Ice diving

[1][2] Because diving under ice places the diver in an overhead environment typically with only a single entry/exit point, it requires special procedures and equipment.

Ice diving is done for purposes of recreation, scientific research, public safety (usually search and rescue/recovery) and other professional or commercial reasons.

Several types of malfunction are possible, including jamming of the first or second stage valves in any position from closed to more frequently fully open, which can produce a free-flow capable of emptying the diving cylinder in minutes, ice formation in the exhaust valve opening causing leakage of water into the mouthpiece, and shedding of ice shards into the inhalation air, which may be inhaled by the diver, possibly causing laryngospasm.

This may be helpful in keeping the demand valve mechanism free to move, but the ice still forms in the regulator and has to go somewhere when it breaks loose.

[7] With most second stage scuba regulators, ice forms and builds up on internal components, and the gap between the valve lever and fulcrum point is reduced and eventually filled by the build-up of ice that forms, preventing the inlet from fully closing during exhalation .

[7] The cold inter-stage air enters the second stage and is reduced to ambient pressure, which cools it further, so it chills the second stage inlet valve components to well below freezing and as the diver exhales, the moisture in the exhaled breath condenses on the cold components and freezes.

Heat from the surrounding water may keep the second stage regulator components warm enough to prevent the build-up of ice.

This is why the CE cold water limit is at 4 °C (39 °F) which is the point at which many scuba regulators start retaining free ice.

Keeping high flow rates to as short a time as possible will minimise ice formation.

[10] Second stage freezing can develop quickly from the moisture in the exhaled breath, so regulators that prevent or reduce contact of the diver's exhaled breath with the colder components and the area where the cold gas enters will usually build up less ice on critical components.

Regulators with exhaust valves that do not seal well will form ice quickly as ambient water leaks into the casing.

Testing may include failure modes and effects analysis, and other issues relating to manufacturing, quality assurance and documentation.

[7] In most cases surface supplied helmets and full face mask demand valves do not get cold enough to develop ice because the umbilical works as a heat exchanger and warms the air up to the water temperature.

If the surface air temperatures are well below freezing, (below −4 °C (25 °F)) excessive moisture from the volume tank can freeze into ice granules which can then travel down the umbilical and end up in the helmet intake, blocking off air to the demand valve, either as a reduction in flow or a complete blockage if the granules accumulate and form a plug.

[7] Kirby Morgan have developed a stainless steel tube heat exchanger ("Thermo Exchanger") to warm the gas from the first stage regulator to reduce the risk of second stage scuba regulator freeze when diving in extremely cold water at temperatures down to −2.2 °C (28.0 °F).

If possible the low pressure inflator hose should be disconnected before it freezes onto the valve, while dumping air to control buoyancy.

This can be a limiting factor on the endurance of the surface team if inadequately insulated and sheltered, and can have an impact on the divers on exiting the water in wet exposure suits.

For the recreational or professional diver it is a high risk environment requiring additional safety measures.

[3] Polar diving experience has shown that buoyancy control is a critical skill affecting safety.

[citation needed] Dry suits with adequate thermal undergarments are standard environmental protection for ice diving, though in some cases thick wetsuits may suffice.

Some prefer to use a full face diving mask to essentially eliminate any contact with the cold water.

[16] When diving under ice it can be easy to become disoriented, and a guideline back to the entry and exit hole is an important safety feature.

The choice between using a tether (lifeline) controlled by a surface tender or a reel line deployed by the diver under ice depends on various factors.

[3] A tether connected to the diver and controlled by a surface tender is usually the safest option for most diving under ice, and the only reasonable choice when any significant current is present.

This practice is more favoured for long penetration distances where entanglement and line fouling become greater risks.

[17] Regions known for ice diving include the White Sea and Lake Baikal, in Russia, Antarctica, the Tromsø region in Norway, Resolute Bay and Baffin Island in Canada, the fjords and coastal waters around Greenland, and the Åland archipelago in Finland.