National Instructor Marg Baldwin is a big fan of the fantastic underwater conditions seen on cold-water scuba dives, but, she says, you need to take some simple steps to keep safe.

The water has cooled down in the UK, but why not carry on diving? While the sea stays calm, or when the winter storms start to move inland, I take every opportunity to get to the coast. You might ask why scuba dive in colder water? My answer would be, quite simply, the improved visibility.

As the levels of sunlight reduce and temperatures drop, many of the tiny organisms that live in the watercolumn die off and sink, leaving us with significantly better underwater conditions. Viz of 15 to 20 metres can be experienced at both UK coastal and inland sites as the water cools. This gives you the chance to see more of the underwater sights; every reason to carry on diving. Seawater generally stays warmer than freshwater lakes, and an added bonus of either is that the water temperature is often higher than on land.

As with all diving, cold water diving – when the water temperature drops to 10°C and below – needs good preparation and planning. Continuing to dive through the autumn into winter can be part of that preparation. As the water cools, you can adapt your equipment and your approach in incremental steps. Start with yourself: are you fit, well rested, hydrated and have you eaten well in the 24 hours before diving? Cold water diving uses up plenty of energy.

Wear warm clothing when scuba diving in cold conditions

Your equipment needs to change for colder water. First, let’s consider protective clothing. You might need to move from a semi-drysuit to a drysuit, and if you are already using a drysuit you’d best make sure it doesn’t leak. Remember to add to your thermal under-layers, but don’t add too much, you need to leave some space for the all-important air in your suit. Feeling like a trussed turkey is not a good option; it may reduce your mobility and doesn’t necessarily keep you any warmer. There are many options available to help keep you warm, ranging from super-insulated undersuits to heated ones. Remember, major undersuit changes are likely to need weighting and buoyancy management changes – so don’t overlook this basic step.

Remember to keep your extremities – head, hands and feet – comfortable too. I indulge in a new, well-fitting hood as the water drops below 10°C on the basis that the one I bought last year will have stretched after a long season of diving.

For warm hands, you could choose dry gloves or thicker wet ones. When choosing, think where you are likely to be doing most of your cold-water diving; the practicalities of kitting up must be balanced with the need to keep your hands comfortable and functioning. Should you choose seals or ring systems for dry gloves? That’s a good debate to have with fellow divers. In cold water, I wear three-fingered mitts that keep my thumb and forefinger free but keep the remaining fingers together to retain the heat. I know some think they come out of the Ark, but they work for me. It’s down to personal choice and the type of cold-water diving you plan to do. On land or underwater, cold feet are never fun, so think about different undersocks, and remember to check that they fit in your boots.

Photo by Stuart Duncan Stuart Duncan-cold water diving

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Regs need to be suitable for use in cold water

What to wear and how to keep warm are important, however, the most vital piece of equipment is your breathing apparatus. It needs to be suitable for use in cold water to reduce the possibilities of a free flow, when the demand valve cannot close between breaths and gas is constantly delivered.

What causes a demand valve to free flow is a good question. When the compressed gas in a diving cylinder flows through the cylinder valve and regulator first stage, the gas pressure is significantly reduced, usually from 232 bar to around 10 bar. This reduction in pressure produces a dramatic decrease in the gas temperature. It can reach as low as 5°C or even colder as it passes through to the second stage. This very cold gas chills the demand valve and can freeze any moisture in the gas and any water droplets that may be present in the second stage. Ice begins to build around the valve mechanism, which prevents it from closing properly between breaths. This ice continues to build with each breath until the valve is stuck fully open and the gas is flowing continuously in a violent free flow.

In the UK, all new regulators are approved to meet the requirements of the standard EN250:2014 and are marked as such on the first stage. The standard now requires the performance of all first stage regulators to be capable of taking an auxiliary breathing system (octopus/alternate source) and be marked EN250A. Older regulators may not have this performance (taking an octopus) and only be marked EN250.

A regulator intended for cold water it should, therefore, be marked EN250 or EN250A, with no temperature. Warm-water regulators must be marked EN250A > 10°C.

