Workbook 2 - Electrical Blasting

Note: Please DO NOT WRITE in workbooks. Answer on separate piece of paper.

Introduction

The three primary factors to be considered when selecting a blasting initiation system are:

1. Safety
2. Reliability
3. Performance

Section 1: Basic Electrical Concepts

Frame 1. The three primary factors to be considered when selecting a blasting initiation system are _____________, _____________, and _____________.

Frame 2. According to Ohm's Law, voltage divided by _____________ equals current.

Frame 3. The amount of current flowing through a circuit (does / does not - which?) _____________ have a direct bearing on the success of the shot.

Frame 4. List the three basic elements in an electric blasting system:

• A. _____________
• B. _____________
• C. _____________

Frame 5. The two most common power sources used for the detonation of electric blasting caps are _____________ and _____________.

Answers to Section 1

1. safety, reliability, performance (IN ANY ORDER)
2. resistance
3. does
4. blasting machines, blasting caps, firing line
5. blasting machines, power lines

Section 2: Power Sources and Wiring

Frame 1. Storage and dry cell batteries are highly recommended for firing EB caps.

• A. True
• B. False

Frame 2. Rackbar and key-twist blasting machines (are / are not - which?) _____________ manually operated (AC / DC - which?) _____________ generators.

Frame 3. The amount of force exerted by the shot firer when activating rackbar and key-twist blasting machines (is / is not - which?) _____________ directly related to the electrical output.

Frame 4. Capacitor discharge blasting machines (CHECK ANY CORRECT ANSWERS):

• A. will fire more caps than key-twist and rackbar blasting machines.
• B. require the physical force exerted by the shot firer for activation.
• C. do not rely on exertions for activation.

Frame 5. The wires in an electric blasting circuit perform specific functions:

• A. The wires which extend from the end of the EB cap and connect to the bridgewire to form a circuit through the heating element are called _____________.
• B. Wire used to extend the length of other wires is called _____________.
• C. Firing line is used to connect the _____________ to the power source; and,
• D. An extension of the firing line is called _____________.

Frame 6. Aluminum wire functions just as well, or even better than copper in an electrical blasting circuit.

• A. True
• B. False

Answers to Section 2

1. B is correct
2. are, DC
3. is
4. C is correct
5. A. legwires; B. connecting wire; C. blasting circuit; D. buswire
6. B is correct

Section 3: Splices and Circuits

Frame 1. Identify the three splices illustrated below:

• A. _____________
• B. _____________
• C. _____________

Frame 2. The best method for insulating splices is to cover the splice with _____________.

Frame 3. When insulating tape is not available, the splices should be (CHECK THE CORRECT ANSWER):

• A. left as is
• B. raised above the ground and kept dry
• C. buried in the ground

Frame 4. A single-series circuit is used when a (large / small - which?) _____________ number of caps is to be fired.

Frame 5. In a series-parallel hookup, each series (CHECK THE CORRECT ANSWER):

• A. need not have the same resistance.
• B. should have the same resistance.
• C. should never have the same resistance.

Frame 6. Connecting the same number of caps to each series (CHECK THE CORRECT ANSWER):

• A. cannot balance the circuit only when the length and type of legwire are the same.
• B. has no effect on the circuit.
• C. will balance the circuit only when the length and type of legwire are the same.

Frame 7. The gauge of copper conductor must be proportionate to the length of the firing line.

• A. True
• B. False

Frame 8. After the blasting circuit is wired, but before it's shot, the circuit should be _____________ and _____________ checked.

Answers to Section 3

1. A. Twisted loop; B. light gauge to heavy gauge wire; C. light gauge to heavy gauge wire
2. electrical or insulator tape
3. B is correct
4. small
5. B is correct
6. C is correct
7. A is correct
8. visually, electrically (IN EITHER ORDER)

Electric Blasting Test Instruments

Frame 1. Test instruments could be considered the most important blasting accessories you'll use. Such instruments are used to measure various features of the blasting circuit and its immediate surrounding area to assure that the blasting operation is safe and efficient. These instruments do save time, but more importantly they increase the safety factors by reducing the chances of (CHECK ANY CORRECT ANSWERS):

• A. premature detonation.
• B. accidental detonation.
• C. misfires.

Frame 2. Test instruments vary in design and function from one manufacturer to another. So it's very important that you study the information which accompanies the instruments you use and carefully follow the manufacturer's recommendations. In our discussion, we'll talk in generalities and your Instructor will discuss the particulars which pertain to your specific test instruments.

Frame 3. The blaster's multimeter, ohmmeter and galvanometer are blasting accessories about which every blaster should be knowledgeable since they are commonly used in conjunction with his/her work. These instruments are used to check cap circuits. They have internal resistors which limit the current output to less than 25 milliamperes, which is one-tenth the (current / voltage - which?) _____________ needed to fire a commercial electric blasting cap.

Frame 4. It's important for safety and accuracy that only batteries recommended by the manufacturer be used in these instruments. It's also important that these batteries never be allowed to come into direct contact with electric blasting caps. Therefore, EB caps (could / should never - which?) _____________ be tested directly with one of these batteries.

Multimeter

Frame 5. The blaster's multimeter is a meter designed to measure resistance, voltage, and current in electric blasting operations. The resistances of a single blasting circuit and the total resistance in a series-parallel circuit would be measured by using a (CHECK THE CORRECT ANSWER):

• A. voltmeter.
• B. blaster's multimeter.
• C. rheostat.

Frame 6. The blaster's multimeter is also used to check a (minimal / wide - which?) _____________ range of resistance(s) to discover the presence of faulty wiring in the circuit.

Frame 7. Another type of electric instrument commonly used in conjunction with electric blasting is the voltmeter. Voltmeters, as suggested by the name, are used for measuring the _____________ of some power sources and some forms of extraneous electricity.

Blasting Ohmmeter

Frame 8. The blasting ohmmeter is the only type of ohmmeter which should be used to test electric blasting circuits. It's used to measure the resistance of blasting circuits and individual blasting caps with a more precise accuracy and range than the blasting circuits. And for caps, (any type of / only a blasting - which?) _____________ ohmmeter may be used.

