The Deepwater Horizon disaster was BP’s second in recent years. An explosion at BP’s refinery in Texas City, Tex., in March 2005 killed 15 people and injured 180. Technicians were supposed to check that all alarms worked before starting up the chemical processing unit, but a supervisor told a technician to stop checking because there was not enough time, according to a report by the Chemical Safety Board, a federal investigative agency. So they did stop, and it turned out that one alarm was not working, leading a control room operator to make a wrong decision in the hours before the explosion.

Image Credit... George Ruhe for The New York Times

In August 1997, a Korean Air jumbo jet hit the jungle four miles short of the runway in Guam because of pilot error, even though the Federal Aviation Administration had installed a system in the control tower to prevent such accidents — a “minimum safe altitude warning” alarm, to tell controllers that a plane on approach was too low. After the crash, investigators found that controllers thought the alarm had sounded too often, so they persuaded a technician to prevent it from sounding under normal circumstances. In New York in 1980, control room technicians at the Indian Point 2 nuclear reactor ignored alarms indicating that there was water in the basement of the containment building; by the time they discovered the problem — by seeing it — 100,000 gallons of Hudson River water had leaked into the building, and the hot reactor vessel was sitting in it. Such a situation, engineers thought, risked cracking the vessel.

In all the cases, the alarms were installed because the things they were watching could not be easily monitored by a person. The common problem was that the humans did not trust the systems set up to assist them.

On the oil rig and in the Guam control tower, the operators were annoyed by false alarms, which sometimes went off in the middle of the night. At the refinery and the reactor, the operators simply did not believe that the alarms would tell them anything very important.