Evaporating solvents from tank eyed as cause of Danvers blast

Federal investigators said yesterday that a heated mixing tank filled with 2,000 gallons of printing ink ingredients, including flammable solvents, may have evaporated and led to an explosion Nov. 22 that leveled much of the surrounding Danvers neighborhood.

"The probable source of fuel for the explosion is vapor from flammable solvents that were used to produce printing inks and paints," John B. Vorderbrueggen , lead investigator of the US Chemical Safety and Hazard Investigation Board, said in a statement.

He said it is possible the vapors built up over night . Factory employees filled the tank the day before the explosion, he said.

"Depending upon the temperature of the tank, solvents could have evaporated during the overnight hours when the facility was unattended, accumulated in the building, and found an ignition source," Vorderbrueggen said.

The 2:45 a.m. explosion on Nov. 22 destroyed the building on Water Street used by CAI Inc., a privately held company that manufactured inks, and Arnel Co. Inc., a custom paint maker. It damaged 70 houses and businesses and left hundreds homeless.

Vorderbrueggen said investigators are still looking at natural gas as a possible fuel source. A high-pressure gas transmission line runs underground several hundred feet south of the facility.

"Although there is no obvious path into the facility for natural gas, we will continue to evaluate the possibility of a leak into the building," said Vorderbrueggen. He said tests detected some methane in nearby soils at a level several hundred times below what would trigger an explosion.

He said his staff is looking at whether similar facilities should be built at greater distances from residences.

Carolyn W. Merritt the board's chair woman , said a similar explosion, which occurred in June at a concrete-products facility near Chicago, also involved the solvent heptane. The explosion killed a driver, injured two workers, and caused extensive damage.

The board plans to present its preliminary findings at a public hearing in early April in Danvers.

State Fire Marshal Stephen D. Coan said a joint investigation by his office and the Danvers fire and police departments will present their results.

"Our investigation is continuing; evidence is being analyzed," he wrote in an e-mail. "When that phase is concluded and we have finished examining the results, we will share our findings with the investigative team, town officials, and the public" in that order.

Coan, who has at times bickered with federal investigators over jurisdiction in the blast probe, added that state and local officials hope to receive assistance from the federal panel.

"We look forward to any concrete analysis the CSB may have to offer and any information their computer or lab modeling may have about the fuel and ignition source," he said. "We hope that they will share that with us directly."

He said the state's investigation has also focused on a solvent explosion. The tanks also contained flammable solvents such as heptane and propyl alcohol.

"We are waiting for the test results before determining the cause of the explosion," he said.

John R. Ellement of the Globe staff contributed to this report.