Frame 9. You should determine whether the blasting ohmmeter is working properly by shorting both test leads and adjusted until the indicator reads zero. Logically, if the ohmmeter cannot be adjusted to a zero reading, or if the indicator drifts when the circuits are shorted, the battery is too weak (CHECK THE CORRECT ANSWER):

• A. and it must be replaced before the instrument is used.
• B. but it will function well enough to use.

Frame 10. Blasting ohmmeters are specially designed so that the current put into a blasting circuit is a maximum of 0.050 amp. It is imperative that all instruments used for testing electric blasting circuits be especially designed and approved for this purpose.

Blasting Galvanometer

Frame 11. Blasting galvanometers are specially designed types of ohmmeters. One type is a single range ohmmeter which can be used to make continuity tests and rough resistance measurements on firing lines, single EB caps, cap circuits and complete blasting circuits.

Frame 12. Another type of blasting galvanometer is a dual range blasting ohmmeter. It's designed with both high and low resistance ranges to provide greater accuracy. The low range is used to test a single EB cap, a short cap series, a series-parallel circuit or firing line resistance. It's logical then that the _____________ range is used to check a long cap series and current leakage.

Frame 13. Just as we mentioned with the blasting ohmmeter, when a galvanometer cannot be adjusted to a zero reading, the battery is probably too weak to function properly. It must then be replaced with (CHECK THE CORRECT ANSWER):

• A. a type of battery recommended by the manufacturer.
• B. any battery as long as it's the same size.

Frame 14. These batteries should never come into contact with electric blasting caps. Therefore, batteries (could / should not - which?) _____________ be changed in close proximity to EB caps.

Section 4: Testing Procedures

Frame 1. EB caps' resistance should be checked by a blasting ohmmeter (CHECK THE CORRECT ANSWER):

• A. before assembly only.
• B. only if a problem is suspected.
• C. before assembly and after the hole is wired.

Frame 2. With a blasting ohmmeter connected at one end of the firing line and the two conductors shorted together at the other end of the line, the blasting ohmmeter should indicate a resistance (CHECK THE CORRECT ANSWER):

• A. higher than the line being tested.
• B. equivalent to that of the firing line.
• C. lower than that of the line.

Frame 3. Current leakage occurs when part of the current leaves the circuit and travels through the earth or other conductive material.

• A. True
• B. False

Frame 4. Careful insulation of splices (can / cannot - which?) _____________ help reduce current leakage in many instances.

Frame 5. One method used to reduce the effects of current leakage is to (increase / limit - which?) _____________ the number of caps in each series.

Frame 6. When a blasting machine is being used, the number of caps in the blast should not exceed the machine's (minimum / maximum - which?) _____________ rating.

Answers to Section 4

1. C is correct
2. B is correct
3. A is correct
4. can
5. limit
6. maximum

Instructions for Remainder of Workbook

We've covered a lot of material in the workbook segment of this program - initiation systems, EB caps, blasting machines, wiring within a blasting circuit, current leakage, etc. We'll review some of this material, as necessary, and introduce several new subjects, too.

Keep in mind while you're studying this program, that it's extremely important that you relate safe working practices to every aspect of the blasting situation. Explosives are a vital element of most mining operations - improperly handled, they can become one of the most dangerous. Apply common sense and good judgment to your job - they could save your life as well as the lives of others.

Blasting Circuit Calculations

Frame 1. Blasting circuits were mentioned earlier. Now, we're going to go into some depth to show how calculations are made to determine the firing current that will be delivered to the EB caps. As discussed earlier, there are three types of cap circuits commonly used for firing EB caps - single series, parallel, and series-parallel. The calculations for these three types of circuits are somewhat similar when you consider that the resistance of the firing line - including any extensions - is added to the cap resistance to determine the total current supplied by the power source.

Single Series Circuits

Frame 2. In the single series circuit, all of the EB caps are connected in a line. Therefore, the current from the power source has (only one / several - which?) _____________ path(s) to follow.

Frame 3. In the single series circuit, equal amounts of current will flow through each cap. This tells us that the current (CHECK THE CORRECT ANSWER):

• A. will be the greatest at the ends of the line of caps.
• B. is the same throughout the circuit.
• C. will vary from cap to cap.

Frame 4. Years of experience have proven that, for best results, the number of caps wired into a single series should be limited to about 50 caps. So, a single series is commonly used to fire a (small / large - which?) _____________ number of caps.

Frame 5. As mentioned, it's important to determine the amount of current which will flow through the series circuit. The first step in this determination is to find the total resistance. As you probably remember, you must add together the resistance of all the elements of the blasting circuit. Therefore, the resistance of the cap circuit plus connecting wire resistance plus firing line resistance equals _____________.

Frame 6. Remember, when determining total resistance, that a duplex firing line has two wires. So if there's a 400-foot duplex line, the total feet of firing line would be (400 / 600 / 800 - which?) _____________.

Sample Problem - Single Series

Frame 7. For our sample problem let's assume that a series circuit contains 50 caps with 30-foot copper legwires, 200 feet of 20 AWG copper connecting wire, and 500 feet of 14 AWG duplex copper firing line.

First, determine the resistance of one cap circuit by multiplying the resistance of one cap by the number of caps. There are tables which tell you the resistance of caps according to the wire type and length. In this example, we're assuming that the resistance of one 20-foot EB cap is 2.1 ohms.

To determine the resistance of all caps in this circuit, multiply 2.1 ohms per cap by 50 caps, for a total of _____________ ohms.

Frame 8. Now, determine the resistance of the firing line and the connecting wire by multiplying the number of feet of each wire by its resistance per foot. Once again, there are tables provided to indicate the wire resistance in ohms per 1000 ft.

Here, we will give you the amounts to use in this problem:

• 14 AWG copper wire is 2.53 ohms per 1000 feet
• 20 AWG copper wire is 10.15 ohms per 1000 feet

There's 500 feet of duplex firing line, or a total firing line of _____________ feet.

Frame 9. The resistance of this firing line equals the total feet of firing line times 2.53 ohms per one-thousand feet - or, in this case, _____________ ohms.

Frame 10. Now, use 10.15 ohms per thousand feet to determine the resistance of the 200 ft. of 20 AWG copper connecting wire. 200 ft. times 10.15, divided by 1000, equals _____________ ohms.

