Danvers (AP/WBZ Newsroom)  -- Federal investigators have concluded that a lack of company safeguards such as alarms and automatic shutoffs led to a massive chemical plant explosion in Danvers. 

The U.S. Chemical Safety Board is expected to issue a final report Tuesday on the November 2006 building, which damaged or destroyed about 250 buildings, but caused no deaths.

The federal report concluded that CAI didn't have any safeguards such as alarms and automatic shutoffs that would have prevented a 10,000-pound mixture of flammable solvents from overheating in an ink-mixing tank overnight.

"Steam heat to the mixing tank was most likely inadvertently left on by an operator before he left for the day. As the temperature increased, vapor escaped from the mixing tank, built up in the unventilated building, ignited, and exploded," the agency said on its Web site.

Twenty people were hurt in the blast at the CAI-Arnel ink and paint manufacturing facility. There were no deaths.

The explosion damaged or destroyed 270 homes and buildings.