Basics About Dust Explosions

034Globally, the amount of devastation incurred by a factory explosion is staggering. The US Chemical Safety Board recently reported that they have “identified 281 combustible dust incidents between 1980 and 2005 that killed 119 workers and injured 718, and extensively damaged industrial facilities. Injuries or fatalities occurred in 71 percent of the incidents.” FM Global reported recently that in a 10 year period the per incident loss due to explosions was $398,000!

 

Combustible dust is present in a variety of different process industries including:

  • Food and Beverage
  • Wood and Biomass
  • Chemical
  • Pharmaceutical
  • Coal
  • Plastics

Dust Explosions are unique and complex phenomena that are as unpredictable as they are dangerous. Although no two dust explosions are ever the same, the five elements listed in the “Dust Explosion Pentagon” must all be present in order to initiate one of these destructive events.

dust-explosion-chart1)  Explosive Dust: The material being handled must be combustible. Some examples are sugar, plastics, coal, grains, flour, starch, and metals.

2) Suspended Cloud: The explosive dust being processed must be entrained in a cloud of sufficient concentration.

3) Confined Area: An enclosed structure surrounding the suspended dust cloud must exist in order to achieve the pressure rise characteristic of a dust explosion. In the absence of a confined area, flash fires are still a hazard but explosions typically are not.

4) Oxygen: O2 in optimum concentration must be the medium for handling the explosive dust.

5) Ignition Source: When all other elements are present, an ignition source is the last piece of the puzzle needed to activate the dust explosion chemical reaction. Often the most elusive of the five elements, ignition sources can be generated in a multitude of applications and come in a variety of forms. Some examples include smoldering or burning dust, open flames, hot surfaces, heat from mechanical impact and electrical discharges.

The maximum pressure developed during an unmitigated dust deflagration is known as the Pmax. The rate at which this maximum pressure is reached as a function of vessel volume is known as the deflagration index, or Kst. Combined, the Pmax and Kst values give the relative severity of a particular dust. If this same dust deflagration, however, is mitigated either through venting or suppression, the maximum pressure developed will be minimized from the Pmax to the Reduced Explosion Pressure, or Pred. The Pred is typically an order of magnitude less than the Pmax and is designed around so that a vessel handling combustible dust is not breached during a deflagration.

Explosion mitigation systems can be categorized into two types of technologies defined as either passive safeguards or active safeguards. CV Technology offers a unique range of products from our Interceptor® line for explosion management that includes both passive and active technologies. By utilizing passive, active, or a combination of both safeguards, CV Technology can design a custom explosion protection solution to mitigate or prevent dust explosion hazards specific to your process needs.