There are risks when diving under the ice, with only one small hole to get out of the water and diving without a tether at water temperatures below Zero C. Divers must take these risks very seriously. Dive Masters Steve Rupp and Rob Robbins are the local Dive Safety Officers who are in charge of the McMurdo Dive Operations. They take an active role in training new divers, they maintain equipment and the make sure everybody is safe down here. Here are some thoughts on what is done in McMurdo to minimize the risks of diving in this dangerous under ice environment.
The first requirement for any aspiring Antarctic diver is to become certified as a science diver. This involves rigorous training and several milestones in terms of classes and checkout – dives: The basic science diving course takes two-weeks, full time with a dozen dives and a final exam. In addition, there are regular medical exams for personal fitness, and first aid courses including CPR/AED and oxygen administration. This will give a science diver license to dive to 30 feet with a licensed science diver as a dive buddy. After a critical number of dives, a diver can request a check-out dive with the dive master for a 60 feet certification. After a series of 60 foot dives, the depth certification can be extended to 100 feet - which is a requirement for Antarctic diving. To remain certified, each diver must dive at least once per month. Once all this is done, an aspiring Antarctic diver has to go through 12 dry suit dives and declared fit to dive in Antarctica by the local dive master. Then, there is more training in Antarctica with the McMurdo dive masters, including a couple of check-out dives. Rob and Steve will have the final say about who dives down here or not, and they can revoke that permission any time they feel safety is at risk.
The most apparent diving hazard is probably the risk of decompression sickness (the bends), in particular in a place as remote as Antarctica. The key safety measure here is to build in a big safety margin by minimizing deeper diving, staying within the limits of no-decompression diving. All divers have to go through a conservative decompression sequence including a three-minute safety stop at 15 feet. Only very experienced divers go deeper than 100 feet if their work requires them to do so. However, if something happens, most dive huts are equipped with an “Unconscious Diver Hoist” to help in the recovery of an unresponsive diver, and there are five helicopters on station that can be mustered for a rescue mission on short notice. The McMurdo Hospital is equipped with a hyperbaric chamber, and the medical personnel are trained for such emergencies.
Diving at water temperature below the freezing point of (fresh) water bears the problem that breathing into the regulator may introduce fresh water that will freeze at these conditions and cause the valve to free-flow the air from the tank. If that happens in the wrong place, there may not be enough time to safely go through decompression and/or return to the dive hole. To minimize this risk, divers use dive tanks that have two valves with two independent regulators, one for the primary air supply, and another one as a back-up. The back-up regulator is included in the valve that also feeds the dry suit inflator and the pressure gauge.
The backup regulator is attached to a shoulder strap with a rubber band and pulled off when needed. The free-flowing primary regulator can be closed off with a shut-off valve that ideally stops the free flowing air. If that is not good enough, the valve has to be turned off at the tank by the Diver’s buddy. However, even if all of that goes smoothly, a dive is done at this stage and the diver returns to the hole, decompresses and gets out.
How to find the way back to the hole without a tether? First, of all, visibility is extremely good in most dive holes and before each dive, strobe lights are lowered into the hole that show up really well in the dark. If there is lots of light, the strobes are somewhat more difficult to see, but then a diver can see the footprint of the hut from below. In particular during the initial dives, it is imperative to constantly check where the hole is and to create a mental map of the dive location. Once a diver has done that it is always obvious where to look for the ice hole and the diver can go on with the work at hand.
The three most important things a diver can do to stay safe when diving under the ice is training, training, and more training:
- First of all, a diver has to learn how to control buoyancy with a dry suit at local conditions, with all the insulating underwear. For warmth and for motility, a diver has to learn how to distribute the buoyancy between arms, legs and torso. This includes a good feel for the control of air venting and inflation of the dry suit. This is not as easy as it sounds, but it becomes second nature with practice.
- The next important thing is to learn how to switch regulators if it free-flows. This is remarkably difficult, at least at the first time because a diver is not necessarily aware of the fact that one’s face goes numb from the cold water. It is much harder to move facial muscles, so it becomes a chore to get your mouth off the free-flowing regulator and then wrap it around the backup regulator. Some divers lose so much sensation in their face that they literally have a hard time finding their mouth to stick the regulator in. In this case it is suggested to stick out the tongue and use it to guide the regulator into the mouth. Once that is done the diver has to learn to turn off the free flowing regulator by pulling back a little slip ring at the hose connector.
- Keeping the (exposed) head warm is another important thing for a diver to learn. Many use complete head and face masks made of thin rubber. I use a double neoprene dive hood and keep my face open to the water.
- It is also important to keeping feet and hands warm. It helps a lot to flush some of buoyancy air through dry gloves and boots in regular intervals. This warms up the insulation immediately, providing a couple of minutes of warmth.
- It may sound obvious but it is important to stay dry in a dry suit. Last year, I managed to unzip the (sealing) inner zipper while I was pulling the outer zipper. This resulted in a catastrophic flooding of my suit and made for a 15 second dive and a very wet diver. This year, a helpful dive tender managed to inadvertently fold inward a part of my neck seal and I had a slow leak for the whole dive. I managed to pool the water on my chest and belly during the dive, but by the time I got out, I had standing water well above my ankles. Not pleasant, but I had a GREAT dive anyway!
These are some rather simple rules and practices, and they make McMurdo a very safe place to dive.
Greetings from the Frozen Continent,
Hubert
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