Gases - Explosive and Flammability Concentration Limits

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The Flammable Range (Explosive Range)  is the range of a concentration of a gas or vapor that will burn (or explode) if an ignition source is introduced.

Below the explosive or flammable range the mixture is too lean to burn and above the upper explosive or flammable limit the mixture is too rich to burn. The limits are commonly called the "Lower Explosive or Flammable Limit" (LEL/LFL) and the "Upper Explosive or Flammable Limit" (UEL/UFL).

The lower and upper explosion concentration limits for some common gases are indicated in the table below. Some of the gases are commonly used as fuel in combustion processes.

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

It is important that areas where flammable gases are stored are well ventilated. When designing the ventilation systems, be aware of the specific gravity of the actual gas. The gas mixture from a leakage will not be homogeneous. and a light gas concentrates along the ceiling. A heavy gas concentrates 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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