Officials from North Carolina, Texas and Mississippi said they had no problems with the U.S. Chemical and Safety Hazard Investigation Board, a federal agency authorized by Congress to look into major chemical accidents around the country.

"Not a bit. They were very helpful, actually," said Mark Haraway, fire chief of Apex, N.C., where an explosion at a hazardous waste company forced the evacuation of 16,000 residents Oct. 5. "They kept us apprised of everything. They didn't do anything we didn't want them to."

Until yesterday, Danvers fire Chief James Tutko and state Fire Marshal Stephen Coan prohibited investigators with the Chemical Safety Board from entering the site of last week's chemical plant explosion on Water Street.

Coan said the five members of the federal agency were kept off the site because they are not trained to carry out criminal investigations, which the Danvers case is considered until foul play has been ruled out. A spokesman for the Chemical Safety Board said this was the first time in the agency's eight-year existence that its investigators had been barred from a site in the first few days after an explosion when access to evidence is critical.

Other public safety officials around the country said the Chemical Safety Board has provided valuable expertise in the aftermath of devastating explosions in their communities.

Fire Chief Gerald Grimm of Texas City, Texas, praised the board's investigators for their work after a series of explosions at an oil refinery in his city killed 15 workers and injured about 170 on March 23, 2005. It was the biggest industrial accident in the United States in 15 years, according to the Chemical Safety Board.

"We found them not to be an impediment but of great assistance to the city," Grimm said. "Their report was very conclusive, very comprehensive. They held a number of forums that were well-attended by the public. Of all the things that happened here, theirs was most often in the light of day and therefore the most credible to the public."

Grimm said the Chemical Safety Board investigators had the kind of expertise in industrial accidents that local officials lacked.

"They bring with them a wealth of talent in that area," he said. "That is their niche in life. They came in unvarnished and unbiased, and they left with that image."

Mark Tolbert, the public safety chief in Morgantown, N.C., said he can understand how local authorities would be wary of a little-known federal agency. Like many state and local officials here, Tolbert said he had never heard of the Chemical Safety Board until it showed up in his town of 17,300 people on the day of the blast.

But he said authorities worked out jurisdictional issues among the 53 agencies that descended on Morgantown after a chemical plant explosion Jan. 31 killed a worker and injured a dozen.

"Let's just say we had some issues (with the Chemical Safety Board) early on, and they were resolved," Tolbert said. "They got what they needed and we cooperated. We entered into a gentlemen's agreement. We sat down and opened up the lines of communication a little bit and did a better job of trying to pull from the agencies as to what they needed and the timetable."

Kevin Butler, the emergency management director for Smith County in Mississippi, said local authorities had no problems with the Chemical Safety Board investigating an explosion June 5 at an oil field in the small town of Raleigh, Miss., that killed three people.

"They wanted to interview all the people involved, and we set up the interviews for them," Butler said. "They were very accommodating. They didn't just come in and exert authority and push people around. They came in and did their job."