 | Cut ends of cord not quite on perimeter through a capillary action. Penetration is generally less than 0.12 m (1/2 in or 1/2 inches) |
| 3 | Place all connectors or detonators at least 0.1 m (4 inches) from the exposed open end to ensure positive initiation. |
| | This includes all knots, MS connector connections, and detonator attachment points. If finished by a distance from a tie-end, straight (unstripped) length of detonating cord will continue to behave well as an inert fuse. |
| | Precaution should be exercised to never lay the connector or detonator over a knot or misfires or at the end of a line, as this connection may not transmit the detonation. Broken cords that have been pulled well away, or in higher or wet ground will have absorber more contaminant |
| 4 | Ensure all connections are at right angles | Avoid sharp angles, which can cause the cord to cut itself off. Angle cutoffs failures are caused when attenuating cord branch-lines or downlines don't knot back at an acute angle toward the trunkline. |
| | The explosion in the knot should not "see" fragments, or lead particles, from the detonation of the main (trunk-line. Cord detonators or donor connectors must create the knot back or closer tie-on detonator follow-up after tie-in. |
| 5 | Do not damage or leave slack in detonating cord | - When pulling or tugging on detonating cord |
| | | - Without the trunk-line all of enough to prevent slack developing |
| | | - or pulling and tugging is not turned or slack |
| 6 | Ensure detonating cord knots tight and in contact | Loose knots may fail to transmit the detonation wave. Avoid leaving knots in the cold within the borehole. |
| 7 | Ensure every borehole has two paths of initiation | The following recommendations are U.S. MSHA regulation: |
| | | - Ensure each borehole has two complete paths of initiation. |
| 8 | Cut all the excess cord in "tails" after tying surface | Always cut off excess cord to prevent the initiation signal from escaping down the trunkline and cutting it off. |
| | connections. The branched layout should be stable, reliable | Always do this prior pattern so allow enough of delays, loops, loose knots, and pigtails. |
| | and secure | |
| 9 | Ensure cords do not cross over each other when | One cord may detonate prior to the other cord in the delay sequence causing it and causing a misfire. |
| | connecting or connect cord downlines, trunklines, or tip | Stress this by taking the slack out of all detonating cord lines |
| | lines | |
| 10 | | Continuously monitor the integrity and the condition of the hooked-up during blasting. Other measures may include: |
| | | (1) Eliminating the trunk line and initiating each down line at the surface with electric or nonelectric detonators. |
| | | (2) Attaching electric or nonelectric detonators to each downline at the detonators. |
| | | (3) Timing with a fast-acting clock recorder and connecting each down line to separate circuits |
| | | (4) Using single detonating cord downlines and slider primers |
| | | (5) Using a shock tube detonator in the primer at the bottom of the explosive column. |
| | | - Initiate detonating cord up-lines from the borehole bottom with electric or nonelectric detonators |
| | | - Add redundant paths of initiation to critical link in the circuit for example, at all trunk line and branch line knots. |
| 11 | Reduce noise from surface detonating cord | |

### Knots and Connections

Detonating cord connections are made with knots or connectors. These connections must always be tight and properly made. The following discussions illustrates how they are made and the importance of using correct techniques.

The square knot (See figure 13.35) is the recommended method for making an in line connection between two lengths of detonating cord. The square knot ensures a non-slipping connection for reliable signal transfer from cord-to-cord.

![Figure 13.35 - Square knot. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 15.1)](images/259.png)

The connections shown in figures 13.36 through 13.38 create strong tight right angle connections with proper cord-to-cord contact for signal transfer from the donor-to-receptor line. Right angle connections prevent accidental cutoff between the donor and receptor lines.

![Figure 13.36 - Double-wrap half-hitch. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 15.2)](images/259.png)

Connections between downlines or up-lines and a detonating cord trunkline, cross-ties between trunklines, or other right-angle hookups should be made with a double-wrap half-hitch as illustrated in figure 13.36.

> **Follow Manufacturer's Recommendations**
>
> Detonating cord initiation system products are available from a number of manufacturers. Many detonating cord products made by different manufacturers look alike. The manufacturer's recommendations must be followed and training by their representatives is important for proper and reliable operation of this system.
>
> Detonating cord manufacturers have extensive training and technical literature available for the blaster to use. The correct knots and connectors are critical for proper continuity from cord to cord. Some cords are not acceptable as donors or receptors to or from other cords.

![Figure 13.37a - Clove hitch. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 11.4)](images/260.png)

![Figure 13.37b - Modified clove hitch. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 11.5)](images/260.png)

The most satisfactory connection between a relatively stiff detonating cord downline and a flexible trunkline is made with a double wrap half-hitch as illustrated in figure 13.36 with the trunkline around the downline. Another satisfactory connection is made with a plastic detonating cord connector as shown in figure 13.38.

Figure 13.37a shows the simpler form of the clove hitch, which is satisfactory, provided there is no subsidence or slumping of the charge in the borehole. If the charge subsides, the downline may be pulled out of the clove hitch. To prevent this, the modified clove hitch in figure 13.37b should be used. It is made by clove hitching the trunkline over a loop in the downline (instead of the single cord) and by tucking the loose end through the loop at the top. After this connection is tightened up, there is no chance for the downline to pull out unless the cord is actually broken.

![Figure 13.38 - Detonating cord connector for trunkline to downline connections. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 15.3)](images/261.png)

### Millisecond "MS" Connectors

Millisecond connectors (MS connectors) as shown in figure 13.39 are used to connect detonating cord trunklines and provide the delay between rows of holes. These connectors have a detonator on each end. The detonators are similar to other detonators in that they produce millisecond delay timing and have similar construction. MS connectors receive a signal in one end from the incoming detonating cord. This initiates the short length of shock tube that connects the detonator at the ends of the connector. The reaction in the shock tube then initiates the detonator on the other end. This detonator in turn initiates the outgoing detonating cord. The blaster should consult the manufacturer's instructions packed with the connectors for proper hookup procedures. Figure 13.40 illustrates one manufacturer's recommended hookup assembly. Be sure to always follow recommended procedures. Long tails of cord on the connector blocks after the tie-in should be avoided as they can damage outgoing tube, caps, or cord.

