WHEN WATER TURNS A FIRE INTO AN EXPLOSION
A combustible dust explosion is an ever present danger for workers in many industries. These two examples show that despite increased awareness, explosive dust still puts lives at risk. One thing they both have in common: water may have actually made them much worse.
The first example shows how even things that seem like safe and practical fire-fighting measures can lead to disaster. In May, a grain dust explosion in a silo injured a worker who was attempting to put out a dust fire with water.
Because the very fine dust was contained in the silo, all the criteria for an explosion were present… except for one. The dust provided fuel for a fire, and the open silo hatch provided oxygen. With the material confined in the closed space of the silo and an ignition source in the form of a grain dryer, an explosion was waiting to happen.
Ironically, it was the worker spraying water onto the fire that created the explosion by adding the last element: dispersal of the dust. Water hitting the dust added more air and also raised a cloud of dust. Dust suspended in the air turns the situation from a fire into an explosion. In this case it blew the roof off the silo and caused serious injuries.
Fish Meal Dust?
The second example is in some ways a classic industrial dust explosion, except that the material isn’t one you’d expect. In September, a seafood processing plant was seriously damaged and had to be shut down because of an explosion caused by the ignition of fish meal dust.
Fish meal is a fine, dry powder that’s often made into fish food. A local official noted that this is the third time he knows of that fish meal has caused an explosion at a local plant. In this case, a burst pipe may have created an explosion by causing dust to become airborne.
While people don’t think of fish as being explosive, they usually don’t think of metal as being explosive either. Both of them are only dangerous when they’re turned into a dust.
While we talk a lot about combustible metal dust and fumes because many of the industries we work with use metals, organic dusts like grain, spices, powdered milk and egg, sugar, tobacco, and yes, even fish are dangerously explosive if all the right elements are present.
While many places that produce metal dust are aware of the risks, some places that produce organic dust don’t realize how dangerous it can be, or how important a dust collection system is for controlling and handling dust. The most catastrophic damage is often done by secondary explosions: a small dust explosion causes accumulated dust to be dispersed in the air, causing a much larger explosion. Spraying water on a dust fire can do the same thing, sending dust into the air.
Removing dust from the facility and collecting it with a dust collection system designed to prevent or safely control explosions is an important safety strategy. Making sure there is no dust dispersed in the air is another key to explosion prevention. In any situation with combustible dust, the system needs to be equipped with safety features such as spark arrestors, explosion venting, and chemical suppressors.