Engineering Disasters: The Failure, Explosion, and Sinking of the Piper Alpha Platform

Engineering Disasters: The Failure, Explosion, and Sinking of the Piper Alpha Platform
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The Piper Alpha Oil Production Platform was built in the Highlands of Scotland for the Piper Field in the North Sea. It started production in 1978 and became one of the largest producers of oil in the North Sea. Later it was converted to produce and gather gas as well as oil.

In 1988, Piper Alpha endured a gas leak with the subsequent fire and explosion reducing her to a wreck, ending up on the bottom of the North Sea.

In the following sections we will examine the causes of the Piper Alpha oil rig explosion and the subsequent inquiry into the incident that claimed 167 crew member’s lives. As the disaster unfolds, we will see how the Piper, Tartan, and Claymore platforms were linked.

To start out, please refer to the image below. It shows the locations of the platforms in the North Sea with their associated gas and oil terminals.

Overview of the Piper Alpha Oil and Gas Platform

The Piper Alpha started life as primarily an oil production platform installed in the North Sea 170 miles N/E of Aberdeen. It pumped processed crude oil to Flotta Terminal on the Island of Orkney. She is shown below from

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The installation of Tartan and Claymore platforms nearby followed Piper’s installation, with these platforms also producing crude oil and gas and their export oil lines joining Piper’s oil export line to the Flotta Terminal.

Piper Alpha then became a hub, processing its own gas, collecting gas from the Tartan, and pumping this gas onto the MCP-01 Platform. A gas pipeline was also installed linking Piper with Claymore, receiving and supplying gas to Claymore as required for gas-lift purposes as shown in the images below.

Sample contents.

Cause of the Piper Alpha Disaster

High pressure condensate pumps are an integral part of the gas processing system on offshore platforms. The Piper had two of these pumps, which were identified as condensates pumps A and B. These were located in the gas processing module “C,” with one operating and one on standby. As well as being exported to MCP-01, Piper also used the processed gas to fuel the main power generators that supplied the electricity to the platform.

On the morning of the accident on July 6, 1988, a Pressure Safety Valve (PSV **#**504) had been removed from pump “A” for routine calibration checks, with the statutory “Permit to Work” being raised and left in the Main Control Room.

Two blanks (machined blind flanges) were bolted to the inlet and outlet flanges, in place of the removed PSV, as shown below.

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Permit to Work (PTW

In any offshore installation a “Permit to Work” is raised before any work can be carried out. This notes the identity and location of the component that the work is to be carried out on, along with mechanical and electrical isolations in place such as valves shut, electric motors isolated, etc. It is raised by an engineer from standing instructions, signed by him and the Oil Installation Manager (OIM) and also signed by the fitters/electricians working on the component. It is an extensive, normally foolproof safety document kept in the control room. Once the component is back into service, the PTW is signed off and filed for future reference.

On the day of the explosion, condensate pump A pressure safety valve was still undergoing calibration, so the PTW was still “live” and in force. Just before 10 PM that night, condensate pump B tripped and could not be restarted. The control room engineer checked the permit to work boxes, but did not find the one for condensate pump A.

So upon finding no PTW, he started pump A. The pressure in the line built up, and gas escaped between the blind flanges and the pump pipework. The escaping gas ignited and exploded. This was the main and initial cause of the Piper Alpha incident.

Next: The Fire and Explosion Sequence, the Survivors Escape and Rescue

The Piper Alpha Fire and Explosion Sequence

The escaping gas triggered numerous gas alarms in the control room, but before the operator could respond to these alarms, a massive explosion disintegrated the firewalls of gas module C. (Because Piper was originally designed for oil, firewalls, and not blast walls, were installed between modules.) This caused many projectiles to be flung at great velocity and force into condensate and oil pipelines. These penetrated the piping, adding both oil and gas to the fire creating thick black smoke and toxic fumes to the area and below C module.

The control room was badly damaged in the explosion, but the operator managed to punch the emergency shutdown button that effectively shut of the oil and gas supplies to the platform.