![Figure 13.39 - MS connectors. (Courtesy: Dyno Nobel)](images/262.png)

![Figure 13.40 - MS connector/detonating cord hookup. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.11)](images/262.png)

### Instantaneous Initiation Method

For many years all detonating cord blasts were fired instantaneously with a detonating cord trunkline and, in a few cases, with regular electric detonators attached to the downline at each borehole. However, now most blasts using detonating cord are delayed either on the surface or in the borehole with millisecond delay techniques. These methods retain virtually all the safety advantages of conventional trunkline initiation, especially when using MS delay connectors or surface shock hole delays.

Very few detonating cord blasts today are shot instantaneously, although some blasters still fire them instantaneously where no vibration and air blast problems exist. Probably the greatest incentive to initiate a blast instantaneously is in a blasting situation where the possibility of cutoffs at the powder column from shifting ground overweigh the improvement in fragmentation gained by using delays. However, there are very few geological formations that are not adaptable to delay blasting.

It is always important to design the blast so that the detonating cord initiate the boreholes in proper sequence with respect to the open face or forward the direction of desired blasted rock movement. The primary consideration is to design the initiation pattern so that boreholes near the free face are initiated first and do not cut off lines firing holes for ground movement. Some slight improvement in rock breakage, fragmentation, and displacement, and reduction in backbreak and flyrock, may be achieved by initiating the holes nearest the free face first. The delay effect is achieved by the detonation rate of the cord is approximately one (1) millisecond/7 meters (23 feet). Therefore, although measurable, the delay effect is minimal. Instantaneously initiating detonating cord surface trunklines and downlines in vertical and horizontal holes in dimension stone blasting is still an effective method for extracting large loaves of stone and trimming blocks to size before sawing. Low-velocity, low-pressure detonating cords have recently been developed to reduce the air shock in the mine that can be generated by conventional detonating cords.

### Surface Delay Methods

It must be realized that surface delay initiation (when used without in-hole delays) by any method tends to be more vulnerable to failures or partial failures from ground movement than when instantaneous methods or in-hole delays are used. This difficulty with surface delays can be minimized by use of proper drift and delay patterns. There are several ways to surface-delay a blast with detonating cord. Three popular methods are listed in table 13.10.

**Table 13.10 - Effective surface delay methods to prevent cutoffs when using detonating cord.**

| Method |
|--------|
| Use MS connectors in the detonating cord trunkline |
| Use MS delay electric or nonelectric detonators attached to the detonating cord downline |
| Use surface shock tube delay assemblies |

The use of detonating cord as up-lines in deep boreholes, bottom-primed with MS delay electric or nonelectric detonators, is a convenient means to multiple-point prime. The detonating cord is attached to the bottom cartridge or booster and is initiated by the MS delay detonator and primer at the bottom of the borehole. The detonating cord will, in turn, detonate the additional boosters in the hole as the detonation progresses up the cord. The excess cord extending from the top of the hole is usually coiled and inserted into the borehole approximately 0.3 meter (1 foot) into the stemming.

If multiple delay explosive decks within a hole are needed, a single downline in conjunction with nonelectric delay "slider" primers is a convenient method to use in medium to large diameter boreholes. MS connectors offer a convenient way to delay detonating cord blasts with short-interval delay timing on the surface. They are simply coupled or tied into the trunkline between the boreholes or between groups of boreholes to segregate the blast.

As a result of early experience with short interval delay firing and surface initiation, spacings under 4.6 meters (15 feet) were believed questionable without risking cutoffs. However, later developments indicated that borehole cutoffs depended more on the general blast layout, depth of boreholes and structural characteristics of the rock formation (dip of strata, fracture planes, or dip of seams) than on the borehole spacings and burden. For example MS connectors can be used to successfully surface delay small-diameter holes in ditch blasts with spacings of 0.9 meters to 1.2 meters (3 feet to 4 feet). If used in this manner, weighting, burying, or other methods may be needed to prevent connectors from pulling apart due to whipping of the cord and delays in the blast progression. Actual recommended delay times are discussed in the Handbook sections on the various types of mining.

### Surface Delay With MS Connectors

MS connectors offer a convenient means of firing detonating cord blasts by the short-interval delay method on the surface. They are simply coupled or tied into the trunkline between the boreholes or groups of boreholes to sequence the blast in a predetermined order. They are manufactured with a wide range of delay intervals: the shorter intervals are generally required for small-diameter drilled in close spacings, while the long intervals are for larger diameter holes drilled on wider spacings. This type of delay firing covers a range of hole diameters and spacings from approximately 100 millimeters (4 inches in diameter via 2.1 meter to 3.6 meter (7 feet to 12 feet) spacings to 0.43 meters (17 inches) in diameter on 7.6 meter (25 foot) spacings or larger. A good practice to minimize cutoffs is to allow at least 0.3 meters (1 foot) between holes for each millisecond of delay and always to locate MS connectors either midway between holes or close to the hole being delayed. Consequently, the usual commercially available MS delay intervals are 5, 9, and 17 ms when the borehole patterns range from 2.1 meters to 7.6 meters (7 feet to 25 feet) or greater if no delay is used in the boreholes. Figures 13.41 to 13.43 show conventional bench shot hookup layouts with point-of-initiation and the location of electric blasting caps (EBCs) for single-row and multiple-row vertical hole blasts with MS connectors.

![Figure 13.41 - Corner opening single-row bench shot with detonating cord system. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 15.4)](images/264.png)

![Figure 13.42 - Corner opening multiple-row bench shot with detonating cord system. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 15.7)](images/264.png)

![Figure 13.43 - Center opening bench shot with detonating cord system. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 15.8)](images/264.png)

Where several rows of boreholes are fired in sequence in a multiple-row blast, at least three cross-ties as illustrated in figures 13.44 through 13.46 with a connector in each cross-tie are good insurance, one at each end and one near the center of the row. In exceptionally long blasts more cross-ties with connectors should be used. Figure 13.44 illustrates this concept.

