HOUSTON, July 11 (Reuters) - The U.S. Chemical Safety Board is analyzing metal blasted away from a unit at Husky Energy Inc's Superior, Wisconsin, refinery as part of an on-going probe of an April 26 explosion, the agency's acting executive said on Wednesday.
The shrapnel blown away from the gasoline-producing fluidic catalytic cracking unit at the 36,000 barrel-per-day refinery tore through other refinery units including a tank containing hot asphalt, which poured out in a wave of flame across the refinery, said Kristen Kulinowski, the board's interim executive.
The risk of further explosions forced most of Superior's 27,000 residents to evacuate for 24 hours.
The metallurgical analysis is proceeding slowly, Kulinowski said.
"It's a painstaking process as much of the metal is covered with asphalt," she said.
The Superior refinery has remained shut since the explosion.
Like the National Transportation Safety Board, the CSB has no regulatory or enforcement authority but recommends changes in industry practices and regulations based on its investigations. (Reporting by Erwin Seba Editing by Chizu Nomiyama)