Deepwater Horizon alarms were switched off 'to help workers sleep'

Alarms and safety mechanisms on gulf disaster oil rig were disabled, chief technician at Transocean reveals

Transocean is under scrutiny after it emerged that Deepwater Horizon’s safety systems were off when it exploded. Photograph: Gerald Herbert/AP

Vital warning systems on the Deepwater Horizon oil rig were switched off at the time of the explosion in order to spare workers being woken by false alarms, a federal investigation has heard.

The revelation that alarm systems on the rig at the centre of the disaster were disabled – and that key safety mechanisms had also consciously been switched off – came in testimony by a chief technician working for Transocean, the drilling company that owned the rig.

Mike Williams, who was in charge of maintaining the rig's electronic systems, was giving evidence to the federal panel in New Orleans that is investigating the cause of the disaster on 20 April, which killed 11 people.

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