Explosion's cause: Two-person contract crew employed by Master Mechanical Inc. (MMI) was not qualified to do the assigned work.

Contributing factor: CenterPoint and MMI failed to adequately specify in writing what tasks the contractor's crew could and could not perform.

CenterPoint did not provide formal illustrations to the contractor detailing the work to be done.


CenterPoint said it made many changes in relevant procedures but declined to endorse the NTSB's findings.

MMI officials said "we appreciate the thorough investigation" but also stopped short of agreeing with the NTSB's conclusions.