Emergency ascent

More specifically, it refers to any of several procedures for reaching the surface in the event of an out-of-gas emergency, generally while scuba diving.

Ronald C. Samson & James W. Miller, 1977[3]Emergency ascent training policy differs considerably among the certification agencies, and has been the subject of some controversy regarding risk-benefit.

In 1977 a formal policy regarding training of emergency ascent procedures was adopted by five major American recreational diver certification agencies: NASDS, NAUI, PADI, SSI and YMCA.

[3] This policy is a general agreement that emergency ascent training is worth the risk on ethical grounds, and recommends those procedures which the agencies consider most appropriate for teaching recreational divers.

[3] The Scottish Sub-Aqua Club holds that training is primarily to deal with potential emergencies and that it should be practical rather than purely theoretical.

Use of a bailout cylinder is the primary source of emergency breathing gas recommended by several codes of practice for scientific and commercial divers.

These unknowns may be minimised by training, practice, prior agreement, and adherence to suitable protocols regarding equipment, planning, dive procedures and communication.

Buoyancy can be reduced during ascent by dumping, but the effect of ditched weights is not reversible, and usually increases as the surface is approached, particularly if a thick wetsuit is worn.

If weight can be ditched partially, this may be a better option, unless the diver feels that he is about to lose consciousness, in which case a substantial increase in buoyancy may be better.

A method of buoyancy control which will automatically jettison weights if the diver loses consciousness during the ascent is to take them off and hold them in a hand while surfacing.

[5] The technique involves simply ascending at a controlled pace, typically about 18 metres (60 feet) per minute, while exhaling slowly.

It also requires the diver to produce propulsive effort, which reduces potential endurance on the single breath or limited gas available.

If the chosen donor has sufficient gas, and is competent to share by this method, an emergency ascent may be accomplished safely.

[citation needed] The standard PADI-trained technique is for the rescuer to approach the face-down unconscious diver (victim) from above and kneel with one knee either side of their diving cylinder.

Then, with the victim's diving regulator held in place,[16] the tank is gripped firmly between the knees and the rescuer's buoyancy compensator is used to control a slow ascent to the surface.

CMAS require this skill for their Self-Rescue Diver certification, using a ratchet reel to control the line, though other methods may be feasible.

This basically requires the diver to ascend with the feet down and dump valves up, an orientation which can be achieved by hooking a leg around the line.

[18] In the event that a wet bell or stage cannot be recovered from a dive on schedule, it may be necessary for the divers to abandon it and make an autonomous ascent.

This may be complicated by decompression obligations or compromised breathing gas supply, and may involve the assistance of a surface standby diver.

Attempting to breathe off the empty cylinder is one way of potentially avoiding these problems, as this has the double advantage of keeping the airways open more reliably, and in most cases allowing the diver several more breaths during the ascent as the reduced ambient pressure allows more of the residual cylinder air to pass through the regulator and become available to the diver.

Of course this air is not available in some cases, such as a rolled off cylinder valve, burst hose, blown o-ring, or lost second stage, where the failure is not simply breathing all the air down to the pressure where the regulator stops delivering, but if it is possible, the demand valve can be kept in the mouth and the diver can continue to attempt to breathe from it during an emergency ascent.

Loss of consciousness during ascent is likely to lead to drowning, particularly if the unconscious diver is negatively buoyant at that point and sinks.

On the other hand, a fit diver leaving the bottom with a moderate lungful of air, relatively unstressed, and not overexerted, will usually have sufficient oxygen available to reach the surface conscious by direct swimming ascent with constant exhalation at a reasonable rate of between 9 and 18 metres per minute from recreational diving depths (30 m or less), provided their buoyancy is close to neutral at the bottom.

The most straightforward and obviously effective method is for the diver to carry a bailout set sufficient to allow the planned ascent profile if the primary gas supply fails.

In freediving the usual emergency ascent involves ditching the diver's weightbelt to increase buoyancy and reduce the effort required.