The U.S. Chemical Safety Board has agreed to investigate the “root causes” of the April 20 blast on the Deepwater Horizon oil rig in the Gulf of Mexico. The board is becoming an expert on probing the British oil company, BP — it’s the third BP incident the board’s investigated since 2005.

The request came in a letter from Reps. Henry Waxman, D-Calif., chairman of the House Committee on Energy and Commerce, and Bart Stupak, D-Mich., who chairs the subcommittee on oversight and investigations.