*** Hot Packs for SAR Use *** Date: Tue, 17 Feb 1998 10:05:12 From: "Keith Conover, M.D., FACEP" Subject: Hot Packs Just recently been playing around with hot packs, in particular, the powdered-iron oxidation type. They have advantages over the heat-of-crystallization reusable type, and the heat-of-dissolution type: 1. They last a lot longer ("up to 15 hours" but it seems more like about 4 hours of useful heat to my trials) 2. If they leak, it's not as messy (they use a powder rather than a sticky liquid) 3. They are a lot lighter. 4. They can be "postponed" by sealing them back in a ziplock bag to keep oxygen away from them However, there are some disadvantages, mostly that they really don't put out that much heat compared to the other types. Nonetheless, they put out heat for a much longer period, and thus may be more suitable for long wilderness/cave rescue operations. I had tried the "HotHands" version by HeatMax, which I got for a couple of dollars for a package of three at WalMart. They are about 3"x5" and weigh 2 oz. each. They provide some significant heat for about 4 hours, but I think it would take two of them together to provide enough heat to be satisfactory for SAR use -- so you'd need twelve of them for a patient, two in each of the standard six areas (lateral neck both sides, axilla both sides, and groin both sides). So I thought I'd try the larger units that HeatMax offers -- called Survival Heat. (BTW all these heat packs seem to be cheaper when ordered in bulk from HeatMax than even from WalMart based on the cost I'd seen previously posted on one of the lists for the big ones ($6 each), I got 12 of the big ones for $45 + 4.06 shipping). Suprisingly, the package for the larger packs seemed much less dense. A different kind of pack maybe? I opened one up, and found that it had a ripstop paper envelope inside. But unlike the paper envelopes of the HotHands that were just full of powder, this envelope had different things inside. I ripped it open, and found that inside are two 4"x6" 3 oz. "HotHands" envelopes full of powder, stapled to a 7"x10" piece of bubble wrap. Both the inner and outer envelopes have a notice "this side next to body" to ensure the bubble-wrap insulation is away from the body. The 4x6" 3 oz. envelopes seem to get a lot hotter than the 3"x5" 2 oz. envelopes -- maybe this is a function of the amount of powder, or the holes created by the staples allowing more oxygen into them, or a different composition, or some combination -- not sure. For SAR use, there is no point in carrying bubble wrap -- you're going to carry better insulation to put around the patient, and the heat packs will be inside the insulation you provide, so the bubble wrap is just wasted space in your pack. BTW, they have a model that is FDA-approved for medical patient use -- and that costs more. I told them to bill them to me as a mountain rescue team member rather than as a doctor and send me the non-approved ones that were cheaper and they were happy to do this. (What does the FDA know about SAR anyway?) I called Heatmax this morning, and they referred me to their chemist, Uma. She explained that the different hot packs that they manufacture have slightly different compositions, based on their expected uses. For example, the tiny ones designed to put in your boots are designed to work in a relatively anaerobic (oxygen-free) environment inside a boot. If they are activated in "regular" air, they will get much hotter and not last as long. The "HotHands" ones to stick in your pocket are designed to last for quite a while in a "regular" oxygen environment. But the ones in the big Survival Heat are designed specifically to work while in the larger, somewhat air-permeable envelope, and with the bubble side of the bubble-wrap against them to provide uniform oxygen access to the mix. She said she'd send me some more detailed information on the packs. I was thinking that the bigger Survival Heat models might be best for SAR use, but the bubble wrap makes them pretty bulky, and they'd be difficult to pack into someone's groin and axilla in a litter. So I tried an experiment -- I opened a Survival Heat hotpack, and then ripped open the inner envelope and left the two actual inner 3 oz. packs out in "regular" oxygen to see what happened. They got much hotter than the individual "HotHands" 2 oz. packs, enough to cause a mild burn if held right against the skin (not that one would want to do this with any heat pack) and the heat lasted for about 4 hours, not the "up to 15" that is standard when used inside the outer envelope. I suspect that in the relatively-anaerobic environment of a litter and packaging they'd last about 6 hours and be just right for amount of warmth provided during that time, but haven't tested this yet (coming up soon). Is anyone aware of detailed studies of various hot packs for SAR use? BTW the company is: Heatmax Inc. POB 119 Dalton, GA 30722 1-800-432-8629 --Keith Conover, M.D., FACEP http://www.pitt.edu/~kconover