Chapter 10: Blasting Safety

Over the past half century, the blasting industry has been made safer with the development of less sensitive explosives, improved initiation systems, and loading equipment. However, the mere use of new products and equipment has not been a cure-all to prevent blasting accidents. Blasting accidents still occur and they are almost always severe. In the past, studies of accidents occurring on the job placed blasting at 0.1% of the total injuries and 1.3% of fatal injuries (BOM 1959). In more recent studies, it was found that when excavating with other equipment, only 7 out of 1,000 are fatal. Various other statistical measures, as well as common sense confirm that blasting accidents will always be more severe than any other type of mine accident. The detonation of explosives releases tremendous power and energy, and the slightest error of omission can have severe consequences.

Planning A Comprehensive Safety Program

A comprehensive and well-supported safety-training program encourages safe behaviors as habits among its work force. Effective safety programs create safe work habits through repetition, personal contact by management, training, and sound safety rules and regulations.

Repetition

Safety is a habit and habits are formed only through repetition. It is unrealistic to expect every routine action performed during the working day will be a well thought-out, conscious act. Good safe working habits protect a person from injury even during brief lapses of attention. Constant training in task performance develops such habits in the correct manner until it is ingrained in the blasters' mind.

Personal Contact

The company safety department or safety director can only provide guidelines and general direction to a safety program. The major responsibility for the success of a safety program depends on the attitude of the line supervisors who are in daily contact with the blasting crew. Their contact with the crew should be directed toward preventive action rather than corrective measures done as a result of an accident or near miss.

Safety Meetings

Formal safety meetings are usually the means to convey knowledge and expertise to a relatively large group of people. It is imperative that management at all levels actively participate in and support these meetings. Failure of management to sincerely promote safety will be noticed by the employees and create an obstacle that even the best planned safety program cannot overcome. Informal "tailgate" or "toolbox" safety meetings held at the blast site are an excellent way to orient the blast crew on the specific plans for a blast or duty activity deemed ahead. A good outline for such meetings is provided by the Institute of Makers of Explosives (IME) in their Safety Library Publications (SLPs) (See SLP 25 and 4).

Training

The most effective step toward preventing accidents is to provide proper training of the blaster and the blasting crew. All members of the blasting crew must recognize the hazards involved in their work and must clearly understand and execute sound procedures and methods to eliminate or reduce these hazards. The fact that modern explosives have become so stable may occasionally cause blasters to lapse into attitudes of complacency when using them. Many organizations provide effective blasting safety training. The Handbook and the ISEE Certificate Programs are two excellent sources of safety information. Another good source of safety information is the IME's SLPs. This SLP collection consists of a series of publications relating to specific areas of explosives and blasting safety, and explosives security. From time to time, new SLPs are added and outdated training retired. Paper copies of these may be obtained through the International Society of Explosives Engineers (ISEE) Blasters' Library Catalogue or electronic versions can be downloaded from the IME web site. The SLPs available at the time of this writing are listed below. For the most complete and current SLP listing please visit the IME website.

List of IME SLP

Table 10.1 – List of IME SLPs (2015).

Certification and Licensing

Many states or cities require that a blaster be certified or licensed to use explosives. Certifications or licensing programs usually require that the blaster demonstrate knowledge and competence through some combination of training, examinations, and supervised work experience. Any new employee who will be working with explosives should be trained in blasting safety, government regulations, and IME SLP 4 before they handle explosives. Attendance at one of the many excellent training courses or seminars on the safe handling of commercial explosives, including the Certificate Program, is strongly recommended. Classroom sessions must be supplemented with on-the-job training by an experienced blaster until trainees demonstrate that they are capable of working without close supervision. Good blasting safety programs take time, effort and careful planning if they are to achieve the ultimate goal of zero accidents.

Type Of Personnel

Explosives alone do not cause accidents. Accidents are caused by the careless or thoughtless acts of people. The most important ingredients in a safety program are the quality of the people and the quality of their training. The following two considerations should be made when selecting a blasting crew.

Personnel designated to handle explosive materials should have intelligence, common sense, and be trained in the safe use of explosives. They must understand the possible consequences of errors or omissions in their actions. Most blasters handle explosives conscientiously and use their skills with discretion and judgment. However, there is a small minority, who, no matter how well they know the technical aspects of blasting, do not have the proper attitude to be safe and efficient blasters.

