Limiting oxygen concentration

Limiting oxygen concentration for solid materials[4] The effect of increasing the concentration of inert gas can be understood by viewing the inert as thermal ballast that quenches the flame temperature to a level below which the flame cannot exist.

[5] Carbon dioxide is therefore more effective than nitrogen due to its higher molar heat capacity.

For instance, to safely fill a new container or a pressure vessel with flammable gases, the atmosphere of normal air (containing 20.9 volume percent of oxygen) in the vessel would first be flushed (purged) with nitrogen or another non-flammable inert gas, thereby reducing the oxygen concentration inside the container.

When the oxygen concentration is below the LOC, flammable gas can then be safely admitted to the vessel, because the possibility of internal explosion has been eliminated.

The limiting oxygen concentration is a necessary parameter when designing hypoxic air fire prevention systems.

Flammability diagram , green dotted line shows safe purging of an air-filled vessel, first with nitrogen, then with methane, to avoid the flammable region. The limiting oxygen concentration is shown in the lower right of the diagram.