Staying Warm; Diving in Cold Water

Staying-WarmThe debate regarding what is “cold water” and what thermal protection should be worn by a diver, in my opinion, will never end. There are no ‘one size fits all’ answers to these questions. Having dived all around the world in lots of different water temperatures brings me to this conclusion. Some of the waters I dived in when I first started diving seemed extremely warm and I swore I would never need a wetsuit. Six months later, I was in a 3mm full length suit. Six months after that, I was in a 7mm full length with hood. This was just for sport level diving, without the long bottom and decompression times associated with technical dives.

Comfort Tip

It’s quite common to overheat while dressing. A couple of tricks: get your hood wet before putting it on. This makes a big difference in your comfort prior to entering the water. Also, once you get fully dressed, take a dip in the water. Getting wet will help you stay comfortable while putting on the rest of your gear.

– Susan Long, DUI

There are many factors to consider when choosing the proper thermal protection, but one that should never be used is the ego. Divers are known to think they are “warm blooded” and dive with minimal thermal protection. This is a bad choice. Making a decision based on this defies the basics of physics, a diver is submerging himself in a medium that is 800 times denser than air and will draw heat away from the body at an incredible rate, no matter how “warm blooded” you are. Starting from the planning stages of the dive, there are two things to consider: target depth temperature and exposure time at that temperature. If the target depth temperature is cold, another serious consideration comes into play – air temperature while gearing up and exposure to the sun. If the outside weather is warm or hot, divers will tend to under dress for the dive out of fear of overheating, an equal concern for sure. A better solution to overheating at the surface is to time the gearing up with the buddy or dive team so you are ready at the same time and dressing in an area that is out of the sun.

As a diver who dives in cold water, defined by me as anything colder than 24°C / 75°F, with temperatures as low as – 2°C / 29°F, I always choose to dive in a drysuit. The drysuit allows you to adjust your thermal protection by the undergarments you use and, in some cases, you can adjust the thermal protection on your upper and lower half with two piece undergarments. There are two big benefits to using a drysuit: no cold water shock and, after the dive is over, your skin is dry when you take the suit off. Thus, you avoid evaporational cooling. For longer dives where water temperature is on the warmer end of the thermometer, and especially during decompression stops, drysuits can present a bit of a problem: the diver can start to overheat. One way to avoid this is to take off your gloves and un-zip your hood (if the hood is equipped with a rear zipper).

Other options for staying warm are wetsuits and semi-drysuits. Both have some very distinct advantages over drysuits. First there is cost; any form of wetsuit tends to be less expensive than a drysuit. You also do not have to worry about leaks, which could end a dive before it even begins or cause you to terminate the dive before the planned turn time. Both wet and semidry suits provide excellent thermal protection, and for those long deco stops in warmer water give you the advantage of unzipping the suit to allow water in so you don’t overheat. A downside to wet or semidry suits is that the neoprene compresses at depth, which reduces the thermal protection properties of the suit, causing you to get cooler quicker.

Staying warm during the dive is vital to the comfort of the diver, as well as his safety. It is commonly accepted that being cold during a dive can increase the risk of decompression sickness. Listen to your body and decide what a comfortable temperature is for you. Don’t accept what is “common knowledge,” just use it as a starting point. Also, keep in mind that the older a suit gets, the less thermal protection it provides. This is especially true in wetsuits and neoprene drysuits, so what kept you warm five years ago may not work now.

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7 replies
  1. Rosemary E Lunn
    Rosemary E Lunn says:

    If you are interested in learning more about thermal physiology and protection, you will find below a useful link. It was a lecture given at Rebreather Forum 3 (RF3) in May 2012 by USA based Dr Neal W Pollock, of Divers Alert Network / Duke University.

    Dr Neal W Pollock
    9:15, Friday 18 May 2012, Boca Room III, Caribe Royale Convention Hotel

    “Diving is carried out in a wide range of environments and conditions. Thermal stress can be an important issue, particularly for the long exposures often associated with technical diving. Proper preparation can improve comfort, performance and safety. This presentation will discuss thermal stress, thermal protection, and implications for diving health.”

    Dr Pollock’s biography can be found here;

    This is a useful training resource for divers.

  2. Neal Pollock
    Neal Pollock says:

    This post was very good until the final paragraph, which is the area I will focus upon. The relationship between thermal status and decompression stress is complicated, but definitely not what was suggested by the author of this piece. If a diver is cold during the descent and bottom phase of a dive he or she will uptake less inert gas, effectively reducing the subsequentt decompression stress. Similarly, being warm during the ascent and stop phase will facilitate inert gas eliminatino and reduce the effective decompression stress. Since divers like to be warm they may tempted to go for a bit of overheating at the start of the dive with the expectation that they will cool as the dive continues. Problematically, this sets up the worst case scenario – augmented inert gas uptake and restricted elimination. A more thoughtful consideration of the interactions between thermal status and decompression sickness is necessary to minimize individual risk.

    • dpace
      dpace says:

      Thank you for your well thought out and articulate response. The articles we put out are intended to be informative and thought provoking and yes at times they lack the depth required to fully present the topic. We don’t do this to mislead the reader and we also don’t intend for the articles to be a replacement for proper instruction from a qualified instructor. We try to strike a balance.

      As I am sure you know, judging by your response, it would be a very long article to blend physiology and decompression theory so that the reader had a full understanding of the effects of cold water diving or any topic for that matter.

      For the other readers of this article who may have been left with the wrong impression or wanting more information, we would encourage you to seek out a knowledgeable dive instructor or attend a seminar on the subject at your local dive center or dive show. In the future we will do our best to cover a topic more thoroughly or beak an article into a few different parts, a series of articles covering a single topic.

      Thank you again and safe diving.

  3. Aaron Heffner
    Aaron Heffner says:

    I use a Thermalution heated rash guard. Diving with a heated wetsuit makes cold water diving MUCH more enjoyable for me and allows me to get by without wearing tons of neoprene.

  4. Joseph A. Felix Sr.
    Joseph A. Felix Sr. says:

    My son Josh is diving in the Beiring Sea. Around 15 to 20 ft. below the surface.They use a hooka air supply and hot water inserted in his wet suit. Would you consider training both my sons on the more technical aspects of cold water diving. 28 and24years old both 6ft+ 210 and 220 lbs. neither is a certified diver but have been dredging for gold for 15 years .
    Joe Felix
    Florence, Az. cell (520) 709-0790


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