If you wish to contribute or participate in the discussions about articles you are invited to join SKYbrary as a registered user

Emergency Breathing Systems (EBS) for Offshore Helicopter Occupants

From SKYbrary Wiki
Article Information
Category: Helicopter Safety Helicopter Safety
Content source: SKYbrary About SKYbrary
Content control: SKYbrary SKYbrary


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

The time needed for occupants to escaped from a submerged or capsized transport helicopter after a ditching or water impact event has been estimated to be between 45 and 60 seconds. It has been recognised for some years that this interval significantly exceeds the time that most individuals can breath-hold in cold water due to 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 available for use in the event an underwater helicopter egress is required:

  • 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, use should normally be delayed until just before immersion unless the user is trained in purging techniques. In that event, it would be possible to successfully deploy this type underwater. These are generally favoured for military use and are used for civil applications 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 from the ambient 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.

Technical Standards for EBS

Although the need for a technical standard to ensure that minimum acceptable levels of performance and health and safety standards were met by EBS systems, progress towards this has been slow. This was partly because EBS were initially seen as a temporary solution pending the development of Emergency Flotation Systems (EFS) which were capable of preventing the capsize which renders EBS necessary. However, when it became apparent that EFS capability was unlikely to be able to meet that target on every occasion, interest in an EBS Technical Standard was revived and a substantive intent to move forward was demonstrated with the publication of CAP 1034, a comprehensive document on the subject, by the UK CAA in May 2013. This intent was further confirmed by the subsequent publication of UK CAA Offshore Helicopter Safety Review in February 2014.

The UK CAA document referred to above defines two standards, ‘Category B’ which equates to EBS currently deployed in the UK North Sea sector and a more stringent ‘Category A’ which would meet the requirements for water impact where EBS deployment at very short notice and/or underwater would be required.

EBS User Training

In the absence of applicable regulatory requirements, familiarisation with the EBS equipment provided is controlled by policy requirements, often voluntarily exceeded by operators. In the case of UK offshore operations, user understanding is currently imparted by means of initial and recurrent classroom training and a pre-flight briefing which is usually delivered through a video. The debate about the effectiveness of user familiarisation is ongoing, with the UK use of hybrid systems being the subject of ‘Safety Action’ documented by the UK AAIB in a Supplementary Bulletin issued in the course of their continuing investigation into a 2013 fatal water impact accident.

More generally, it is recognised that the extent to which user training is required depends on whether the equipment in use is cleared for underwater deployment or not as successful use of the former type will require significantly more training.

Further Reading