Blasters who, due to lack of knowledge or training, carelessness, or bravado, follow unsafe practices, constitute the greatest threat to blasting safety. A blaster who is reckless, and unwilling to use and insist on sound safety practices should be removed from all contact with explosives.

Qualifications

It is important that the responsibility for the conduct of all activities on the blasting operation be assigned to the blaster-in-charge. Supervisors or managers who do not possess the experience, training and certification of the blaster should not be making decisions affecting the safety of the blasting operations. Nor should they exert undue pressure on the blaster to meet production goals if such goals would necessitate or encourage "shortcuts" or other unsafe practices.

Often many various levels of governmental authority may require people handling or responsible for the use of explosive materials meet specific background check criteria.

The "Part-Time" Blaster

Explosives should be used only by well-trained, experienced, and skillful blasters who are engaged in the use of explosives on a daily basis. The practice of filling a blasting crew with employees not needed elsewhere on the job should be avoided. When substitute employees are assigned to the blasting crew, they must work under the direct and constant supervision of the blaster-in-charge. Even if the "part-timer" has past experience using explosives, the technology and procedures in blasting change so rapidly that the knowledge of a few years ago may not only be useless, but dangerous as well.

Safety Rules And Regulations

Safety rules must be explained to all personnel, stressing not only what the rules are, but also the reasons why each rule exists. The rules must be enforced uniformly, without exceptions. Disciplinary action must be taken on a fair and equal basis. Conversely, outstanding contributions and performance in safety should be publicly recognized and rewarded in a manner that will reinforce the emphasis and importance attached to safety.

Personal Protective Equipment

Personal Protective Equipment (PPE) is essential for all job sites and mining operations. The basic equipment required is shown in figure 10.1. In addition to the basic equipment, some job sites require specialized safety apparatus. It is vital for each employee to be properly trained in the use of all PPE they may be required to use. Please familiarize yourself with the regulations for each mine or jobsite to ensure compliance.

Mandatory PPE may vary from country to country. There are a multitude of scenarios that may require additional specialized equipment for the blaster. A few examples of required specialized equipment and their uses in the United States are listed in table 10.2.

Figure 10.1 – Basic personal protective equipment.

Specialized PPE and Their Use

Table 10.2 – Specialized PPE and their use.

General Hazards

Blasters must avoid all situations and practices that can create hazards. Lightning, flyrock, misfires, and working environments present general safety hazards common to all blasting applications.

Lightning

The blaster must suspend all explosives loading and handling activities whenever electrical storms are at or approaching the blast site. This is true regardless of the types of explosive materials or initiation systems being used. A direct lightning strike can initiate any explosive material or detonator. U.S. Mine Safety and Health Administration (MSHA) and Occupational Safety and Health Administration (OSHA) are very specific concerning the suspension of loading activities during electrical storms.

Some blasters may have the misconception that electrical storms are not a threat when nonelectric initiation systems are used. However, even detonating cord or nonelectric shock tube will be initiated by a direct hit. Although the risk of an initiation by a nearby lightning strike is significantly reduced, the precautions required are the same as those for electric detonators.

There are a number of lightning detectors and warning systems designed to monitor a storm's approach. Detection can occur while storms are many miles away. One type of electronic device is kept on the bench and emits a warning sound when lightning is detected within a certain range. Other more sophisticated systems rely on computer workstations with a weather satellite tracking to track active thunderstorms.

Figure 10.2 – Lightning Strike. (Courtesy L. Reilly)

Flyrock

Since flyrock is a leading cause of blasting injuries and fatalities, the blaster's most critical concern at the time of detonation must be that the area is completely clear and access to the site is controlled. A predetermined plan should be prepared for safeguarding all personnel and the public prior to the blast. This is a matter where the blaster can make no assumptions. The blaster must be absolutely certain the area is clear. Flyrock has been known to travel remarkable distances from a blast, and a plan to protect against flyrock is crucial for safe blasting. Flyrock's worst-case possibilities must take into account. Furthermore, when blasting in a public area, the blaster must realize that the public is both curious and misinformed about blasting.

Since many injuries are caused by excessive flyrock, safety documents must emphasize the precautions related to flyrock. Precautions are taken by proactively using sound blast designs, loading practices, and security procedures. Establishing an adequate safety perimeter prevents flyrock injuries and damage. A detailed discussion of flyrock causes and the establishment of the safety perimeter is found in chapter 15.

