Charlottesville, Virginia (Platts)--9Feb2010/503 pm EST/2203 GMT

It may be days before investigators can pinpoint the cause of Sunday's fatal explosion at a natural gas- and fuel oil-fired power plant that was under construction in Middletown, Connecticut, a deputy fire marshal on the scene said Tuesday.

"We still don't know what happened. It is going to be a slow methodical process. There is a lot of debris," said Al Santostefano, deputy fire marshal for the Middletown Fire Department, which is investigating the incident, along with the Connecticut State Police and Office of the State Fire Marshal.

"When we investigate a house fire, a little house fire, it takes hours and sometimes a whole day," he said.

Santostefano said investigators have found nothing to indicate any criminal activity led to the blast that killed five workers and injured at least fourteen, as the 620-MW Kleen Energy plant reportedly purged a natural gas line. They are, however, treating it as a crime scene and limiting access to preserve evidence, he said.

A US Chemical Safety Board team and other investigators were turned away from the site Monday because local investigators were concerned evidence would be trampled and destroyed, he said. About 50 people from various agencies were at the site Tuesday, but not all were being allowed into the area of the explosion.

CSB spokesperson Daniel Horowitz said Tuesday afternoon that his seven-person team now had "limited access." Horowitz said "the primary issues now relate to access to witnesses and particularly to physical evidence from the site." The US Occupational Safety and Health Administration had been allowed onsite Sunday, Horowitz said. "We believe OSHA and others should be there and the CSB should have been there from the beginning as well," he said.

Local investigators are focusing on the origin of the blast now that they have accounted for all plant workers who were supposed to be at the site Sunday, according to a statement issued Tuesday afternoon by Middletown Mayor Sebastian Giuliano.

Meanwhile, investigators were preparing for a snow storm expected to hit Connecticut Wednesday, which may slow the inspection. Fire officials and other workers were trying to remove hazards and conduct GPS mapping of cylinders and other damaged equipment before the snow begins, according to Giuliano.

Santostefano said it is not clear yet whether the snow storm will require investigators to halt their work.

The team has yet to determine the extent of damage to the combustion turbines, he added, because they are focused on finding the cause of the explosion first.

--Lisa Wood, newsdesk@platts.com