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Emergency Breathing Systems (EBS) for Offshore Helicopter Occupants

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Definition

Emergency Breathing Systems (EBS) provide a way to extend time underwater so that escape from a helicopter which has capsized as a result of an attempted controlled ditching or an uncontrolled water impact is achievable if not constrained by other factors. This type of equipment is sometimes referred to as Emergency Underwater Breathing Apparatus (EUBA).

Discussion

It has been recognised for some years that the time needed for occupants to escape from a submerged or capsized transport helicopter after a ditching or water impact event, which has been estimated to be between 45 and 60 seconds in a real accident, exceeds the time that most individuals can breath-hold in cold water because of the effects of cold shock. Research suggests that for those wearing immersion suits and immersed in water colder than 10˚C, the average breath-hold time is probably around 20 seconds but with a wide range about that figure. This means that maximum breath-hold time is often a limiting factor in the survival of the individual. An EBS can provide a means of extending the time that can be spent underwater and is thus an important means of increasing the chances of survival. An EBS which can be deployed with one hand and, if necessary, underwater is considered preferable.

EBS becomes particularly important where higher sea states prevail and/or the event is a water impact rather than a controlled ditching because of the absence of much if any prior awareness.

There are currently three EBS designs in use to aid helicopter escape:

  • Compressed Air systems - a miniature version of a ‘Self Contained Underwater Breathing Apparatus’ (SCUBA) cylinder with a mouthpiece. This is simple to deploy but because the air supply is activated immediately, this should normally be delayed until just before immersion unless the user is trained in purging techniques when it would be possible to successfully deploy this type underwater. These are favoured for military use generally and for civil use in Canada.
  • Rebreather systems - allow the user to rebreathe expelled air by directing it into a bag prior to immersion. They require that the mouthpiece is in place before activation but have the advantage that, where time permits, the user can fit the mouthpiece in advance whilst still breathing to the atmosphere and only switch to rebreathing just before immersion. Although some of these systems are automatically activated when immersed, the disadvantage is that unless the mouthpiece has been fitted in advance, water will enter and successful activation will be unlikely. These are used in the Norwegian offshore sector.
  • Hybrid systems - these consist of a rebreather bag and a small cylinder of compressed air and were originally designed for the controlled ditching scenario. However, if manually activated underwater, the air supply can provide time to purge water from the rebreathing system before switching to it, so although not originally designed to be used in this way, underwater deployment is possible. These are used in the UK offshore sector.

All three systems are usually carried in a container which can be fitted to an immersion suit or lifejacket. In general, most rebreather systems have been designed for the scenario where there is time to deploy before submersion, whereas compressed air systems have the capability for underwater deployment. Some authorities regard EBS which make use of compressed air (including hybrid systems) as diving equipment with the result that specific medical fitness requirements may be imposed.