Misfires

Misfires are a serious hazard that like flyrock is prevented by using sound blast designs, loading and tie-in practices. Misfires are discovered during the post blast inspection and are discussed in chapter 16.

Work Environment

Working environments present hazards unique by their nature. In surface mines, work is on benches or near highwalls. Underground mines are confined and are low light environments. In all applications, rock stability is an important requirement of safety. Measures are often taken after each blast to remove unstable rock and stabilize the remaining walls or roofs. Construction blasting is often done in a restricted space or near people or property off the blasting site. Precautions should be taken to protect people and property within and beyond the blast area.

Managing The Blast Site For Safety

Use of explosives materials and equipment on the blast site directly impacts the safety of an operation. Good blast site management eliminates or greatly minimizes negative safety issues at the blast site. Concerning this, two basic rules must be observed: First, all materials used on a blast site should be designed for that specific operation and used in accordance with the manufacturer's recommendations. Secondly, the blasting crew members must be familiar with these materials and equipment or thoroughly trained prior to their use. This includes the type of explosive and detonators to be loaded as well as all the tools used on the operation. The blaster-in-charge must have sole authority to limit equipment, materials, and people on the blast site at any given time.

Explosive Materials

Explosives are energetic materials that must be secured and accounted for at all times at the blast site. Chapter 13 discusses hazards and general use techniques for each type of initiation system. Consult chapter 19 for a discussion of standard borehole loading issues and practices. Because specific commercial products often have different recommended use practices, blasters should always follow manufacturers recommendations for the products they select.

Tools and Supplies

A blaster uses a variety of tools and instruments designed to facilitate the work. These tools include sample items such as powder punches, tamping poles, or complete equipment like the Blaster's Multimeter or Blasting Galvanometer.

A blaster should use only a powder punch to create an opening in the explosive cartridge to be used as a primer. This powder punch must be made of a nonsparking material, normally of brass with a wooden or plastic handle. The blaster should never attempt to force a detonator into explosive materials, nor should a powder punch or drill be used to enlarge a hole in a cast booster that is too small to accept the detonator. Improperly manufactured or unplated products must be returned to the manufacturer or properly destroyed.

Likewise, tamping poles used on a blast site must be made of nonsparking materials with connecting joints made of nonferrous metal. The pole should be smooth and free of sharp edges that could damage legwires, shock tubing or detonating cord. When tamping charges or stemming in a borehole, always use a firm steady movement in the borehole to avoid violent or abrupt force on the explosive. Never tamp a primer.

Equipment On the Blast Site

The only equipment permitted on the blast site is that equipment used for the direct loading of the boreholes. All machinery and tools not used for preparing or loading explosives shall be removed from the blast site. MSHA, OSHA, and international agencies have written regulations to enforce this rule. OSHA regulations specify a minimum distance of 15 meters (50 feet) to operate any non-loading equipment. Variances may be applied for if special circumstances exist.

Drilling On the Blast Site

Before drilling near loaded or previously shot areas, the blaster must be able to identify the location of charges or previously fired boreholes. Never drill in a previously fired borehole. The presence of a misfired or unexploded charge in the vicinity constitutes a serious hazard. Patterns that were drilled in poorly measured or irregular patterns make it difficult to predict where the previous boreholes were located. MSHA forbids drilling holes where there is a danger of intersecting an explosive charge. Other regulatory authorities may have more specific or stringent rules. The best way to eliminate such drilling accidents is to be certain that all explosives have successfully detonated. However, if misfires are encountered undetonated explosives must not be located and properly handled before any personnel or equipment return to the blast area.

Initiation System Safety Issues

In addition to the specific information concerning types of initiation systems in chapter 13, the following remarks are made to remind the blaster of issues that must be addressed in the blast area to ensure safety.

Initiation systems carry the energy signal to the primers to initiate the explosive charges. Each type of initiation system has its own unique method of initiation (See chapter 13). All system components are subjected to the forces created during the loading and firing processes. The blaster-in-charge must ensure they are not abused or damaged prior to firing time. Specific system safety and hazard concerns; and hookup techniques are discussed in chapter 13. The blaster is encouraged to consult with the manufacturer to resolve and clarify any issues regarding the system used.

Although systems and their components may look alike, in general, the various manufacturers systems are not compatible with one another and components from different types of systems should never be mixed in a single blast unless specifically approved by the manufacturers.

Caution

Lightning can detonate any type of detonator, so when a storm approaches, standard precautions for clearing all personnel from the blast area must be followed.

