How do you go from 2 severed fingertips to a collision, explosion, fire, and 22 dead? The devastating chain of events of the Mumbai High North (MHN) major accident of 2005 is summarized in this Practical Lessons Bulletin.

In last month’s bulletin we announced our June 18 complimentary, two-hour breakfast seminar covering the siting of permanent and temporary process plant buildings and API 752 and 753. Our website (www.ircrisk.com) will be updated with more details in a few days. Our May bow-tie seminar “sold out” within four hours and feedback from the event indicated it was a roaring success.

If that is any indication, you should quickly reserve your seat for the siting seminar. In fact, act now. Reserve your seat via email.

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Introduction

Mumbai High Field and Facilities

It has remained the largest producer of oil in the country since its discovery in 1974. The field has more than 551 oil wells and 33 gas wells. Well fluids are imported from 11 wellhead platforms (not normally manned), exporting oil and gas to shore and providing gas for gas lift operations. Around the time of the accident, Mumbai High produced 10.2 MMSCMD of gas and 260,000 barrels of oil per day.

The central complex comprises four bridge-linked platforms:
• NA small wellhead platform built 1976
• MHF residential platform built1978
• MHN processing platform built 1981 (third unit from left in photo above)
• MHW recent additional processing platform

The seven-story tall MHN platform had five 12-inch gas export risers at 1200 psi and ten 14- to 16-inch import risers outside the platform jacket.

The Accident—Initial Events

The leeward crane on MHN was not working, so the vessel came to the windward side (wind 35 knots, swell 5 meters, sea current 3 knots). The leeward side would have been favored since the MSV would tend to be pushed away from the platform rather than toward it.

Also, the MSV experienced problems with its computer-assisted azimuth thrusters so it was brought in stern-first under manual control. During the transfer, the MSV experienced a strong heave and its helideck struck one or more of the risers, causing a high-pressure gas release. The subsequent fire escalated to the other risers because they were so close to each other and had no fire protection. The fire engulfed virtually all of MHN and MHF; NA and the Noble rig were severely affected by heat radiation and sustained damage.

The fire was so intense that it destroyed MHN in two hours. The fire also impeded rescue; only two of the eight complex lifeboats and only one of ten life rafts could be launched. Similarly, only half of the rig’s lifeboats could be launched.

Six divers in saturation chambers on the MSV were left behind when the vessel was abandoned. Amazingly, they were rescued 36 hours later. The MSV sank soon afterward.

Emergency shut-down valves (ESDVs) were in place at each end of the risers, but some risers were up to 12 km long and riser failure caused large amounts of gas to be released near deck level.

The risers were routed outside the jacket, and riser (protection) guards were fitted just above sea level. However, they were for protection from smaller offshore supply vessels not from large MSVs.

Subsurface safety valves isolated the flow from the affected wells, preventing an even worse spill.

Some of the Costs
• 22 dead (362 rescued over 15 hours)
• Loss of the MSV
• Damage to other facilities
• Complete loss of MHN and the helicopter on it
• Over $200 million damage (insured cost); probably $300 million to replace

Note from a Survivor
The fire was so sudden and intense that it hardly gave them time to think about using lifeboats according P.K. Mishra, an Oil and Natural Gas Corporation (ONGC) engineer aboard the MSV.

"I was drinking tea with some colleagues when we heard an explosion. We then saw the fire,” Mishra said. “My colleagues and I grabbed the lifejackets, climbed down a ladder, jumped into the sea, and swam really hard to get away from the platform."

They floated in the turbulent waters for about five hours in the darkness before being saved by rescue boats.

"I cannot believe I am alive," he kept saying.

UKHSE Collision Risk Database

Practical Lessons and Considerations

Unaware of the Hazards and Threats
• Was the Offshore Installation Manager blind to the problems with the MSV?
• Did he expect it to have full dynamic positioning capability?
• Was the Master of the MSV blind to the riser risk?
• Did they both think the risers were protected and not a problem?
• Did the riser guards actually contribute to the accident? Key people may have thought the guards would protect the risers.

The Hazard
In general, gas risers should be considered a major hazard because of the large volume of flammable fluid at high pressure. Consider the inventory that is likely to be discharged if the riser fails below its topsides ESDV.

Critical Barriers (managing the threats)
The risk assessment processes and subsequent controls did not control the threat to the risers. In particular, the procedures to manage ship impact were poor or poorly followed.

Global industry standards promote the practice of installing risers inside jacket structures. However, options for equivalent protection may be suitable if appropriate risk and hazard assessments are made. Those equivalent protection options may include:

• Properly designed fenders, addressing all credible threats
• Install risers within protective sleeves such as caissons or J tubes
• Locate risers away from platform loading zones
• Protect risers from hazards by location, barriers, or other means
• Avoid vessel operations near riser locations
• Provide subsea isolation valves (SSIVs) to limit consequences of riser damage

Hydrocarbon risers on UK offshore installations generally are considered safety-critical elements and, therefore, are subject to independent verification and assessment.

Guidance on avoiding ship/installation collision and potential consequences of collision is provided in the United Kingdom Offshore Operators Association (UKOOA) “Guidelines for Ship/Installation Collision Avoidance”, the accepted standard of good practice on the UK Continental Shelf.

The Need for Better Design
With this complicated accident, anyone would have been hard pressed to have an adequate appreciation of the hazard (the high pressure gas in the riser), the threats (MSV with failed station holding ability), and associated barriers or lack thereof (inadequate protection of the riser guards).

An inherently safer design focusing on managing the threats may have avoided the accident—with the risers well protected inside the jacket. A set of robust rules for marine operations detailing what could and could not be done would also have helped.

Since the initial incident (the cook’s severed fingertips) probably was viewed as an emergency, it is questionable whether people would have followed a task risk assessment process if one had been in place.

References

1. United Kingdom Offshore Operators Association (Feb 2003) “Guidelines for Ship/Installation Collision Avoidance” Issue 1. London: UKOOA. Online at http://www.marinesafetyforum.org/upload-files/guidelines/guidelines-for-ship-installation-collision-avoidance.pdf. Accessed May 22, 2009.
2. Prof. Colin Bailey (n.d.) “Mumbai High North Platform Fire, India” One Stop Shop in Structural Fire Engineering, University of Manchester. Online at http://www.mace.manchester.ac.uk/project/research/structures/strucfire/CaseStudy/HistoricFires/Other/default.htm. Accessed May 21, 2009.
3. Sreejith Pillai. (July 27, 2005) Mumbai High North Platform Fire. Online at http://www.scribd.com/doc/5034321/Mumbai-Offshore-platform-Fire. Accessed May 22, 2009.
4. Photos: Walker Steve (6 June 2007) “Mumbai High North Accident,” Oil and Gas. Presentation to Oil & Gas UK Seminar. Online at http://www.oilandgasuk.co.uk/new/features/pdfs/safety8.pdf. Accessed May 19, 2009.