22 replies to this topic

[Dive_Girl]

As many others above have noted, you will over your dives lose body heat, unless you are diving in 98.7 degree F, , or your exact body temp, water.

A common misconception. Water temps higher than skin temperature (93° F) will cause you to overheat with no thermal protection.

I disagree. I dove in Homestead Crater in constant 93° F water (top to bottom as it is a spring fed crater). I certainly did not overheat. And discussing water 93° F is sort of moot point to me as it is not a constant or readily available diving environment for most people, nor the specific topic here.
[editorial note, the topic the body heat loss comment was made in connection with was in regards to a topic about wetsuits for diving in FL and the Bahamas. Click here for that dicsussion]

Water temps in the upper 80s/low 90s will draw heat away from your body, but so slowly that unless you are spending many hours in the water, thermal protection will not be necessary. Admittedly, areas with water temps this high are pretty rare.

Splitting hairs here is unproductive to me. I stand behind my comment that people will lose body heat - regardless of the rate, body heat loss occurs when diving in water temps less than your body temp. I also note that while some waters may hold high temps, those temps, typically drop as you get deeper. After repeated dives, I tend to exit the water shivering.

You can dive without a wetsuit. I dive one for several exposure reasons. While I respect your opinion, it is not for you to tell me my thermal protection will not be necessary.

[finGrabber]

As many others above have noted, you will over your dives lose body heat, unless you are diving in 98.7 degree F,

A common misconception. Water temps higher than skin temperature (93° F) will cause you to overheat with no thermal protection. Water temps in the upper 80s/low 90s will draw heat away from your body, but so slowly that unless you are spending many hours in the water, thermal protection will not be necessary. Admittedly, areas with water temps this high are pretty rare.

Walter,

do you have any reference for this:

Water temps higher than skin temperature (93° F) will cause you to overheat with no thermal protection.

I've always heard anything under 98.7 degrees cools your body


I can also tell you from our Turks and Caicos trip, I was diving a 5mil all week and added another 1mm under it for the last 2 days of diving because I was getting cold. I suspect part of the equation is the climate you live in as well. I was getting chilled in 80 degree water but our California divers and NY divers weren't. Since my body is acclimated to 100 degree heat then I would have a more difficult time diving cool/cold water

[Dive_Girl]

Found this on Hypothermia from the book Diving Science by Michael Strauss, MD and Igor Aksenov, MD, PhD:

"Hypothermia is a lowering of body temperature. Unless water temperatures are near the core temperature, immersion initiates feedback mechanisms. Initially, these are positive if the water temperature is moderately warm (78-85 degrees F/25-29 degrees C) as the swimmer or diver “adjusts” to the water temperature. This usually occurs through a combination of metabolic heat production (increased activity such as swimming), warming the trapped water in the wet suit if one is being worn, and stabilizing of the skin temperature-sensing structures to the water temperature. Chilling denotes the perception of discomfort as the body’s heat-conserving mechanisms no longer meet the demands of the cold. When positive feedback mechanisms, primarily metabolic heat production, are exceeded, negative feedback mechanisms lead to progressive lowering of the core temperature. Responses occur in a continuum to the endpoint at which the stimulus to breathe is lost. At this point, metabolic heat production ceases; the core temperature approaches that of the surrounding water."

"Almost all diving and other water-related activities are conducted in water temperatures less than the core temperature. With minimal activity, the diver is usually comfortable in water warmer than 82 degrees F (28 degrees C). Diving in water with temperatures below this level usually requires thermal protection suits. Diving at deep depths also contributes to hypothermia because of the loss of effectiveness of the wet suit from compression of its air cells, layering of cold water (thermoclines), and insensible heat loss from ventilation at increased pressures."

Michael B. Strauss, MD, is medical director of the department of hyperbaric medicine at Long Beach Memorial Medical Center in Long Beach, California. An experienced diver, he is familiar with almost all types of equipment, from snorkel to closed-circuit scuba to tethered diving out of a personal transfer capsule.

Igor V. Aksenov, MD, PhD, works in the department of medicine at the University of Florida at Gainesville. Dr. Aksenov has a diverse background in medicine, including internal, critical care, clinical toxicology and pharmacology, and hyberbaric and diving.

Interesting stuff! I like it when topics come up that interest me to learn more and then I find good books to add to my diving library!

[BubbleBoy]

Wow, this sounds like a HEATED topic Something I can't resist.