Frame 11. Okay, so far you know that the resistance of the:

• A. 50 EB caps is _____________
• B. firing line is _____________
• C. connecting wire is _____________

Frame 12. Now you're ready to determine the total circuit resistance, or "R". Add together the cap circuit resistance, the firing line resistance and the connecting wire resistance for a total of _____________ ohms.

Practice Problem

Frame 13. Before we calculate the current delivered to the EB caps let's make sure you understand the procedures used to find total resistance. In this series circuit we have 40 EB caps. The resistance in this circuit is 2.2 ohms. The 20 AWG copper connecting wire is 300 ft. in length (10.15 ohms/1000 ft.). The firing line is 1200 ft. of 14 AWG (2.53 ohms/1000 ft.) duplex copper wire.

Use these figures to calculate the:

• A. resistance of the cap circuit = _____________
• B. resistance of the connecting wire = _____________
• C. resistance of the firing line = _____________
• D. total resistance of this circuit = _____________

Frame 14. All right, now that you've determined the total circuit resistance, you're ready to calculate the current delivered to the EB caps, using Ohm's Law, or I = E/R.

Let's assume a 230-volt power source, and determine the amps by using the total resistance from the first example - 109.56 ohms.

Therefore, I = E/R = 230V/109.56 ohms = _____________ amps.

Frame 15. Use the same formula to determine the current for the circuit with a total resistance of 92.57 ohms - _____________ amps.

Frame 16. Generally, the minimum DC firing current for a single series circuit is 1.5 amps. Since the amps calculated in the above examples (2.1 and 2.48 amps) exceed this minimum, these are considered to be (satisfactory / unsatisfactory - which?) _____________ circuit arrangements.

Series-Parallel Circuits

Frame 17. When individual series are wired in parallel with other series, this type of circuit is known as a (CHECK THE CORRECT ANSWER):

• A. single series.
• B. parallel.
• C. series-parallel.

Frame 18. This type of circuit is often used when more than 40 EB caps are to be fired. Series-parallel circuits are often used in construction, stripping, quarrying and underground operations. Commonly, each series wired into a series-parallel circuit is limited to 40 caps each with a maximum resistance of 100 ohms. Logically, then, if the EB caps have especially long legwires, it may be practical to use (less / more - which?) _____________ than 40 EB caps per series.

Frame 19. And, when current leakage is a problem, the number of caps per series should be (CHECK THE CORRECT ANSWER):

• A. wired as usual since the number of caps will not add to this particular problem.
• B. increased.
• C. decreased.

Frame 20. In a series-parallel circuit, the total current flowing in the firing line divides into each series. It (is / is not - which?) _____________ important that the resistance in each series be the same or very close to the same.

Frame 21. As you'll recall from earlier in this program, the sameness of the current flow in each series is called _____________.

Frame 22. The use of the reverse hookup between the firing line and the buswire, as discussed earlier, (will / will not - which?) _____________ also help assure equal current distribution to all individual series.

Frame 23. If a total of 100 EB caps with 30-foot legwires are to be fired, a (CHECK THE CORRECT ANSWER):

• A. single series circuit will be used.
• B. series-parallel circuit is recommended.

Frame 24. In this case, a single series circuit should not be used because it is recommended that (CHECK THE CORRECT ANSWER):

• A. no more than 50 EB caps be wired into a single series circuit.
• B. more than 50 EB caps should be wired into a single series circuit.
• C. less than 20 EB caps be wired into a single series circuit.

Frame 25. However, in a series-parallel circuit there should be no more than (30 / 40 / 50 - which?) _____________ EB caps wired into each series.

Frame 26. So, in this example of 100 EB caps, to have an equal number of caps in each series there should be (2 / 4 / 6 - which?) _____________ series, with (25 / 50 - which?) _____________ caps in each series.

Series-Parallel Sample Problem

Frame 27. As you'll recall from previous segments of this program, the reason for circuit calculation is to determine whether there's enough current to fire all of the caps. So, regardless of the type of power source, you must find "R", or the _____________.

Frame 28. We've already said we're using 100 EB caps in our example... there's also 200 ft. of AWG copper buswire and 500 ft. of 14 AWG duplex firing line.

First, determine the resistance of one series of caps by multiplying the resistance of one 30 ft. EB cap (2.2 ohms) by the number of caps in the series. Remember, we've already established that you'll need 4 series.

So you'll multiply the ohms per cap, _____________, by the caps in one series, _____________, for a total of _____________ ohms.

Frame 29. The cap circuit resistance is equal to the resistance of one series divided by the number of series for a balanced series-parallel circuit. So, in our example, 55.0 ohms divided by 4 series equals _____________ ohms.

Frame 30. Now, determine the firing line resistance (500 ft. of 14 AWG duplex copper firing line) by multiplying the resistance of the wire by the resistance per foot (2.53 ohms per 1000 ft.).

In this example, the resistance of the firing line is 2 (duplex) x 500 ft. x 2.53 ohms/1000 ft. = _____________ ohms.

Frame 31. To determine the total circuit resistance in this problem, find the sum of the resistance of the cap circuit, the buswire (in this case, 1.02 ohms), and the firing line.

Total circuit resistance = _____________ ohms.

Frame 32. Use Ohm's Law to find the total current just as you did with the single series circuit calculations. Assume a 230-V power source and use the formula I = E/R to find the amps for the above problem: _____________ amps.

Frame 33. Since the individual series are balanced, the total current of 13.3 will divide equally into the four series for a total of (3.3 / 5.0 / 13.3 - which?) _____________ amps per series.

Frame 34. It is usually not necessary to perform blasting circuit calculations for blasts which are fired by blasting machines if the number of caps per series, the number of series, and the resistance of the firing line and EB caps fall within the recommended ratings of the _____________.

Frame 35. Sometimes, it's just not possible to divide EB caps equally in number throughout several series when wiring a series-parallel circuit. This situation will cause an uneven distribution of current because the series will not have a _____________ resistance.

