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NOTE: This is an unformatted excerpt from our online fire protection training library.

Identifying Materials & Equipment

Liquids, Vapors & Gases

Flammable Limits

The flammable limits for a specific material are expressed as percentages. These are the minimum and maximum percentages by volume of a gas or vapor in a mixture with normal air that is ignitible. The minimum percentage is the LFL Lower Flammable Limit and the maximum percentage is the UFL Upper Flammable Limit. Most materials have a relatively small range For example, the LFL of gasoline is 1.4% and the UFL is 7.6%. Gasoline engines whose fuel-air mixture is too "rich" or "flooded" may not start because the fuel-air mixture is essentially above the UFL for the gasoline. between the LFL and UFL, and the concentrations outside of this range are not flammable. Materials with a large range of flammable limits Hydrazine, a highly toxic and flammable material sometimes used as a booster fuel in military jet engines, has no LFL and the UFL is 98%. Similarly, the LFL and UFL of acetylene are 2.5% and 99.9% respectively. may be somewhat more hazardous. The flammable limits do not have much effect on the design of electrical equipment, but they do affect other protection methods such as ventilation or purged and pressurized Ventilation and purged and pressurized enclosures reduce the fire and explosion hazard by keeping the air mixture below the LFL of a material. (Sometimes purging and pressurizing is done with inert gases rather than air.) enclosures.
NOTE: This is an unformatted excerpt from our online fire protection training library.

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