The obvious problems are those of cold and hypothermia. They are so obvious that most people will avoid them by the use of heating systems, drysuits or efficient wetsuits. See Chapters 27 and 28 for the effects of a cold environment on physiological performance.
A major difficulty with cold and ice diving is the tendency of many single hose regulators to freeze, usually in the free-flow position, after about 20 to 30 minutes of exposure to very cold water (less than 5°C). This situation is aggravated if there is water vapour (potential ice crystals) in the compressed air and if there is a rapid expansion of air, which produces further cooling in both first and second stages. The first stage or the second stage may then freeze internally.
Expansion of air as it passes from the high tank pressure to the lower pressure demand valve and then to environmental pressures (adiabatic expansion) results in a drop in temperature. It is therefore not advisable to purge regulators if exposed to very cold temperatures. The freezing from increased air flow follows exertion, hyperventilation or panic. Octopus rigs become more problematic to use under these conditions, or at great depth, because of this increased air flow. An emergency air source (pony bottle) has replaced buddy breathing and octopus rigs.
‘External’ ice is formed in and around the first (depth compensated) stage of the regulator, thus blocking the orifice and interfering with the spring. Moisture from the diver’s breath or water in the exhalation chamber of the second stage may also freeze the demand mechanism, causing free flow of gas or ‘internal’ freezing with no flow.
Modifications designed to reduce freezing of the water in the first stage include the use of very dry air and the replacement of first-stage water-containing areas with silicone, oils or alcohols (which require lower temperatures to freeze) or with an air flow from the regulator. The newer, non-metallic second stages are less susceptible to freezing. Despite all this, regulator freezing is common in polar and ice diving. Surface supply with an emergency scuba, or twin tank–twin regulator diving, as with cave diving, is probably safer. It must be presumed in under-ice diving that the regulator will freeze and induce an out-of-air situation, and this must be planned for.
Under ice there is little use for snorkels, and so these should be removed to reduce the likelihood of snagging. Rubber suits can become sharp and brittle. Zippers are best avoided because they freeze and may also allow water and heat exchange. Buoyancy compensators should be small and with an independent air supply.
As a general rule, and if well-fitting drysuits are unavailable, the minimum thickness of the Neoprene should increase with decreased water temperatures, as in the following examples:
<5°C – 9-mm-thick wetsuit
<10°C – 7-mm-thick wetsuit
<20°C – 5-mm-thick wetsuit
<30°C – 3-mm-thick wetsuit
Hood, gloves and booties should be of a considerable thickness, or heat pads can be used. Heat pads must not be in contact with high-oxygen gases because overheating can result.
Unheated wetsuits do not give sufficient insulation at depth (beyond 18 metres) when the Neoprene becomes too compressed and loses much of its insulating ability. In that case, non-compressible wetsuits, inflatable drysuits or heated suits are required. In Antarctic diving, to gain greater duration, we had to employ a wetsuit or other thick clothing under a drysuit.
Ice diving is in many ways similar to cave diving. It is essential that direct contact must always be maintained with the entry-exit area. This should be by a heavy-duty line attached to the diver via a bowline knot. The line must also be securely fastened at the surface, as well as on the diver. The dive should be terminated as soon as there is a reduced gas supply or any suggestion of cold exposure with shivering, diminished manual dexterity and so forth.
The entry hole through the ice should be at least two divers wide. Allowing room for only one diver to enter ignores two facts. First, the hole tends to close over by freezing. Second, in an emergency two divers may need to exit simultaneously. There should be a surface tender with at least one standby diver. A bright light, hanging below the surface at the entry-exit hole, is also of value in identifying the opening. If large diving mammals contest the opening in the ice, they should be given right of way.
If the penetration under the ice is in excess of a distance equated with a breath-hold swim, then a back-up scuba system is a requirement, as with cave diving.