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- 4 - Materials sensitive to shock and heat at normal temperatures and pressures. Can undergo detonation or explosive decomposition at normal temperatures and pressures. Examples of Instability Hazard 4 include ammonium perchlorate, 3-bromopropyne, chlorodinitrobenzenes, fluorine, nitromethane, peracetic acid and picric acid.
- 3 - Materials sensitive to shock and heat at elevated temperatures and pressures. Subject to detonation or explosive decomposition or explosive reaction, but need a strong initiating source or must be heated under confinement. Examples of Instability Hazard 3 include, tetrafluoroethylene, silane, n-propyl nitrate, perchloric acid, nitroethane, hydrogen peroxide greater than 60%, hydrazine, ethylene oxide, chloropicrin and ammonium nitrate.
- 2 - Chemicals which will undergo violent chemical change at elevated temperatures and pressures. Examples of Instability Hazard 2 chemicals include trichlorosilane, titanium tetrachloride, sulfuric acid, styrene monomer, sodium hydride, potassium, phosphorus trichloride, phosphorus, methyl isocyanate, hydrogen cyanide, ethylene, epichlorohydrin and aluminum chloride.
- 1 - Materials that in themselves are normally stable, but that can be come unstable at elevated temperatures and pressures. Examples of Instability Hazard 1 materials include acetic anhydride, allyl alcohol, aluminum powder, ethyl ether, hydrogen chloride, magnesium, nitrobenzene, phosgene and potassium hydroxide.
- 0 - Materials that in themselves are normally stable, even under fire conditions.
Special hazards listed in the text of NFPA 704 are limited to water reactive and materials with oxidizing properties that require special firefighting techniques. Special hazards are indicated by a symbol located in the quadrant of the diamond at the "6 o'clock" position in the white section. Materials that react violently or explosively with water are identified by the letter W with a line through the center. Materials that possess oxidizing properties are identified by the letters OX. Examples of chemicals with an OX hazard include sodium peroxide, potassium peroxide, peracetic acid, oxygen, nitric acid, hydrogen peroxide, chromic acid, bromine and ammonium nitrate. Water-reactive materials include calcium carbide, calcium hypochlorite, fluorine, lithium aluminum hydride, potassium and sodium.
NFPA 704 is just one of many tools available for emergency responders when evaluating an incident scene for the presence of hazardous materials. More information needs to be gathered before mitigation tactics are decided upon. Generally, firefighter turnouts do not provide much protection against hazardous materials, although self-contained breathing apparatus (SCBA) provides a high-level of respiratory protection. A thorough evaluation of the hazards present along with a risk/benefit analysis must take place before personal protective equipment (PPE) and tactics are selected.
Robert Burke, a Firehouse® contributing editor, is the fire marshal for the University of Maryland. He is a Certified Fire Protection Specialist (CFSP), Fire Inspector II, Fire Inspector III, Fire Investigator and Hazardous Materials Specialist, and has served on state and county hazardous materials response teams. Burke is a veteran of 24 years in fire and emergency services, with experience in career and volunteer departments. He has attained the rank of lieutenant, assistant chief and deputy state fire marshal. Burke is an adjunct instructor at the National Fire Academy and the Community College of Baltimore, Catonsville Campus, and the author of the textbooks Hazardous Materials Chemistry for Emergency Responders and Counter-Terrorism for Emergency Responders. He can be reached in the Internet at email@example.com.