(43d) Secondary Dust Explosions: How to Prevent Them or Mitigate Their Effects?

Dust explosions are frequent and particularly devastating in the process industries, and secondary dust explosions are the most severe ones.

A secondary dust explosion can occur when the blast wave from a primary explosion entrains dust layers present in the plant, creating a large dust-air flammable mixture ignited by the first explosion. As the blast wave propagates through the plant, dust fuels the emerging flame, leading to extensive explosions because of the large quantity of dusts involved and the very high energy of ignition.

Several cases of secondary dust explosions were noticed and analyzed by Eckhoff. Major accidents have occurred in the US in recent years, conducting the Chemical Safety Board to produce a specific report that highlighted the increasing risk of dust explosions. An illustration of this is the massive explosion that occurred on 7 February 2008 at the Imperial Sugar Company in Port Wentworth (Georgia), causing 14 fatalities and injuring 36 people.

As consequences of secondary dust explosions could be very dramatic, only a minor explosion (beginning in equipment for example) can quickly develop into a major secondary explosion if appropriate precautions are not taken.

This article aims to give an overview of secondary dust explosion accidents and present practical solutions to prevent or mitigate these disasters.