Definition - What does Flammability Limit mean?
Flammability limit refers to the upper or lower limits of the gaseous or vaporized fuel or combustible material at a fixed temperature and pressure that can lead to flame propagation, detonation or an explosion. Fuel or combustible concentrations outside the both limits are considered to be non-flammable.
Safeopedia explains Flammability Limit
Flammability limits vary with temperature and pressure. However, the normal expression is in terms of % of volume at 25 °C at sea level atmospheric pressure. The flammability limits are important to note, due to easy combustion or making safe mixtures. Optimum combustible mixtures are important for internal combustion engine’s ignition.
For example, lower flammability limit of Jet A fuel in the air at sea level is about 0.7%. However the optimum would be about 4.8%. Flammability limits also depend upon the type and strength of the ignition source and atmosphere (% of oxygen in air, pressure and the temperature).