MS connectors are successfully used in pipeline construction work. In this application they can improve the fragmentation, reduce flyrock, cut down on overbreak, and help pull a smooth bottom on trench blasting jobs. Thus, they joined top-hole bottom procedures, reduce cleanup work, and minimize overblasting and other potential result. When the bottom of the ditch is pulled smooth and clean, the amount of padding (crushed stone or other material) necessary to prevent the pipe from resting on solid rock or from being suspended over voids) under the pipe is reduced. Figure 13.45 shows the layout for delaying a ditch shot. Figure 13.46 shows a typical MS connector connector layout for horizontal boreholes used in coal stripping shots. In general, two delay connectors in parallel are recommended for each interval when individually decks are being fired.

Although the delay element and high explosive base charge is enclosed within a plastic block, MS connectors should be protected from abrasive shock, heat, impact, or friction as they have an impact sensitivity level equivalent to regular delay detonators. Consequently, all unnecessary personnel and equipment should be removed from the shot area before the MS connectors are tied-in.

![Figure 13.44 - MS connector cross-ties in boreholes. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 15.9)](images/265.png)

![Figure 13.45 - Typical MS connector layout for ditch line blast. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 15.10)](images/265.png)

![Figure 13.46 - Typical MS connector dual path layout for horizontal boreholes. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 15.11)](images/266.png)

### Surface Delay Using Millisecond Delay Electric Detonators

These short-interval delay detonators have been widely used for firing detonating cord blasts. This technique was especially prevalent prior to the introduction of MS connectors. They are attached on the surface, either to the downline at the individual borehole or to trunklines connecting rows or groups of boreholes. The recommended techniques of attaching an electric detonator to detonating cord are illustrated in the section *Detonating Cord Initiation Methods* in this chapter. Be aware that the time interval between some periods of MS delay electric detonators may be as long as 100 milliseconds, and they should be used only in conditions where this delay interval will not cause cutoff of the downline due to ground movement.

When using MS delay electric detonators, surface noise can be minimized because the use of a surface trunkline is eliminated. The system requires as much wiring as an electrical blast of equal size, and the usual precautions must be observed to prevent premature initiation by extraneous electrical sources.

### Surface Delay Using Nonelectric Shock Tube Detonators

These can be used in surface operations to reduce noise levels where use of electricity is not feasible. In this application the "J-hook" on the shock tube is connected to the first detonating cord in the sequence. The shock tube transfers the detonation between the boreholes to the delay detonator at the other end of the tube, which is connected to the next detonating cord downline. The type of connection will vary with manufacturer, but is usually made through some type of a plastic block/fitting.

### Surface Delay Using Shock Tube Trunklines to Detonating Cord Downlines

When detonating cord downlines are used with short load units, it is sometimes preferable to use shock tube trunkline delay units on the surface to initiate the in-hole cord. Shock tube is virtually noiseless. Therefore the loud snap associated with detonating cord will not be heard. It is sometimes easier to design a blast using shock tube surface delays. The shock tube has a detonating cord connector attached. The bunch block has a door configuration that allows secure the detonating cord downline in placed in the plastic block as shown in figure 13.47. The unit going to the next borehole or row is connected to the downline via the detonating cord connector ensuring adequate distance is maintained between the detonator cord connector and the outgoing trunkline delay unit. The outgoing cord should extend straight from the bunch block. Once the connections are made, the connectors should be covered with shovelfuls of dirt or stemming material. Covering these units will reduce the possibility of shrapnel cutoffs. Shock tube and detonating cord should never be placed in the same bunch block. Because of the different detonation velocities of shock tube and detonating cord, the detonating cord will cause the shock tube to cutoff. This incorrect connection is illustrated in figure 13.48.

![Figure 13.47 - Detonating cord downline with shock tube trunklines. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.14)](images/267.png)

In deep boreholes an MS delay electric or nonelectric detonator and primer at the bottom of the borehole are frequently supplemented by a detonating cord up-line, which is tied-in and initiated by the primer assembly. This provides a convenient method for multiple point priming in which cast boosters or detonator sensitive cartridges are slid down or alongside the up-line to minimize borehole cutoffs and failures due to separation in the powder column.

![Figure 13.48 - Do not place detonating cord and shock tube in the same bunch block. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.15)](images/267.png)

### In-hole Delay Methods

In some blasting situations surface or collar initiation may not be practical. Some examples are (1) quarries in congested residential areas that cannot tolerate the noise associated with detonating cord trunklines; (2) blast patterns and geological formations which can result in borehole cutoffs; and (3) heading rounds, shaft rounds, and other "tight" shooting conditions which require hole initiation for adequate yield, displacement and fragmentation.

### In-Hole Delay with In-Hole Delays with Detonating Cord Downlines

Different types of in-hole shock tube delays exist for use in the borehole with detonating cord downlines. Short lead units are the most common product of this type used in the commercial market today. Short lead delays have approximately 76 centimeters (30 inches) or more of shock tube crimped to the detonator. The other end of the shock tube has a loop to facilitate tying it to the detonating cord downline. A square knot or double wrap square knot, depending on the detonating cord strength, is recommended for securing the shock tube to the cord. These delay units ensure bottom borehole initiation and have the added advantage of down borehole delays as shown in figure 13.18 in section *In-Hole Delays With Detonating Cord Downlines* earlier in this chapter.

### In-Hole Delay with Detonating Cord Downlines and Slider Primers

The nonelectric detonator "slider" system can also be used in medium-to-large vertical boreholes to delay different decks. In this system each delay detonator in a given deck is connected to the detonating cord downline by a tube attached to the outside of a booster. The booster/detonator assembly is slid down the cord to the approximate point at the loading sequence in order for it to be at the desired part of the borehole load. By using shock tube delays between boreholes, an infinite number of delays are possible.

