Safety in blasting is extremely important because of the inherent danger in explosive use. These publications, from The Institute of Makers of Explosives, are made available to the blaster to ensure that blasting is accomplished in a safe, efficient manner. It is not the intent of this writing to recite safety rules of review material which the Institute of Makers of Explosives has published. It is the intent of this writing to describe commonly violated guidelines and the causes of accidents in transportation, storage, and use of explosives.
Storage of Explosives
Explosives should be stored in accordance with federal, state and local regulations. When explosives are stored in a magazine, the magazine should be clean, dry, cool and well-ventilated. The magazine should be constructed so that it is bullet-proof, fire-resistant, and meeting all federal or state codes. Magazines should be locked with shielded locks to discourage theft.
Figure 1: Electric Blasting Caps
Initiators such as electric blasting caps, nonel, or any other type of blasting cap should not be stored in the same magazine with high explosives. Blasting agents require less stringent storage requirements than high explosives. However, if they are placed in a high explosive magazine, their weight would count toward the total weight allowable in that magazine. Explosives in magazines should be thoroughly marked as to the date of purchase and the oldest products should be used first. Hazardous conditions sometimes arise when explosives, especially those contain nitroglycerin, begin to deteriorate due to age and leak onto the floor of the magazine.
No source of fire flame should be brought near an explosive magazine, and the magazine should be located so that there is no grass, brush, or debris nearby. When explosives are brought to the job, they must be stored in day boxes that meet federal or state codes. They should be placed in a area that is not in any danger from falling objects, fire or heavy equipment.
Transportation of Explosives
When explosives are transported on the highway, they should be transported in vehicles in proper working condition and equipped with federal, state or locally approved containers for safe transport. If the load is an open body truck, it should be covered with waterproof, fire-resistant tarpaulin. Unless the explosives are in the proper approved containers, caps and explosives should not be carried on the same vehicle. Smoking should not be permitted while loading and unloading the vehicle containing explosives. Trucks and vehicles containing explosives should bypass cities, towns or villages, if possible. The explosive cargo should be gently unloaded and cases should not be thrown onto the ground. Sometimes accidents can occur when truck fires have occurred during explosive transit. Personnel, including fireman, should be evacuated when explosive begins to burn. When the fire has reached the cargo, many types of explosives will detonate.
Handling of Explosives
>>> Electrical Hazards
Premature initiation of electric cap circuits have occurred. The hazards associated with electric blasting should be recognized and known by the blaster and all in charge on the job. Electrical hazards can be broken down into six categories: current leakage, lighting, static electricity, stray currents, galvanic action, and radio frequency energy.
Current leakage into the ground is a hazard, but not because it results in premature initiation. It can, however, cause a round to misfire or partially fire since a large portion of the current may flow into the ground and not through the cap circuit. Conductive material such as wet shale, clay, magnetite, galena, and ammonium nitrate are more prone to current leakage problems. The reduced current which reaches the cap may be insufficient to fire the entire round. If such environmental conditions occur, the cap series should be set up such that the ground resistance is at least 10 times that of the series resistance. A blasting multi-meter can be used to make the proper tests.
Lightning is a hazard to both surface and underground blasting. Should a lightning bolt strike the blasting circuit, a detonation would most probably result with both electric or non-electric initiators. The probability that a direct hit would occur is remote, but a lightning bolt striking a far away object could induce enough current into an electric circuit to cause a detonation. The danger from lightning is increased if a fence, stream, or power transmission line exists between the blasting site and the storm. Underground blasting is not safe from lightning hazards since induced currents large enough to cause detonations can and have been transmitted through the ground. All blasting operations should cease and the area should be guarded when a storm is approaching. Commercially available lightning detectors can be purchase in areas where electrical storms are common.
Static electricity, both that occurring in nature and man-made, is a hazard to blasting. Electrical storms are not only dangerous because of lightning, but also because of the build up of a static electric front at some distance from the storm's center. The static charge can be stored on any ungrounded object. The insulations on the cap wires will not prevent the cap, whether shunted or unshunted, from detonating from static electrical discharge. The movement of particles under dry conditions can generate static charges. Particles of dust or snow driven by high winds, escaping steam under pressure, or motor driven belts can accumulate a static charge. To throw the wires of blasting cap into the air to straighten them in a snow or sandstorm can be dangerous. To minimize the hazards of static electric buildup from man-made sources, the equipment near the loading site should have all moving parts grounded. All metallic parts of any machinery should be kept away from the blasting circuit. Moving equipment should be shut down in the immediate area when the blasting circuit is being connected. Pneumatic loading of explosives constitutes a possible hazard. Some materials act as capacitors and become charged from small static charges and cause a premature detonation.
Stray currents can result from any power source. Electric current originating from a battery, transformer, or generator will always return to the source by any available path. Normally, it is expected that the current will return along insulated transmission lines or by a ground, which is the earth itself. If the return path is interrupted by a broken line or a blown fuse, high ground currents can result in an earth-grounded system. Under normal operating conditions, the return is continuous, the resistance of the earth is usually sufficiently high and the potential difference between two points close together on the ground is usually low. Exceptions can occur when two highly conducted beds are separated by a narrow bed of low conductivity material.
Dangerous currents in excess of 0.05 amps can be produced when leg wires contact rails, pipes, or ventilation ducts in underground operations. The maximum current which can be tolerated is 0.05 amps or 1/5th of the minimum firing current for one EBC which is 0.25 amps.
Power transmission lines are another source of current which can be hazardous. The cap wires or lead wires can be thrown by the blast. If this occurs and the wires touch the power transmission line, electrocution of the blaster can result. Ground currents can also exist near high power transmission lines, therefore, ground currents should be checked.
Galvanic action occurs when two dissimilar metals are in the presence of a conducting fluid. Premature explosions have occurred in the case where aluminum tamping poles were used in steel casing in the presence of an alkaline mud. The above situation can be compared to a crude battery.
Radio frequency (RF) transmitters which include television, radar, and A.M. and F.M. radio create powerful electromagnetic fields which decrease in intensity at distance from the transmission point. Tests have demonstrated that under certain conditions, electrical blasting wires may receive enough electrical energy to cause them to detonate. Although the possibility of premature detonation due to radio waves exists, the chance that they will occur is remote.
Commercial A.M. broadcast transmitters 0.555 to 1.605 MHz are potentially the most hazardous. They combine high power and low frequency resulting in small loss of radio frequency energy in the lead line. Mobile radio transmitters are a potential hazard because they can be brought directly into the blasting areas. The leg wires of blasting caps whether shunted or unshunted can act as a radio receiving antenna. The most hazardous condition exists when the circuit wires or leg wires are elevated a few feet above the ground.
>>> Blast Area Security
Blasting accidents have occurred due to the failure of the operator to clear the blasting area. Failure to clear blasting area can be broken down into other functions such as failure to follow instructions, inadequate guarding, having personnel under insufficient cover, or at an unsafe location. The end result can be injuries or fatalities from flyrock in the blasting area.
An additional cause of fatalities, injuries, and property damage outside of the blasting area is flyrock. Occasionally flyrock can travel thousands of feet from poorly designed blast. Even with the best care and competent personnel, flyrock may not be totally avoided. The majority of flyrock problems which exist today are due to carelessness in the loading, execution, and design of blasts.
Accidents can occur during the routine disposal of explosives. Safety rules are violated and workmen are often too close to the fires at the time of burning. When detonation occurs, workmen can be injured.