Combustible gases combine three elements – fuel, oxygen and an ignition source. The primary risk associated with these elements depends on the specific fuel and oxygen mixture.
A combustible gas in a quantity which is either too small or too large will not ignite. The gas levels are measured as a percentage and referred to as the
Lower Explosive Limit – LEL Upper Explosive Limit – UEL
Any gas level between the 2 limits will ignite and should be considered explosive with the maximum explosive limit at some mid level point between the upper and lower limits.
Each gas has it’s own LEL and UEL values. The following table gives examples of the LEL and UEL values (although these can vary slightly depending on testing conditions).