Frame 36. In most cases, when the series in a series-parallel circuit is within one cap, this "unbalanced" condition will not be created. However, if an error has been made and all series contain 30 caps except for one series which has been wired with 15 caps (CHECK THE CORRECT ANSWER):

• A. the resistance in this series will be almost the same as series with 30 caps.
• B. 15 caps should be added to the short series to make it about the same resistance as the others.
• C. it probably won't present any problem.

Frame 37. As we've discussed balancing the resistance throughout this program, we've worked on the assumption that the EB caps all had the same length legwires. But, when EB caps with varying lengths of legwires must be wired in series-parallel, it's logical that (CHECK THE CORRECT ANSWER):

• A. an equal number of caps will balance.
• B. the series should be selected so that it's equal in resistance rather than equal in the number of caps.

Frame 38. A blasting ohmmeter should be used to check the resistance of each series. Then, caps should be (added / removed / added or removed - which?) _____________ as necessary to balance the series.

Extraneous Electricity

Frame 39. In electric blasting operations, extraneous electricity can be defined as any unwanted electrical energy. In other words, extraneous electricity is any electrical energy other than the firing current or the small current introduced into the blasting circuit by a blasting ohmmeter. Since EB caps are designed to be detonated by electrical energy, extraneous electricity (could / could not - which?) _____________ present a potential hazard at blasting sites.

Frame 40. For our purposes here, we're going to break down extraneous electricity into five categories:

1. Stray current
2. Static electricity
3. Electrical storms
4. RF energy
5. High voltage power lines

The rules and regulations concerning the detection, control and treatment of this energy, as they pertain to your particular situation, must be strictly followed.

Stray Current

Frame 41. Stray current occurs when, for whatever reason, current flows outside the conductor which is supposed to carry it. This condition usually is the result of defective insulation on electrically-operated equipment or power systems. So, as a form of extraneous electricity, stray current is definitely classified as (CHECK THE CORRECT ANSWER):

• A. a source of useful energy.
• B. unwanted electrical energy which could present a potential hazard at a blasting site.
• C. a nuisance, but not a dangerous source of energy.

Frame 42. Examples of sources of stray current include:

• Electrified fences
• Cathodic protection on pipelines
• Broken wires
• Broken or improper bonds on tracks which carry electric equipment
• Worn insulation around trailing cables

These defects can be detected and treated so that electric blasting can be conducted safely.

Frame 43. If this condition should arise at a blasting operation, the stray current could cause (CHECK ONLY ONE ANSWER):

• A. Premature detonation of EB caps or explosives.
• B. Sparks which cause a fire, or an explosion.
• C. Both A and B are correct.

Frame 44. Commercial EB caps manufactured in this country are all designed to have a minimum firing current of more than 0.25 amp. This minimum limit - or "no-fire" range - serves as a guideline for measuring safe levels of stray current to prevent accidental _____________ of explosives.

Frame 45. Any power source which can deliver .05 amp or more to a one-ohm resistance should be looked upon as a source of a potential hazard. These currents can cause a problem where there's electric blasting. Because they are too small to operate standard circuit-protection devices such as fuses and breakers, they (CHECK THE CORRECT ANSWER):

• A. are usually detected immediately.
• B. often are not detected.
• C. are not considered a potential hazard.

Frame 46. A check can be made at a blasting site for stray current. This can be done with a voltmeter capable of accurate readings as low as .05 volt for both AC and DC, a length of connecting wire, and a 1 ohm resistor to simulate an EB cap.

Connect the wire with a one ohm resistor from the suspected sources of stray current to the earth and measure the voltage drop across the resistor. If the voltage reading on the meter is .05 volt or more - AC and DC, not just one - there is a hazard.

So the possibility of a hazard exists when the voltmeter indicates a reading of (CHECK THE CORRECT ANSWER):

• A. less than .05 volt.
• B. .05 volt or more, AC and DC.
• C. more than .03 volt, AC or DC.

Frame 47. If a voltage of .05 or more (AC and DC) is indicated, the test should be repeated. Then, if the voltage reading is still .05 volt or more, AC and DC, the source of the _____________ should be discovered and eliminated.

Frame 48. So far, you know that stray current:

• A. occurs when current flows (inside / outside - which?) _____________ the conductor which normally carries it.
• B. (could / could not - which?) _____________ prematurely detonate EB caps.
• C. can be detected by using a _____________ capable of accurate readings at .05 volt or more, AC and DC.

Frame 49. There are safety procedures which should be followed to minimize the possibility of stray currents - and to reduce the chances of stray current getting into an electric blasting circuit if they should occur. For example, electrical power distribution systems and any electrically-operated equipment located near a blasting site should be checked periodically. Such checks should assure that all wiring and insulation are in good condition. Many mining operations utilize ground fault detection devices which will open a circuit breaker if a fault occurs in the system.

Therefore:

• A. special precautions such as periodical _____________ can help prevent the formation of stray current, and
• B. special _____________ devices can prevent stray current from forming by opening the circuit to the source of the electrical energy.

Frame 50. Another precaution which will help minimize the possibility of stray current is that all metal pipes, tracks, framework, housings and so forth, should be bonded and cross-bonded to each other and to a satisfactory earth ground. As in every case, any practices suggested in this program must be carried out in accordance with (CHECK THE CORRECT ANSWER):

• A. the personal preference of the supervisor.
• B. federal, state, local, and company laws, regulations and specifications.
• C. each mine's policy.

Frame 51. It makes sense that all potential sources of stray current should be removed from the blasting site (before / after - which?) _____________ the start of any explosives loading.

Frame 52. It is recommended that a buffer zone be allowed between the blasting area and possible stray current sources such as power lines, lights, batteries, electrical equipment, etc. In other words, it's a good practice to keep all potential sources of _____________ as far away from all explosives as practical.

Frame 53. Sometimes, it's necessary to have electrical equipment close to a blast area. When this is the case, the approved types of electrical systems must be used. Specific rules and guidelines are provided to make such systems safe. If the presence of stray current is suspected, a stray current _____________ should be made as discussed earlier.

Frame 54. Then, if more than (0.02 / 0.03 / 0.05 - which?) _____________ amp of AC and DC stray current is detected, the source should be found and eliminated.

