Reactive chemicals are defined as substances which may in the presence of air-water temperature changes, shock, friction static discharge or contamination release very large and potentially harmful amounts of energy. Reactive chemicals are classified based on the stimuli needed to induce a hazardous reaction.
Stimulus – The stimuli needed to induce a hazardous reaction varies according to compound and may be thermal, physical, electrical, a chemical reaction, or no stimulus at all.
The 6 classifications of stimuli are:
D-Spontaneous Decomposition. Materials that in conditions associated with undisturbed storage, could with no apparent stimulus, spontaneously decompose. This classification includes Peroxide formers such as isopropyl ether, monomers such as styrene, and forbidden such as Butoxycarbonyl Azide.
T-Temperature Sensitive. Materials which are unstable at or above a specific temperature. Organic peroxides such as Dibenzoyl Peroxide and self-Reactives such as azobisisobutyronitrile are examples of Temperature sensitive materials.
S- Shock Friction or Static discharge. materials which will violently decompose when initiated by the stimulus of shock, heat, friction or static electricity. Includes fulminates such as Mercury fulminate and explosives such as trinitrotoluene.
A – Air Exposure. Materials which will react and decompose when exposed to air or moist air. This classification includes Pyrophorics such as trimethyl aluminum and pure elements such as phosphorus.
W-Water Exposure. materials which will react and decompose when exposed to water. This includes Reactive metals such as sodium or lithium and carbides such as calcium carbide.
O-Strong Oxidizing Materials. Materials that readily yield Oxygen or other oxidizing gas to stimulate the combustion of organic material. When exposed to or contaminated with organics or materials, these materials can become shock sensitive. This includes inorganic acids, such as Perchloric Acid and halogens such as Fluorine.
Sensitivity. The relative ability of a material to react with its stimulus is referred to as Sensitivity. Reactive chemicals are broken down into three classes of sensitivity, Low, Moderate, or High
L–Low Sensitivity. Materials which require a great deal of stimulus to initiate hazardous reaction, severe shock or exposure to high temps.
M–Moderate Sensitivity. Need only moderate amount of stimulus to initiate hazardous reaction. i.e. exposure to room temp or hot moist air.
H–High Sensitivity. Materials which need very little stimulus to initiate hazardous reaction and can be initiated by normal handling, i.e. twisting cap, exposure to temps above freezing, or spontaneously ignite upon contact with cool dry air.
We will discuss the effects of each of these in the next post.