It also found that audible alarms on some of the gas detectors on the rig had been altered to avoid disturbing crew's sleep with false alarms and that the crew had become complacent over routine fire drills. The damning document also contains findings which show that gas detectors on the oil rig were not set up to shut down the flow from the well in an emergency. The Coast Guard found evidence that suggested the explosion happened when electrical equipment on the rig ignited a cloud of flammable gas that rose from the Macondo well.