### Low Energy Detonating Cord Systems

There are two variations of this system, one which is simply a delay detonator attached to cord as a factory assembled unit. The other is a more complex and versatile combination of connectors, delay units, and/or detonators. Systems utilizing low core load detonating cord continue to have application in some areas.

The first system has the delay detonators attached to 0.8 grams/meter (3.8 grains/foot) detonating cord. In practice the cord is tied to a trunkline of at least 5.5 gram/meter (25 grains/foot). All central control is at the detonator that is permanently attached to the low energy cord. The delay detonators are the same as used in shock tube systems except that the energy output from the detonating cord crimped to the detonator initiates the functioning of the built-in delay elements. Although the energy output from the detonating cord is low, it will still have a disrupting effect on a column charge. The cord will likely initiate NO2 dynamite column charges. Consult your manufacturer for recommendations for products to be used with these systems. Factory assembled units are primarily used in underground operations where release from the initiating system, such as plastic tubing, is unacceptable. Examples of such operations are in underground salt and chemical line mines. The unit shown in figure 13.49 has either a detonating cord connector attached or has to be tied to a detonating cord trunkline. Timing of the round is identical to that using other similar in-hole delay detonation systems.

![Figure 13.49 - Detonating cord with attached detonator. (Courtesy: Dyno Nobel)](images/269.png)

![Figure 13.50 - Low-energy detonating cord underground face-to-tie. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 19.19)](images/269.png)

## Detonating Cord Initiation Methods

Detonating cord may be initiated with individual detonators or blasting caps and fuse. Electronic, electric or nonelectric shock tube detonators are preferred since they will permit optimum control of the time of initiation. In such case, the initiation hookup requires specific configurations of the detonator to detonating cord for reliable initiation. Use two detonators at each point of initiation to provide additional reliability where the cord may be damp or other adverse conditions may exist. Figures 13.51 through 13.53 show the correct methods for attaching detonators to dry detonating cord for initiation. The detonators are oriented parallel to and securely attached along side the detonating cord with the base charge (ends) pointing in the direction that the detonating cord will fire. They are securely fastened with tape (never electrical) direct contact between the detonator and the detonating cord as illustrated in figure 13.51. Shock tube initiation without a bunch block is identical to the fuse and cap or electric method.

![Figure 13.51 - Recommended attachment of electric or electronic detonator to detonating cord. (Source: ISEE Blasters' Handbook, 17th Ed. figure 15.12)](images/269.png)

Note that the detonator is connected, in figure 13.51, to a separate piece of detonating cord (pig tail). The final knot connections should not be made until the blast safety area is cleared. In addition, the connection of an electric detonator should be made first to the electric lead in line (after testing for current in the lead line). The electric cap should be shielded from the blaster at the time of this connection in case there is sufficient current in the lead to detonate the electric cap or caps. If there is current at the lead line and the cap is attached to the detonator the blaster will initiate! The pig tail should then be attached to the detonating cord or blast trunk-line. The recommended method of initiating detonating cord with a shock tube detonator is shown in figure 13.52.

![Figure 13.52 - Recommended attachment of shock tube detonator to detonating cord (Reprinted with permission from IME: SLP 4, 2009).](images/270.png)

![Figure 13.53 - Shock tube initiation with a plastic bunch block (Courtesy: Dyno Nobel).](images/270.png)

## Cap and Fuse System

Prior to the invention of safety fuse in 1831, black powder charges were initiated by the use of straws, quills or other hollow materials filled with finely-divided powder. Prior to the introduction of detonating type explosives such as nitroglycerin and dynamite, the fuse alone was the initiator, no attachment being required. After the detonating explosives were introduced, and until electrical methods became widespread, the cap and fuse system was the dominant initiation method for small diameter holes. Due to economics, this method remains in wide use in some areas of the world. In the U.S., this system has fallen into relative dis-use to its high accident potential and the fact that better breakage and higher productivity are possible with modern electric and nonelectric systems.

The terms "cap" and "fuse" historically have been used to identify "blasting cap" or "fuse caps" and "safety fuse." In the U.S. Department of Transportation shipping classification, blasting caps ("blasting caps" or "blasting caps" or "fuse caps") are described as "Detonators, nonelectric" and fuse is described as "Fuse, safety". The use of cap and fuse as a means of initiating explosives should be limited to situations where no practical substitute is available or the cost of alternatives is prohibitive. This is still the case in some parts of the world where this initiation system. By and large cap and fuse as an initiation system has been replaced by other initiating systems. Cap and fuse is still used for avalanche control work and agricultural applications of explosives such as ditching and stump removal.

Cap and fuse assemblies can fire single charges or multiple charges designed to initiate in rotation. Charges that must be shot instantaneously, as in pre-shear (perimeter control), pre-splitting, c-work, or which require short delay intervals, cannot use this initiation method because blast timing with fuse is not sufficiently precise. Cap and fuse should be used only by experienced, trained, and skilled blasters completely familiar with the use of explosives on a day-to-day basis. Cap and fuse blasting should only be used where a long delay time between the detonating of individual holes will not create a problem. This section discusses the proper storage, handling, and transportation of cap and fuse and assembles; proper storage, handling, and transportation assemblies of caps and fuse; and safe methods for priming, loading, and firing shots. An instruction sheet is enclosed in every case of fuse. This should be studied and the warnings should be observed.

Safety fuse and caps are best adapted to slow delay underground mining and excavation work in development and narrow vein mining. Its simple and intuitive construction with relatively few potential benefits in these situations. It should be confined to relatively few charges or holes per round.

### Use Benefits

The ease of make-up and simplified requirements are a potential benefit for operations where very few holes are shot per round. Cap and fuse line is a conventional form of nonelectric initiation. Misfires make-up carried or cut into surfaces is does not require the fuse and fuse end/covered to roll out just survive as a lead line.

### Use Limitations

Using cap and fuse to initiate a surface nonelectric blast is unsafe as it allows a period of time after lighting and before detonation in which security may be violated and the blast cannot be stopped. A minimum length of 1 meter (3 feet) is required by law for any length of fuse. This length could take over 2 minutes from lighting to detonation. Such blasts should be initiated with a more certain signal.

