The main reason for the preference of re-breathers over gas-under-pressure systems (STASS/HEEDS) is the reduction of the potential of embolisms. If practical training is called for - as it should be as the 15 seconds breath-hold (that you have correctly identified is the norm in cold seas) indicates that a single action fumble-free implementation is required - it can ensure the avoidance of training risks.
Sue Coleshaw previously of Robert Gordons of Aberdeen produced an excellent treatise on Emergency Breathing Systems (EBS) for the UK CAA some years ago (including case studies). The CAA may have published this paper which also contained the basis of an objective standard for systems which are intended for passenger use. (If it did I’m sure someone will post the reference.)
It was in Canada that the breath-hold issue was researched and on which the figures were based - they conducted practical escape trials that were based upon the AS332. Research is still proceeding into methods of providing a breathing gap in a helicopter that has inverted following a ditching - side floating is seen as one way of achieve this.
Last edited by Mars; 21st Aug 2004 at 12:11.