When the Dust Settles

Over the past year, a number of articles have been published regarding the high risk of explosion in seemingly harmless dust applications. The backlash that resulted from an increasing number of dust-related incidents has been felt throughout those industries. Through a national emphasis campaign, OSHA has made it very clear that facilities dealing with dust hazards should take a more proactive approach to avoid ignition of dust clouds.

Dust-related fires and explosions are a realistic threat to the workplace, and they may occur when five different factors are present: oxygen; an ignition source (heat, an electrical spark or a spark from metal-to-metal contact, i.e., by machinery); fuel (combustible or conductive dust); dispersion of the dust (layers or clouds); and confinement of the dust (to create sufficient concentration to be ignitable). These five factors are referred to as the “dust explosion pentagon.”

If any one of these factors is removed or missing, an explosion cannot occur. However, while the risk of explosion is eliminated by removing a leg of the pentagon, the risk of fire still remains when dust is allowed to build up on surfaces which may become hot. The subsequent fire may then create the dust explosion pentagon and lead to an explosion.

Requirements to protect against arcing and sparking electrical components are well known and accepted. Over the years, there has been an increasing awareness about the dangers caused by the buildup of static electricity, which is another dust ignition source. However, even today, very few codes and regulations pay attention to the dangers of surface temperatures. This is especially true for the protection of powered industrial equipment.

If housekeeping is not managed to minimize dust within the facility, most powered industrial equipment operated in dust hazardous facilities can create significant dust clouds as they move loose material or travel throughout facilities during normal operations. Combine this dust cloud development with the large number of ignition sources within this type of equipment and you will find plenty of reasons to be concerned.

With powered industrial equipment, special care should be given to limit surface temperatures, especially for internal combustion (IC) equipment. IC-powered equipment can be compared to a vacuum cleaner. They suck up all the dust from the ground and the atmosphere and deposit it inside the engine compartment and onto unprotected manifolds, exhaust, catalytic converters and inside radiators. Allowing dust to build up on components that can reach temperatures up to 600 °F significantly increases the risk of a fire and explosions as a result of smoldering and dust combustion.

If dust is allowed to build up inside the radiator, it may result in a reduction of airflow and radiator cooling performance. This, in turn, may lead to an increase in the engine running and surface temperatures. Dust may collect in open rotating parts, where rubbing of the component against the dust may increase the risk of ignition by friction.