I’ve recently received the note below from the Superintendent of Diving which needs to be widely disseminated:
Fellow Divers, a recent tragic incident which occurred during an Expedition which took place overseas, has identified a number of lessons, which the Service Sub-Aqua Diving community needs to be informed about. While the investigation process is still ongoing to fully explain the cause of this incident and which I can therefore not comment on at present, one clear aspect of the circumstances needs to be carefully considered by all those enjoying SCUBA diving for authorised Adventurous Training and Service recreational purposes, namely the practice of snorkelling and breath-hold diving, after diving using SCUBA.
The risk of a shallow water blackout when conducting even shallow breath- hold diving is well documented and while it is virtually impossible to ‘police’ this activity, I would strongly advise anyone indulging in this activity to cease doing so in the future. The risk of decompression sickness being aggravated by the practice of breath-hold diving after SCUBA diving is the subject of debate within the hyperbaric medicine community. But it does appear that there is a possibility of DCS occurring during breath-hold diving following diving involving the use of compressed gas. Therefore, until this risk can be discounted, it must be made clear to divers by the SADS, that during Service Sub – Aqua diving projects, divers must not engage in breath-hold diving activity until they are clear of residual gas as indicated by dive computer or calculated from dive tables. By breath-hold diving I mean that activity where individuals take a breath on the surface and ‘duck dive’ underwater to any depth. This obviously also means ‘free-diving’ and a number of free-diving websites already warn against this practice. Military divers have been prohibited from breath-hold diving since the death of Lt MacAuley RN in 2002 and in light of the recent incident it is clear that this prohibition must apply to Service Sub – Aqua Diving also.
With regard to snorkelling, many divers, me included, carry a snorkel for use on the surface and if used on the surface only, I do not believe that there is any potential increase in risk of DCS or actual risk of shallow water blackout.
Indeed in an ‘out of gas’ situation, the availability of a snorkel could be considered to be a piece of emergency equipment. However, while there is no clear guidance from BSAC, it is considered reasonable to ask Service Sub-Aqua Divers to wait until they have completed their off-gassing period before undertaking anything other than snorkelling on the surface activities.
C M Baldwin, Cdr RN, MOD SofD