Cold Water Diving

Cover photo: Petri Laaksonen - Montala mine, Finland

Many of the training agencies and organisations define it as less than 15°C but many would argue that is still pretty temperate and that it should be lower before being considered ‘cold’. I guess it depends on your opinion and what you are used to. One warm water diving friend that came to Sweden for an early season trip, when finding out that the water temp was 3°C asked ‘What is the other missing number?’. Needless to say he was a bit wide eyed when informed there was a 0 but it was in front of the three.

Photo: Tiffany Norberg - Kitting up on the Baltic Sea

For the purposes of this article, and the fact that I predominately dive in less than 10°C, we will call cold 6°C and less, as the core topic here is handling the conditions not only underwater, but also on land, so let’s look at why this article has even been written and what is challenging in regards to these conditions.

Photo: Tiffany Norberg - getting ready for winter diving in Sweden

To begin let’s consider the fundamental consideration with diving in cold water, staying warm, both on the surface and underwater. Drysuits are basically a must in modern diving for this environment as are suitable undergarments to stay warm. These are often very bulky, though comfortable, and require more weight depending on the purpose. The big key consideration is the wicking ability of anything worn under a drysuit. It must remove moisture from the body away from the skin and as such the primary rule is no cotton or material that attracts water, especially against the skin. In addition to this, you will sweat in the suit while moving around on land so to make life nicer, a good base layer that wicks moisture fast but can also be cleaned easily makes your cold water experience more enjoyable. I would recommend a merino wool base layer, then a suitable thicker layer on top and maybe a middle layer if diving in even lower temps or on longer dives. While warm you also need to consider the range of movement as you still need to reach valves, swim, and have a range of freedom, so the actual drysuit may be bigger in size than a warm water suit. I have a multiple suits for different temperatures and diving ranges which have room for this base layer. A big component of diving in these conditions is staying warm prior to diving. Wear suitable clothing, gloves and a hat that keep your extremities warm before even getting changed to go in the water, as they will not warm up after you have.

Photo: Marcin Wojturski - Ready for a 6 hourmine exploration dive

What about heating? It is great in these conditions, but again comes with its own challenges and issues. The first consideration is getting a system where the battery is external to the suit. Pressure increases reaction rates and if you get a rapid increase or burn you cannot turn off an internal system. The same applies to chemical heating pads, do not use them diving or you will get burned. With heating you need to consider the physiological effects as well related to decompression and complications caused if for example your battery fails on ascent so you get colder during that phase. Often many divers will use their heating later on in a dive when getting cold, or during ascents to offset this risk, but not always; sometimes it’s just nice to stay warm on shallower dives.

Photo: Edd Stockdale - Getting gear ready for a dive

It’s not only you that needs to stay warm as well, so does your diving gear. Due to the very nature of diving, equipment is not really designed for sub 0°C temperatures and freezing. If diving open circuit you have the risk of free flows when opening regulators in cold conditions on the surface and of drawing to much gas underwater, even in 2-6°C. As such pre dive checks and protocols need to be slightly different while still testing everything. Ensuring your gear spends the minimum amount of time standing in low temps, testing functionality in the warmth before heading to water, and no purging or breathing of regulators until in-water. When it’s -20°C surface temp we don’t even open valves until they are submerged. Underwater itself you need to reduce high flow, breathe slower and use repeated small presses of BCD and drysuit inflation buttons instead of long fills.

Photo: Edd Stockdale - Diver in the Arctic ready to jump into the ice hole

Rebreathers in the cold, while having huge benefit with warm gas returning for inhalation helping maintain body heat, also have careful considerations, most critical of which is the CO2 absorbent. Chemical reactions slow down when cold and this applies to the rate at which scrubbers work, so reduced usage of time compared to warm conditions is important and needs to be considered when planning dives. In addition all the electronics, both on the CCR, and also other items get effected as well. Batteries run shorter times, pressure sensors can get damaged by water on them freezing (common issue with dive computers and handsets that have sensors on them) and plastics/ O-rings become more brittle and can crack. Consideration of the model of CCR for the conditions they are designed for is important as well, both for resilience to the conditions and operational design, for example use with heavy dry gloves. Having seen a neck seal of a drysuit freeze and crack you can imagine what can happen to other items.

So with all this trouble and cold, why go diving in it at all? Cold water environments are often amazing regardless of whether you are a nature diver, wreck enthusiast or an overhead junkie. It is a different fascinating world which, while challenging, can offer an entire new aspect to your diving. Granted you will have to get some specific equipment, learn how to use everything with dry gloves and change some of your protocols, but you will have the opportunity to see places less visited, greater preserved wrecks or mines, and amazing wildlife. Huge development in drysuits, active heating, CCR technology and batteries mean what was once a more obscure area of diving is now becoming accessible to even the most warm water diver.

Photo: Alf Norkko - Survey of seagrass beds in the Gulf of Finland

Hopefully you get to try it soon.

Author: Edd Stockdale