Reprinted from the ACJ - November, 2000
Oh, the weather outside is frightful...or not. And the fire is so delightful...or not. We write these articles a month or so in advance so it's hard to foresee what weather you are dealing with as you read this article. But, it is November so I'm taking a guess. If El Nino, or La Nina, or Nina Cherry haven't screwed up our weather it's getting cold outside and we are looking for a place to hibernate. As the temperatures drop the threat of `Cold Stress' increases. Granted the P.R. department for cold stress has taken a back seat to the Heat Stroke folks, but yes cold stress and cold stroke, a.k.a. Hypothermia, are a valid concern during the winter months.
Low temps, wind chill, and evaporative cooling all contribute to the lowering of our body temperatures, possibly to a dangerous level, a condition known as Hypothermia. Low air temperature effects are easy to understand. But what is evaporative chill? Here's an easy experiment. Squirt a little rubbing alcohol on the back of your hand and blow on it. Feels cold, right? OK now go wash the hazardous material off of your hands. As you are doing so, picture the same effect but; you are out in the parking lot, it's 10 F out there, the wind is blowing at 20 mph and you just missed the carburetor, coating your hands with `starting fluid'. In that situation the evaporation of the fluid can rob your skin of enough heat to freeze it, viola, evaporative cooling. We have all heard of wind chill, that is just evaporative cooling using the water in our skin rather than some mis-sprayed solvent.
Low temperatures and evaporation can lower your skin temperature to the point of pain, this is `frost nip'. Keep going and the skin can die or the flesh and nerves below the skin can be injured, `frost bite'. Your hands and feet are the first to tell you it's cold but the real danger lies in the lowering of our body's internal temperature. This is known as Hypothermia. Hypothermia progresses in stages. If we recognize the symptoms, we can protect ourselves from freezing to death.
99.6 F - Normal rectal temperature
98.6 - Normal oral temperature
96.8 - Body metabolic rate increases
95.0 - Maximum shivering
91.4 - Hypothermia threshold
88.0 - Consciousness cloudy, low blood pressure, shivering stops
85.0 - Loss of consciousness
80.6 - Voluntary motion ceases
75.6 - Pulmonary edema ( lungs fill with fluid)
68.0 - Cardiac Standstill
64.4 - Lowest `accidental' hypothermia survivor
48.2 - Lowest ` induced' hypothermia survivor (who volunteered?)
40.0 - Ideal temperature to serve dark beer.
27.5 - Temperature outside today...or not
In light of this information our objective is; to keep our beer below 41 F, and our `Core' body temperature above 96.8 F. Thus keeping us 100 % alert and rational. `Core' body temperature is indicated by a rectal temperature measurement. My opinion is that if a shop guy allows you to take his `Core' temperature he is less than 100 % alert and rational already. To keep us warm enough we should provide full body insulation if working in conditions below 40 F (including the wind chill factor). That's not likely in the shop but it is as you are trying to raise a pickup truck from the dead out in the parking lot. If shivering becomes constant we are already too cold. Move inside until the shivering subsides. Watch out for someone sneaking up behind you with a thermometer. Older folks and those with circulation problems are at increased risk.
OK, so our `Core' is warm but our ears and fingers are freezing. Here are some guidelines for protecting our extremities. If working below 40 F you must wear gloves. If working below 60 F for more than 20 minutes you may need to warm up to keep full dexterity. Do your best to keep your hands, feet, gloves, and clothing dry. If wet your adjusted temperature will be much lower - evaporative cooling. Having spent 10 years as an auto mechanic in Wisconsin these guidelines seem a little `weenie', but that is what the Industrial Hygienists recommend. Now let's talk reality. You are in danger of immediate injury if you are working continuously below 25.6 F, or if you are wet, or sweaty, and it's less than 35.6 F. Tool handles will freeze your skin if below 30.2 F and can cause immediate frostbite if below 19.4 F. A fact not found in the literature but personally tested, never touch your tongue to a metal object below 32 F, Nuff Thaid. Remember to drink plenty of fluids. Dehydration increases in cold dry weather and adds to the Hypothermia risk.
In summary, if you can't stop shivering get inside and warm up. If your hands or feet are beyond tingling cold and moving toward numb, get them warm immediately. And if you like cold beer, drink it, don't hold it. Now that we know...Let it snow, let it snow, let it snow...or not.
The above article was written by David M. Brown, Chief Engineer of Johnson Manufacturing Company, Inc. and is published by JOHNSON with the expressed approval of the National Automotive Radiator Service Association and the Automotive Cooling Journal. Other reproduction or distribution of this information is forbidden without the written consent of JOHNSON and NARSA/ACJ. All rights reserved.
JOHNSON MANUFACTURING COMPANY
114 Lost Grove Road / PO Box 96 / Princeton, Iowa 52768-0096
Phone 563-289-5123 or Fax 563-289-3825