The burning rate and sensitivity of the black powder core of safety fuse can be affected by various contaminants (e.g. oil, gasoline, kerosene, solvents, paint, and other petroleum-based products) absorbed directly through the fuse covering. The powder core can be contaminated by water absorbed through cracks in the covering or at the end of the fuse. Moisture in the powder core at an end of the fuse can prevent that portion of the fuse core from igniting properly or slow the burning rate of the fuse.

Fuse may fail to detonate if contaminated with moisture or other materials. Moisture condensation on the cap's metal shell or in the safety fuse coverings may desensitize powder when these items are stored from a cold to a warm environment. This can happen in both wet and dry working conditions. In such conditions caps and fuse should always be allowed to reach the warmer temperature before being unpacked or disturbed. Overnight storage in the warmer air is usually sufficient.

> **Caution**
>
> Refighting fuse after a misfire is very dangerous and should never be attempted.

Misfires and accidents have also been caused when small particles of contaminants have become lodged between the ignition charge of a fuse cap and the end of a safety fuse. All foreign material must be kept out of the fuse cap and off the ends of the safety fuse. If foreign material is present in a fuse cap, the cap should be disposed of in an approved manner. Consult your explosives supplier for details.

> **Caution**
>
> Never attempt to remove fuse or other material from a blasting cap.

To guard against contaminants, safety fuse and caps should be stored in approved, clean, dry, well-ventilated areas or in magazines which have as low humidity as possible. Blasting caps and safety fuse should always be stored at normal temperatures. Storage temperatures over 60°C (140°F) can melt some waterproofing materials in the covering thus reducing the water resistance of the fuse. At temperatures below 7°C (45°F) the fuse covering can become stiff and brittle. If stored at cold temperatures, the fuse should be warmed before being bent or flexed. Bending cold or frozen fuse can crack its covering and expose the powder column to contaminants. Blasting caps should not be stored near any heat source (hot water, steam lines, radiators, or heaters). Heat for storage or crimping stations should be supplied from circulating air or water installations rather than from direct heating units in the area.

The oldest fuse in the magazine should be used first, since some types of fuse coatings tend to become stiff with age and may crack when bent or flexed. Purchase should be limited to requirements of the job on hand, and prolonged storage should be avoided.

### Characteristics

Safety fuse is a medium through which flame is continuously conveyed at a relatively uniform speed to initiate the heat-sensitive charge in an ordinary blasting cap.

Before using safety fuse the blaster must know the burning rate of the particular fuse he is using. Although a burning rate of approximately 131 seconds/meter (120 seconds/yard) as measured at sea level has been considered as a standard for commercial safety fuse in North America, fuses with different burning rates are manufactured.

Do not depend on all fuse burning at that rate. Although manufacturers state that they use every care and precaution to manufacture a safety fuse which will burn within an allowable variation of 10 percent either way from the specified burning speed, they make no warranty or representations regarding the burning speed of their product because of the many circumstances and conditions the fuse is subjected to after leaving the factory. Differences in altitude, weather, storage conditions, effects of tampings, and mishandling can affect the burning rate of the fuse. MSHA regulation in the United States require that the burning rate of each spool be measured, and the rate posted for all those using the fuse on the property.

### Construction

Modern blasting caps (fuse detonators) consist of aluminum or bronze shells loaded with an ignition powder pressed on top of a base charge of secondary explosive that is tightly pressed into the bottom of the shell. A primer charge may or may not be located between the top charge of ignition powder and the base charge. The ignition powder assures flame pickup from the safety fuse, while the primer charge converts the burning into detonations and initiates the base charge. Above the ignitor charge the shell is open for varying depths (depending on the manufacturer and the underlying explosive train) for insertion of the fuse. Since the ignition powder is exposed in the open end of the shell, blasting caps should never be tampered with or abused in any way as such treatment can lead to premature detonation resulting in serious injury.

Figure 13.54 illustrates the cross section of a factory assembled cap and fuse unit. The base charge and the hat shaped ignition charge are clearly seen at the bottom of the cap. This image shows a square cut of fuse end sealed onto the cap. The crimp is an indentation on the cap shell to join the cap and fuse together. It should be tight enough to hold the cap securely in place and provide a watertight seal. A loose crimp permits the fuse to pull away from the cap charge or out of the cap entirely, and may allow water to get into the ignition powders. This can result in a misfire, a burning charge, or a delayed shot. All crimps must be made near the open end of a cap shell no more than 9.5 millimeters (3/8 inch) from the open end of the shell. Crimping more than 9.5 millimeters (3/8 inch) from the open end of the shell or within of the explosive charge can prematurely initiate the cap. When only a small number of capped fuses are required, a ring-type cap-crimper, designed as both cap crimper and fuse cutter, is generally used to cut the fuse and to crimp the cap onto it. Today, cap and fuse is not widely used as a primary initiation system in the U.S. In the past, operations that used large quantities of cap and fuse established central assembly stations. These stations usually have a workbench with a bench-type cap crimper and fuse cutter, an apparatus to hold one or more reels of fuse; some means of measuring length of fuse for assemblies, and approved storage areas for the fuse, caps, and fuse connectors. Fuse connectors, metal shells similar in appearance to fuse caps, have a heat-sensitive ignition charge that is ignited by igniter cord type products, which are inserted into the slotted end of the connector. The connectors should be crimped onto the other end of the fuse at the same time the fuse caps are crimped. If a central capping station is utilized, approved storage sufficient for one (or more) day's supply of fuse and enough blasting caps for one day's operation is generally provided. Some of the important factors in cutting fuse are listed in table 13.12.

![Figure 13.54 - Cap and fuse assembly. (CXA, 1980). (Courtesy: Orica USA)](images/273.png)

The burning front of the fuse reaches the ignition charge in the cap and then detonates the base charge.

Safety fuse is the medium through which a burning reaction is conveyed at a relatively uniform rate to the ignition area of the blasting cap. The core of the safety fuse is a black powder train, tightly wrapped by multiple coverings of tape, textiles, and waterproofing materials such as asphalt and plastics (See figure 13.55). The functions of the coverings are listed in table 13.11.