Frame 55. Known sources of stray current close to a blasting operation - cathodic protection on metal pipelines, electrified fences, electric railways, etc. - should be de-energized and locked off when explosives are present. If for some reason this de-energization cannot be accomplished, a stray current survey or check should be made to determine the effect on the blasting circuit. Whenever possible, then, de-energization of known stray current sources should be carried out to prevent this form entering the _____________ circuit.

Frame 56. We mentioned earlier the importance of shunting EB cap legwires. So, just as a reminder, these shunts (CHECK THE CORRECT ANSWER):

• A. should only be removed just before the legwires are tied into the blasting circuit.
• B. can be removed at any time if everyone in the area is aware that they are unshunted.

Frame 57. In fact, except when firing the shot, all free blasting circuit wiring ends (should / should not - which?) _____________ be shunted.

Frame 58. The importance of sound insulation has been discussed several times, so it's enough to say that all splices should be properly _____________ from the ground and other potential stray current sources.

Frame 59. And, because stray current can enter a blasting circuit in the same manner that current can leak out (current leakage), proper _____________ will help reduce the possibility of both of these problems.

Static Electricity

Frame 60. Static electricity, like stray current, is another form of "unwanted" or extraneous electricity. This type is electrical energy which is actually stored or accumulated on an object - or even on a person.

Research has shown that static electricity will present a hazard to EB caps only if three conditions occur in a specific order - generation, accumulation, and discharge.

Since the proper sequence of these conditions is necessary to present a potential hazard to EB caps, the elimination of one condition would, logically (CHECK THE CORRECT ANSWER):

• A. cause the potential hazard to be produced more rapidly.
• B. would not affect the process.
• C. eliminate the potential hazard.

Frame 61. Let's discuss these three conditions briefly. Static electricity is generated by the contact and separation action of dissimilar materials or of the same material if the components are of different temperatures, or when certain materials are rubbed together - especially if one or both of these materials are poor conductors of electricity.

Some good examples of static electricity generators found in mining operations are:

• Moving conveyor belts
• ANFO which is pneumatically loaded into a borehole through a hose
• Snow and dust carried by high winds
• Different synthetic-fabric clothing rubbing together
• The formation of electrical storms

It could be assumed, then, that the conditions necessary for the generation of static electricity are (often / rarely - which?) _____________ found in blasting areas.

Frame 62. But, you must remember, after static electricity is generated it must be _____________ on some object or person that can serve as a capacitor.

Frame 63. To present a hazard to the blasting circuit, the static electricity must first generate, then accumulate, and then _____________ and deliver enough energy into the EB cap to cause it to fire.

Frame 64. The static electricity problem could be solved by the elimination of the three necessary conditions: (NAME THEM IN ORDER) _____________, _____________, and _____________.

Frame 65. The generation process is often inherent in nature, so the elimination of this condition (CHECK THE CORRECT ANSWER):

• A. could be impossible.
• B. should be easy to accomplish.

Frame 66. Even though there's little that can be done to stop the generation of static electricity, the accumulation of this energy can be prevented, and the susceptibility of EB caps can be minimized. These safety procedures include the cross-bonding and grounding to earth of all objects and people on which static electricity might be (generated / accumulated - which?) _____________.

Frame 67. And, also EB caps with built-in protection against accidental detonation by static electricity (accumulation / discharge - which?) _____________ can be used.

RF Energy

Frame 68. Radio frequency energy, or RF as it is commonly called, is yet another form of extraneous or unwanted electricity. RF energy is produced by transmitting antennas. Electric blasting circuit wires can act as receiving antennas, and, theoretically, could extract or interpret enough energy to fire an EB cap.

Even though the possibility of accidental detonation of EB caps by RF energy may appear to be unlikely, precautions (should / should not - which?) _____________ be taken to avoid even the slightest possibility of accidental detonation.

Frame 69. For example, tables which give safe operational distances for all commercial EB caps from all non-military radio transmitters have been developed by the Institute of Makers of Explosives. These tables should be considered should any questions arise.

Frame 70. To determine the safe distance which should separate the transmitting antenna and the blasting site, it is necessary to know the transmitter's frequency and effective radiated power. In fact, all transmitters near to or affecting a _____________ should be considered.

Frame 71. Blast sites in proximity to military transmitting facilities should be evaluated in conjunction with the technical authorities at the military installation. These transmitters are often rated as to power and purpose, and, therefore, are not covered by the Institute of Makers of Explosives.

Frame 72. We mentioned that the probability of premature or accidental detonation of EB caps by RF energy is rather remote. This conclusion was reached because of the fact that throughout the years - and through the use of literally millions of EB caps - few if any accidents have occurred from RF energy. However, all safety practices (should / should not - which?) _____________ be followed so that this accident record remains unspoiled.

Electrical Storms

Frame 73. Lightning, associated with electrical storms, is really tremendous amounts of discharged static electricity. Since lightning is a type of electrical atmospheric disturbance, it (can / cannot - which?) _____________ present a hazard to any operation where explosives are used.

Frame 74. In some instances, the cases of explosives carry warnings which state that all persons must stay away from the enclosed explosives products during the approach and duration of an electrical storm. It stands to reason that, when this is the case:

• A. all explosives loading operations (must / need not - which?) _____________ be stopped until the storm has passed; and,
• B. all persons in and near the blast area should move to a (safe / working - which?) _____________ area.

Frame 75. Lightning storms occur most frequently during the summer months and in certain geographical areas. Those areas where electrical storms are commonplace should have guidelines to follow for evacuation of blasting areas when these storms approach. Such rules would include the move to a safe position as mentioned above and the assurance that this safe position would logically provide protection not only from lightning itself, but also protection against rock or other objects which could be thrown by any explosives which might be accidentally _____________ by lightning.

Frame 76. We're going to suggest some safety recommendations which could be used as the basics for the establishment of guidelines to follow for protection against the potential hazards of electrical storms. First, early detection or advance warning of the approach or development of electrical storms will provide the time necessary to _____________ the mine site.

Frame 77. There are three methods which can be used for the detection of an electrical storm. The first and most accurate method is to use a thunderstorm warning device which monitors the characteristics of _____________ storms.

Frame 78. The next method which is not quite as accurate as the device just mentioned is the services of the local weather station. These stations often use radar and can track electrical storms. So the approach of an electrical storm to a blast area (CHECK THE CORRECT ANSWER):

• A. can be detected.
• B. cannot be tracked to a blast site.
• C. would be detected much too late for evacuation.

