Located about 120 miles northeast of Aberdeen, Scotland, the Piper Oil Field was one of the first deepwater oil reservoirs to be exploited in the North Sea. The surprisingly productive oil field contributed significantly to the economy of the United Kingdom by reducing energy costs and dependence on imported oil.
In the late evening of 6 July 1988, Piper Alpha, one of the platforms responsible for extracting oil from the Piper Oil Field, suffered a series of explosions and was engulfed in fire. Over the following hours, most of the oil platform was destroyed and fell into the North Sea, causing the death of 167 workers. What happened to cause such a terrible disaster on Piper Alpha?
Timeline of the Disaster
- 9:45 pm: (6 July 1988): Condensate Pump B tripped off. Operators attempted to manually start Condensate Pump A, which had previously been shut down for maintenance. Operators were unaware that the pressure relief valve on Pump A had also been removed and replaced with a blind flange.
- 10:00 pm: Topside workers on the oil rig heard a sustained, high-pitched screeching noise, then a large explosion that violently shook the oil platform. Fires begin engulfing the top of the oil platform.
- 10:20 pm: A high-pressure gas line connected to the nearby Tartan platform, operated by Texaco, ruptured and released gas at an alarmingly high rate (about 3.4 tons per second). A second explosion occurred.
- 10:50 pm: Another gas line, operated by Total, ruptured. A fast rescue craft, launched from a standby vessel, was destroyed by the consequent explosion, killing two of the three-man crew and six Piper Alpha workers they had just rescued from the sea.
- 11:20 pm: Another gas line to Claymore Platform, operated by Occidental, ruptured and caused another explosion.
- 11:30 pm: The topside structure of Piper Alpha, badly weakened by the intense fires and explosions, started to collapse. The main living quarters, a four-story structure in which some 81 workers were sheltering, slid into the sea. All 81 workers died.
- 6:30 am: (7 July 1988): Only about one-quarter of the topside structure of Piper Alpha was left above water. The rest had been destroyed by fire and explosion and sunk almost 500 feet to the bottom of the North Sea
What caused this disaster?
Incomplete Maintenance Procedures. Condensate Pump A was isolated for maintenance on 6 July 1988. Unbeknownst to the operators, the pressure relief valve had been removed as part of a separate maintenance event and was replaced with a blind flange. Because they were unaware, the operators had no reason to believe that Pump A could not be safely started. Also, the blind flange, which was installed in place of the pressure relief valve, was only hand tightened and thus unable to prevent the pressurized condensate from leaking when Pump A was started.
No centralized work permits or maintenance program. The method of organizing work permits –suspended work permits were not posted in the control room – on Piper Alpha meant that the nighttime operators were unaware that the day shift had removed the pressure relief valve. While they would have known that Condensate Pump A was marked for maintenance, the operators had no reason to believe that restarting the pump would cause a problem.
Locating hazardous equipment near the Quarters Building. Several years after production on Piper Alpha began, a project was undertaken to retrofit the platform to add natural gas processing equipment. The new equipment was located near the control room and the quarters building, which contributed to the high loss of life. The decision was made not to build new blast walls suitable for a natural gas explosion, nor was the new equipment installed in a manner that would segregate it from the non-hazardous areas of the platform, including the quarters building and control room.
Connecting platforms refused to shut down. Piper Alpha was connected to multiple platforms in the area that delivered natural gas and oil through pipelines between the platforms. Although the other platforms clearly knew that Piper Alpha was on fire, they continued to allow natural gas and oil to flow to Piper Alpha and feed the fire.
Effects of the disaster
Piper Alpha was the world’s biggest offshore disaster, reducing 10% of the UK’s oil production and causing the death of 167 men.
During the disaster, fires from the wells and from the oil and gas lines, which had all ruptured and fed the fires, produced flames as high as 650 feet and represented about 100 gigawatts of energy, three times the rate of peak UK energy consumption. Extinguishing the fires took more than three weeks. What was left of the Piper Alpha oil platform was toppled into the sea on 28 March 1989.
Of the 226 people on board that night, only 61 survived. Of the deceased, 109 died from smoke inhalation, 13 by drowning, 11 of injuries including burns. In 4 cases, the cause of death could not be established, and 30 bodies were never recovered.
The first explosion was violent enough that the workers in the control room were knocked off their feet and onto the floor. Other operators in the oil platform’s living areas were thrown off their chairs or tumbled out of bed.
The subsequent investigation, headed by Lord Cullen, was hampered by the fact that the evidence available was both scanty and heavily damaged, and no senior management of the oil platform survived the disaster.
The investigation concluded, however, that when operators restarted Condensate Pump A to compensate for the tripped-off Pump B, some 70 pounds of natural gas condensate (mostly propane) were released in 30 seconds through the not-fully-secured blind flange. This natural gas ignited and caused the first explosion at 10:00 pm. The sequential failure of the gas lines, as a result of the first explosion and the resulting fires, then caused a rapid escalation of the disaster.
The Cullen investigation concluded by making 106 recommendations for changes to safety procedures on oil platforms, which led to the Offshores Installations (Safety Case) Regulations of 1992. The main effect of this legislation was that oil platform operators were required to present a “safety case” before commencing operations and that safety enforcement on offshore installations would no longer reside with the Department of Energy, but rather be the responsibility of the Health and Safety Executive in order to prevent a conflict of interest by having both production and safety overseen by the same agency.