**Table 13.11 - Functions of the fuse covering.**

| Function |
|----------|
| Protect the powder train from water, oil or other substances that might affect its burning rate or deteriorate it |
| Produce finer sheath between its stiff shell where maintaining flexibility |
| Minimize the chance of setting fire to the charge of explosives by sparks coming through the side of the fuse before the fire has reached the cap |
| Prevent intercontamination of fusing between adjacent lengths of fuse |

![Figure 13.55 - Fuse construction. (CXA, 1980). (Courtesy: Orica USA)](images/274.png)

Construction begins with a center thread and a blend of special grades of black powder. The fuse powder is enclosed in woven layers of natural and synthetic textiles bonded by a layer of asphalt. A transparent plastic sleeve is applied and then a countering of cotton yarn followed by a final coat of colored finishing wax.

### Performance Features

Standard safety fuse burns at approximately 40 seconds (131 seconds/meter) at sea level. Altitude changes, humidity, and temperature affect this velocity, so test burning of fuse is a necessity each time it is used. At burning typical of safety fuse is subject to variation, it must not be used where precise delay times or control over unmet detonations is required. It must not be used as a measuring device. The burning rate of any fuse should be periodically verified and posted for the blasting personnel.

### Safety Features

Safety fuse has very good resistance to water as long as the structure is not damaged. It is affected by oil including that used in ANFO. It should not be exposed to such explosives or other oil sources for more than 24 hours. It may conduct static electricity or stray current and these hazards should be considered. The addition of a metal staple to the fuse end under the cap crimp will serve as a discharge path in this event.

> **Caution**
>
> In the presence of lightning, operations involving the handling and loading of explosives should be immediately suspended and the areas secured until the threat is gone. In the United States federal regulatory authorities forbid the handling and loading of explosives upon the approach of a storm.

### Cap and Fuse Assembly

Blasting caps should not be removed from the box until they are to be used. They should always be examined to make sure they are not wet and that foreign material has not gotten inside the cap onto the ignition powder. The fuse should be inserted gently into the cap until it seats on the charge. It is absolutely necessary that the powder core in the end of the fuse is in contact with charge of the cap.

> **Caution**
>
> Fuse should never be twisted into place or seated with any force or violence.

The crimp is an indentation on the cap shell to join the cap and fuse together. It should be tight enough to hold the cap securely in place and provide a watertight seal. A loose crimp permits the fuse to pull away from the cap charge or out of the cap entirely, and may allow water to get into the ignition powders. This can result in a misfire, a burning charge, or a delayed shot. All crimps must be made near the open end of a cap shell not more than 9.5 millimeters (3/8 inch) from the open end of the shell. Crimping more than 9.5 millimeters (3/8 inch) from the open end of the shell or within of the explosive charge can prematurely initiate the cap. When only a small number of capped fuses are required, a ring-type cap-crimper, designed as both cap crimper and fuse cutter, is generally used to cut the fuse and to crimp the cap onto it.

**Table 13.12 - Factors to observe when cutting fuse.**

| Factor | Comment |
|--------|---------|
| Ensure fuse has a minimum temperature of 20 °C (45.7F) | Fuse should be warm and flexible before unrolling. |
| Cut ends a minimum of 25 mm (1 inch) (Se figure 13.57) | Cut when fuse ends have been exposed to air for a considerable time |
| Determining length | Length must be sufficient to reach from primer to the collar plus some extra |
| Measuring length | Never wind fuse around small diameter nails of pegs. This can cause sharp bends likely to cause breaks in the water proof coat. |
| Make clean square fuse cuts | Fuse cutter should have a clean, sharp blade |
| Insert fuse into cap | |
| Never forcibly twist before or after inserting | Fuse fuse into cap immediately after cutting |

**Factors to observe when cutting fuse:**

(1) Make sure every fuse is cut initially the same length. Short fuse or unequal lengths of fuse cannot be tolerated. In all blasting of this type the approximate burning speed of the fuse should be known, and the minimum length should be planned to allow the blasters sufficient time to reach a place of safety after lighting the fuse. Under no circumstances should less than 0.9 m (3 ft) of fuse be used. The burning speed of the fuse should be determined by burning a 0.9 m (3 ft) length to determine the burning rate and determining before any charge has been spit and or loaded.
(2) A clean, sharp blade prevents smearing the waterproofing material over the powder axis. Such smearing could result in misfires. An approved cap crimper, either hand or bench type, with a fuse cutter is a satisfactory tool for cutting fuse but not for crimping.
(3) Starting caps should be avoided because of the possibility of impaled ends folds/kinks over and blocking the end up/air when inserted in the cap. Also, a starting cap permits putting the fuse powder against the charge in the cap. Shorts or scissors of any kind are poor fuse cutters because they tend to squash the fuse.
(4) Misfires have resulted from the fuse (powder or at the end of the fuse before it was inserted in the cap. In some cases this was caused by slipping the end of the fuse roughly on the cutting bench or by shaking the fuse after it had been cut.

![Figure 13.56a - Proper square end face cut Ensures proper seating. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 14.1)](images/276.png)

![Figure 13.56b - A failed non-square cut prevents proper seating. (Source: ISEE Blasters' Handbook, 17th Ed. figure 14.1)](images/276.png)

The finished fuse assemblies should be stored in an approved storage facility that is located away from hot sources and personnel. Because bench-type cap crimpers and fuse cutters assured proper cutting of the fuse and automatically provided a double crimp of the fuse cap or the fuse connector to the safety fuse, they were used for many years whenever large numbers of cap and fuse assemblies had to be made. Today, bench-type cutters and crimpers are no longer commercially available in the United States for any new installations and the crimping of blasting caps to safety fuse is generally done with an approved hand-type cap crimper or bench-type crimper.