Frame 79. The least reliable of the methods for tracking storms is the assignment of a person to monitor atmospheric conditions for visual evidence of an approaching electrical storm. This method of detection is better than none at all, but it (can / cannot - which?) _____________ be relied upon for obvious reasons.

Frame 80. Number the three methods of electrical storm detection by their reliance:

• A. _____ Individual assigned to visually monitor atmospheric conditions.
• B. _____ Storm warning device.
• C. _____ Local radar weather station.

Frame 81. When it is evidenced that an electrical storm is imminent, all personnel (CHECK THE CORRECT ANSWER):

• A. should continue working in case the storm should pass by.
• B. must evacuate away from the blast area to a position of safety.
• C. take cover at the blasting site.

Frame 82. When personnel leave the blasting site because of a storm, they must leave all individually shunted EB caps undisturbed whether or not they are in a loaded borehole. And all shunts and closed wire loops in the blasting circuit should be opened if there's time - don't unnecessarily delay getting out of the area. In addition, care must be taken to keep all bare wire from the earth.

Frame 83. After the storm has passed, the work situation should return to normal as soon as possible. So, immediately upon return to the work area, all shunts should be _____________.

Frame 84. Because lightning is a phenomenon of nature that cannot be controlled, it is imperative that every precaution possible be taken to prevent the accidental detonation of any type of explosive due to lightning strike.

In summary, the precautions we've discussed include:

• A. adherence to the warning in every case of _____________
• B. early detection of a storm approach, preferably through the use of a _____________; but, if this method is not used, the local radar _____________ can detect an approaching storm
• C. as a last resort, an individual can be assigned to check atmospheric conditions
• D. when a storm is approaching, all personnel must move from the blast area to a _____________ location
• E. upon leaving the blast area, leave shunted EB caps _____________
• F. open all shunts in closed _____________ circuits

High Voltage Power Lines

Frame 85. Because of the increased need for high voltage power, more mining operations are finding it necessary to work closer to these power lines than ever before. When this type of situation arises, the safety precautions to be taken are electrical in nature. The power lines must not present a hazard to electrical blasting, and the blasting must not interfere with the _____________.

Frame 86. In most cases, high voltage power lines are balanced, 3-phase, AC systems consisting of four or five conductors. There are usually three high voltage phase wires suspended by or supported on insulators. These are the wires which carry the electrical _____________.

Frame 87. Then, one or two overhead ground wires are usually strung on top of the phase wires. These ground wires act as the neutral _____________ for the system.

Frame 88. Ground wires also protect phase wires from being struck by lightning and they are usually grounded to earth at each tower or pole.

When determining the effects a high voltage power line might have on a blasting circuit, there are four primary factors which must be considered:

1. Capacitive and inductive coupling - this is the electrical energy that may be introduced into the blasting circuit by electric and magnetic fields which are associated with power lines. Both of these elements are normally very inefficient, but if lightning strikes the phase wire, or if there's a fault in the system (CHECK THE CORRECT ANSWER):
   • A. a current surge could be produced which would increase inductive coupling.
   • B. inductive coupling would be weakened.
   • C. power would be cut off instantaneously.

Frame 89. From previous discussions, you realize the seriousness of stray current. So it's enough to say here that even though the current flow through neutral wires is low for balanced 3-phase systems, it is possible for some unbalanced current to exist. And, since the neutral wires are usually grounded at towers or poles (CHECK THE CORRECT ANSWER):

• A. stray current cannot leak out.
• B. some stray current may leak out into the earth.

Frame 90. Lightning is another consideration. Overhead ground wires are supposed to intercept lightning strikes and dissipate the surge of current to the earth. This is usually accomplished near where the lightning strikes. It should be taken into consideration, however, that this surge of current from the lightning could be carried a greater distance. Or, it could travel closer to the _____________ area than initially thought.

Frame 91. The fourth element concerning high voltage power lines is wires thrown over the power line. It is conceivable that the firing line or other blasting circuit wires could be thrown over a high voltage power line by the force of the blast. Should this occur, it would result in (CHECK THE CORRECT ANSWER):

• A. short circuit from the phase wire, through the blasting circuit wires to the earth.
• B. an unimportant shorted circuit.
• C. a short-lived inconvenience.

Frame 92. Over the years, it has been proven that this throwing of wires over high voltage lines is the greatest hazard to electric blasting caused by power lines. In fact, several shotfirers have been injured or killed by this short-circuiting. Studies have also shown that by following a set of safe operating procedures, this work can be accomplished safely and efficiently.

Frame 93. First of all, there are laws and regulations, both federal and state, which govern certain aspects of working around or near power lines. These laws must be followed in every instance. Our purpose here is to make you aware of the potential hazards and the importance of common-sense and good judgment used in conjunction with the law.

First, blasts should be planned so that effects will be controlled and will not damage _____________.

Frame 94. Consider the incorporation of the following procedures into your blasting plan to help minimize the hazards of electric blasting in proximity to high voltage power lines. Conduct a survey for stray and coupled current (CHECK THE CORRECT ANSWER):

• A. before any blasting is started.
• B. after a blast.
• C. only when lightning is striking near the blast area.

Frame 95. Keep all blasting circuit wire close to, but insulated from, the earth. In fact, if a source of stray current exists, you may want to switch to non-electric components in that part of the system. If not, keeping circuit wire close to - but insulated from - the ground helps to minimize the effects of capacitance coupling and keeps _____________ out.

Frame 96. Use duplex or twisted pair wires or lay out the circuit so that large closed wire loops are not formed. The firing line should run perpendicular - rather than parallel - to the power line. This will help (minimize / maximize - which?) _____________ inductive coupling effects.

Frame 97. The blasting circuit wiring should be firmly anchored to the ground by wooden stakes or large rocks to help prevent the wires from being thrown (CHECK THE CORRECT ANSWER):

• A. across the blast area.
• B. over high voltage power lines.

Frame 98. It should be mentioned that, in addition to the safety procedures suggested here, the shotfirer can be even further protected from electrical shock and extraneous current resulting from high voltage power lines if the firing line (is / is not - which?) _____________ run under or parallel to the high voltage power lines.

