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How to be warmer

By Dick Long, Founder DUI
5/18/1999

Most divers don’t think much about the problems associated with diving in cold water. Either they grin and bear it, or if they complain, other divers give them a hard time and say they aren’t tough enough. The reality is that diving in cold water poses a significant threat to your safety and robs you of diving enjoyment.

Why Be Warm in the Water?

Warm diving is fun; cold diving is miserable. Although being cold is tolerated in many types of diving, cold is a factor in most underwater accidents. This is a big mistake.

Cold is predictable and preventable. We have the knowledge, technology, and equipment to eliminate cold as a problem in the modern diving world. Our goal is to keep the diver’s body at its normal operating temperature. We do that by controlling the rate of heat loss from the diver to the water.

Where Does Your Body’s Heat Come From?

The muscles are the body’s heat engines. They create heat by metabolizing food during exercise. The circulatory system distributes the heat generated by the muscles. If we exercise a lot we produce a lot of heat. If we exercise little, we produce little heat. To keep warm, we must maximize the blood circulation within our body.

Heat is lost primarily by conduction through your skin. In conduction, heat is transferred from your skin to the water by direct physical contact. Your diving suit is used to control the rate of that heat loss.

Large divers tend to produce more heat than smaller divers. Bigger people have less surface-to-mass ratio so they cool slower, and thereby need less thermal protection. Female divers tend to chill faster than males. Divers with low metabolic rates and older divers also tend to chill faster. The colder the water, the more insulation you will need to control the heat loss.

The important thing to remember is that each individual has separate, distinct thermal needs. Two divers of the same size and sex may require different amounts of insulation. This difference may be as much as three times what the other person must wear to be comfortable.

Even the same diver will require different amounts of insulation depending upon his activity in the water. There’s a big difference in the heat production created by strenuous wreck diving and casual underwater photography.

Being warm is not a comfort issue — it is a safety issue. Today we know that running out of heat is just as deadly as running out of air.

Principles of Operations of Wetsuits

Wetsuits are made to cover your body with foam neoprene. The water enters the suit and the diver gets wet. Your body heats the water that enters the suit. The air bubbles in the rubber insulates the water and keeps it warm just like a thermos keeps your coffee hot. The proper fit of a wetsuit is critical to minimize water circulation within the suit. Water circulation draws heat energy away from the diver’s body.

What Can You Do To Improve the Efficiency of Your Wetsuit?

A hood attached jacket is recommended to help eliminate water flow coming in around the neck. Any wetsuit that is open at the top, despite how the hood is flanged, allows water to enter between the jacket and suit body. That water circulation, no matter how small, will drain heat from the diver’s body.

Any zippers in the suit allow water circulation unless they are totally waterproof. The use of “skin in”, or smooth neoprene inside, rather than a nylon lining, will eliminate the wicking that naturally occurs through nylon linings.

What Can You Do Prior to Your Dive to Reduce Heat Loss?

Before you dive, avoid drinking anything with caffeine in it, or smoking. Both of these actions cause a shut down of the blood vessels in the extremities, reducing blood flow and making you colder sooner.

Alcohol increases your blood flow to your skin. It is a depressant and will ultimately increase your heat loss.

Prior to the dive you want to keep warm. Make sure you have had good quality food and lots of rest prior to the dive. Your body should be properly fueled with fluids.

Avoid heavy meals just prior to diving and have a diet high in carbohydrates. It’s always wise to do some good stretching and warm-up exercises prior to the dive to get the heart moving in anticipation of the exercise rate.

Overheating prior to the dive causes sweating and disrupts your fluid balance. Overheating also diminishes the body’s capability to produce heat during the dive. It hastens the onset of hypothermia (reduced body temperature) once the diver enters the water.

How to Reduce Heat Loss Between Dives and on Subsequent Dives

If your suit is wet on the outside, stay out of the wind to avoid cooling from evaporation. Cover yourself with a large plastic bag with a hole cut for the head and arms. This helps keep the wind from evaporating the water on the outside of your suit during your transit to and from the next dive site.

On your second and third dives preheat your suit in a hot water shower before you put it on to reduce body heat loss. Start the dive by putting warm water inside your suit, eliminating that first cold shock.

During your dive, avoid urinating in your wetsuit. Although it feels good, it will cause your body to open up your blood vessels in the groin region. This brings warm blood up to reheat cold tissues. The area soon cools off and you end up with a greater net heat loss.

The best way to rewarm is to get out of your wetsuit, dry yourself off and put clothes back on. If warm water is available such as from a shower or the cooling system of an engine, it’s acceptable to use it for rewarming.

The Limitations of Wetsuits

Wetsuit technology is a good reliable technology, but it has its limitations. Do not expect it to do what it cannot. Wetsuits can’t keep you warm at depth. Remember, the wetsuit’s ability to keep you warm is more controlled by the water depth than by the water temperature.

What About Dry Suits?

A dry suit is a waterproof shell, the sole purpose of which is to keep the diver dry. It does not keep the diver warm. It is the insulation that is worn under the dry suit that keeps the diver warm. The primary advantage of a dry suit from this perspective is that it allows you to vary your insulation with the needs of the dive.

There are many factors that will affect the selection of insulation to be worn under your dry suit. These include your exercise rate, your body size and type, and the water temperature. The colder the water or the less you exercise, the more insulation you will need.