In addition, care must be taken so that vehicles, such as trucks, do not drive over initiation system components. No tools should be used to pry on any component containing a detonator, nor should any tool be used to open, close, fasten, or clean out any connector containing a detonator or detonating device. Components of these initiation systems should be used as originally manufactured and for the purpose they were designed. Attempts to modify or alter any of these parts should not be permitted. Any components that are found to be defective, damaged, or incompatible should not be used, but rather returned to the manufacturer.

Electronic Systems

Electronic detonators cannot be mixed with different manufacturers (and sometimes different systems from the same manufacturer) and must be used only with the manufacturers' approved testing and blasting machines. Electronic systems have the safety characteristics of nonelectric systems because they can be detonated only by a special encoded frequency, which makes them safe around stray electrical currents and two-way radios or phones.

Nonelectric Systems

While one of the advantages of nonelectric initiation systems is their immunity from the hazards of radio frequency (RF) energy, current leakage, induced currents, and stray currents, they are susceptible to premature initiation by a lightning strike. Since nonelectric detonators contain sensitive ignition and base charges, they are also as susceptible to detonation by heat and impact. Due to the variety of nonelectric systems, the blaster must be knowledgeable about the system being used and ensure the manufacturer's recommended practices are followed. General information and use techniques are discussed in chapter 13.

Particular care must be exercised during nonelectric hookup procedures. In general, the various systems are not compatible with one another and components from different types of systems should never be mixed in a single blast unless specifically approved by the manufacturers. Since the continuity of most nonelectric blasting systems can only be checked visually, it is important that the system hookup is done in a systematic and orderly fashion. Omitting a charge, failing to make a connection, or making an incorrect connection will result in a misfire. Some surface tube components produce metal and plastic shrapnel when detonated. The blaster should follow the manufacturer's directions to prevent this flying debris from causing cutoffs or damage to other components in the initiation system. Effective protection from shrapnel often entails simply covering these surface units with dirt or drill cuttings to confine the shrapnel.

In addition, care must be taken so that vehicles, such as trucks, do not drive over the tubing, connectors, or any surface components.

Caution

No tools should be used to pry on any component containing a detonator, nor should any tool be used to open, close, fasten, or clean out any connector containing a detonator or detonating device.

Components of these initiation systems should be used as originally manufactured and for the purpose they were designed. Attempts to modify or alter any of these parts should not be permitted. Any components that are found to be defective, damaged, or incompatible should not be used, but rather returned to the manufacturer.

Electric Systems

Electric detonators are designed to fire when electrical energy is applied. Thus, extraneous electric current sources create potential initiation hazards. Extraneous sources such as lightning, RF energy, high-voltage power lines, stray ground currents, or static electricity must be recognized and protected against. Each of these hazards and methods to measure and/or calculate their severity are discussed in chapter 13.

Before using electric initiation systems, the blaster must verify the presence of electrical hazards in the blast site area. When electrical hazards are discovered, they must be measured to ensure the safe use of the electric system. Common electrical hazards and situations include static electricity, stray and induced ground currents, RF, and current leakage. Information to characterize RF hazards, whether from a variety of transmission or power lines is also provided.

Electric initiation system detonators and circuits must be tested for continuity and resistance only with a blasters' multimeter, blasters' galvanometer, or blasters' ohmmeter. Resistance measured must match with those calculated. If they do not, the discrepancy must be discovered and corrected before initiation. Chapter 13 discusses methods used to calculate, measure the circuit resistance, and troubleshoot circuit problems.

The proper time to check individual detonators is prior to primer assembly and then again before stemming is placed in the borehole. At this point, if a detonator is found defective and cannot be safely removed and replaced, another primer should be placed in the borehole.

After the circuit has been completely wired, a resistance measurement should be made. If several circuits are to be wired in parallel, the total resistance of the entire firing circuit should be measured after each individual circuit is checked and connected. Finally, when the lead line is connected to the circuit, the resistance should be checked at the end of the lead line where the blasting machine will be connected.

In addition to lightning, electric detonators are susceptible to initiation from a variety of electrical energy sources (See chapter 13 and appendix F).

The danger of electrocution also exists when the blaster is working under or near high-voltage lines. A blast may throw the wires up in the air and onto any nearby power line. To avoid this, the total length of the leadwires, connecting wire, and detonator legwires must be too short to reach the high-voltage lines. If this is not possible, the leadwire and the connecting wires must be securely fastened to the ground so they will never reach the high-voltage line. It is also possible to connect a short delay detonator in such a manner so cut the leadline when the blast is fired. If such a method is used, it is extremely important that the blaster connect it in such a manner that the leadline will be completely severed when it is fired.