This action should have been sufficient to kill the fire, but gas was still being supplied from Claymore and Tartan, and would continue for some time, despite the fire on Piper being visible from both these platforms.

The fire water pumps, operated from the control room could not be remotely started as there were divers in the water, and it had been switched to manual “hand control.”

This was a standard safety measure as there was the danger of pump suction inlet pipes pulling the divers into the inlet grills if the pumps were operated.

This meant that the pumps had to be started by hand in the fire-pump room, but the black, choking smoke prevented access. Two men, Bob Vernon and Robbie Carroll, donned BA Sets (breathing apparatus) and made their way down to the start the fire pumps manually. These brave men were never to be seen again.

So, with no firewater ring-main or sprinkler system, the fire raged on, still being fed by gas from the Claymore and Tartan platforms, creating very high temperatures and causing steelwork to melt.

Eventually at around 10.20 PM, twenty minutes into the Piper Alpha disaster, the gas riser from Tartan burst, adding 20-odd tons of gas to the fire and causing a horrific instant inferno that engulfed the Piper Alpha.

Those left alive were now faced with the decision to stay on board and perish due to the fire and explosions or jump into the sea.

The export oil riser then burst. This allowed the pressurized oil in the subsea pipeline to Flotta from Claymore and Tartan to back-feed to Piper, stoking the established gas fires. This caused black smoke to spiral into the night sky, joining the gas fireballs and creating the worst inferno ever witnessed offshore.

At around 11:30, the gas lines to/from Claymore and MCP-01 then burst, sending more fireballs high into the sky and downwards underneath the now doomed Piper Alpha.

One of these fireballs of 500 feet diameter engulfed a fast rescue boat from the Sandhaven, a standby vessel from a nearby rig. This killed two of three crew members and cruelly, six survivors it had just pulled from the water.

Eventually at about midnight she succumbed to the flames, the topsides sliding away into the waters of the North Sea, taking with it the power generation, utility, and accommodation modules, along with the remaining crew members.

Of the 226 crewmembers, 167 were killed, 30 of whose bodies were never recovered. Only 59 men survived and most of these were scarred for life, not only from horrific burns, but from the memory of the explosion and fire on the Piper Alpha on 6th July 1988 and the loss of lifelong friends and workmates.

Now all that remains of Piper Alpha are pieces of the production deck flares, angled on the stubs of the steel jacket, with some risers still burning.

The Survivors Escape and Rescue

As we have seen the fire and explosion created massive fireballs accompanied by clouds of black, toxic smoke, and high temperatures. These combined barred any escape by the lifesaving equipment.

The Tharos fire fighting and rescue floating platform was on station and came in close to Piper. From here it attempted to extend its 30m portable walkway towards the men gathered on Piper, but the operating mechanism failed, maybe because of the intense heat being radiated from the Piper’s blaze. In any case she had to retreat due to the fireballs erupting as the gas risers ruptured.

Some men climbed down the platform as far as they could and jumped into the sea. Most of these men survived, albeit with horrendous burns as the sea was by now on fire from Piper Alpha oil spills, but were fortunate to be picked up by the fast rescue crafts. Other men were trapped higher up and jumped from nearly 200 feet; from that height they did not have much chance of survival after collision with the water.

The Silver Pit, a converted trawler, was the Piper Alpha’s dedicated safety boat. She along with her fast rescue craft picked up 37 of the 59 survivors from the water. The Silver Pit’s master John Sabourn kept his vessel as close as possible to the burning Piper in order to pick men from the water. This was carried out by him and his crew in the true tradition of bravery, in the face of fireballs erupting and missiles flying through his wheelhouse windows.

The fast rescue craft from the Tharos and other small rescue boats picked up the remaining men from the burning sea.

