DANVERS, Mass. (AP) – Federal investigators have confirmed that vapor from chemicals mixed in a tank at a Danvers paint and ink factory was volatile enough to cause last year’s massive blast.

The explosion last November damaged 270 homes and businesses. No one was killed or seriously injured.

The U.S. Chemical Safety Board previously said that due to neighborhood noise complaints, the factory’s ventilation system was routinely shut off at night.

When the tank accidentally overheated, flammable vapors collected and then ignited.

The board tested the exact solvent blend used that night, and issued a statement Thursday confirming its volatility.

One of the two companies that occupied the building, CAI Incorporated, had previously rejected the board’s findings and said it was conducting its own investigation.

AP-ES-11-15-07 1109EST