Detonating Cord

The three major concerns that must be considered when detonating cord is used are (1) air overpressure produced by any exposed detonating cord (2) training blasters and helpers to use proper tie-in techniques with both additional cord and other initiation systems (the cord may be used in conjunction with millisecond surface delay blocks or connected to any or all other types of initiators. The blaster must ensure they are using the proper grain strength cord for their application and take care in loading to mitigate any damage to the cord, particularly in wet borehole conditions), and (3) that the PETN inside the cord is hydroscopic.

Detonating cord should be buried sufficiently to avoid excessive air overpressure in neighbor sensitive areas. Open ends of the cord must be protected from moisture and it is common practice to cut of the ends to ensure the cord has not been desensitized in storage due to humidity or exposure to water.

A detonator should be properly attached to detonating cord (See figure 10.3 and chapter 13).

Figure 10.3 – Taping a detonator to detonating cord.

Cap and Fuse

Although cap and fuse systems are not common, they are still in use. They have special considerations and training requirements. They must be crimped properly and the blaster must have a thorough knowledge of the fuse and its burn rate (See chapter 13).

Procedures

A blasting operation, with qualified people, using proper equipment and materials for the job is an excellent safety start. To complete a safe operation, everyone involved must be committed to safe working practices and assure that every step of the operation is done in a manner using the correct methods and procedures. Neither management nor the blaster's co-workers should sacrifice safety status, due to overconfidence or carelessness.

Ideally, the personnel on the blast site should be limited to the blasting crew of a maximum size necessary to load the shot efficiently. Personnel and equipment not directly required for loading or tying in should be barred or removed.

Survey the Area

Conduct a preliminary check before beginning the loading process to identify unsafe working, loading and blasting conditions. A recommended checklist is located in chapter 1 in the section Planning and Design. When working at the base of a highwall or near a natural cliff, the danger of falling rocks or other loose overhanging material is very real. When working in underground mines or projects, walls and roofs should be carefully inspected, cleaned, and stabilized before proceeding with work. A survey of the area should look for other hazards in the area such as power lines, cables, potential sources of fire, or uncontrolled access roads. Drilling into explosives is a frequent cause of blasting accidents.

Signage

Safety signs may be required for any or all types of blasting (See figure 10.4). Public road signs will warn of blasting ahead and possibly require turning off two-way radios for electric detonator concerns. "Blasting Zone" and/or "No Blasting Today" are common signs for quarry and mining to warn the workers onsite as well as any visitors to the operations.

Figure 10.4 – Typical Blast Warning Signage.

Securing the Blast Area

The blaster-in-charge is responsible for blast site security during the loading and blast initiation process. Unauthorized personnel and equipment must be restricted and controlled. All explosive materials must be kept secure to protect them from abuse, theft, and unauthorized use.

Loading the Blast

The blaster-in-charge ensures maximum safety by following the loading process steps outlined in chapter 13. In addition to following established proper and safe loading procedures, the blaster-in-charge from time—to-time must recognize and properly deal with hot boreholes if they occur. The direct safety issues associated with the loading process as outlined in table 10.3.

Safety Issues Associated With Borehole Loading

Table 10.3 – Safety issues associated with borehole loading.

Hot Boreholes

To reduce this hazard, it is best to keep the drilling equipment and all loading crew personnel separated as far as possible and not load the borehole immediately after it is drilled. This is a standard MSHA rule. If it is necessary to load following the drilling, as allowed by MSHA exemption, the borehole temperature should be checked and determined.

Borehole Loading

The primer should be the first cartridge loaded in a small diameter borehole. However, when blasting with large diameter boreholes and bulk explosives, it can be good practice to load a small quantity of the bulk explosive prior to placing the primer. This method allows the primer to be completely surrounded by the explosive or blasting agent, which ensures more good product coupling. It can reduce the possibility of the primer being lowered into shot dirt or mud at the bottom of the borehole.

