Alarm Systems Switched Off on the Deepwater Horizon Rig

According to testimony given during the Congressional investigation of the Deepwater Horizon disaster, the drilling rig's alarm systems had been switched off on the day the rig exploded:

Williams told the hearing today that no alarms went off on the day of the explosion because they had been "inhibited". Sensors monitoring conditions on the rig and in the Macondo oil well beneath it were still working, but the computer had been instructed not to trigger any alarms in case of adverse readings.

Both visual and sound alarms should have gone off in the case of sensors detecting fire or dangerous levels of combustible or toxic gases.

The evidence of deliberate dilution of the rig's safety mechanisms is likely to have wide ramifications for BP and Transocean, the world's largest offshore drilling company. It switches the spotlight of blame away from BP and towards the subcontractor which took the decisions. Of the 126 crew on board the rig on 20 April, seven worked for BP and 79 for Transocean.

Williams said he discovered that the physical alarm system had been disabled a full year before the disaster. When he asked why, he said he was told that the view from even the most senior Transocean official on the rig had been that "they did not want people woken up at three o'clock in the morning due to false alarms".

Also:

In a third significant disclosure, Williams also revealed that a computer system used to monitor the drill shack was constantly freezing up, and on one occasion even produced wrong information. The system failed to indicate that a vital valve inside the blowout preventer, the device designed to shut down the well in case of problems, had been damaged.

It is likely that fewer crew members would have died if the alarms had been working. Whether the alarms would have prevented the explosion and subsequent spill remains unclear (to me, anyway). I hope that future hearings will explore that point in more detail.