A search and rescue SeaKing helicopter based at Lossiemouth, an RAF base 50 miles north of Aberdeen, was diverted from another incident. It made the journey to Piper in record time, but was unable to land on the heli-deck. Nonetheless it picked up survivors and flew them to Aberdeen Royal Infirmary, undoubtedly saving lives and shortening the men’s torture from their burns.

Next: The Official Investigation & Findings about the Accident

The Piper Alpha Cullen Report

The inquiry into the Occidental Petroleum Piper Alpha Disaster was commissioned by the Department of Energy, their being the UK Government Body responsible for the operation and safety of offshore oil and gas installations. They appointed Lord Cullen, a very experienced Scottish Jurist, to conduct the Public Inquiry into the cause of the disaster. The subsequent inquiry began in January 1989 and was to last 6 months, with 260 witnesses giving evidence.

The inquiry, published in 1990, was divided into two parts;

  1. The Cause of the Piper Alpha Oil Rig Disaster
  2. Lessons to be Learned and Recommendations

The Cause of the Piper Alpha Oil Rig Disaster

The cause has been explained in detail the preceding section, therefore only salient points raised from the inquiry are noted below.

  • Initial Cause

The initial cause was the escape of gas following the starting of the standby Condensate Pump A, regardless of a current PTW being in force (the PTW was never found). It was suggested by a witness that that because the PTW was for the removal of the PSV (this being a separate component from the pump), the permit therefore may have been stored in the Safety Office and not in the pumps PTW section in the control room.

  • Permit to Work System

The adherence to the Permit to Work System had become too relaxed, with no verbal confirmation taking place at shift handovers. This was noted in Lord Cullen’s criticisms of Occidental Petroleum’s Management of Maintenance Safety Systems.

  • Firewalls

Firewalls were not upgraded to blast walls; therefore they disintegrated on the gas explosion, penetrating gas and oil pipe work and machinery, adding to the fire.

  • The Tartan and Claymore Platforms

These platforms continued to supply oil and gas, despite the flames from Piper being visible to them. If they had shut down the supplies to Piper, the fire and subsequent explosions would have been much less severe and may have been have been limited to the Gas Module. Although the explosion and fire caused by the escape of gas from the PSV blinds was the initial cause of the disaster, the failure and rupture of the gas risers were responsible for Piper’s destruction and preventing the crewmembers evacuation.

Recommendations and Lessons Learned

Lord Cullen made over 100 recommendations following an extensive and well warranted Inquiry.

  • Firewalls Upgrading

Once conversion to gas had taken place, the firewalls between modules should have been replaced or upgraded to blast walls. These would have withstood the initial explosion containing the resultant fire to Module C.

  • Emergency Shutdown Valves (ESD Valves)

It was recommended that ESD valves be located on the deck as well as subsea locations on hydrocarbon risers, with the ESDs on the deck being installed within a blast-proof container.

  • Limitation of Supply of Hydrocarbons

Lord Cullen recommended that in future the design of offshore installations should limit the supply of hydrocarbons to the installations, and not use them as a “hub.”

  • Temporary Refuge

Lord Cullen noted that many of those killed had died from asphyxiation in the accommodation. He recommended the installation of a gas, fire, explosion, and smoke-proof temporary shelter for the crew on offshore installations, for use until evacuation is arranged.

  • Control of Smoke

It was recommended that the HVAC systems be upgraded to prevent ingress of smoke to accommodation modules, pressurizing them and providing air locks to prevent smoke/toxic fumes entering these areas.

  • Maintenance Safety Procedures

Lord Cullen was critical of Occidental Petroleum’s Management of Maintenance Safety Procedures, finding them guilty of negligence in this department and recommending their revision in line with the offshore oil and gas installation governing body.

  • Offshore Oil and Gas Responsible Body

This was by far the most important change to come out of the Piper Alpha Disaster Inquiry.

The responsibility for the safety of offshore oil and gas installations would be removed from the Department of Energy, a Government Body, and become the responsibility of the Health and Safety Executive (HSE) an independent body with wide-ranging powers.

