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Mechanical Seal Failure and Explosion in a Chemical Blending Vessel

APTECH was retained to investigate the cause of an explosion in a blending vessel in a chemical processing facility. The explosion destroyed the plant and caused fatalities and injuries among the plant workers. The toxic plume from the ensuing fire injured several firefighters. The plume also fumigated the city downwind of the plant. At the time, the vessel was mixing together powdered sodium hydrosulfite and aluminum powder. Several hours before the explosion, the mixture began bubbling and producing heat and hydrogen sulfite fumes. Because this exothermic run-up to the explosion was typical of what happens when sodium hydrosulfite reacts with water, APTECH's investigation focused on identifying how water might have been introduced into the blender. We determined that the water would have to have been injected into the interior of the powder bulk, and that the built-in agitator bar would have been the water conduit. The agitator's drive shaft had an outboard mechanical seal, which was water-cooled. The carbon-graphite sealing face was examined and found to be worn out. This wear would have allowed the cooling water to leak between the faces. Such a leak would have flowed along the agitator, through the felt packing, and into the middle of the bulk solids. The carbon sealing face had been damaged by particles in the water. APTECH determined that the vessel manufacturer, who advertised that their product could blend a wide variety of chemicals, had incorrectly used a water-cooled seal instead of a dry-running seal. The elimination of the risk of a water leak would have prevented the explosion. APTECH provided expert testimony during depositions.

Satish Almaula		Plant failure and root cause analysis; process and design engineering analysis; process technology development and testing; plant engineering, operations, maintenance and safety management; plant and process control system management.

Richard Schreiber, P.E.		Machinery and mechanical device failure analysis, mechanical testing, combustion and heat transfer, industrial fires and explosions, gas appliances.

Kimble Clark, Ph.D.		Failure analysis, heat transfer & thermodynamics, process plant equipment failures & explosions, fuel science, combustion, industrial fires and explosions.

Eric Sullivan, P.E.		Metallurgy, welding, failure analysis, fire and explosion investigations, equipment, piping.