WASHINGTON - The U.S. Chemical Safety Board (CSB) has announced that laboratory testing of chemicals involved in the November 22, 2006, explosion at a Danvers, MA, printing ink manufacturing company is complete and confirms that the mixture in the tank was sufficiently volatile to cause the explosion.

The CSB tested the exact solvent blend in use on the night of the explosion at the CAI/Arnel facility in Danvers. The testing revealed that the blend was significantly more volatile than its individual components, due to the formation of what chemists refer to as an azeotropic mixture.
“The mixing tank could have easily overheated due to 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,” said CSB Supervisory Investigator John Vorderbrueggen, P.E. “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.” The facility also lacked safety interlocks to prevent accidental overheating of the mixing tank. However, national fire codes do not currently require such interlocks.
At a public meeting in Danvers in May 2007, CSB investigators presented evidence that on the night of the explosion, a mixing tank containing highly flammable heptane and alcohol solvents overheated, releasing vapor that filled the building and then ignited. 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 CSB’s final report is planned for release at a public meeting in Danvers in April 2008.