How the Flammability is measured?

asked 04 Sep, 14:49

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The vapor which given off by a liquid burns but not the liquid itself. A mixture of vapor and air lies between two concentrations known as the:
Lower Flammable (Explosive) Limit (LFL or LEL)
Upper Flammable (Explosive) Limit (UFL or UEL)

The limit depends upon the type of liquid cargoes. Concentrations below the lower limit (too-lean), or above the upper limit (too-rich), are incapable of burning but it is important to remember that concentrations above the upper limit can be made to burn by diluting them with air until the mixture is in the flammable range.

Vapor concentrations depend upon the vapor pressure and temperature of the liquid. As the temperature increases so does the vapor pressure and vapor concentration above the liquid. For each liquid, there is a temperature at which the vapor concentration reaches the LFL and another higher temperature at which the concentration exceeds the UFL. The more readily the liquid vaporizes, the lower the temperature at which the LFL is reached.

The flash point of a liquid is an indication of the temperature at which a liquid produces sufficient vapor to give a concentration in air equivalent to the LFL. Some liquid cargoes form flammable mixtures at all ambient temperatures: others only at higher ambient temperatures and others again only when heated.

The LFL and UFL limits vary somewhat for different pure hydrocarbon gases but for the petroleum gases occurring in normal tanker practice the overall range is from a LFL of 1% gas by volume in air to an UFL of 10% gas by volume in air.

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answered 04 Sep, 14:53

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