Though I don't have much to add from diving experience, I do know the following relevant facts from my general reading and engineering training, which may help to enlighten this debate.

1) Your body is always generating thermal energy. This energy must be dissipated into your environment if you are to survive. The three thermal processes that facilitate most of the heat removal are conduction, convection, and evaporation (sweating). You can not have heat flowing into your body from the environment for any significant period of time or you will quickly die.

2) When you feel cold or warm, it is not so much the ambient temperature you are sensing as the rate of heat loss from your body. When the heat loss rate is high you feel cold. When the heat loss rate is low you feel warm, or even hot.

3) The temperature difference between your body and its environment does contribute to heat loss, but it is not the only factor. The thermal resistance between you and your environment is the other big factor. Water has lower thermal resistance than air, so heat flows away from your body into water much faster than air. That is why you feel much colder in 70 degree water than in 70 degree air. Wetsuits have a high resistance to heat transfer, which is why we wear them, to reduce the heat transfer rate for any given temperature difference. The other big factor contributing to thermal resistance is convection (see 4)

4) Convective heat transfer (caused by either moving through the environment or the environment moving around us) is much higher than conductive heat transfer. We always feel colder when the wind is blowing than when the surrounding air is still. Similarly, our heat loss and sense of being cold in a moving water environment, i.e., rivers, waves and currents will always be greater than in still water of the same temperature.

3) In addition to temperature difference, motion, and thermal resistance of your surroundings, heat loss is a function of the rate at which your body is burning energy. When you are highly active, your body is generating more heat. It becomes harder for so much heat to be disipated into the environment. At some point, the only way for the heat transfer rate to keep up is for your body temperature to rise, thus increasing the temperature difference between the heat source and sink.

Good divers learn to expend as little energy as possible, in order to conserve breathing gas. They are less susceptible to overheating, and more susceptible to chills because they aren't generating as much heat to be removed.

4) Heat transfer occurs accross surface boundaries. Therefore, another significant factor in heat transfer and heat loss is the surface area between the heat source and the surroundings. An object with a large surface area dissipates heat into its environment faster. It is less likely to overheat and more likely to chill.

It is a physiological fact that a normal weight woman has more surface area than a man of the same normal weight. I got this from a medical journal, not Playboy. It is no surprise then that women tend to feel colder than men in many environments, because on average they lose heat to their environment faster than men do.

[drbill]

You all are full of such puffery that I can't believe I'm reading this. A truly "hot body" will not lose any of her heat regardless of water temperature... unless she begins to shrivel up like a prune!

[Starfish Sandy]

Dr Bill - your really bring a smile to my face some days!

[Walter]

Walter,

do you have any reference for this:

Water temps higher than skin temperature (93° F) will cause you to overheat with no thermal protection.

I've always heard anything under 98.7 degrees cools your body


I can also tell you from our Turks and Caicos trip, I was diving a 5mil all week and added another 1mm under it for the last 2 days of diving because I was getting cold. I suspect part of the equation is the climate you live in as well. I was getting chilled in 80 degree water but our California divers and NY divers weren't. Since my body is acclimated to 100 degree heat then I would have a more difficult time diving cool/cold water

I've heard it too, but that doesn't make it so. Our bodies produce heat. We have to release heat to keep from overheating. Sit calmly when the air temperature is 98.6° F. You will overheat. That is dangerous as it results in heat exhaustion and if we don't do something to cool off, heat stroke. OTOH, if we release too much heat, our body temperature will drop resulting in hypothermia. That is also very dangerous and something we need to avoid. You only lose heat if the surrounding environment is cooler than skin temperature. If you're in water, you'll lose heat 24 times faster than if you're in air, but in either case, you will lose heat if the surrounding temperature is cooler than your skin and gain heat if the surrounding temperature is warmer than your skin.

Actually, it looks like I was wrong, skin temperature is 91°F, not 93.

Kim, there is a very big difference between 80° and 91 or 93°. At 80°, I'm comfortable, but only for a limited amount of exposure. If I'm going to be in 80° water for long, I'll put on a wet suit.

From The Physics Factbook™
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website]

The skin is the largest organ in the human body. It protects the body from the sun's rays. It also keeps body temperature normal (37 °C).

