THE SUMMER COLD
(Photo by author)
Just because it’s warm outside doesn’t mean that you can forget about hypothermia when performing dive rescue.
HYPOTHERMIA CAN BE a deceptive killer of dive rescuers. Usually, you don’t recognize you have it until it’s too late. Hypothermia decreases your ability to function safely. (See “Hypothermia and the SCUBA Diver,” Fire Engineering, March 1987.) As it progresses, your thought patterns, reaction time, and muscle coordination become poor. The most dangerous aspect of the condition is the denial of its presence as you continue to tell yourself that you can handle it “just a little while longer.” On land we can usually tell when the weather has gotten to us and it’s time to go inside for additional thermal protection. In water, however, our sense of self-preservation, in terms of heat loss, may not be so well-attuned.
Even though summer is around the corner and warmer water is close at hand, the hypothermia problem still exists. It does not disappear just because the sun is out or because you happen to live in Florida. The danger is deceptively there all the time.
When it comes to safety and exposure, we should not give in to the natural urge to take warm-weather dive rescue operations any less seriously than we do such operations in colder weather. There may be even greater incidence of hypothermia during the warm months, when many divers take shortcuts during in-water operations. Typical shortcuts include entering the water without gloves or a hood, or worse, diving without wet-suit pants. You may he thinking that no trained diver would ever go into the water with half a wet suit; well, if you are, you’re wrong—some do, and most of the time it happens during the summer months.
All divers, from the Caribbean sport diver to the professional rescue diver, have safety concerns in common. However, though hypothermia is a generic hazard, the in-water rescue diver has special problems and concerns that put him at greater risk. Rescue divers often make numerous dives under bad weather conditions and may have to make extended stays in the water. An adequate supply of warm clothing, food, and shelter for surface interval times is very important, since the chances of becoming hypothermic are greatly increased if the body core temperature is already lowered from previous dives. Removing wet suits between or after dives is another important consideration, because our bodies will actually lose heat by remaining in them. Furthermore, in-water rescue teams, generally as a result of inadequate funding, often lack the proper equipment or were not given proper instruction and training to use what gear they have effectively. Stress and fatigue, which limit the body’s ability to maintain its core temperature, figure strongly in dive rescue operations. These and other factors make it especially important for the rescue diver to be concerned with the prevention and treatment of hypothermia.
And let’s not forget the support personnel on the shore: Though they won t lose their body heat as quickly as the divers, they will still lose it, and, like the diver, mostly through their head, hands, and feet. (In water, 60 percent of heat loss occurs from the head and 20 percent from the hands and feet; on land, the figures are 25 and 10 percent, respectively.) Over a long rescue operation, heat loss to air can be sufficient so as to cause hypothermia. These members should be prepared and protected from the elements. Sure, you might be able to send someone for that extra clothing, but hypothermia probably won’t be foremost on the minds of personnel when there’s a rescue at stake. They, too will be inclined to “tough it out.” Why risk it? Be prepared at all times—that means for warm months, too.
THE SUMMER COLD
The high risk of hypothermia during all dive rescue operations should be utmost in the mind of the officer in charge of the team. He must consider: What types of exposure suits are necessary for the type of diving we do? What kind of monetary costs might I be facing in purchasing suits? Can I use the same suits and dive plans for each member of the team, or are there individual considerations to be aware of?
These and other questions were addressed by Diving Unlimited International, Inc. of San Diego, California in a two-year study of men and women, wet and dry7 suits, divers at rest and at work, warm and cold water conditions, and thermal stress itself. The results of this inclusive research have been practically set forth in DUJ’s Thermal Guidelines, a concise, 14-pagc manual, and in the handy, wallet-size “Misery Index” charts. These are designed so that you can incorporate body weight, personal temperature sensitivity, activity level, water temperature, and depth into a prediction of exposure suit performance for a particular dive.
DUI devised an arbitrary numbering system whereby the diver can order the Misery Index chart specific to his or her body weight. This is important because usually an increase in body weight correlates with a decrease in the “mass to body surface area” ratio (that is, the larger the surface area in relation to the total mass, the larger the heat loss). This numbering system is called the “plus rating table,” which supplies a “plus factor” for eleven body weights ranging from 90 pounds to 245 pounds. A body weight of 180 pounds, for example, receives a “ 4-12″ from the plus rating table, meaning that this person should order the “ + 12” chart from DUI.
To order the DUI literature, write to Diving Unlimited International, Inc., 1148 Dclevan Drive, San Diego, California 92102-2499, or write to me, Walt Hendrick, care of Tire Engineering. and request a copy oi Dili’s Thermal Guidelines and accompanying charts. There is a slight cost of one dollar and a self-addressed, stamped envelope, but I promise you’ll find it worth your while.
By taking into account the water depth and temperature and your expected activity level, you will arrive at a value on the Misery Index. This predicts your level of discomfort when using the type of exposure suit and underwear for that particular dive. If the Misery Index is too great for dive safety or wet suit comfort, either change the dive plan or consult the “Dry Suit +12 Diver” chart to see what kind of exposure suit and underwear you should use.
Water depth is an important factor on these charts for several reasons. Increased depth is accompanied by an increase in pressure, which compresses the insulating air bubbles trapped in the foam rubber of the wet suit, thus diminishing their insulating effect. Increased depths are also usually accompanied by colder water temperatures, which means that more heat is conducted from our bodies at a quicker rate. Cold water also causes problems by cooling our compressed air source. The body must warm cold air as it is inhaled; this not only uses up some of our body heat but also causes dehydration, which affects how the kidneys function. And remember—under heavy work loads we are breathing more air, creating greater body heat loss and dehydration.
Summer is coming, and with it comes a lazy diver. None of us want to endanger our support crew or rescue personnel needlessly, yet almost every day we put improperly protected divers in the water. Then we attempt to support them with personnel who may not be prepared any better for the weather.
Divers should not accept the cold as something that is an inevitable occupational hazard to be endured. By using the literature available on hypothermia and the information supplied by the DUI booklet and charts, divers can better understand what is happening and learn to dress, hopefully, to beat the “summer cold.”
For more information on dive rescue operations, please refer to the following articles published in past issues of Fire Engineering.
“In-Water Firefighting Units,” Ray Downey, October 1985.
“Rescue vs. Recovery,” Walt Hendrick. April 1986.
“Gear Up For In-Water Rescue,” Hendrick, May ’86.
“Underwater Breathing Systems,” Hendrick, June ’86.
“Air: Most Important When It’s Not There!” Hendrick, July ’86.
“Make Rescue A Reality,” Hendrick, August, ’86.
“Moving Water,” Hendrick, October ’86.
“In-Water Rescue Vessels,” Hendrick, January 1987.
“Hypothermia and the SCUBA Diver,” Hendrick and Bridget Thompson, March ’87.