DANVERS, Mass.- The U.S. Chemical Safety Board (CSB) said in its preliminary findings Wednesday that a November 2006 explosion at an ink and paint manufacturing plant was most likely caused by overheating solvents which released flammable vapors that accumulated and ignited.
The solvents were left overnight stirring in an unsealed mixing tank. The report described the overheating as “inadvertent.”
The solvent ventilation system was turned off when workers left the facility each day, which the CSB said was unsafe and the “immediate cause” of the explosion that destroyed the plant and damaged several buildings nearby.
In all, 10 community members were hurt, over 100 homes and businesses up to a mile from the site were damaged or destroyed, and several vehicles and boats were damaged. No workers were injured in the after-hours blast.
“The Danversport explosion caused the most serious community damage of any U.S. chemical accident since the CSB was established in 1998,” said CSB Chairman Carolyn W. Merritt. “But for the fortuitous timing of the explosion, nearby residents could have easily been killed by flying debris or the collapse of heavy building structures. We all have a strong stake in preventing such devastating accidents that disrupt communities.”
CAI, Inc. produced solvent-based commercial printing inks and Arnel Corp. produced solvent-based stains and coatings at the plant, but only CAI was operating its solvent-based process on the night of the explosion.
The CSB found that the plant did not comply with federal and state regulations for the storage and use of flammable liquids and solids. It also did not have the related licenses and permits required by the state fire code.
The building did not have OSHA-required floor-level ventilation systems to stop the spread of flammable atmospheres from process equipment.
The plant also did not follow the Massachusetts fire regulations that require flammable liquid storage equipment located inside buildings to be vented to the outside and have automatic shutoff valves and fire-resistant materials for attached piping.
On the day of the explosion, CAI had been operating a 3,000-gallon mixing tank with powdered resin and flammable solvents, such as heptane and propyl alcohol, and heated by opening two manual valves on a connected steam piping system. The mixer was left on overnight.
The CSB found that the overheating was likely due to a malfunction of the steam heating valves, or operator error that left the valves open. However, the valves were destroyed in the resulting explosion, so an exact cause for the overheating cannot be confirmed.
With the steam valves leaking or open, 240 degree steam would have continued to heat the tank and evaporate off highly flammable solvent vapor that would have accumulated throughout the building until a spark caused ignition.
“By the process of elimination, that’s likely to be what happened,” said CSB Supervisory Investigator John Vorderbrueggen, P.E. “If the ventilation system had been left on, however, the accumulation of flammable vapor would have been greatly reduced. The practice of turning off the ventilation system at night- which is unsafe in a facility that handled large volumes of flammable- solvents was the immediate cause of the accident.”
A final report is expected to be completed within six months, pending further laboratory analysis of the volatility of ink mixtures produced at the facility, further explosion modeling, and analysis of opportunities to improve applicable codes, regulations, inspections and enforcement.