Gases - Explosive and Flammability Concentration Limits

Flame and explosion limits for propane, methane, butane, acetylene and other gases

The flammable (explosive) range is the range of a gas or vapor concentration that will burn or explode if an ignition source is introduced. Limiting concentrations are commonly called the "Lower Explosive or Flammable Limit" (LEL/LFL) and the "Upper Explosive or Flammable Limit" (UEL/UFL). Below the explosive or flammable limit the mixture is too lean to burn and above the upper explosive or flammable limit is too rich to burn.

The lower and upper explosion concentration limits for some common gases may be found in the table below. Some of the gases are common as fuel.

Note! The limits are for gas, air and oxygen at 20^oC and atmospheric pressure.

It is important that the area where flammable gases are stored are well ventilated. When designing the ventilation system, be aware of the specific gravity of the gas. The gas mixture is not homogeneous. A light gas will concentrate along the ceiling. A heavy gas will concentrate along the floor.

Ventilation, natural or mechanical, must be sufficient to limit the concentration of flammable gases or vapors to a maximum level of 25% of their "Lower Explosive or Flammable Limit" (LEL/LFL).

• Minimum ventilation required: 1 cfm/sq.ft.
• Recommended ventilation: 2 cfm/sq.ft or 12 air changes per hour - half the air supplied and exhausted near the ceiling and half the air supplied and exhausted near the floor

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