ASTM E2931: A New Standard for the Limiting Oxygen Concentration of Combustible Dusts

Abstract

Explosions can be very destructive in industrial and process situations. The mitigation of these devastating effects can be accomplished by disrupting the classical fire triangle. The fire triangle is made up of three elements 1) the fuel, 2) the ignition source, 3) the oxidizing atmosphere. Inerting the combustion atmosphere with nitrogen or carbon dioxide (negating the oxidizing atmosphere) has been a common approach in mitigating gas and vapor explosions for years. ASTM International even has a test standard to determine the amount of oxidizer reduction required for preventing flame propagation - ASTM E2079 Standard Test Methods for Limiting Oxygen (Oxidant) Concentration in Gases and Vapors.

Solids, in the form of dusts/powders, can also be involved in explosions as well without the need for flammable gases or vapors being present. A dust explosion requires two additional parameters; dispersion and confinement – thus creating an explosion pentagon. Mitigating dust explosion hazards are covered in NFPA 654: Standard For The Prevention Of Fire And Dust Explosions From The Manufacturing, Processing, And Handling Of Combustible Particulate Solids. One of the mitigation techniques discussed is the use of inert gases to prevent dust combustibility. Specifics about inerting as a design methodology are covered in NFPA 69: Standard On Explosion Prevention Systems. The standard calls for the reduction of the atmospheric oxygen levels to below the combustible dust propagation limit – or Limiting Oxygen Concentration. However, instructions to determine this level are vague. In the past we only had EN 14034-4: Determination of explosion characteristics of dust clouds - Determination of the limiting oxygen concentration LOC of dust clouds for guidance on determining this level. No such ASTM standard had been in place for dust explosions; until now.

ASTM International has just introduced a new standard, ASTM E2931: Standard Test Method for Limiting Oxygen (Oxidant) Concentration of Combustible Dust Clouds. This paper discusses the nuances of this standard and compares experimental results between this method and the EN method using tests conducted in both the 20-L Siwek chamber and the 1-m³ chamber. Differences between the methods may have safety ramifications to the end user of the data as well as reporting consequences in MSD Sheets.