The CSB has issued a report on the carbide furnace explosion. The CSB states that:
"The investigation report proposed two scenarios for the development of
cooling water leaks that likely resulted in the overpressure and
explosion. In one scenario, fouling – or the accumulation of solids
inside the hollow chamber where water flows – resulted in localized
overheating, eventually causing sections of the cover to sag and crack.
Another possible cause of the leaks could have been the sudden eruption
of hot liquid from the furnace, which operators called a “boil-up.” Hot
liquids contact the underside of the furnace cover, eroding its ceramic
lining, and eventually melting holes through which water
leaks. Post-incident examination revealed recurring water leaks in
multiple zones of the furnace cover. Rather than replacing the furnace
cover, the company directed workers to attempt repairs. The
investigation found that the company would inject a mixture of oats and
commercially available “boiler solder” into the cooling water, in an
effort to plug the leaks and keep the aging cover in operation.
Water leaks into the furnace interfere with the steady introduction of
lime and coke raw materials, through an effect known as “bridging” or
“arching,” the report noted. In a carbide-producing electric arc
furnace, this can result in an undesirable and hazardous side reaction
between calcium carbide and lime, which produces gas much more rapidly
that the normal reaction to produce calcium carbide itself. Industry
literature described the phenomenon as early as 1965, and an independent
CSB analysis confirmed that operating conditions at Carbide on the day
of the incident could have resulted in this effect, causing hot
materials to be expelled from the furnace.
CSB lead investigator Johnnie Banks said, “One of our key findings was
that Carbide Industries issued 26 work orders to repair water leaks on
the furnace cover in the five months prior to the March 2011 incident.
It was distressing to find that the company nonetheless continued
operating the furnace despite the hazard from ongoing water leaks. We
also found that the company could have prevented this incident had it
voluntarily applied elements of a process safety management program,
such as hazard analysis, incident investigation, and mechanical
integrity.”
Read the report in
this link.
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