Published on 11 Dec 2016 by Tadd Pham
This paper attempts to provide the escape, evacuation and rescue assessment for personnel surviving the topsides events on a drilling & production platform; the measures would significantly reduce the risk of becoming a fatality on route to the Living Quarters, lifeboats or other evacuation means.
Escape from the Incident - Escape from the incident is the process of personnel moving along escape routes towards muster points. It is assumed that personnel will have preference for moving to the primary muster point (e.g. Living Quarters).
Evacuation - Evacuation is the planned method of leaving the platform without directly entering the sea. Successful evacuation results in those on board the platform being transferred to an onshore location, or to a safe offshore location or vessel. This usually takes place by helicopter, lifeboats or lifefloats.
Escape to sea - Escape to Sea is the process of leaving a platform in the event of part or all of the evacuation system failing. In these circumstances personnel make their way to the sea either by escape devices or by jumping.
Rescue - Rescue is the process by which both escapees and man overboard casualties are retrieved to a safe place where medical assistance is available.
3. Escape, Evacuation and Rescue Assessment Method
Full evacuation and escape to sea would occur under the following situations:
- An explosion damaging a deck area
- A medium or large sustained fire (i.e. where both the ESD and blowdown systems have failed)
- A fire as a result of escalation from another initiating event such as an explosion
- Smoke ingress into the Living Quarters
For each of the topsides release scenarios the associated fatalities are classified as:
- Immediate – these occur at the time of the hazardous event, before personnel have chance to move away. For example, fatalities that occur amongst personnel working in the process area when a release is ignited to give a jet fire are classified as immediate fatalities.
- Transit – these occur when personnel try to move away from the event area, toward a muster location. For example, fatalities as a result of personnel becoming trapped in a hazardous location or smoke inhalation are classified as transit fatalities.
- Evacuation and Rescue – If the decision to evacuate the platform is taken, then fatalities due to failures of the lifeboats or failure to be rescued from the sea are included in this category.
The escape routes can be assessed by examining any cases where personnel, who survive the immediate event, do not reach the primary muster station in the Living Quarters. In a similar manner, the numbers of fatalities associated with evacuation and rescue is a measure of the adequacy of the evacuation arrangements.
4. Escape, Evacuation and Rescue Assessment
4.1 Gas Jet Fire Events
- For most releases, the majority of personnel would be able to muster in the Living Quarters.
- The Potential Loss of Life associated with immediate fatalities is the main contribution to risk from the majority of gas jet fire events in the Cellar Deck and the Production Deck.
- Transit fatalities are higher than immediate fatalities following a fire on the Wellhead Deck. Personnel in the Wellhead Control Building are exposed to high thermal radiation levels during evacuation and so are likely to become transit fatalities.
- In general, transit fatalities are higher than immediate fatalities following a fire on the Top Deck. Personnel on the Top Deck are exposed to high thermal radiation levels following a fire on the Top Deck and so are likely to become transit fatalities.
- In general, systems with higher operating pressure, such as Main Gas Compression lead to more severe consequences. This is reflected in the increased number of immediate and transit fatalities following larger releases.
- Following a large fire from many of the systems on the Wellhead Deck, Production Deck or Top Deck, personnel are able to muster and escape using the lifeboat located on the Cellar Deck. Without the use of these facilities, these personnel may become immediate or transit fatalities.
- Following a large fire from a number of systems on the Production Deck or a medium fire from the Main Gas Compression system on the Cellar Deck, a small number of personnel are able to muster and escape using liferafts located on the Cellar Deck. Without the use of these facilities, these personnel may become immediate or transit fatalities.
- ESD, or ESD with Blowdown, have an impact on the number of transit fatalities following a large release.
- The effect of smoke has a negligible effect on the number of immediate or transit fatalities. This is mainly due to the relatively low levels of smoke generated by a natural gas jet fire.
4.2 Oil Jet Fire and Smoke Events
- For large releases, two thirds or more of personnel should be able to muster in the Living Quarters. For medium and small releases, the number of personnel able to muster in the Living Quarters can be increased.
- Transit fatalities are higher than immediate fatalities following an oil fire. This is mainly due to the hazard from the smoke produced by oil fire events. This results in personnel trying to escape to the Living Quarters from areas of the platform outside the event deck becoming transit fatalities.
- Following a fire from many of the oil systems, some personnel may need to muster at points other than the Living Quarters. These are personnel trying to escape from the decks below the event area and find that routes are blocked due to smoke ingress. These personnel are unable to reach the Living Quarters and so assemble at one of a number of lifeboats, lifefloats or jump points.
- Because ignition is assumed to be immediate ESD, or ESD with Blowdown, has little effect on the number of transit fatalities following a release. If ignition were not immediate, the ESD and Blowdown systems would reduce the inventory of the release, therefore reducing the level of smoke impairment and hence the number of transit fatalities.
4.3 Gas Explosion Events
- All personnel that are not an immediate fatality due to being in the vicinity of the initial explosion event should be able to muster at the Living Quarters.
- If there are no explosions that lead to platform-wide damage (greater than 500mbar), and so there are no fatalities as a result of evacuating the platform following an explosion.
There are two recommendations to reduce the risk to personnel on the drilling & production platform:
- Under certain weather conditions, personnel on the top deck may be exposed to fire hazards. To mitigate against this, thermal radiation shielding could be installed between the workshop and the Living Quarters. Such a barrier would provide personnel with a protected escape route from the workshop to the Living Quarters.
- If smoke-hoods were to be introduced then the risk associated with smoke could be eliminated.
The above two recommendations would significantly reduce the risk of becoming a fatality for personnel on route to the Living Quarters, lifeboats or other evacuation means.
Extra protection of the stairwell may reduce the number of transit fatalities following evacuation of the Wellhead Control building in the event of an incident on the Wellhead Deck.
5.1 Gas Jet Fire Events
- There may be little change in the number of immediate fatalities following a fire on the Top Deck following the introduction of thermal shielding. However, the number of transit fatalities will be significantly reduced. This is due to a reduction in the number of personnel, on the Top Deck who are exposed to thermal radiation.
- The majority of personnel who mustered at lifefloats on the Cellar Deck will also be able to muster in the Living Quarters.
5.2 Oil Jet Fire and Smoke Events
- The Potential Loss of Life associated with transit fatalities can be significantly reduced following a release on either the Wellhead Deck or the Production Deck. The introduction of smoke-hoods and/or a protected escape route minimizes the risk due to smoke and allows the majority of the personnel outside the event module to muster at the Living Quarters or Lifeboats.
5.3 Gas Explosion Events
- The above recommendations have no benefit following a gas explosion event.