Rule on hot showers after diving

[Superlyte27]

@Akimbo want to weigh in?
I know that as a commercial diver the coldest I've ever been was during a full vent in a chamber after a cold dive in 32 degree water. Soon as we got out of the chamber, we were in the hottest shower we could find.

 

[Aris Penaranda]

Just remember the dive theory about the balloon that was always used as an example. There are 3 ways that the balloon will increase its size:

1. Reduction in the ambient pressure.
2. Increase in the temperature of the gas inside the balloon.
3. Both 1 & 2 are applied.

Of course the change in volume will be proportional to the difference in pressure and/or temperature.
You can estimate the approximate values using the ideal gas law formula. Use absolute values for P and T.

 

[Compressor]

Look at it a bit differently. If you are found in the field on a cold winter day (car accident, discovered 4 hours lat), you are brought to the hospital barely conscious as you are hypothermic. You will be warmed like this:

1. Warm room
2. Warm coverings (blankets)
3. Warm IV fluids

Now the person is not at risk for DCS because there was no dive. But the warming is done aggressively and will take time.

The fastest way to warm someone is to put them on cardiopulmonary bypass and heat them up. Typically someone goes from 20 degrees to 37 in about 20 minutes.

Dan has been saying avoiding DCS after a cold dive for a while by avoiding hot showers and hot tubs. Physiologically it makes sense. Many have ignored the advice and got away with it since we are all different physiologically.

 

[Storker]

Leaving DCS aside, you are contradicting CDC recommendations for hypothermia treatment: Warm the center of the body first—chest, neck, head, and groin—using an electric blanket, if available. You can also use skin-to-skin contact under loose, dry layers of blankets, clothing, towels, or sheets. And warm drinks only come next on their list. So taking a hot shower seems like a substitute for an electric blanket.

Current first aid instructions warn against too rapid warming to treat hypothermia, and recommends that passive warming preferably should be used. Here's an explanation of why:

Active external rewarming is simply the application of heat directly to the skin, and is only effective in the presence of intact circulation that can return peripherally rewarmed blood to the core. Hot water bottles and heating pads (applied to truncal areas only) may cause burns to cold and vasoconstricted skin. [...]

A major complication of active external rewarming is “core temperature afterdrop,” which results when cold peripheral blood rapidly returns to the heart. Historically, this has led to many unwarranted deaths because patients were thought to be getting worse and rewarming was aborted. This complication can be minimized by always using minimally invasive core rewarming before active external rewarming.

(Emphasis mine)

Also:

Cite: LYNNE MCCULLOUGH and SANJAY ARORA, "Diagnosis and Treatment of Hypothermia", Am Fam Physician. 2004 Dec 15;70(12):2325-2332.

I'd be very reluctant to throw a hypothermia victim into a hot bath or a hot shower.

 

[Kharon]

I hear that sort of advice a lot, but I'm skeptical.

So, you're a doctor? I'm pretty sure it's the physicians and not old wives that came up with the idea. I'm not saying biomedical ideas are always right, just that they're more likely to be than gut feelings.

A warm shower probably isn't as bad as wrapping an electric blanket around the entire surface of the body,

Based on what? Never heard to use an electric blanket just a blanket to retain heat - not increase it. Also, water is a far better conductor of heat than air & cloth. Just sayin'.

 

[Akimbo]

@Akimbo want to weigh in?
I know that as a commercial diver the coldest I've ever been was during a full vent in a chamber after a cold dive in 32 degree water. Soon as we got out of the chamber, we were in the hottest shower we could find.

I experienced a little different phenomenon. Most of my work was in the North Sea in the early days of hot water suits. The tables were field tested in warmer water like the Gulf of Mexico, but not like a hot-tub inside the suits. As a result, DCS rates went way up because the divers were toasty on the bottom and during water stops.

My "gut" is saying that a hot shower after Sur-D-O2 (Surface Decompression using Oxygen) runs will have less impact than all in-water decompression. In general you probably have a lower diluent gas load after Sur-D-O2 dives because the practical imperatives to get the diver out of the water is far less and the efficacy removing diluant from tissues is much higher on O2 at 60'/18.3M.

Once we learned to adjust for hot water suits, we had a lot less DCS on Sur-D-O2 dives than all in-water decompression. There just wasn't a big motivation to keep the decompression time short in the chamber. We needed to get divers out before the next dive could start so those tables were still much less conservative. Does this make sense to you?

 

[Storker]

So, you're a doctor? I'm pretty sure it's the physicians and not old wives that came up with the idea. I'm not saying biomedical ideas are always right, just that they're more likely to be than gut feelings.

What @scagrotto is arguing isn't "gut feelings", it's physics. And without having checked their math, it seems rather plausible to me.

Let's do some math. The body is some 70% water, and it isn't unreasonable to assume that the other components have a heat capacity of some 25-50% of the heat capacity of water. Let's assume 25% to be on the conservative side. If a hypothermia victim with a body weight of ~80kg has a body temperature of ~35 degrees C, the amount of heat required to bring their body temperature back to 37 degrees C is (37-35)K·(0.7·80kg·4.19kJ/kg·K + 0.3·80kg·(0.25·4.19)kJ/kg·K) or about 520 kJ. If your soup's temperature is 47 degrees C (the pain threshold for the human tongue) and we assume it's cooled to 37 degrees C in their stomach, they'll need to drink 520kJ/[(47-37)K·4.19kJ/kg·K] or 12kg of soup to heat up their body. Assuming that the soup is basically water.

So, if your body temperature is only 2 degrees C (about 4F) too low and you want to drink hot soup to get it back up, you need to drink more than 10L (about 3 U.S. gallons) of the hottest soup you can take to bring your body temperature back up to normal. Since at least I would probably struggle a mite with that, I suspect the hot soup/drink is more for comfort and psychological effect than for any medical effect.

 

[drbill]

Years ago I used to do up to 7 dives in a day and carried all my gear (SCUBA and video) on a hand cart up my steep hill. I would get in my bathrobe and download the day's video, then begin to edit it before I took my shower. I figured with the physical exertion of walking my gear up the hill, a hot shower right away wasn't a good idea.

 

[CT-Rich]

My two PSI on a subject I am totally unqualified to comment on...When going into decompression, the deco is based on the slowest tissue to off gas (I.e. the least oxygen requiring tissues absorb gasses absorb the slowest and will off gas the slowest). The deco models we follow were created by human experimentation on Navy personnel. There are real limits to how a twenty something seaman is going to react versus a paunchy fifty something. Add in additional factors, like water temperature, depth, breathing mix and a bunch of uncontrolled factors (cardiac health, body fat, circulatory health and suit fit, scar tissue, surgical history, joint replacement etc.) and you have to accept riding the NDL is a bit of a crap shoot. A warm diver will shunt Nitrogen to the periphery much faster than a cold dive. Cold divers off gas much slower than a warm diver. This seem like a perfect description of how to get skin bens to me.

There have been a couple interesting threads recently concerning the use of heated vests during dives and their effect on DCS.

I think my parents would have pulled the plug on my dive career if I had gotten skin bends at 16.

 

[davehicks]

It's my understanding that immersing electric blankets is a very bad idea.

Sorry, couldn't help myself.. I'm bound to get moderated.

My Thermolution heated vest is basically a wet-suit approved Electric Blanket...