Flammable liquids, vapors, and gases

Other than reactive metals explosions, which do not truly fall in the types noted above, the two main categories of explosions are flammable gases, liquids/vapors, and dusts. Because their sources are different, they cannot be treated in the same manner for discussion. 

Safeguarding against external hazards, such as ignition sources if the piping or equipment could contain flammable material, and sealing off drains or other possible sources of noxious liquids, vapors, or gases. 

Certain materials can deflagrate or explode under adverse conditions. These include several organic peroxide formulations and oxidizers, compressed or liquefied flammable gases and flammable liquid vapors. 

When subjected to high temperature, some Class IV oxidizers (NFPA 430) can decompose and deflagrate. Additionally, compressed or liquefied flammable gases and flammable liquid vapors, especially Class IA liquids, can also produce an explosive atmosphere if released within a building or room. Chapter 2 provides additional details regarding the deflagration potential of various commodities. 

Fuel and oxygen lines that are unmarked or improperly identified Absence of No Smoking signs in areas where flammable liquids, vapors, gases, or other highly combustible materials are stored or used spark-producing tools in such areas... 

NFPA 497 Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, 1997 edition. National Fire Protection Association, Quincy, MA. 

Fuels such as diesel and kerosene readily absorb hydrocarbon vapors, the total uptake and absorption rate depending on both chemical and physical factors. If a soluble test gas is introduced above a charged test oil the concentration of flammable test gas therefore decreases with time. Liquid mist and spray produced by charged liquid increase the absorption rate relative to a quiescent liquid surface. As discussed in A-5-4, absorption could lead to an underestimation of test gas MIE near the liquid surface unless the rate of test gas introduction is sufficiently high to offset the rate of removal. Table 3-8.1.2 shows solubilities of a selection of gases in a mineral-based transformer oil at ambient temperature and pressure [200]. 

Vaporization and diffusion of flammable/toxic liquids or gases ... 

Small cocks have often been knocked open or have vibrated open. They should never be used as the sole isolation valve (and preferably not at all) on lines carrying hazardous materials, particularly flammable or toxic liquids, at pressures above their atmospheric boiling points (for example, liquefied flammable gases or most heat transfer oils v./hen hot). These liquids turn to vapor and spray when they leak and can spread long distances. 

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