What is meant by LFL in terms of the residual blowing agent?
Some amount of the flammable blowing agent gas can remain in the foam for a long time. Generally, this is not a flammability concern as long as it stays within the foam. Residual blowing agent that escapes the foam may have the potential to remain in the vicinity of the foam, where it may be possible to build up to a flammable concentration. This is of special concern when the foam is placed in airtight containers. The concentration of this gas surrounding the foam, then, is of interest in comparison with the Lower Flammability Limit (LFL; also known as LEL, Lower Explosive Limit) for that gas. The LFL is the lowest concentration in air in which a particular gas mixture will burn. If the concentration of a particular combustible gas in air is below the LFL, the air-gas mixture cannot ignite, and that mixture is not flammable. If, however, the concentration of combustible gas in air exceeds the LFL, the air-gas mixture can be ignited by a spark or flame. There is also an Upper Flammabil
