Hypothermia: It’s All a Matter of Degrees

Full face mask diver in drysuit

Dive team members should be equipped with the right protection for cold water diving. In most circumstances, this would include a dry suit with insulating undergarments, dry gloves, a dry hood, and a full-face mask.

In the real world of public safety diving, there is no single definition of what constitutes “cold water.” Defining cold water is difficult because it depends on so many factors, i.e., the water temperature, the diver’s size, amount of subcutaneous fat, state of acclimatization to cold water, individual physiology, and activity level. What one person perceives as a comfortable water temperature may be intolerable to another.

The real issue here is at what point does exposure to cold water become debilitating? For the moment, we’re assuming we’re talking about a diver who either is wearing inadequate thermal protection, or whose thermal protection has been compromised, i.e. a flooded dry suit. There is a continuum of responses to cold water that runs the gamut from mild discomfort all the way to unconsciousness and death. As far as I am concerned, the line is drawn at “debilitating effects” because once the diver cannot perform at the peak of his ability, the risks in diving increase to unacceptable levels.

Debilitating effects range from loss of concentration to shivering and the inability to use one’s hands properly. Any of these situations puts the diver at elevated risk and indicate that the diver is not wearing adequate thermal protection for the task at hand. If you notice these signs in yourself or another diver, it’s time to terminate the dive and regroup.

When divers discuss diving in cold water, the term “hypothermia” frequently comes up. Although we all think we know what we mean when we discuss the issue of hypothermia, the reality is that physiologists have a very different perspective on hypothermia than most divers. For a physiologist, hypothermia is defined as a body core temperature below 95 degrees F. Above this temperature, while you might be uncomfortably cold, by definition, you are not hypothermic.

Dr. Neal Pollock, Ph.D., Research Director for Divers Alert Network (DAN), points out that, “The threshold core temperature for hypothermia is 35C (95F), a substantial drop. It is unlikely that a diver with even modest protective garments will reach that point. There is a big gulf between being cold and being hypothermic. Shivering (episodic or continuous) and general impairment will develop long before the definition of hypothermia is met. I think that the focus on the structure of hypothermia stages (mild, moderate and severe) is unhelpful, confusing cold impairment with hypothermia. You do not need both for serious problems to develop.”

Dr. Pollock knows that of which he speaks, and has experienced a flooded dry suit during a polar dive on a 43 minute excursion in 29 degree F seawater. Since he was wearing Thinsulate® under his dry suit during the dive, he was able to continue the dive, which was being conducted to measure his core temperature (don’t try this at home!). The only reason he continued the dive was that it was being conducted for the express purpose of measuring core temperature, otherwise this type of occurrence would normally call for the dive to be aborted. Interestingly enough, the largest drop in Dr. Pollock’s core temperature took place after he exited the water.

True hypothermia is a very serious condition and can lead to unconsciousness, cardiac arrhythmias (irregular beat), and death. Clearly, these are scenarios that you don’t want to occur underwater.

As mentioned earlier, you don’t have to be hypothermic to place yourself at risk in cold water. A dry suit (with insulating undergarments) alone is not adequate thermal protection in cold water. Proper protection of the head and hands is equally important, and dry hoods, full-face masks, and dry gloves are vital, especially for diving under the ice. One issue that may occur with dry gloves and dry hoods are that if they are compromised, their insulation value will be lost. Keep in mind that every piece of equipment has its own advantages and disadvantages.

The language you use as a public safety diver is important, since your actions may be scrutinized and challenged in a court of law. In most cases, you will not be able to properly diagnose a dive team member as hypothermic, unless you are using some very sophisticated equipment. In any situation where you must describe a diver’s inability to perform in cold water, it’s best to say that he suffered from “cold stress.” Leave the medical diagnosis to the physiologists and physicians.


About the author:
Steven M. Barsky is a professional diver, diving consultant and author. He has written 18 diving texts and and produced 9 diving DVDs. His latest DVD video, Careers in Diving, was released in December 2013.
Get in contact with Steve


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