This test is conducted to determine the lower and upper concentration limits of flammability of chemicals having sufficient vapour pressure to form flammable mixtures in air at atmospheric pressure at a specific test temperature. The test can be conducted on vaporised liquids and gaseous materials. Refrigerant gases are tested to ASHRAE 34, using the method detailed within ASTM E681, with specific ignition criteria and air moisture content.
LOWER FLAMMABLE LIMIT OR LOWER EXPLOSIVE LIMIT (LFL / LEL)
Lower limit of flammability or lower flammable limit (LFL)—the minimum concentration of a combustible substance that is capable of propagating a flame in a homogeneous mixture of the combustible and air, under the specified conditions of test. Generally 1% v/v of the material is added to a glass vessel under vacuum. Air allowed back into the system, the material and air mixed, before an electrical ignition source is activated and observations for flame propagation observed. The material is then incrementally increased in 1% steps until ignition is observed and the LFL defined.