Tuesday, May 18, 2010

Multiple Explosions

In a recent chemical facility fire in North Georgia there were reports of multiple explosions which hampered fire fighting efforts. There were no explosive chemicals stored on site so what caused the explosions? It was just another example of a phenomenon that I have discussed before, the BLEVE (boiling liquid expanding vapor explosion) writ small. In a fire any liquid chemicals in containers impacted by flames are likely going to quickly reach their boiling points. This is going to result in a rapid rise in pressure in the container. Larger storage containers should have pressure relief devices designed into the system to safely vent those fumes, protecting the containers from catastrophic failure. Unfortunately, drums do not come equipped with formal pressure relief devices. This means that they will burst. The two weakest points of the construction are where the bottoms and tops of the drums are joined to the side. One or the other of these seams will fail catastrophically, releasing a cloud of chemical vapors that will almost certainly ignite in a quick ball of fire. The loud boom is not technically an explosion; it is a pressure release event. To make matters worse, when the failure is along the base of the drum the upper portion of the drum is launched into the air like a rocket. It looks especially impressive at night as the flaming gasses shoots out of the bottom of the drum flying through the air. The flaming residues in the drums can cause an expansion of the fire perimeter depending on where they land. This is one of the reasons that fighting fires at chemical facilities can be so dangerous. Even when the drums are not launched into the air, drum lids and other pieces of flying metal are hazardous to fire fighters. The only way to prevent this problem is to keep the flames away from the drums; this requires a properly designed fire suppression system in chemical warehousing areas.

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