When preparing the primer, the detonator should be placed in a preformed detonator well such as those found on cast boosters or inserted into a hole made in the cartridge, by a non-sparking powder punch. These wells and holes must be of sufficient diameter to easily accept the detonator without the application of excessive force. Likewise, the depth of the opening should be sufficient so the detonator is completely embedded in the booster. The detonator should be placed so that when the primer is loaded in the borehole, the charge end of the detonator points in the direction of the main explosive charge in the borehole. The directional effect of initiation is critical in cartridge booster diameters up to and including 75 millimeters (3 inches). The legwires of electric detonators or the tubing attached to nonelectric ones should be attached to the primer in a manner to prevent the detonator from being pulled out of the booster and to prevent excessive force on the legwires or tubing during borehole loading (See chapter 19 for recommended primer assembly procedures). These assembly procedures are also illustrated in IME SLP 4, and the Warnings and Instructions pamphlet contained in each case of detonators shipped from the manufacturing plant.

Tying-In the Blast

Incomplete or improper tie-in is a major cause of misfires. Disciplined and methodical procedures must be followed to prevent misfires and their hazards. Initiation system manufacturer's tie-in recommendations must always be followed. A discussion of proper tie-in procedures and considerations is found in chapter 25.

Proper Cover For Construction Blasts

Construction blasting often requires the blast to be covered with earthen material, blasting mats, or a combination of to control rock movement. It is impossible to give exact directions for covering a blast but certain precautions must be taken. All circuit wires, shock tubing, and detonating cord should be cleanly and securely connected with extra lengths neatly coiled to avoid confusion. If there is a cut off or misfire it must be excavated and served reconnected.

The wires or tubing and connections must be covered with a layer of clean dirt in order to protect them from damage (See figure 10.5). After the initial clean fill covers the connecting lines, mats and/or additional clean fill can be placed on the entire shot (See figure 10.6). Extreme care must be taken during the covering process so detonator wires or shock tube wire are not damaged. Place mats or cover in a way that keeps equipment clear of the sensitive lines and "do not" allow equipment to drive on top of any portion of the blast.

Electric and electronic blasting systems provide equipment and methods to test the circuits or individual detonators and guarantee the lines have not been damaged or broken. Nonelectric detonators do not allow testing. Therefore, an extra detonator should be connected to the circuit, and placed and covered outside of the cover and mats. This creates a check that the system has fired. These "check detonations" are not a 100% guarantee that the shot has fired, so always use caution during the excavation process.

Figure 10.5 – Covering the blast with dirt.

Figure 10.6 – Carefully covering a construction blast with dirt and mats to control rock movement.

Initiating the Blast

Initiating the blast involves several important tasks that must be followed by the blaster to ensure the safety of all people and property. The blaster must in order perform the safety procedures in table 10.4.

Safety Procedures When Initiating the Blast

Table 10.4 – Safety procedures when initiating the blast.

Clear the Blast Area

After a blast has been loaded and the initiation systems connected, the blast should be cleared, secured, and detonated as soon as possible. Many operations schedule detonation at lunch break or at shift end since the work force is normally absent from the area. When there will be a delay between the time the blast is prepared and the time of detonation, the blast must be guarded or attended. The schedule for blasting may be restricted by regulatory requirements or by local considerations. Reducing the time a loaded blast is left in the ground obviously reduces the time of exposure. The blaster must be alert to the possibility that when blasting underground the blast may break through to an adjacent entry or room and ensure that that these areas are cleared. Regardless of the distance of that location where the personnel and equipment are moved, it must be an area of stable roof and floor.

Secure the Blast Area

All roads leading into the vicinity of the blast area must be physically guarded. The blast area is that area where flying rock, concussion, and detonation gasses are expected to occur. All personnel and equipment must be removed from the area to a well-protected safe location. A thorough visual inspection of all possible areas that could be affected is essential prior to sounding the warning signals. It is imperative that control of access to the site be strictly and continuously maintained. If such control is lost or removed for even a few seconds, a repeated inspection of the area is mandatory. Regulations are included in Annexures/Schedules of the Bureau of Indian Standards Regulations concerning blast area security.

Warning Signals

Once the blaster is certain the area is clear and controlled, the warning signals may be sounded. The set of warning signals used must be thoroughly familiar to all those on the blasting operation and should be posted conspicuously on the job site. The signals, which may be given by a siren, air horn, whistle, or other device, must be loud enough to be clearly heard in all areas that could possibly be affected by the blast or flyrock from the blast. The signals used must be distinctive and unique so that they cannot be confused with any other signaling system that might occur on the site. A typical warning system that is often used is given in the table 10.5. Warning signals are also discussed in chapters 25 and 31.

