The Tech Center >Useful formulae--Conversions, etc. > Combustibles

Although Interscan is in the toxic gas detection business, many of our customers are also involved with flammable and combustible compounds, so we are pleased to provide the following information.

Flammable and combustible chemicals are those that evaporate fast enough to generate sufficient vapor to ignite in the presence of an ignition source. The temperature at which this can occur is the chemical's flash point.

In addition, flammable and combustible chemicals are those that can react with oxidizers, to cause a fire or explosion. Combustible materials will generate sufficient vapors at or above 100°F (37.8°C). Flammable chemicals will generate sufficient vapors at temperatures below 100°F (37.8°C).

Material Safety Data Sheets may also list a chemical's auto-ignition temperature, which is the lowest temperature at which there is enough heat energy to ignite vapors spontaneously.

Other important characteristics of flammable and combustible chemicals are their explosive limits. The Lower Explosive Limit (LEL or lower flammable limit) is the lowest concentration of the substance in air that will produce a flash of fire when an ignition source is present. The Upper Explosive Limit (UEL or upper flammable limit) is the highest concentration of the substance in air that will produce a flash of fire when an ignition source is present.

At higher concentrations than the UEL, the mixture is too rich to burn. At concentrations lower than the LEL, the mixture is too lean to burn. Note that for flammable chemicals that are also toxic, concentrations at which the flammability is a hazard are usually well above the toxicity hazard concentrations.

Table of LEL's/UEL's

The flammable liquids of most concern in industry and laboratories are those that have flash points below room temperature. These include...