Naked Science Forum
Non Life Sciences => Chemistry => Topic started by: somewakko on 24/11/2009 02:55:18
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I often user air-activated hand warmers. One I own is the HotHands product by HeatMax. They have some information on their website, but basically says:
Our HeatMax® family of air activated warmers all contain a mixture of natural ingredients that when exposed to air react together to produce heat. This is accomplished through an extremely fast oxidation (or rusting) process. Ingredients include: iron powder, water, salt, activated charcoal and vermiculite. HeatMax® has perfected the process so that our warmers, depending on the individual product, produce heat anywhere from 100°F to 180°F for duration of 1 to 20+ hours.
I want to try these in a scuba dry suit. The partial pressure will be up to 5 atmospheres absolute. This will raise the partial pressure of O2 above 1.0. But the percentage of oxygen will remain at about 20.9. Will this change the rate of oxidation?
I'm worried that I may get a much hotter (dangerous) reaction when I pressurize them in my dry suit gloves. But discussing combustion with someone led me to remember that combustion depends only on the percentages of oxygen, not the partial pressure. But I'm no chemist, and I'd rather not use my own hands as the test subject.
Will these hand warmers become dangerously hot when pressurized? Or will the rate of oxidation remain constant?
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Quick answer becaue I have a bus to catch.
You are right to worry. Don't try it.
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I'm not sure exactly what would happen if you tried using these things in a dry suit under pressure but I'm sure of one thing. The reaction will depend on the partial pressure of oxygen and if you raise that you will raise the reaction rate. It might not be quite 5 times faster but it will be close. Also there's the possibility that any carbon containing material (including CO2 or charcoal) will be converted to CO which wouldn't be nice.
I know some people who know a bit about dive safety. If I remember I will ask them.
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seal the hole in the dry suit place the thing inside throw it in water and if it explodes dont do it
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seal the hole in the dry suit place the thing inside throw it in water and if it explodes dont do it
Thank you for demonstrating your grasp of the subject.
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I'm not sure exactly what would happen if you tried using these things in a dry suit under pressure but I'm sure of one thing. The reaction will depend on the partial pressure of oxygen and if you raise that you will raise the reaction rate.
Well there are some physical differences between a dry suit and a regular pressurized container. The dry suit has a bubble of air that moves to the highest point. Rarely are our hands the highest point, so the air is generally squeezed away by the outside water. But when we do allow some air to transfer into the gloves, it seems like a safe bet that they'd get hot much faster than on the surface.
The other consideration is how quickly the water will conduct the extra heat away. It's likely we'll need something that is quite a bit hotter underwater than we would on the surface.
The science seems to say that there's a lot of potential for a serious burn. But an aware diver might be able to use these safely. I'll work on some controlled experiments to see what happens.