BOSTON (AP) – The state fire marshal has officially ruled out criminal conduct as the cause of last week’s massive explosion at a Danvers ink and paint plant.

Fire Marshal Stephen Coan said on Wednesday that the cause and origin of the blast remain under investigation, but he said investigators have determined that a single explosion took place on Nov. 22 inside the building occupied by CAI Inc. and Arnel Co.

With the fire marshal’s onsite probe completed, Danvers Town Manager Wayne Marquis said the Environmental Protection Agency will now move in and begin cleaning up the chemical-laden debris.

Coan said his investigators will continue to analyze data collected from the rubble while federal authorities assume control of the blast site. He said the probe “will benefit enormously from the findings of the EPA’s Chemical Investigation Unit and the Chemical Safety Board.”

About 200 residents were forced to evacuate their homes, but no one was killed or seriously hurt. At least 10 homes and businesses were destroyed and dozens more were damaged.

Marquis said 15 families had moved back into their homes as of Wednesday evening. He said other residents of the neighborhood in the Danversport area will be displaced for weeks or months until their houses can be repaired.

AP-ES-11-29-06 1758EST