Typical Warning Signals

Table 10.5 – Typical warning system.

Blaster Safety

The blaster must take adequate protection precautions. This means that the blaster must be at a safe distance and under sufficient cover/shelter. No one, including the blaster, should ever be located in front of the blast, that is, in the direction of the intended rock movement. Recently, mobile blast shelters have been constructed of steel plates and used in some blasting operations; the shelter provides a certain amount of protection from flyrock when the blaster initiates the blast from inside them. The open side or doorway should be positioned away from the blast and out next to a surface that could deflect a flying rock onto the shelter.

The blaster must maintain control of the blasting machine or firing device and all test equipment when taking the blast firing position. If blasting electrically the blaster should make one final resistance and continuity check of the blasting circuit before connecting it to the blasting machine. The lead line, shock tubing, or fuse should not be connected to the blasting machine or the device until that blast is ready to be fired. When the final warning signal is given, the blaster should wait the predetermined time, connect the firing line, and initiate the blast.

The blaster must immediately disconnect the leadline and shunt it after firing electrically. This is the ideal time to test the lead line so repairs, if necessary, can be made before the next blast.

Post Blast Inspection

After the blast is initiated, the blaster must wait for the dust and fumes to clear before approaching the blast area to make the post blast inspection. The entire post blast inspection process centers on ensuring that the blast has performed as planned, the area is free of post blast fumes, and the work area is stable and safe before clearing it for the resumption of work in the blast area.

Fumes

Workers must delay returning to the blast site until the area is well ventilated because some toxic gasses or fumes are produced by all blasts. The waiting time to ensure post blast fumes have dissipated depends on the natural ventilation of moving air in a surface operation and the effectiveness of an underground ventilation system. Frequent testing of the ventilation system should be conducted to ensure it supplies adequate fresh air and removes all harmful fumes and smoke. While the toxic oxides of nitrogen are visible and have a pungent odor, carbon monoxide, which can be extremely lethal, is colorless, orderless, and tasteless. The fact that the air is visually clear does not guarantee that a lethal concentration of carbon monoxide is absent. Chapters 11, 12 and 28 provide more information about blasting fumes and their causes.

In some cases, it is a good practice to spray the blasted face and the muck pile with water. This settles some smoke and dust out of the air and reduces the level of certain soluble toxic gases. Be aware that spraying the muckpile may also displace insoluble gasses from the broken rock and water will not diminish any carbon monoxide present.

Misfires

The blaster's search for misfired explosives after the blast must be thorough. Every charge that does not detonate represents a potential accident. The maxim in blasting is, or should be, that the best way to handle a misfire is to prevent it from occurring using sound blast design principles. If the blaster follows proper methods of priming, loading, stemming, and tying-in the shot, and firing it, the likelihood of a misfire is extremely small. However, if a misfire does occur, the blaster must be prepared to handle it. It is strongly recommended that the blaster attempt to get professional help, such as the explosives manufacturer's technical representative or distributor, to assist in analyzing the problem and finding the safest way to dispose of it. There are so many different types of blasts that it is impossible to give blanket instructions on handling misfires.

Restrict Work in Blast Area

The blaster must restrict or guide any work, especially drilling near or digging into material containing explosives. This work is exceedingly dangerous. Any activity performed near a misfired blasthole, even that done to remove the misfire must proceed with extreme caution. Basic guidelines for dealing with misfires are given in chapter 16.

Addressing a Misfire

Under most conditions the safest way to dispose of a misfire is to reblast it in place, provided there is sufficient burden, spacing, and stemming around the misfired charge to prevent flyrock hazards. If the legwires of an electric detonator are accessible, the detonator should be tested for continuity with an approved blasting meter. If the detonator tests "good," it can be rewired and fired in the usual manner. If the original misfire was caused by a faulty connection or insufficient power, the detonator will fire properly when this procedure is followed. The legwires of electric detonators, particularly in multise situations, should never be pulled or have any force exerted on them. Such force on a live detonator may cause a detonation.

If the electric detonator fails again, if its wires cannot be reached, or if nonelectric detonators fail, an attempt to reblast the misfired charge with a fresh primer may be made if deemed safe by assuming to be removed, such work must be done with great care. Crushed stone especially used as stemming to control the blast is very difficult to remove by conventional methods, but they should be tried first. The best method to remove stemming is with a stream of water or air jet through a plastic pipe or hose. The hose should be equipped with a mechanism to control the flow of water or air. Metal pipe, even if tipped with rubber or plastic, should not be used for this purpose. It is unsafe to use metal tools, sponels, or augers to approach explosives.

