Explosion prevention begins when one piece of the Dust Explosion Pentagon is removed.
Remove Combustible Dust
If you can go without storing combustible dust in your facility, you don’t have a dust explosion hazard. This approach is safer than any other prevention technique because the fuel is no longer present.
Keeping fuel below the minimum explosive concentration, or MEC, can be done through regular cleaning of your present equipment or selecting new equipment that doesn’t allow dust to accumulate inside it or in the ductwork.
Oxidizer reduction is inerting the atmosphere to bring the oxygen level down below the limiting oxygen concentration, or LOC. This method involves the injection of an inerting gas like nitrogen into a closed system.
Spark Detection and Control
With this active system, possible ignition sources are detected. Examples include hot screws, smoldering piles, or a hot ember that has been sucked into a dust collection system. These hazards can be detected through the presence of smoke, radiation and high temperatures, and must activate a control method such as:
- an abort gate that shunts a hot ember out of the processing line;
- a suppression system that quenches it before it can get downstream and start the incipient stages of a flash fire or explosion.
Proper Hot Work Systems
Hot work such as welding and cutting should not be done in a dusty environment or on tanks or hoppers containing combustible dust. Clean up the material or empty it from the equipment being worked on before hot work begins.
Self-ignition can happen in silos where smoldering combustion is deep inside the stored material and turns into flaming combustion when it reaches the surface. This event can ignite a dust or gas explosion in the headspace.
Self-ignition can also occur in equipment like spray dryers. Material sticks to the inside edge, heats up and becomes an ignition source for a dust explosion. It is critical to remove this material safely; striking the vessel to dislodge the buildup could ignite an explosion.
Ignition Source Control
Minimum Ignition Energy, or MIE, is the minimum amount of energy required to initiate the combustion of a cloud of dust, vapor or gas. The lower the number, the more hazardous it is. Making sure the ignition sources in your system or surface temperatures are below the MIE of the dust cloud removes the ignition piece of the Dust Explosion Pentagon and is the final way to prevent an explosion from occurring.
Explosion mitigation - protecting workers, equipment or the environment from an incident or incident sequence – begins after the incipient stages have already begun.
Containment refers to increasing the confinement. Explosion-proof pressure vessels on a dust collector can avoid the need for an isolation channel between them. In other cases, such as hammer mills, the equipment is built strong enough to withstand an explosion inside.
Venting is a passive approach. The explosion vent is designed to open at a set pressure. When an explosion reaches the set pressure, the vent opens and the pressure is expelled into the surrounding area.
Flameless venting usually involves a passive explosion vent panel and flame-inhibiting device located within equipment such a dust collector. As an explosion begins, the explosion vent panel opens, permitting flame and dust to enter the flame-inhibiting device, reducing the flame’s temperature below the dust’s ignition temperature and thereby keeping the flame from spreading and causing an explosion.
Suppression systems actively monitor for the beginning of an explosion. A pressure sensor detects an incident at its incipient stage and activates a control system. This system could suppress the flame or inert the atmosphere so that the flame can’t develop further.