The agency now is the sole investigator at the blast site.
Media reports have indicated that propane gas exploded around 10:45 a.m. on Jan. 30 at the Flat Top Little General Store and gas station in Ghent, W. Va., near the Winterplace Ski Resort.
Two of the men who died were working on the propane tanks that supplied fuel to the pizza ovens. The other two fatalities were volunteer firefighters from the Ghent Volunteer Fire Department.
Calls made to the West Virginia State Fire Marshal Office for updated information were not returned.
Full-Scale CSB Investigation Likely
Sandy Gilmour, a CSB spokesperson traveling with the investigation team, told OccupationalHazards.com that the West Virginia State Fire Marshal Office, the Bureau of Alcohol, Tobacco and Firearms and other agencies are pulling out of the investigation "because they have determined there was no criminal involvement or intent."
CSB deployed an investigative team, led by Jeff Wanko, on Jan. 31 to assess the damage and to collect information, which will assist the board in deciding whether to conduct a full investigation of the root causes of the incident.
The team has met up with West Virginia State Fire Marshal Office to assess the damages on the site.
"We have been going through the wreckage with a fine-tooth comb," Gilmour said.
Although a final assessment still needs to be made, Gilmour said that "there was some certainty that CSB will be conducting a full investigation" based on what they have seen.
Wark: Destruction Mimics Category 5 Hurricane
Recently appointed CSB member William Wark, who will serve as the agency's principal spokesperson, told OccupationalHards.com that he was surprised by the amount of devastation the explosion caused.
"It looked like a Category 5 hurricane went through the town," Wark said. "Total destruction there."
Wark said that some people who were around the explosion site indicated that the explosion was heard and felt 5 to 6 miles away from the blast site.
Wark said the CSB team will continue to assess the damages and will probably stay there through the weekend.
"We're continuing to look into the incident," Wark said. "Our condolences to the victims, their families and to the entire Ghent community and we hope we can get to the root cause of the incident to prevent the same thing from happening in the future."