The term 'explosive waste' commonly is used to refer to propellants, explosives, and pyrotechnics (PEP), which technically fall into the more general category of energetic materials. These materials are susceptible to initiation, or self-sustained energy release, when present in sufficient quantities and exposed to stimuli such as heat, shock, friction, chemical incompatibility, or electrostatic discharge. Each of these materials reacts differently to the aforementioned stimuli; all will burn, but explosives and propellants can detonate under certain conditions (e.g., confinement).
Explosives are classified as primary or secondary based on their susceptibility to initiation. Primary explosives, which include lead azide and lead styphnate, are highly susceptible to initiation. Primary explosives often are referred to as initiating explosives because they can be used to ignite secondary explosives.
Secondary explosives, which include TNT, cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX or cyclonite), high melting explosives (HMX), and tetryl, are much more prevalent at military sites than are primary explosives. Because they are formulated to detonate only under specific circumstances, secondary explosives often are used as main charge or bolstering explosives. Secondary explosives can be loosely categorized into melt-pour explosives, which are based on TNT, and plastic-bonded explosives (PBX), which are based on a binder and crystalline explosive such as RDX. Secondary explosives also can be classified according to their chemical structure as nitroaromatics, which include TNT, and nitramines, which include RDX. In the TNT molecule, NO2 groups are bonded to the aromatic ring; in the RDX molecule, NO2 groups are bonded to nitrogen
Propellants include both rocket and gun propellants. Most rocket propellants are either Hazard Class 1.3 composites which are based on a rubber binder, and ammonium perchlorate (AP) oxidizer, and a powdered aluminum (Al) fuel; or Hazard Class 1.1 composites, which are based on a nitrate ester, usually nitroglycerine (NG), nitrocellulose (NC), HMX, AP, or polymer-bound low NC. If a binder is used, it usually is an isocyanate-cured polyester or polyether. Some propellants contain combustion modifiers, such as lead oxide.
Gun propellants usually are single base (NC), double base (NC and NG), or triple base [NC, NG, and nitroguanidine (NQ)]. Some of the newer, lower vulnerability gun propellants contain binders and crystalline explosives and thus are similar to PBX.
Pyrotechnics include illuminating flares, signaling flares, colored and white smoke generators, tracers, incendiary delays, fuses, and photo-flash compounds. Pyrotechnics usually are composed of an inorganic oxidizer and metal powder in a binder. Illuminating flares contain sodium nitrate, magnesium, and a binder. Signaling flares contain barium, strontium, or other metal nitrates.
Safety precautions must be taken at sites contaminated with explosive wastes to avoid initiation. USAEC, which has been involved in sampling and treating explosives waste sites since the early 1980s, has developed protocols for identifying sites that require explosives safety precautions and for handling explosives wastes at these sites.
Under its current protocol, USAEC can determine quickly and inexpensively whether materials are susceptible to initiation and propagation by analyzing the composition of samples from the site. According to the deflagration-to-detonation test, soils containing more than 12% secondary explosives by weight are susceptible to initiation by flame; according to the shock gap test, soils containing more than 15% secondary explosives by weight are susceptible to initiation by shock. As a conservative limit, USAEC considers all soils containing more than 10% secondary explosives by weight to be susceptible to initiation and propagation and exercises a number of safety precautions when sampling and treating these soils. Sampling and treatment precautions are exercised when handling soils that contain even minute quantities of primary explosives.
Work, sampling, and health and safety plans for explosives waste sites should incorporate safety provisions that normally would not be included in work and sampling plans for other sites. The most important safety precaution is to minimize exposure, which involves minimizing the number of workers exposed to hazardous situations, the duration of exposure, and the degree of hazard.