Central heating, free-flow beating
Its the reality for many UK-based divers - cool water in our seas and colder water at inland sites, especially in winter. How to stay warm Louise Trewavas and her guest experts have the answers, while John Bantin finds out how ice-divers beat the risks of regulator free-flows.

What coldwater divers say Learn from the ice-divers.

REMEMBER WHAT IT FELT LIKE WHEN YOU FIRST JUMPED INTO UK WATERS in an ill-fitting semi-dry The shock was enough to take your breath away. The first UK divers didnt even have the luxury of a semi-drysuit, they had to make their own wetsuits by sticking bits of rubber together. No wonder they think todays divers are a bunch of softies.
     Diving has come a long way since those early days, when a 15m dive for 15 minutes was considered daring stuff. With largely home-made kit that had limited performance qualities, most divers never came near doing a decompression dive.
     These days, with superior equipment and specialist thermal protection, UK divers like me can spend far longer in the sea, and at depths that would once have been considered unthinkable. We have tables and computers to work out our deco, we have regulators that can perform to ridiculous depths, and we have twinsets and rebreathers to give us shedloads of gas.
     But in UK waters they would all be rendered pointless without a decent drysuit and undersuit. Cold is a significant limiting factor for the British diver.

     If youve ever been in central Newcastle on a Saturday night in November, youll know that not everybody is bothered about the cold. Men wearing short-sleeved shirts and girls in flimsy dresses and bare legs happily parade about in practically sub-zero temperatures. Are we just being wimps to get so concerned about feeling cold Is it really just a question of mind over matter
     Different individuals seem to have wildly different tolerances of low temperatures. Scientists will cheerfully tell you that womens bodies are better designed to survive spending long periods immersed in cold water, yet most women will cheerfully tell them where to stick that piece of research.
     Being able to survive in cold water and being able to put up with the cold without getting really pissed off and complaining are entirely separate things.
     Humans are poor when it comes to awareness of core body temperature. Were more likely to notice that our hands and feet are cold than to realise that our bodies are becoming hypothermic.
     But despite the boundless opportunities for UK divers to chill themselves to dangerous levels, it is rare to see hypothermia cited in the BSACs annual Incident Reports, other than when divers become separated from their boat and spend hours drifting at sea.
     Apart from discomfort, the main problem is that a cold diver can use up to 29% more gas, suffer stress and become more prone to decompression illness.
     Being cold can also affect your dexterity, co-ordination and ability to think. This is serious stuff. Dont let anyone tell you that youre being a wimp if youre concerned about getting cold.

Mental effects
I have done hundreds of coldwater dives but regulator free-flows have never been a problem. Many hours of training and debate have, however, been devoted to the subject. A quick read through the incident reports indicates that bad decision-making and panic are far more significant factors than equipment failure.
     Any equipment failure is survivable if a diver stays calm and takes appropriate action. This is easier said than done. Anyone who has had to share air, deploy a delayed SMB, keep their buddy calm and control their buoyancy while working out what stops need to be made will know the meaning of task-loading. The last thing you need is additional stress, but being in cold water is a stress.
     Ever wondered why warmwater diving seems so easy Its because youre less stressed. Ever wondered why so many diving fatalities happen in lakes and quarries You could blame inexperience at Stoney Cove, or deep diving at Dorothea Quarry, but the common factor is very cold water.
     There is little evidence that fatalities are down to equipment failure. Research by the National Oceanic and Atmospheric Administration (NOAA) into the effects of cold water on divers shows that speed of reasoning, the ability to think clearly and short-term memory can all be seriously impaired. Add these factors to the physiological stress of being immersed in very cold water and the number of accidents seems less surprising.

Numb and number
The coldest dive I ever did was in Coniston Lake. There was snow and ice on the ground, and it was freezing. All I had to do was go to the bottom, locate a piece of wreckage and tie a lifting bag onto it. In the 10 minutes it took to locate the wreckage, my hands had become so numb that I couldnt feel the line well enough to tie it.
     On the ascent, I could barely locate the inflate button on my rebreather to add oxygen on the stop, and as for routine stuff like buoyancy control, it can become quite tricky when you cant feel any of the controls on your BC.
     At the end of the dive I threw out my old gloves and bought a new, thicker pair. Ironically, I had chosen the thinner pair of gloves because I thought the thicker ones would stop me being able to feel what I was doing! And I wont even mention the pain I experienced after my fingers thawed out...
     Another problem in very cold water is that your lips go numb. If youve ever tried to replace a regulator thats been accidentally kicked or swept out of your mouth by another diver, you may be familiar with the strange sensation of not being able to locate your mouth.
     Its a situation that could have great comedy potential if you werent facing the imminent prospect of drowning.

