Lax safety at US calcium carbide plant led to fatal blast - agency

07 February 2013 17:17  [Source: ICIS news]

Lax safety at US calcium carbide plant led to fatal blastHOUSTON (ICIS)--A fatal explosion at a calcium carbide plant in Kentucky was caused in part by a lax safety culture in which dangerous operating conditions were tolerated for years, the US Chemical Safety Board (CSB) said on Thursday.

The March 2011 explosion at the Carbide Industries plant killed two people.

The blast was caused by water leaking into an electric-arc furnace, causing a build-up of pressure that overwhelmed the vessel, the CSB said in a report about the explosion.

As a result, the furnace spewed out molten calcium carbide and other debris, material that was heated to about 3,800 degrees Fahrenheit (2,100 degrees Celsius), the CSB said.

The debris blew through the double-paned reinforced-glass window of the plant's furnace-control room, which was 12 feet (4 metres) away, the CSB said.

The two workers inside died within 24 hours from severe burns, the CSB said. Two others in different parts of the plant were injured.

The bureau said two scenarios may have caused the water leaks.

In one, solids may have accumulated inside the hollow chamber where the water flowed. This would have caused localised overheating and would have resulted in sections of the furnace's cover to sag and crack, the bureau said. Those cracks could have led to the leaks.

In another scenario, sudden eruptions of hot liquid could have come in contact with the underside of the furnace cover, eroding its ceramic lining, the CSB said. This would have eventually melted holes in the cover, through which water could leak.

The company had planned to replace the cover in May 2011, too late to have prevented the explosion, the bureau said.

In the meantime, it directed workers to attempt repairs by plugging the leaks by injecting a mixture of oats and boiler solder into the cooling water, the bureau 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," according to a statement by Johnnie Banks, CSB lead investigator.

"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 programme such as hazard analysis, incident investigation and mechanical integrity," Banks said.

This was not the first blast at the plant.

In 1991, the furnace had an excessive build-up of pressure, which blew out the window in the control room, the CSB said. A similar event happened in 2004.

For both events, Carbide's response was to replace the windows, the bureau said.

"Despite these previous incidents, Carbide’s response to the previous incidents did not sufficiently address the hazard nor prevent the events from escalating," the bureau said in its report.

In fact, Carbide did not thoroughly determine the root causes of these smaller blows, the CSB said, nor did Carbide move the control room further away from the furnace and employ remote cameras to monitor the vessel.

Instead, the blasts became regarded as part of the day-to-day operations of the plant, the bureau said. "The behaviour was a tolerance to what should have been abnormal events," the CSB said.

This so-called normalisation of deviance has played a role in other fatal accidents investigated by the CSB, including the explosion at the BP refinery in Texas City, Texas; the dust explosion at the Imperial Sugar site in Port Wentworth, Georgia; and the phosgene leak at the DuPont plant in Belle, West Virginia.

"In spite of past warnings," the CSB said in its report, "each of these companies failed to control a hazard, and a high severity incident occurred later."

In its report, the CSB recommended that the National Fire Protection Association (NFPA) develop safety standards for electric-arc furnaces that operate with flammable materials and low-oxygen environments.

Once the NFPA develops those standards, Carbide Industries should adopt them, the board said.

The CSB is a federal agency charged with investigating industrial chemical accidents. It does not issue fines.

Carbide Industries produces calcium carbide and supplies the material to the iron and steel industry as well as to acetylene producers.

The company did not immediately respond to a request for comment.


By: Al Greenwood
+1 713 525 2645



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