Explosive Limits

The explosive limits (also called limits of flammability or limits of inflammability) determine whether a gas or vapor mixture with air/oxygen will combust.

For a gas mixture, two explosive limits should be given:

• The Lower Explosive Limit (LEL). Below this concentration, the fuel mixture is too lean to combust.
• The Upper Explosive Limit (UEL). Above this concentration, the fuel mixture is too rich to combust.

Any gas mixture with a concentration between the LEL and UEL can cause an explosion!

Also keep in mind:

• LEL and UEL are dependent on temperature and pressure. Generally, higher pressure and temperature will expand the explosive regime (more danger).
• LEL and UEL are usually specified for mixtures in air, but will be different for mixtures in oxygen.
• Free flowing, explosive gas mixtures with concentrations above the UEL can easily mix with surrounding air, and consequently cause an explosion.
• The presence of other explosive gases in a mixture will also affect the LEL and UEL

If you ever need this data, verify it in reputable sources, such as the CRC Handbook of Chemistry and Physics.