Frame 99. We've mentioned several times the responsibilities that anyone who works with or around explosives has some specific responsibilities which must be carried out after the shot is fired. For instance, the blaster should not leave the area until he/she has looked for hazardous conditions, including wires thrown over power lines, or damage to power lines themselves. If any such hazards are found, it's logical to assume that (CHECK THE CORRECT ANSWER):

• A. work should continue with extra precautions.
• B. the area should be barricaded and guarded.

Frame 100. When this problem occurs the barricade and guard should remain until the power company has been notified and the necessary repairs made. Such repairs can be made by (CHECK THE CORRECT ANSWER):

• A. anyone working in the blast area.
• B. experienced and capable power company personnel.
• C. any electrician available at the time.

Frame 101. When blasting operations are necessary anywhere near power lines, the laws - including any distance requirements - must be rigidly followed. Laws and regulations mean federal, provincial, local and company policies. When these standards are used in conjunction with experience, common-sense, and good judgment, blasting operations (can / cannot - which?) _____________ be performed in a safe, efficient manner.

Frame 102. This concludes the coverage of extraneous electricity in electric blasting. The suggestions given in this segment of this program are intended to be just that - suggestions. Any questions you may have concerning the procedures utilized at your operation should be discussed with your supervisor.

Misfires

Frame 103. A misfire is defined as the failure of an explosive charge to detonate at the proper time, or explosive charges which fail to fire when the firing signal is applied. In this discussion, then, a misfire means explosives (CHECK THE CORRECT ANSWER):

• A. which fire ahead of the planned timing.
• B. that remain unfired after the blast.
• C. fired after the planned delay time.

Frame 104. By thoroughly understanding the cause of misfires, you can help prevent them. Although it is possible for defective EB caps or explosives to cause a misfire, rigid manufacturer quality controls have greatly reduced this probability. In many misfire situations, improper techniques in wiring the circuit, etc., have been the cause.

Knowledge of these causes and the proper corrective action (CHECK THE CORRECT ANSWER):

• A. probably won't help all that much since you have no control over the quality of explosives.
• B. could greatly reduce the possibility of misfires and increase the efficiency of the blasting operation.
• C. could help in rare situations but there's little that can be done to prevent misfires.

Common Causes of Misfires

Frame 105. Okay, let's talk about some of the most common causes of misfires and the corrective action to be taken. For example, poor wire connections can result in misfires. The solution to this problem is quite simple - make sure that all corrosion, dirt and insulation is cleaned off wire ends before making _____________.

Frame 106. And, in addition to making certain the wire ends are clean, the connections must be made strong and secure. Bare wire splices in water is another cause of misfires. You're well aware that these splices should be kept out of water and away from wet areas. And, a good rule to follow which has been discussed earlier is to (CHECK THE CORRECT ANSWER):

• A. keep the splice on the ground.
• B. cover the splice with dirt.
• C. keep the splices off the ground by raising them or placing them on cardboard.

Frame 107. Another common cause of misfires - an improper cap circuit. Use what you've learned from previous sections of this program to determine corrective action for this problem (CHECK ANY CORRECT ANSWERS):

• A. Never exceed the power ratings for the power source used to fire the shot.
• B. Never use more than the recommended number of caps.
• C. When using a series-parallel circuit, the resistance of the individual series should be balanced.

Frame 108. Caps not properly wired into the circuit can misfire. To help eliminate or prevent this problem, someone should be assigned to check the circuit by walking the shot and visually checking the wiring and counting the holes.

Frame 109. Mixed caps can misfire. The corrective action for this condition is simply to (never / sometimes - which?) _____________ use caps from different manufacturers in a cap circuit.

Frame 110. You're probably well aware of the fact that defective or inadequate firing line can cause misfires. As is true in most problems, the solution or preventive action is quite simple - just take the few moments necessary to make sure the job is done right. In this instance, the firing line should be well insulated - and the splices on the firing lines should be well _____________ with electrician's tape.

Frame 111. The size and gauge of the firing line should be large enough to allow the delivery of the proper firing current to the cap circuit. This will prevent any problems caused by an _____________ firing line.

Frame 112. Inadequate power source is yet another cause of misfires. The power line or blasting machine should always be checked (prior to / after - which?) _____________ shot firing.

Frame 113. We've given you a capsule view of the most common causes of misfires and the prevention or corrective measures which should be taken. Mostly, these procedures are so simple that they're second nature. But, on the other hand, care must be taken not to overlook anything because it appears unimportant at the time. It could very well be important enough to prevent a serious accident. As we've said so many times, common sense and good judgment go hand-in-hand with a safe, efficient operation.

Handling Misfires

Frame 114. Okay, let's talk about what to do if one or more holes in a shot should misfire for whatever reason. Remember, there are federal, provincial and company regulations which deal with the handling of misfires. These rules (must always / need not - which?) _____________ take precedence over any other suggestions.

Frame 115. With this in mind, here are some suggested procedures which can be used, when appropriate, should a misfire occur. Never attempt to check out a misfire too soon. If there are no specific rules to follow at your operation, wait for at least an hour. In any case, never approach the blast area immediately after a shot which contains _____________.

Frame 116. The cap circuit in any misfired holes should be checked with a (blasting ohmmeter / voltmeter - which?) _____________ as discussed previously.

Frame 117. If this check proves the cap circuit to be sound, and if there's adequate burden on the holes, the caps should be rewired into a blasting circuit and refired with an adequate power source. If everything else checked out good, the power source (probably / could have - which?) _____________ caused the misfire.

Frame 118. Sometimes it is wise to contact the explosives supplier or manufacturer for recommendations as to how to handle specific problems. For instance, they may suggest how to dispose of misfired holes which do not have adequate burden. Or the supplier may want you to keep undetonated EB caps or explosives so they can be examined to determine whether a defective product was the cause of the misfire.

Frame 119. It's always important that a thorough investigation of misfired holes be carried out to determine the real cause. Discovery of the real cause will allow for the establishment of procedures to prevent future _____________.

Frame 120. This completes your study of electrical blasting. Combine what you've learned here with your own experience, sound judgment and the laws which govern your particular operation and you'll help make your working area safer and more efficient for yourself and your fellow workers.

