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Flammable vapours: Unignited

Hazard Knowledge

In addition to generic hazards and controls applicable to all hazardous materials, flammable vapours pose additional specific hazards when uncontained, which should be considered when encountered at incidents.

As well as posing a threat of fire, most flammable vapours also present a health hazard. This section deals only with properties that directly influence their fire hazard. For the purposes of this guidance, no distinction is made as to the way flammable vapours are produced, as the control measures for the vapour will be the same. Generally, flammable vapours will be produced following a spillage of a volatile flammable liquid or where flammable vapours under pressure have escaped their container. It should be noted that a release of a pressurised flammable liquid can produce a pool of liquid at a very low temperature (below the material’s boiling point); in addition to producing a significant vapour cloud, cryogenic hazards should also be considered (See Hazard – Cryogenic material release). Control measures for minimising vapour production are covered in Hazard – Flammable liquids: Unignited).

Generally, gases and vapours, including flammable vapours, have no size or volume; they expand to fill their container or spread out in the open until they are equally distributed throughout the space available to them. Therefore, gases and vapours are the most difficult state of matter to control. When they are also flammable, they can pose significant challenges and risk to responders and the public.

Flammable gases ignite or burn producing heat and, in most cases, light (certain flammable gases have no visible flame, e.g. hydrogen and methanol). In certain conditions, they can also cause explosions. The terms used to describe flammable liquids are included in the Foundation for Hazardous Materials. These terms should be understood to assess the risk posed by this hazard.