![Figure 13.57 - Cut off a sufficient length of fuse before using. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 14.2)](images/276.png)

![Figure 13.58 - Sliding a cap onto the end of the fuse. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 14.3)](images/277.png)

### Accessories and Tools

Accessories and tools are required to squarely cut fuse and crimp it into the fuse cap. Several initiation accessory products are available to initiate fuse. These are discussed below.

#### Fuse Cutters

Bench mounted fuse cutters for pre-assembled units and hand cutters are made, but not available in the United States. Cutting in a controlled and clean environment for the make-up of pre-assembled units is the recommended method for multiple borehole rounds. Fuse cutters must be kept clean and sharp at all times. Dull cutters can smear the asphalt coating across the powder core and cause a misfire. Contamination of the fuse ends or caps can cause misfires. Poorly cut fuse ends may keep the black powder core from contacting the cap ignition charge or fire igniter cord connector burning compound. Hand fuse cutters and crimpers are also available, but it is recommended that the process also be done in a clean and controlled environment to make up assembled units for use in the blasts.

![Figure 13.59 - Crimping a cap to the fuse with an approved hand crimper. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 14.4)](images/277.png)

#### Crimpers

Crimpers for bench mounting and use in making up pre-assembled units are the cleanest and most dependable way to put the crimps on caps and igniter cord connectors. Hand cutters and crimpers are also available. A bench crimper is shown in figure 13.60.

![Figure 13.60 - Bench mounted cap crimper. (Courtesy: Dyno Nobel)](images/278.png)

#### Hot Wire Fuse Lighters

The hot wire fuse lighter is a device similar in appearance to a fireworks sparkler. It consists of a wire covered with an ignition composition that burns slowly and at a fairly steady rate with an intense heat. The hot-wire fuse lighter is lighted by a match and can be used to ignite fuse merely by holding the burning portion of the lighter against the freshly cut end of fuse. These lighters are supplied in several lengths.

#### Pull Wire Fuse Lighters

The pull wire fuse lighter is a paper tube closed at one end and containing an igniting device consisting of striker compound on a wire, which protrudes through the closed end of the tube. As fuse is inserted into the open end of the lighter until it touches the end of the wire. The fuse is securely held in this position by an arrangement of metal gripper teeth on the inside of the tube. The fuse is lit by pulling the protruding wire out of the tube.

#### Igniter Cord

When lighting more than a very few cap and safety fuse assemblies igniter cord and igniter cord connectors should be used. Delay timing results from the burning rate of the igniter cord. Igniter cord was available in several different burning speeds, slow, medium, and fast. The fast cord burned at 13 seconds/meter (4 seconds/foot), the medium at 25 seconds/meter (8 seconds/foot), and the slow at 40 seconds/meter (13 seconds/foot). These burning rates were average and not reliable. The igniter cord was marked at 30 centimeter (1 foot) intervals to assist in timing the blast. It may be that only one speed is now available.

Igniter cord and igniter cord connectors are the most convenient and safest means of igniting safety fuses in planned rotations or sequence. The igniter cord system eliminates the need for trimming the fuse or lighting in rotation. It should be the only system used when lighting more than one fuse. All fuses in the round to exactly the same length, since the rotation of firing depends entirely on the length and burning speed of the igniter cord. When the connections are made in the proper order and with the proper igniter cord spacing between connections, the rotation of the round is positive. The expiring time for the man lighting the round is reduced to the time necessary to light the igniter cords of ignition. If the correct core of igniter cord is extremely difficult or slow, a single "map" or flair should be used to ensure the igniter cord or the starting point. In planning a blast using igniter cord and safety fuse, the blaster must take the so-called "5 minute" Group Cord Interval" into account. This is the maximum length of igniter cord that can be used and still assure that all fuses are burning and the equipment boundary time for the first boreholes to fire. This length of igniter cord—determined by the length and burning speed of the safety fuse and by the burning of the fuse—is set for a figure that assures all fuses are firing and lighting prior to the first.

The "Limiting Cord Distance" would be 2.1 meters (7 feet) of fuse at 4 ripest and face = 9.5 meter (28 feet). In other words, 9.5 meters (28 feet) of cord is the maximum length that can be used and still assure that all fuses are lighted and burning inside the boreholes before the first hole fires. Frequently there were igniter cords manufacturers which provided a choice of three burning speeds, however at present in the U.S. the one cord above (formerly the "medium" speed) is the only one available. Igniter cord can be spliced together by means of a tight "Western Union" splice (See figure 13.61). For branch lines connections the branch cord is wrapped tightly around the main line four or five times and the end half hitched to prevent loosening. Igniter cord splices cannot only be made in the manner shown in figure 13.61.

![Figure 13.61 - "Western Union" splice.](images/279.png)

Although igniter cord is simple to use and greatly increases the safety of cap and fuse initiation, the following potential hazards should be avoided:

**Table 13.13 - Igniter cord performance limitations.**

| Limitation |
|------------|
| Igniter cord is subject to ignition by open flame, sparks, friction, or a sharp blow. |
| Igniter cord connectors can be ignited by heavy impact such as Safety fuse. |
| Igniter cord may "jump light" an adjacent line of igniter cord if it is too close or in contact at the cross. |

**Table 13.14 - Igniter cord use limitations.**

| Limitation |
|------------|
| Igniter cord must not be used as a substitute for safety fuse. The proper length of safety fuse must be used. |
| Igniter cord must not be used in any place where an open flame is prohibited. |
| Igniter cord should not be cut with a sharp knife or cutting pliers. It should not be "sawed" or cut with a sawing action since this might generate enough friction to ignite the igniter cord |
| The spool should be placed in the open, not kept in the pocket, when cutting off the required length. |

#### Igniter Cord Connector

The igniter cord connector is a small metal capsule with a slot on one end and an internal ignition compound that burns with an intense heat. The connector is crimped to the safety fuse, the igniter cord is inserted into the slot and the slot is closed with thumb pressure.