Test - Workbook 2

Electrical Blasting

1. One of the most important factors in the blasting operation is the:

• A. Number of blasters working at the mine.
• B. State in which the mine is located.
• C. Selection of the proper blasting initiation system.

2. According to Ohm's Law, voltage divided by resistance equals:

• A. Current.
• B. Wattage.
• C. Ohms.

3. The three basic elements in an electric blasting system are:

• A. Safety, reliability, performance.
• B. Blasting caps, firing line, power source.
• C. Government standards, company regulations, local permits.

4. One of the most common sources of power used for ignition of electric blasting caps in surface mining is a:

• A. Power line.
• B. Blasting machine.
• C. Storage cell battery.

5. In an electric blasting circuit, the wires which extend from the end of the EB cap and connect to the bridgewire to form a circuit through the heating element are called:

• A. Connecting wires.
• B. Legwires.
• C. Buswires.

6. In an electric blasting circuit, wire used to extend the length of other wires is:

• A. Insulated legwires.
• B. Buswire.
• C. Connecting wire.

7. In a parallel circuit - which requires high current - most important in controlling the amount of current to the cap circuit is the:

• A. Resistance of the firing line.
• B. Resistance of the legwire.
• C. Size of the insulating connected wire.

8. The extension of the firing line along which individual or individual series of EB caps are connected is the:

• A. Connecting wire.
• B. Bridgewire.
• C. Buswire.

9. The best method for insulating splices is to cover the splice with:

• A. Electrician's tape.
• B. Rubber tubing.
• C. Filament tape.

10. An important factor in the safety and efficiency of electrical blasting is:

• A. Series balancing.
• B. Series staggering.
• C. Abstract series.

11. The series in a series-parallel circuit:

• A. Need not have the same resistance.
• B. Should never have the same resistance.
• C. Should have the same resistance.

12. In balancing the resistance of a series, connecting the same number of caps and checking the lengths of their legwires is:

• A. Not important or necessary.
• B. Slightly important, but not always necessary.
• C. So important that you should not use caps from different manufacturers in the same shot.

13. Buswire, used to connect individual series to the firing line:

• A. Cannot be re-used, but is relatively inexpensive.
• B. Can be used over and over.
• C. Is used only when absolutely necessary because of the cost.

14. In series-parallel circuits, a reasonable maximum resistance is:

• A. Four ohms.
• B. One hundred ohms.
• C. Two ohms.

15. The most important blasting accessories you will use are:

• A. EB cap carriers.
• B. EB test instruments.
• C. Dry cell batteries.

16. Multimeters, ohmmeters and galvanometers are used to:

• A. Measure cap circuits.
• B. Survey the mine size.
• C. Control the blast.

17. The only type of ohmmeter which should be used to test electric blasting circuits is the:

• A. Rheostat.
• B. Voltmeter.
• C. Blasting ohmmeter.

18. With the two conductors shorted together at one end of the firing line and a blasting ohmmeter connected at the end of the line, the blasting ohmmeter should indicate a resistance:

• A. Lower than that of the line.
• B. Equivalent to that of the firing line.
• C. Higher than the line being tested.

19. The cap circuit resistance plus connecting wire resistance plus firing line resistance in a series circuit equals:

• A. Total resistance.
• B. Total wattage.
• C. Total voltage.

20. The type of circuit where individual series are wired in parallel with other series is a:

• A. Single series circuit.
• B. Series-parallel circuit.
• C. Parallel circuit.

21. The reason for circuit calculation is to:

• A. Make sure there's not excessive current for firing.
• B. Determine the firing current.
• C. Calculate unwanted electrical energy.

22. Extraneous electricity in electric blasting operations can be defined as:

• A. Electrified fences, broken wires.
• B. Worn insulation around trailing cables, cathodic protection on pipelines.
• C. Both A and B are correct.

23. Examples of stray current sources are:

• A. Electrified fences, broken wires.
• B. Worn insulation around trailing cables, cathodic protection on pipelines.
• C. Both A and B are correct.

24. You can check for stray currents at a blasting site by using:

• A. A voltmeter - capable of readings as low as .05 volt for both AC and DC.
• B. A blastometer - capable of readings as low as .05 volt for both AC and DC.
• C. An ohmmeter - capable of readings as low as .05 volt for both AC and DC.

25. Shunts on EB cap legwires:

• A. Can be removed at any time, if everyone in the area is made aware.
• B. Need never be removed.
• C. Should only be removed just before the legwires are tied into the blasting circuit.

26. The type of electrical energy which is actually stored or accumulated on an object or person is called:

• A. Static electricity.
• B. Kinetic energy.
• C. Energy throw-back.

27. To present a hazard to the blasting circuit, static electricity must:

• A. Generate and accumulate energy.
• B. Generate, accumulate and store energy.
• C. Generate, accumulate and discharge energy.

28. Another form of extraneous or unwanted electricity is:

• A. Radio frequency energy.
• B. Radio energy.
• C. Transmittal electricity.

29. In most cases, high-voltage power lines are:

• A. Balanced, 3-phase, DC systems consisting of four or five conductors.
• B. Balanced, 3-phase, AC systems consisting of four or five conductors.
• C. Balanced, single-phase, AC systems consisting of four or five conductors.

30. Ground wires strung on top of high voltage power lines act as the system's neutral:

• A. Phase wire.
• B. Guide wire.
• C. Conductor.

31. To keep blasting circuit wiring from being thrown over any high-voltage power lines in the area, the wires should be:

• A. Anchored to the ground with metal stakes.
• B. Anchored to the ground by wooden stakes or large rocks.
• C. Tied down with rubber tubing.

32. (Question number skipped in original)

33. Misfires are shots which:

• A. Remain unfired after the blast.
• B. Fire ahead of the planned timing.
• C. Are fired after the planned delay time.

34. Common causes of misfires are:

• A. Poor wire connections, bare wire splices in water.
• B. Improper cap circuit, caps not properly wired.
• C. Both A and B are correct.

35. The cap circuit in any misfired holes should be checked with a:

• A. Seismograph.
• B. Voltmeter.
• C. Blasting ohmmeter.

Answer Key