Energetic Materials 101
Energetic materials are liquid or solid materials with a high amount of available stored chemical energy. Common energetic materials include propellants, explosives, pyrotechnic (PEP) compositions, and other fuel / oxidizer mixtures. Energetic materials are characterized by their sensitivity (the ability to initiate a reaction from an energy stimulus) and reactivity (propagation and effect characteristics after ignition).
Ignition or initiation of an energetic material requires an energy stimulus. Forms of energy stimulus include impact, friction, electrostatic discharge (ESD) or electrical spark, shock and thermal / heating among others. Sources of energy stimulus include:
- Pinching, cutting, grinding, or slicing
- Sliding surfaces together
- Drilling, hammering, welding
- Static discharge, electrical spark, or mechanically produced spark (hand tools, power tools).
High explosives residue in a cut 4-inch processing pipe
Any tool, power device, or equipment has the potential to create an initiation event. “Non-sparking”, “spark-resistant” or “spark-proof” tools may not produce hot mechanical sparks, but may still initiate energetic materials by electrical spark, static discharge, being dropped (impact energy), or being dragged / rubbed (friction energy).
Reactivity levels define the type of event that can be expected once a material has been ignited or initiated. Reactivity levels of concern include burning, deflagration, and explosion / detonation.
Any lower level reaction (burn, deflagration) can escalate to a higher level (explosion / detonation) given the right conditions:
- Confinement: All energetic materials respond with greater violence when confined. For D3 operations, material ignited in a crack or joint may accelerate to an explosive event due to pressure buildup.
- Critical Height: Materials in sufficient quantity (depth), with minimal confinement, can progress to an explosion or even a detonation when bottom ignited by flame or heat.
- Dusting: Very finely divided materials can transition to explosive reaction events if fluffed during an ignition event. Fuels such as flour, sugar, and metal powders can become explosive under this condition.
- Fine Particles: Smaller particles of an energetic material may also have increased reactivity and sensitivity. For example, Ammonium Perchlorate (AP) with a particle size greater than 200µ has a hazards classification of 5.1 Oxidizer, whereas AP with a particle size smaller than 20µ is a Hazards Division (HD) 1.1 explosive.
- Mixtures: Addition of contaminants or combinations of ingredients in vacuum systems, filter systems, and other processing areas can be more sensitive or reactive than ingredients alone.