Abstract
CSB (US Chemical Safety Board) identified 281 combustible dust incidents between 1980 and 2005 that killed 119 workers, injured 718 others and damaged several industrial facilities. These incidents occurred in 44 states, many different industries and involved a variety of different materials. Seven of the incidents, which have occurred in the past decade, had catastrophic results with multiple fatalities and significant community economic impact.
Like all fires, a dust fire occurs when fuel is exposed to heat in the presence of oxygen. Removing any one of these elements of the classic fire triangle eliminates the potential for a fire. In addition to the familiar fire triangle of oxygen, heat and fuel, dispersion of dust particles in sufficient quantity and concentration can cause rapid combustion known as a deflagration. If the event is confined by an enclosure such as a building, room, vessel, or process equipment; the resulting rise in pressure may lead to an explosion. These five factors (oxygen, heat, fuel, dispersion, and confinement) are collectively known as the dust explosion pentagon.
Suspended dust burns more rapidly and confinement allows for pressure buildup. Removal of either the suspension or the confinement elements prevents an explosion, although a fire may still occur. Furthermore, the concentration of suspended dust must be within an explosible range for an explosion to occur. This is analogous to the flammability range commonly used for vapors; such as natural gas and propane. Dust explosions can be very energetic creating powerful waves of pressure that can destroy buildings and hurl people across a room. People caught in dust explosions are often either burned by the intense heat within the burning dust cloud, injured by flying objects or falling structures.
On January 29, 2003, a massive dust explosion in Mersin, Turkey resulted in the deaths of two workers, serious injuries of two more and destruction of the facility. The casualty count would have been higher; had the time of the explosion been on a crowded workshift.
The explosion occurred in a building which had nine huge semolina silos inside. The day of the accident there was planned work that included some welding atop of the silos. Also, there was organizational fault when they failed to check about the methane gases which escape from the semolina spoilage. All of the fire triangle were present. The ambient air for oxygen, welding work for heat and methane for fuel. After the primary small explosion and fire started, the dust which accumulated on the equipments dispersed in the ambient air above the silos in the building. At that time, all the conditions for dust explosion were present; with the addition of dispersion and confinement.
The investigation of the accident, accomplished by the Turkish Labour Inspection Board, will be evaluated with conditions that formed the dust explosion, findings about the accident, precautions for prevention and control of the accident.
