(43c) Methods for Precluding the Existence of a Dust-Explosion Hazard

The "generic" standard for preventing fires and explosions involving combustible dusts is the National Fire Protection Association publication NFPA 654. In this document, fifteen of the requirements are prefaced with the phrase "if an explosion hazard exists", and an additional four requirements are prefaced with the phrase "if a fire hazard exists". An objective of this paper is to show how fire and explosion hazards can be avoided in many dust-handling processes, by well-designed, well-constructed, and well-maintained systems that involve reliable control of pertinent variables.

The handling of combustible dusts can be hazardous to personnel and property, if the fine-particle dust is dispersed in air, at a concentration that is above the Minimum Explosible Concentration [MEC], and if an energetic ignition source is present within the cloud. The result could be a flash-fire if the cloud is relatively unconfined, or an explosion if the cloud is confined. In the absence of a cloud or if the concentration is below the MEC or if there is no energetic ignition source, neither a flash-fire nor an explosion would occur.

Strong efforts should be made to minimize ignition sources and accumulations of dust in the workplace, to prevent primary and secondary explosions. Similarly, preventing ignition sources and explosible dust concentrations within equipment can minimize the likelihood of explosion. This paper shows how the formation of an explosible dust cloud can be precluded within equipment, primarily by controlling the accumulation of dust and by ensuring an adequate flow of air.