Skin temperature depends on air temperature and time spent in that environment. Such weather factors as wind chill and humidity cause changes in skin temperature. The normal temperature of skin is about 33 °C or 91 °F. The flow of energy to and from the skin determines our sense of hot and cold. Heat flows from higher to lower temperature, so the human skin will not drop below that of surrounding air, regardless of wind. If a person was to be in a warm room and her skin temperature was cooler than the air, her skin temperature would rise. The opposite would happen in a cold room and warm skin temperature. The person's temperature would decrease. Humans fight air temperature by becoming warm or cold. When warm, they sweat. When cold, they get chills.

On a trip during a windy and snowy day, a man recorded his skin and body temperature while climbing a mountain. The skin temperature of his toe was about 15 °C. At the same time, the temperature of his chest was 32 °C. This shows that different parts of the body have different skin temperatures.

[Dive_Girl]

Humans fight air temperature by becoming warm or cold. When warm, they sweat. When cold, they get chills.

Concerned that the discussion of body heat loss differs in rate and such from air to water, I posted information regarding body heat loss from a source looking at the issue within a diving context.

[BubbleBoy]

.....A truly "hot body" will not lose any of her heat regardless of water temperature...

Like I've said in other threads, some people just won't admit that they pee in their wetsuit to keep warm

[ScubaDadMiami]

"The temperature range at which heat loss and heat production are approximately equal is . . . 91.4 to 95 [degrees Farenheit]." A. Bove and J. Davis, Diving Medicine (2d ed.), p. 96. "As a general rule, water temperatures of . . . more than 35C[/95F] may lead to hyperthermia." C. Edmonds, C. Lowry and J. Pennefather, Diving and Subaquatic Medicine (3d ed 1992), p. 298.

Edited by ScubaDadMiami, 24 May 2006 - 08:25 PM.

[drbill]

Like I've said in other threads, some people just won't admit that they pee in their wetsuit to keep warm

I readily admit to that fact! Actually I didn't realize you could dive without doing it until I went a record 13 straight dives "dry." Amazing.

Starfish Sandy... glad I could bring a smile to your face. I like doing that to people (and am known to do it to myself almost daily).

[Cairo]

I'm a boardshorts and rashguard (short sleeve) kind of guy. I never use my wet suit anymore at least not in Hawaii.

[Walter]

Humans fight air temperature by becoming warm or cold. When warm, they sweat. When cold, they get chills.

Concerned that the discussion of body heat loss differs in rate and such from air to water, I posted information regarding body heat loss from a source looking at the issue within a diving context.

First, you are crediting me with something I did not write. The quote you used is From The Physics Factbook™ Edited by Glenn Elert -- Written by his students.

Next, there are two differences with regard to heat in water vs air. The first is the rate. Heat is conducted 24 times faster by water than by air. Heat transfers in either from the warmer to the cooler and does not transfer when temperatures match. The second is when a body overheats, it uses evaporation to cool when in air, this is not an option in water. If you are overheated in water and that water is not cooling you, you need to exit the water ASAP. As previously stated, water that warm is unusual, but it does occur in the Gulf of Mexico in late summer.

[Walter]

"The temperature range at which heat loss and heat production are approximately equal is . . . 91.4 to 95 [degrees Farenheit]." A. Bove and J. Davis, Diving Medicine (2d ed.), p. 96. "As a general rule, water temperatures of . . . more than 35C[/95F] may lead to hyperthermia." C. Edmonds, C. Lowry and J. Pennefather, Diving and Subaquatic Medicine (3d ed 1992), p. 298.

Thanks Howard, that's an excellent reference.

[Diverbrian]

As was pointed out, it is rare to be diving in 95 degree water. I know that I have never done so. I normally dive water in the 35 to 45 degree range and the few times that I go to warm water I might see water as high as 85 degrees. And yep, I get cold doing two one hour dives a day after the second day in that kind of water. That is wearing a 3mm wetsuit and hooded vest.

I also will note that from a practical standpoint, Dick Long (the founder of DUI) addressed the topic of needing to regulate his hot water suits (which he tested with people sitting in an ice bath of thirty-eight degree water) as the divers would accidently overheat themselves on many occassions if they controlled the water temp going into their warm water suits. He compared it to standing in the shower and getting used to the water temp. So, you turn up the water temp because that warm water felt good before. So, yes divers can get too warm and not quite realize it.

But, he was also the first to admit that he didn't start DUI because he was smarter than anyone else. He just got colder than anyone else and was trying to design suits that allowed him to dive all of the time with that metabolism.