Limiting Oxygen Concentration (LOC) Testing

BS EN 14034 part 4

The Limiting Oxygen Concentration (LOC) test determines the minimum quantity of oxygen, within an atmosphere, that would be sufficient to enable combustible dust, when dispersed in the air, to ignite when in contact with an ignition source.

Working through a range of concentrations, a powder is dispersed into a 20L explosion vessel (sphere) using dry compressed air and an inert gas i.e., nitrogen. Using partial pressures, oxygen content within the sphere at the time of ignition is controlled.

These suspended dust clouds are then exposed t a large 2 kJ chemical ignition sources and the following dust explosions are monitored, measured, and recorded, using high-accuracy piezoelectric transducers.

Once ignition occurs at a specific oxygen concentration, oxygen concentrations are reduced, and powder concentration is varied, until the hightst oxygen concentration is established. This, in essence, means that ignition is not possible, and the ‘LOC’ is established.

Data obtained by the Limiting Oxygen Concentration test is predominantly used for either the design of nitrogen inerting systems or to confirm if combustible dusts or powders are appropriate for processes with an established limited oxygen atmosphere.

As many ventilation systems now are set at a much lower oxygen level than required, this can result in large nitrogen costs. This can be avoided or reduced, by knowing a combustible dust’s specific limited oxygen concentration and then setting the concentration of oxygen levels accordingly.