- When the metal igniter cord connector is properly attached to the end of the safety fuse with a ring-type crimp, it protects the powder core from moisture and then tends to eliminate this cause of misfired holes. The combination of igniter cord and connectors is sufficiently water resistant to permit the use of safety fuse under certain wet conditions where fuse firing was not previously feasible. When properly crimped on to safety fuse, the connector will function after 14 hours exposure to water (zero pressure). The metal connectors are the same as without Molotov caps. However, the connectors are readily identifiable so they are not likely to be inserted in the primer cartridge instead of the cap. Before inserting the igniter cord in hooking up a shot, the slot of a connector should be examined to be sure it is free of grit and dirt. The igniter cord is then inserted and the slot is closed by thumb pressure.

![Figure 13.62 - (left) Igniter cord inserted into connector. (right) Igniter cord crimped into connector (CXA, 1980).](images/280.png)

### General Use Techniques

Safety fuse and igniter cord can be used to initiate conventional underground development rounds. The hookup of safety fuse rounds of multiple-boreholes must not be attempted without the use of igniter cord and igniter cord connectors.

![Figure 13.63 - Igniter cord hookup for a "V-cut. (Source: ISEE Blasters' Handbook™, 17th Ed. figure 14.3)](images/281.png)

> **Follow Manufacturer's Recommendations**
>
> Cap and fuse initiation system products are available from a number of manufacturers. Products from different manufacturers look alike. The manufacturer's recommendations must be followed and training by their representatives is important for proper and reliable operation of these systems.
>
> The manufacturer's technical literature, recommendations, and extensive training must be used before attempting to use safety fuse and cap products as safety fuse and cap systems can present serious hazards for blasting personnel.

A typical igniter cord hookup for a V-cut showing initiation beginning at the bottom of the pattern and delayed progressively upward and outward is illustrated in figure 13.63. Figures 13.64 through 13.66 illustrate a method for igniter cord hookup of a paralleled borehole round in underground work.

![Figure 13.64 - Igniter core hookup for opening round boreholes.](images/282.png)

![Figure 13.65 - Hookup for upper face of round.](images/282.png)

Igniter cord firing of these types of rounds should not be attempted unless igniter cord connectors are used. The crossed hash marks between holes indicate the relative length of igniter cord between connections.

![Figure 13.66 - Ignitor cord hookup for lower face of round.](images/283.png)

### Cap and Fuse Initiation Methods

Hot wire lighters, pull wire lighters, or even a match or other open flame will ignite safety fuse. Igniting more than one safety fuse at a time with a hot wire lighter or open flame device is not recommended. Any ignition of more than one fuse should be done with igniter cord and connectors. If a match or flame is used (hand lighting), the blaster must have experience recognizing the typical flame "spit" that is characteristic of a lit powder core.

### Fuse Initiation Safety Precautions

Safety fuse should never be hand lighted. To hand light safety fuse reliability, an intensely hot flame must be used and the fuse ends must be clean and freshly cut. Several approved methods, and devices for doing this are discussed in this section. Fuse should never be lighted by a gasoline or kerosene torch, a miner's cap lamp, a burning stick of wood, a roll of paper, or cigar, or a cigarette. No method of hand lighting should be used which results in excessive or erratic evidence that the fuse has been lit. These methods are not only slow and undependable, but they are also extremely dangerous. The powder core of safety fuse insists its wrapping and cannot be seen after the fire from the initial spot. Some brands emit sparks through the wrapping as the powder burns. Visual observation on the outside of the fuse is nearly impossible, however, this may be some distance behind the point of the burning core. For this reason it is not a reliable indication of where the core is burning. The end spit of a lit piece of fuse is readily observed, however, this should not be the method of verification.

**Table 13.15 - Fuse practice reminders.**

| Factor | Comment |
|--------|---------|
| Never flame at the core, soot the end | The cover may burn without the ignition of the core. When properly ignited, the core spits with a jet of flame called the "ignition spit". This spit shows the core is lit. Practice ignition until you know the igniter spit. |
| One person lights the round | Persons must fully recognize the ignition spit, as there are actually two spit(s) the lit fuse. Only then have fuses been lit from a sparky to single fuse to multiple fuses handling igniter cord. |
| Have two persons present when firing | One person does the lighting and the other keeps an accurate account of time and observes all conditions. In this way premature action can be taken in the event that there is an otherwise change in conditions where neither blaster is alone. |
| Know the explosive character of the cap | Never hold the charge in your hand when lighting, with the intent of throwing or relocating after the fuse is burning. This is covered under U.S. MSHA regulation. |
| Misfire waiting time | If the charge does not detonate, or you do not hear the detonation of the calculated time, do not return to the blast area until the fuse has burned and the unexploded charge has been detonated. |

## Squibs and Electric Igniters

Squibs and electric igniters are used to start a burning reaction, and their primary use in blasting is to ignite black powder. They are constructed very much like electric detonators except that they emit a high temperature flame yet when activated rather than detonating. Squibs have limited use in commercial blasting and are becoming very difficult to obtain.

> **Follow Manufacturer's Recommendations**
>
> Squibs or electric igniters should only be used after appropriate training.

### Applications

They are not used any more in any conventional mining applications. Their present use is primarily for special effects, fireworks, and other pyrotechnical purposes.

### Characteristics

A squib generally consists of a small tube filled with an explosive substance, with an initiator through the length of its core. The initiator can be a slow-burning fuse, or as is more common today, a wire connected to a remote electric or electronic trigger. Squibs range in size, anywhere from 2 millimeters to 15 millimeters (0.08 inches to 0.6 inches) in diameter. Squibs are sometimes confused with electric matches as well as with detonators. While those are specifically used to trigger larger explosions, squibs are generally (but not always) the main explosive element.

### Safety Characteristics

Squibs normally have a charge of black powder as the primary explosive. As such, it is very sensitive to heat or flame and should be stored and handled carefully.

## Additional Resources

Atlas Powder Company. 1985. Handbook of Electric Blasting, Atlas Powder Company, Dallas, TX.
CXA. 1980. Product Information Bulletin No. 104. CXA Brownsburg, Quebec.
Hustrulid, W. 1999. Blasting Principles for Open Pit Mining. A. Balkema, Rotterdam, Netherlands.