BLASTING SAFETY IS CRITICAL AT MINES
by Harold Hough
Blasting is one of the safest aspects of mining because miners pay close attention to safety procedures when they are around explosives. The excellent record of the explosives industry and mines in the last few decades prove that. In fact, blasting today is actually safer than many occupations that are supposedly less dangerous.
Although blasting professionals are usually familiar with explosives safety, anybody who works around the mine needs to be aware of blasting safety, not only for their own well being, but because the overriding need for safety can effect mine operations in many different ways. With that in mind, here are some recommendations.
BE AWARE OF HAZARDS ASSOCIATED WITH TRANSPORTATION OF EXPLOSIVES. During transport, packages of explosives undergo numerous stresses and motions that they don’t encounter when standing still. These usually cause leaks of explosives material from packaging tears or ruptures. Even a rivet that rubs through a package of explosive during a rough trip is a problem.
This may seem like a minor problem, but a common mining explosive, ammonium nitrate, can change characteristics when contaminated. If the contaminant is organic, the ammonium nitrate is no longer an oxidizing agent, but an explosive. In addition, some inorganic materials can act as a catalyst to cause the decomposition of ammonium nitrate and eventually create a risk of explosion.
ELECTRONIC AND ELECTRIC DETONATORS ARE INCOMPATIBLE. Many mines are moving from electric detonators to electronic detonation systems to initiate blasts. With this change comes the hazard associated with the incompatibilities between the firing systems of the two technologies. An accident occurred recently where an instantaneous electric detonator was unintentionally tied in with a production blast being initiated with electronic detonators. A blast occurred during the test sequence for the electronic detonator system. Fortunately, there were no casualties thanks to the mine following other safety practices.
Conventional electric detonators and electronic detonators must not be connected in the same firing circuit. The testing and programming voltage of electronic systems can be sufficient to initiate electric detonators.
EVERYONE ON A MINE SITE MUST BE AWARE OF SITE SPECIFIC BLASTING PROCEDURES. It isn’t just the blasting crew that needs to know about blasting. Everyone must be aware of blasting procedures, where blasting agents are stored, and where they are transported. They also need to be aware when blasting takes place, how, and where it will happen.
One of the biggest problems is that although the mine employees are usually well acquainted with blasting procedures, visitors and contractors are not kept informed. It’s not enough to ask what blasting is taking place when they start a job. The contractors should ask every day what blasting is taking place and where, because changes do occur. Each mine, with contracting crews, should have a procedure to make sure such activities are well publicized. Blasting safety always rests on every individual, so contractors must ask the question each day.
IT ISN’T JUST THE “BANG” THAT MAKES EXPLOSIVES HAZARDOUS. Although we focus on the explosive danger, there are other hazards. Many explosives are
toxic when inhaled, ingested, or absorbed through the skin. There is the threat of a stray spark setting off a detonator. Many explosives burn violently even though flames don’t cause them to explode. Dust-air mixtures can present an additional hazard. And, there are the toxic fumes that are created after a blast. Don’t assume that just avoiding the blast area protects you from the hazards of explosives.
ONLY QUALIFIED PEOPLE SHOULD BE AROUND EXPLOSIVES. This is one of the basic rules, but it can be broken without thinking about it.
Experts note that not only does a professional blasting crew know how to handle explosives safely, they are usually the only ones that are aware of MSHA rules and can make sure that the mine remains in compliance. If a non-qualified person must be in the area, that person must be under the direct supervision of someone qualified.
ALL EFFECTED ROADS MUST BE BLOCKED WHEN INITIATING A BLAST. This doesn’t just include major roads. It has to include trails and even paths where people or off road vehicles can pass
One way to make sure that all trails and paths are covered is to study an aerial map of the area and look for other ways a person could enter the blasting area. It also pays to check for flat, easy to transverse ground where someone just taking a walk could accidentally enter the blasting area.
BE AWARE OF STRAY ELECTRICITY PROBLEMS DURING THE SUMMER THUNDERSTORM SEASON. During the summer, many parts of the country are liable to get sudden, severe thunderstorms. In fact, in Tucson, home of several copper mines, an isolated thunderstorm can form, strike, and disappear in less than an hour. Because preparing for a blast can take half a shift, it’s not uncommon for a blasting crew to be halfway through drilling and loading a blast pattern when a storm comes through.
Every mine should have procedures for such an occurrence. According to regulations, when a storm comes within 10 miles, the crew has to stop. However, experts note that storms can move onto a site quickly. “You can be counting the seconds between the lightening and thunder and they are 15 miles away,” an expert says, “when suddenly the next lightening strike is just 200 yards away.” One suggestion is to avoid tying in the blast holes until the shot is ready. That way, if lightening strikes one hole, the whole blast pattern doesn’t go off.
GO THROUGH YOUR PRE-CHECKS WHEN BLASTING UNDERGROUND. Underground blasting is more dangerous because of the threat of rock falls and toxic fumes. The mine must be clear of methane and other flammable gasses, roofs and sides must be checked, areas must be cleared of miners and then blocked, and electrical equipment must be deenergized. When the blast has been completed, the fumes must be cleared and the areas checked to make sure that there is no threat of rock falls.