Chemical Vapor Build-Up Cited in Mass. Paint Factory Explosion

A build-up of chemical vapor was the fuel for a massive explosion at a Danvers, Mass. paint and ink factory that leveled the building and forced a neighborhood evacuation, according to a preliminary conclusion by federal investigators.

The Chemical Safety and Hazard Investigation Board’s lead investigator, John Vorderbrueggen, said the probe is also looking into the possibility that natural gas collected inside the building, which was used by ink manufacturer CAI Inc. and Arnel Co., Inc., a custom paint maker.

But Vorderbrueggen stressed to The Boston Globe that solvent fumes that collected inside the building were the most likely cause of the blast.

Both companies used highly explosive chemical solvents in manufacturing, he said.

“If you can’t control the vapors, then you minimize them,” he said. “In this situation, we apparently had neither of those features. We didn’t minimize the vapors, and we didn’t control the vapors. We didn’t ventilate it safely out of the building. And then it found an ignition source.”

The early morning blast on Nov. 22 damaged 70 houses and businesses and left hundreds homeless.

CAI said in a statement that the preliminary conclusions were unexpected and premature.

“We are surprised by the remarks of the U.S. Chemical Safety Board, given the Board’s previous public statements that a final determination of cause could take as long as one year,” the statement said.

“Given the complexity and size of this explosion, as well as the extent of scientific analysis and sophisticated computer modeling that remains to be completed, it is simply too early in the investigative process to determine with any degree of certainty what caused the blast.”

An Arnel Co., Inc. spokesperson could not be reached for comment. A spokeswoman for State Fire Marshal Stephen Coan said the state probe into the explosion has not yet reached any conclusion.

Vorderbrueggen discussed two main theories on how the solvent fumes accumulated. The first is that a leaking drum of solvents spewed fumes which were not properly ventilated by the building’s systems. The second theory is that a worker left a heat source going on the open-topped vats that the companies used to mix and make their products, and the fumes built up, he said.

Because the building was destroyed, investigators may never learn what ignited the fumes, Vorderbrueggen said.

He said the companies have provided the board with the recipes for their products. Investigators will now try to recreate conditions inside the plant in a laboratory to further confirm their preliminary conclusion.

Natural gas cannot be eliminated as a fuel for the explosion because evidence of natural gas was found in soil testing. But Vorderbrueggen said it was unclear if that gas was naturally occurring from decomposing vegetation or leakage from gas networks in the neighborhood.