Prone to sickness
As you become colder on a dive, your body responds by restricting the blood flow to extremities and concentrating on keeping your vital organs warm.
     Tissues that have on-gassed at the start of the dive now have a greatly reduced blood supply and a less effective means of off-gassing safely, so you are more prone to a bend.
     Diver training agencies that teach decompression diving advocate that you follow a more conservative profile if youre diving in cold water.
     I recently met a veteran of deep, challenging diving who, though he followed his deco schedule to the letter, managed to get bent on a number of occasions.
     However, he told me that he had never suffered a bend in a wetsuit because, in his extensive experience of DCI, if it was warm enough to wear a wetsuit the likelihood of bending was substantially reduced.
     Another coldwater problem is that once you start shivering on a dive, your body is taking drastic action to warm you up. Your oxygen consumption increases, your breathing rate is likely to go up significantly and youll get through your gas a lot faster.
     Youll also feel much less inclined to hang around doing stops. Getting cold is a recipe for surfacing too soon.

Intelligent suits
When Stoney Cove reopened on 2 January 2003, divers were queuing from the crack of dawn to get their first dive of the year - even if it did mean breaking the ice. Despite the difficulties, were addicted!
     Innovations in thermal protection have made it increasingly possible to dive without getting too cold. Weezle won a Millennium award for its Snugpak undersuits, C-Bear has introduced Tricore 300gm undersuits, and Fourth Element added a high-tech base layer, the Xero-therm, to help increase heat-retention.
     A number of heated undersuits have been tentatively developed, but there are problems. Battery-packs and large quantities of sea water are not necessarily a happy combination. Also, any continuous heating device connected to a power source could cause a diver to become dangerously overheated without realising. Unless used carefully, the heating can interfere with the bodys own efforts at temperature-regulation.
     Having said that, one benefit of the mobile-phone industry is the development of small, efficient batteries.
     Undersuits powered by a battery the size of a cigarette case, and with thermal capacities that prevent the possibility of over-heating, are now being developed for a range of extreme sports.
     Fourth Element is now working with intelligent , responsive fabrics which will gently absorb excess body heat and either gradually re-emit it automatically, as the diver cools down, or release heat in response to a direction from the diver. Fantastic - and no need for batteries at all!
     Of course, once the limiting factor of getting cold on a dive has been sorted and we can all spend hours on our rebreathers, the next problem to tackle is taking a wee in a drysuit. But thats another article entirely...

The Bluebird Project in Lake Coniston was carried out in waters between 4 and 6°C
divers queue up to enjoy the cool waters of Stoney Cove all year round
cold bell in one hand, hot cuppa in the other
you cant beat a warming cup of tea after a dive - you can even have one under water on a deco stop if someone brings it down in a suitable dispenser

  1. Keep yourself warm before entering the water.
  2. Hardboats are preferable to RIBs - they offer more shelter.
  3. On a hardboat, make sure you have a fleece designed for diving use.
  4. Avoid getting your undersuit wet before you dive.
  5. On a RIB, get a suitable boat coat to keep you warm on the way out and back.
  6. Wear a drysuit with a good-quality undersuit.
  7. A snug-fitting hood and decent gloves are a must: many Scandinavian divers use dry gloves for water under 10ÂC.
  8. Use your drysuit for buoyancy: the more gas in it, the better the insulation.
  9. Some divers swear by argon suit inflation, but it appears to be effective only if you flush it thoroughly through your suit several times before diving.
  10. Exercising/working at depth to keep warm makes you more prone to DCI and drives the blood from your core to your extremities - increasing your heat loss. Avoid it.
  11. Being a fat bloater might actually be an advantage. You may not feel warmer, but all that blubber means that you lose less heat.
  12. Nearly 20% of heat loss is through breathing dry, cold gas, so rebreather divers have a distinct advantage.
  13. If you start to feel cold, stop and ascend. You wont feel any warmer, and could feel considerably worse, the longer you stay in the water.
  14. Prolonged and repeat diving can produce cooling over long periods. If youre cold, dont do a second dive. If you feel progressively chillier over a week, take a day off to allow your body to recover.
  15. On a RIB, wrap up after the dive. Bring a flask of hot soup for post-dive warming.
  16. On a hardboat, get out of your drysuit and into the cabin. Make sure you have dry clothes to change into if necessary. And get the kettle on!

What coldwater divers say

Learn from the ice-divers.

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