The head of a US federal agency is calling into question the safety culture throughout BP, the UK-based oil and gas group, given the "errant" state of the Texas City refinery where an explosion this year killed 15 people and injured more than 170.

"It's rare that you are going to have one facility that is so far off the mark in an organisation that has a good culture," Carolyn Merritt, chairwoman of the US Chemical Safety and Hazard Investigation Board (CSB), said. "An errant facility would not be able to continue on a bad path without being exposed."