In water 10°C or less use only regulators marked with EN250 or EN250A EN 250 A - Cold Water
Regulators marked (EN250 or EN250A) > 10°C (temperature in excess of 10°C) are only suitable for use in warm water.EN 250 A Warm water 1000x500

Demand valves that work well in cold water have been specifically designed for use in extreme cold water and are normally tested in the range of 2-4°C. Manufacturers use heat conductors and vanes to help prevent the build-up of ice. Other regulators that perform very well in cold water, although not generally available, have second-stage housings and components made from chrome brass. Such components conduct the heat energy from the surrounding water into the valve mechanism to help prevent ice forming.

Practice and preparation

Most divers have been required to breathe from a free-flowing regulator in basic training. Practising this in a swimming pool helps prepare you for the experience of a frozen regulator going into free flow. Just occasionally on a dive you will get a hint of what is about to happen, a very brief partial free-flow, but often the onset of a free-flow is sudden and without warning. The big thing to remember is that you can breathe from a free-flowing regulator, even if it feels like your teeth are being frozen.

On most recreational dives following safe diving practice, say no deeper than 30m, there should be sufficient gas for you to make a normal ascent to the surface during a free-flow. But when diving in cold water, carrying a redundant gas supply is strongly recommended even if you are using a suitably rated regulator. This could be a pony set-up or a twin set configured to allow a free-flowing regulator to be isolated. For deeper and decompression diving in cold water, such redundancy is essential.

Good kit preparation can help reduce the risk of free flow. Avoid storing your kit in a cold garage or the boot of your car the night before a dive – particularly if you are going into fresh water. Keep all your kit warm and dry the night before, regulators alongside undergarments and suits; and if possible set it up in a relatively warm, dry environment and keep it there until you are ready to dive. Often this is not possible – but do avoid your scuba set lying around on a frosty car park surface.

When doing a buddy check on your regulators do not be over zealous. On a cold frosty morning, particularly if you are about to jump into fresh water, over-enthusiastic breathing during checks or immediately after jumping into the water, can put enough moisture into your demand valve to encourage a freeze at the surface. The air temperature is very often colder than the water temperature, so once you’re in submerge without delay.

Scuba skills and instructing

We all like to keep our skills, such as delayed surface marker buoy (dSMB) deployment, in practice. Lack of dexterity due to cold hands, or perhaps the use of dry gloves, brings different dimensions to them. Practice with your dSMB but also think about the method of inflation you are using.

In cold water I always use a dSMB with its own gas cylinder (that could be a refillable mini cylinder or a carbon dioxide cartridge) and I take a backup, smaller dSMB that fills with exhaled gas from my primary second stage. dSMB inflation using the gas from an alternate source is best avoided in cold water. Using the purge button can lead to the AS regulator free flowing with a rapid loss of your primary gas. By the way, cold-water conditions are likely to increase your gas consumption, so keep an eye on your contents gauge.

Instructors sometimes have to teach skills in cold water, because of student availability or to meet agency standards. Be flexible when this happens and think about how to manage and mitigate the associated risks. Do all you can to keep the divers comfortable. Remind yourself what it is like to, for example flood, remove and replace a mask in cold water. Shorter shallower dives may be appropriate to limit students’ exposure to cold water. Planning shorter, more conservative dives to reduce risk applies to us all in cold conditions.

Keeping comfortable between dives

Finally, creature comforts between dives are very important. Warm hats and large thick gloves are a must. Go for gloves two sizes too big, as they are easier to put on cold hands. I get out of my suit between dives to allow my body to breathe. I find if I keep my suit on there is a moisture build-up that leads to me getting cold on the second dive. Warm drinks between dives can be especially welcome.

One of my great pleasures is diving the west coast of Scotland with the surrounding hills covered in fresh falls of snow against a backdrop of clear, blue skies. On one trip we had temperatures of minus 8°C on the boat deck and plus 12°C in the water but the underwater visibility was wonderful; as we submerged the whole wreck came into view, it was fantastic. Ice-diving in Austria and hopefully trips to Norway and Alaska to experience some extreme cold diving feature on my bucket list.

Do try cold-water diving. If it’s not for you – and none of us should allow ourselves to be subject to peer pressure to dive in conditions we are not comfortable with – it’s not a problem, just hang up your fins until the temperatures start to increase or plan a diving trip to warm water. You can still be part of the support team helping divers put on their last pieces of equipment and supplying the warm drinks when they come out.

Learning Curve article from SCUBA issue 85

Feature image by Kerry MacKay

See Marg's 'Hints and tips for diving in the cold' 



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