Several chemical drums that became "active" Monday at a smoldering factory where a stubborn fire spewed a toxic chemical cloud and forced 25,000 to evacuate did not pose a threat of re-igniting the blaze, officials said.

Most of the 4,600 who remained away from their homes overnight were allowed to return Monday, officials said. Only those abutting the burned-out Advanced Laboratories factory were not going to be allowed to go home until later.The chemical drums were found by fire and safety officials who patroled inside the factory to make sure the fire that erupted Friday did not flare up for a fourth time.

"The chemical drums are active, but are under control," a spokesman for the state Department of Environmental Quality Engineering said. "We've neutralized them by using a chemical solution. There is no danger from them."

A team of state, local and federal health and safety officials decided at midday to allow most of the remaining evacuees beck into their homes. Officials today increased their estimate of evacuees still to 4,600.

Officials also hoped to make a decision on when they would re-open schools and day-care centers closed Monday near the factory where the three-day fire that injured 300 people broke out. The incident triggered officials' calls for an investigation into possible safety violations at the factory.

At the height of the incident, the cloud of toxic chlorine forced the evacuation of 25,000 residents, including 120 nursing home patients.

The stubborn fire erupted anew three times since it started Friday, but Fire Chief Raymond Sullivan said, "From this point, I hope the danger level will be minimal."

State and local officials said they would investigate possible code violations at Advanced Laboratories, which manufactures a solid form of chlorine used to treat water in swimming pools. The plant, a subsidiary of the adjacent Armory Pool Co., has a record of safety problems, a state official said.

The fire started at 9:59 a.m. Friday apparently when rain poured through an open window at the factory and came into contact with chlorine, which burns when mixed with water, officials said.