Once the stemming is removed, a new primer may be inserted in the borehole. The primer should contact the explosive charge or column. Care must be taken after this attempt is tried. There have been cases where the second primer did not initiate the entire powder column but generated enough to close the original misfired charges to jam blasting. This will result in a dangerous "sleeper," which may detonate several months later. The sound made by a sequence charge is not a certain indication that the original misfire has completely detonated.

Sometimes a misfire cannot be safely reblast in place. In this case, the least dangerous method is to remove the explosives with a water jet, in the manner described above for removing stemming. If the explosive column is ANFO or other bulk explosives, this method will normally work well. Occasionally, a primer will detonate, but not initiate a portion of the powder column. These misfires are often due to ground movement cutoffs, inadequate priming, deteriorated explosives, or bridged charges in the borehole. When these partial misfires occur, it may be very difficult to detect unexploded charges in the muckpile or in a remaining bootleg of the blast. For this reason, no one should ever fall into a borehole or the remnants of a borehole that has previously contained explosives. Many injuries have also occurred when drilling was done too close to a misfired charge. Such a misfire can be detonated, if the drill rod wanders and strikes the charge. It is also possible that merely drilling in close proximity to a misfire can cause it to detonate. When undertonated explosives are suspected of being in the muck pile, it is critically important to warn the equipment operators, shovelers, backhoes, or front-end loaders to be on the alert for the explosives while digging.

Hangfires

A hangfire occurs when the explosive in the borehole begins burning and may eventually detonate when the fire reaches the area of the base charge of the failed detonator. This detonation may take place a few seconds after the blasting machine was fired to a few or more minutes later. Due to this delayed detonation of hangfires, no one should approach a misfired charge for at least 15 minutes after a shot is fired electrically. The best way to avert any danger from arcing is to use a capacitor-discharge (CD) blasting machine; these machines deliver their energy in a very brief time interval, usually less than 5 milliseconds, which is too short a time for arcing to occur. Use of batteries, generators, welding machines, or ordinary electric lines may produce a continuous high firing current and result in arcing.

Unsafe Ground Conditions

Solid ground conditions are paramount in assuring a safe work place. Before working on benches or other job sites, the driller and blaster must check highwalls for loose material and or overhangs, as in conjunction with good stability onto potential cracks and voids. Scaling the highwall may be required to eliminate loose rock hazards. Ground conditions must be checked for edge failure, cracks, or other unsafe conditions. A safe distance must be maintained from mow spots such as the crest of a free face or hack break from a previous blast. Painting the ground or using flagging ribbon are a few methods utilized to mark the edge of the danger zone providing a visual or physical barrier to keep personnel out of the potential fall zone. Fall restraint or fall arrest harnesses may be required when working near the crest, as well as in near any open cracks. Blasters must also take precaution when performing post blast inspections so they do not walk across a blast or muckpile where there is a potential to fall into a void, to overcome by fumes, or have a section give way on the crest of a highwall.

All Clear

The all-clear signal may be sounded when the blaster is certain that the blast area is safe, and free of any misfired charges, fumes, and unsafe ground conditions. The blaster must make a thorough inspection and report for loose highwalls, unstable slopes, or any other condition that may pose a hazard to personnel returning to the site.

When blasting in underground areas, all of the precautions previously discussed apply. However, due to the enclosed area, sufficient ventilation is an additional concern. The ventilation system must be working properly and the blaster must know where the air current will carry the smoke, dust, and fumes. The most important way to control the fumes when blasting underground is to use the specific detonator fails again, its wires by selecting the proper explosive for the job and properly priming it. If the blaster-in-charge. This work will require the if

Additional Resources

Institute of Makers of Explosives (IME). 2009. Safety Library Publication 4, Warnings and Instructions, October. IME, Washington D.C.

Institute of Makers of Explosives (IME). 2006. Safety Library Publication 25, Explosives Manufacturing and Processing Guideline to Safety Training. IME, Washington D.C.

Mine Safety and Health Administration (MSHA). Code of Federal Regulations (CFR), Title 30, MSHA, Washington, D.C.

Occupational Safety and Health Administration (OSHA). Code of Federal Regulations (CFR), Title 29, OSHA, Washington, D.C.