Limiting oxygen concentration
Limiting oxygen concentration, often abreviated LOC, is defined as the limiting concentration of oxygen below which combustion is not possible, independent of the concentraion of fuel. It is expressed in units of volume percent of oxygen. The LOC varies with pressure and temperature, and it is dependent on the type of inert (non-flammable) gas.
The concept has important practical use in safety engineering. For instance, to safely fill a new container or a pressure vessel with flammable gasses, the atmosphere of normal air (containing about 21 volume percent of oxygen) in the vesseel would first be purged with nitrogen or another non-flammable gas, thereby reducing the oxygen concentration in the container. When the oxygen concentration is below the LOC, the flammable gas can be safely admitted to the vessel without risk of internal explosion.
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