It would soon introduce radical safety measures such as requiring a “Safety Case.” This involved the presentation of a full management safety statement from offshore oil and contractors before any platforms were installed in British waters.

This report was to be compiled by an independent expert and paid for by the oil/gas company.

Author’s Notes:

I saw many changes during my employment as Engineer at the former Brown, Root, and Wimpey offshore construction yard at Nigg in the North of Scotland. Our yard was just across the Firth from McDermott’s facility where Piper Alpha was built. In fact McDermott’s were our major competitor when bidding for the offshore installations construction contracts. We ended up amalgamating with them and being known as BARMAC (Brown and Root, McDermott).

The changes I saw after the Piper Inquiry included:

  • Regular production Quality Assurance audits at the yard, high level of NDT inspections of pipe welding and piping pressure testing.
  • Heavy gauge steel blast and firewalls fitted to all vulnerable areas and similar enclosures around ESD Valves.
  • HVAC design upgraded such as the number of fire-dampers fitted and rooms pressurized to prevent ingress of smoke or gas fumes.
  • The introduction of “free-fall” fully totally enclosed lifeboats. Once all survivors were aboard and strapped in, the lifeboat could be launched from inside the lifeboat. Once launched these hit the sea at an angle and force that allowed the lifeboat to travel underwater for a distance to emerge clear of any fires at sea level. There was also an increase in the number and locations of self-inflating life-rafts, ladders and lifebuoys installed at all deck levels.
  • The main firewater pumps could still be switched from automatic control room operation to manual local operation from the fire-pump room. This may have changed since I retired, but if not, it still requires to be investigated as I did not see any recommendation regarding this in the Cullen Report. The seawater pumps could be used to supply the firewater ring main, but again these are down-hole pumps and would cause the same problems to the divers.

Perhaps a large steel mesh cage around the pump suction (the pump is submerged being at the bottom of the caisson) would be adequate protection for divers.

A typical firewater pump used on oil and gas production platforms is shown below.

Medals and Memorials

At a ceremony at Buckingham Palace, HM Queen Elizabeth II bestowed medals to the rescuers and medical staff in the aftermath of the Disaster. George medals for bravery were awarded to the following civilians.

George Medals

The Sandhaven, a North Sea standby vessel, launched its Fast Recovery Craft with 3 crew members. It had managed to pick up six survivors, but was caught in ropes hanging from Pipers deck and engulfed in a gas explosion. Only crewmember Ian Ketham survived; he received the George Medal, with the other crew members being posthumously awarded theirs and their relatives receiving them from Her Majesty.

George Medal from Wiki Commons by NZDF Medals

James Clarke, the Cox of the Fast Rescue Craft from the Silver Pit, along with crewmembers Charles Haffery, Andrew Kiloh, and James McNeill, all received the George Medal. This was in recognition of their picking up 37 survivors and their craft going very close to fire and explosions.

Sea Service Memorial

One year to the day after the Piper Alpha Disaster, bereaved relatives of the missing visited the site of the Piper Alpha, which is marked by a wreck buoy. They were aboard the ferry SS Sunnivar and were said to be comforted by the thought that they were near their loved ones final resting place beneath them.

Piper Alpha Memorial Safety Scholarship

The scholarship was launched on 20th April 2011 by Industry Skills and Safety Body OPTIO as a long lasting tribute to those lost in the Piper Alpha Disaster.

Several other memorials were erected in Glasgow and Aberdeen; these are shown below.

In July 1991, the Queen Mother unveiled a memorial in the Grounds of Hazelhead Park, Aberdeen, dedicating it to the 167 men who lost their lives in the Piper Alpha Disaster.

This bronze larger than life statue depicts three oil workers atop of a marble plinth that has the names of those lost engraved as a lasting memorial to them. Under the plinth is buried the remains of an unidentified victim.

The image of the memorial is from Wikipedia by Angusmclellan.

Other memorials were raised to remember those who were lost on Piper; this one is in Strathclyde, part of the City of Glasgow from Wikipedia by Gordon Brown.