Volatile Vapor Mix Caused Danvers Blast: CSB

The U.S. Chemical Safety Board yesterday completed a nearly year-long investigation of a Nov. 22, 2006, explosion at CAI/Arnel, a Danvers, Mass.-based printing ink manufacturing company, and concluded that the chemical blend in a mixing tank was sufficiently volatile to cause the explosion due to the formation of what chemists refer to as an azeotropic mixture.

The explosion damaged or destroyed approximately 100 homes and businesses in the surrounding neighborhood. The facility was not staffed during the overnight hours, and there were no eyewitnesses to what occurred inside the building.

"The mixing tank could have easily overheated due a single steam valve inadvertently left open or leaking. Our testing and calculations confirm that overheating the tank in this way would cause the building to fill with a large quantity of explosive solvent vapor. As we pointed out earlier this year, the CAI/Arnel facility did not follow state and federal fire safety regulations when they turned the ventilation system off," said CSB Supervisory Investigator John Vorderbrueggen, P.E., referring to a public meeting in Danvers in May 2007, where CSB investigators found that the building's ventilation system was routinely turned off at night to reduce noise in the community, allowing the accumulation of the flammable vapor.

The facility lacked safety interlocks to prevent accidental overheating of the mixing tank; however, national fire codes do not currently require such interlocks.

"The CAI/Arnel site was originally licensed under state law for just 250 gallons of 'lacquer' back in 1944, to a company that long since sold the property," Vorderbrueggen said. "During the 62 years that followed, the amount permitted by the license was increased to some 11,500 gallons of flammable and combustible substances. State law does not require any safety review or public impact review when a licensee obtains increases in the registered quantity."

Vorderbrueggen added that each year when the occupying business went to pay its license renewal fee, it was simply asked how much flammable material was stored at the site so fees could be properly collected. As a result, CSB is currently reviewing the state's licensing and land-use rules and oversight of facilities that handle flammable substances to determine if recommendations are appropriate.

CSB's final report is planned for release at a public meeting in Danvers in April 2008. For more information, click here.

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