Ice diving is a type of penetration diving where the dive takes place under ice. 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.
The most obvious hazards of ice diving are getting lost under the ice, hypothermia, and regulator failure due to freezing. Scuba divers are generally tethered for safety. This means that the diver wears a harness to which a line is secured, and the other end of the line is secured above the surface and monitored by an attendant. Surface supplied equipment inherently provides a tether, and reduces the risks of regulator first stage freezing as the first stage can be managed by the surface team, and the breathing gas supply is less limited. For the surface support team, the hazards include freezing temperatures and falling through thin ice.
Procedures
Whether ice diving inherently constitutes technical diving is debated within the recreational diving community. For the professional diver it is a high risk environment requiring additional safety measures.
Ice diving is a team diving activity because each diver's lifeline requires a . This person is responsible for paying out and taking in line so that the diver does not get tangled, and for rope signal communications with the diver. Professional teams will also require a and diving supervisor.
Under some circumstances a guide line can be used instead of a lifeline as a reference for the divers to return to the hole at the end of the dive or in an emergency in a similar way to cave diving or wreck penetration. In these cases the divers should be competent in procedures for diving with a guideline.
Polar diving experience has shown that buoyancy control is a critical skill affecting safety.
Typical procedure for a scuba dive under ice: A snow shovel is used to clear the snow and ice from the area. An ice saw or a chain saw is used to cut a hole in the ice. A weatherproof area is used for the divers to suit up. The diver and tender on the surface are connected by a rope lifeline and harness. The harness is typically put on over the dry suit but under the BC or other buoyancy device so that the diver remains tethered even if he or she must remove the air cylinder or buoyancy control device. The harness fits over the shoulders and around the back such that the tender on the surface can, in an emergency, haul an unconscious diver back to the hole. The harness should not be able to slide up or down the diver's torso when pulled in line with the body. Rope signals or voice communications systems must be used. A tethered standby diver is ready on the surface. One or two divers may dive at the same time from the same hole, each with his or her own rope. Using two ropes runs little risk of getting tangled together, but using three significantly increases this risk. If the regulator free-flows and freezes, the diver should close it down and switch to the backup, and terminate the dive. When diving in pack ice, the surface team must constantly monitor ice movement to ensure that the exit is not compromised. The diver must ensure that there is always a positive indication of the route to the exit area. A tether to a surface tender is usually preferable as it can be used to communicate, but if this is not practicable a reel and distance line is an alternative. The risk of attack by predators and aggressive wildlife should be considered. Polar bear, walrus, and leopard seal are potential hazards within their ranges. Gas management for an overhead environment is appropriate. Deployment of a single tethered scuba diver is a reasonably safe alternative to free-swimming buddy team diving. The tethered scuba diver is equipped with a full-face mask with voice communications, high capacity scuba air supply, and an independent emergency air supply. A lifeline with communications cable is secured to a body harness on the diver and is handled by a surface tender who is in constant voice communication with the diver. A similarly equipped standby diver is available on the surface.
Equipment
Since diving under the ice takes place in cold climates, there is typically a large amount of equipment required. Besides each person's clothing and exposure-protection requirements, including spare mitts and socks, there is basic scuba gear, back-up scuba gear, tools to cut a hole in the ice, snow removal tools, safety gear, some type of shelter, lines, and refreshments required.