How insulation is applied is critical to its effectiveness. Your insulation must be equal to the demands of the dive. It’s important to adjust the system to meet your needs and to choose insulators that are highly efficient. Some are much more efficient than others. It is also important that the underwear be loose enough to achieve maximum freedom of movement.

You need to develop an insulation strategy. You want to maintain thermal equilibrium so you are neither too hot nor too cold. These goals can be achieved by layering your insulation. You can use up to three layers of insulation of varying thicknesses. If this is not enough, don’t add a fourth layer but make one of the layers thicker.

Most people don’t need more than four undergarments to choose from to achieve their desired level of insulation for diving. You can probably use some of the garments you already own from other outdoor activities. Your insulation should include the use of a polyester or polypropylene expeditionary underwear or non-absorbing liner. You might also want to own a heavy vest and a primary set of underwear. For very cold water (under 10 degrees C), or for less strenuous activities, you may want an even heavier set of primary underwear. You now have many combinations from which to choose.

In the warmest of waters, the synthetic liners may be all that you need. As your insulation needs increase, use the liner plus the vest. As the water cools down, you may only use your primary underwear. In colder water, use your primary underwear plus the vest. In the coldest waters, you will want to use the liner, your primary underwear, and the vest. Using this strategy, each person will switch their combinations at different temperatures.

The temperatures at which the individual will change combinations will depend on their being “warm blooded” or “cold blooded”, and their anticipated exercise rate. Trial and error is the best way to work out your personal temperature reference points. Keep in mind too that as you change your underwear, you will need to change your weights. The more insulation you wear, the more weights you will need to wear.

What Can You Do to be Warmer in the Water in Your Dry Suit?

The best insurance to being warm in the water is to maintain your dry suit properly. Make sure your suit is in good repair and doesn’t have any punctures or gouges.

Make sure your dry suit zipper is well lubricated and the valves are clean. A clean, well-lubricated zipper won’t leak, nor will clean valves. Make sure the seals are in good condition and not deteriorating. Be sure they are adjusted for the proper size of your wrist and neck. They should be tight enough to keep the water out, but loose enough to allow blood circulation to be high.

Prior to the dive you should know the water temperature and your expected activity so you can choose the proper kind of insulation. It is helpful to record water temperatures, exercise rate, insulation used and the amount of lead required to neutralize buoyancy in your logbook for future reference.

Remember that the insulation combination you choose will be the major determining factor in how much weight you will require. If you want to wear less weight choose efficient insulation material.

Keep your underwear dry prior to the dive, particularly the boots if the decks are wet. Check to see that your seals are adjusted properly and make sure the zipper is totally closed. A zipper left slightly open is the most common cause of leaks in dry suits.

During the dive you can control your thermal insulation in several ways. If you expect a high exercise rate at the beginning of the dive, you can create a squeeze in your suit during descent and never quite equalize it once you reach the bottom. This will reduce the insulation of your dry suit system.

You can also modify the gas you use to equalize pressure in your suit to help control your warmth. There are some divers who use air in their suits only during the descent and working part of the dive. When they come to their decompression obligation, if it’s a long one, they purge their suits of air and fill them with argon.

Argon is a more efficient insulator than air. Divers who use argon in their dry suits carry a special small cylinder for this purpose. This can increase the insulation capacity of your undergarments by as much as 25 percent.

Underwater photographers may choose to use argon in their dry suits throughout their dives. The best procedure is to inflate the suit with argon prior to the dive from a spare bottle. Allow the argon to mix with the air, purge all the gas mixture out of the suit, then refill and vent three times prior to the dive. As long as you don’t break the seal prior to the dive, you will have close to pure argon in your suit, and maximum warmth.

During the dive, fluid control by the diver is highly important. You want to maintain good hydration. Underwater, due to weightlessness, there’s a natural desire to urinate. There are urination elimination systems which are somewhat complex or you can simply use adult diapers for long duration dives. The adult diapers are usually good for two ventings which will cover the requirements of almost any recreational diver.

Keeping your hands warm is very important. You will find that the use of mitts will always be warmer than gloves. Likewise, the use of dry gloves or mitts will be warmer than wetsuit mitts or gloves.

Wrist rings provide a special sealing system between your dry glove and your dry suit. They lock together to form a watertight seal. The use of wrist rings with your dry gloves will be warmer than using the standard cone latex seals found on some dry gloves and mittens.

After Diving With Your Dry Suit

Even in a dry suit, you want to be sure to stay out of the wind after your dive. One way to add insulation after diving is to put additional air in your suit.

It is as important to keep yourself warm after the dive as it is before the dive, because this will affect decompression. You want to restore blood circulation to its maximum potential as soon as possible after you have exited the water. The placement of a dry suit necklace in the neck seal can be used to take the pressure of the neck seal off the neck. This is an inexpensive ring that relieves the pressure on the neck seal.

If you are cold and want to rewarm, drink warm fluids such as soup and hot cocoa. Again, avoid alcohol for all the obvious reasons.

Between dives keep your underwear dry. Dry out the condensation that has occurred in your suit after each dive.

Most good quality underwear can be wrung out if it gets wet and put back on if necessary. Even though it will feel cold when you first put it back on, once the moisture inside the underwear becomes warm it will still trap a great deal of air. Good quality damp underwear will still be reasonably effective.

Get the Most Out of Your Diving!

Whether you dive with a wetsuit or a dry suit, you can increase your diving safety and pleasure by following these simple tips. Given what we know about keeping divers warm, there is no reason why anyone should not dive in complete comfort. If you get cold on your next dive it’s because you want to be, not because you have to be.