Limiting Oxygen Concentration (LOC) is defined as the oxygen concentration below which combustion is not possible, independent of the concentration of fuel. The LOC is dependent on the type of inert (non-flammable) gas used. Dust samples of varying quantities are dispersed in a 20-liter spherical vessel and attempts are made to ignite the resulting dust cloud with an energetic ignition source. Tests are repeated for decreasing oxygen concentrations (replaced with the inert gas) until the LOC is determined. Data obtained provides a relative measure of the deflagration characteristics of dust clouds. A dust cloud atmosphere having an oxygen concentration below the LOC is not capable of supporting deflagration.

The Limiting Oxygen Concentration (LOC) test is performed in accordance with the requirements of the current edition of the American Society for Testing and Materials (ASTM) E2931.