How long does it take to get Frostbite?

How long does it take to get frostbite? Sounds like an easy question but I find many different answers on the Internet (including one tough old New Englander who answers, "never", with proper clothing). Part of the confusion lies in the definition of "Wind Chill". See http://perpetualpreparedness.blogspot.com/2010/01/wind-chill.html for details. There have been two changes.

1st:  In Nov. 2001 the wind chill values were changed based upon a new equations, see http://www.crh.noaa.gov/ddc/?n=windchill. Whereas 15°F used to be extreme cold in 20mph wind, now it's "safe" at all wind speeds and never drops below -11 wind chill.

2nd: Some revised charts appear to use the new wind chill values but kept the color bands the same for exposure times. See this NOAA chart from 2010 which still has 15°F freezing within 5 minutes with strong wind. http://www.srh.noaa.gov/jetstream//global/chill.htm

A new NOAA chart from 2011 (pictured above) updates the color zones. http://antarcticfudgesicles.wordpress.com/afsa-student-page/how-long-does-it-take-to-get-frostbite/ The exposure time colors don't exactly match the wind chill numbers anymore (for instance -40 wind chill is in two different color zones).
Wind chill of -20°F to -35°F (approx) Frostbite in 30 minutes for exposed face, at night.
Wind chill of -35°F to -50°F (approx) Frostbite in 10 minutes.

There used to be a -30-30-30 rule that -30°F with a 30 mph wind could freeze skin solid in 30 seconds. Under the new chart it's -30 & 30mph & 5 minutes for frostbite.

Bottom Line
So what happened to the NOAA charts? During the fall of 2000, the Office of the Federal Coordinator for Meteorological Services and Supporting Research (OFCM) organized a joint U.S.–Canadian government-sponsored action group to develop, test and implement a new Wind Chill Temperature Index. Human trials were done in Toronto, Canada with 12 volunteers in chilled wind tunnels with thermal transducers stuck to their face while walking on a 3mph treadmill. Brrrrr.

So the new chart is based on solid human evidence of facial skin instead of mathematical modes and time to freeze bottles of water.  See http://www.nws.noaa.gov/om/windchill/images/wind-chill-brochure.pdf for more information.

Treating Frostbite

I'm dreaming of a white Christmas
Just like the ones I used to know
-White Christmas by Irving Berlin

While we may have wished for a White Christmas, too much exposure to cold and snow can be dangerous. Your body is 60% water and the water in your skin can freeze to ice. This is called frostbite.

Think about water in a ice cube tray. When it freezes, the ice cubes are larger than the water poured in. (The expansion of ice is why ice floats in water.) When ice crystals form in skin or muscle cells the ice expansion and sharp icy prongs bursts the cells and kills them. If the damage is small, it may be painful, but recoverable. However extensive freezing and cell death may result in gangrene and the loss of fingers, toes, ears, nose, etc.

Frostbite usually develops below -12°C (10°F), but may occur at a temperatures near freezing (0°C/32°F) when high winds and/or dampness chills the body faster than your blood can keep it warm. Hands, feet, noses, and ears are the most likely body parts to be affected.

Avoid frostbite by staying out of extreme cold. If you must go out (or become lost, stranded in extreme cold) cover all extremities - winter boots for the feet, gloves for the hands, a hat or earmuffs for the the ears and a mask or scarf for the face. Mittens are more effective than gloves for warming your hands since the fingers can share body heat instead of isolated on their own. Avoid caffeinated beverages (like coffee) as they constrict blood vessels and prevent warming of your extremities. Alcohol should also be avoided since it reduces shivering, which is one way of keeping warm. Cigarette smokers may be at higer risk with reduced blood flow to hands and feet.

Wiggle your fingers and toes frequently to increase blood flow to these areas. Keep your feet and hands dry. If you begin to loose feeling in your fingers and toes, or they begin to tingle, or feel painful, go inside and warm up.

Signs and symptoms of frostbite include:

• A "pins and needles" sensation, followed by numbness
• Hard, pale, cold skin

Different Degrees of Frostbite

• First degree: ice crystals forming on top of your skin
• Second degree: your skin begins to feel warm, even though it is not yet defrosted.
• Third degree: your skin turns red, pale, or white.
• Fourth degree: pain lasts for more than a few hours, and you may see dark blue or black areas under the skin. See a doctor immediately if these symptoms arise. Gangrene is a real threat.

Bottom Line

If your skin is blue or gray, very swollen, blistered, or feels hard and numb even under the surface, go to a hospital immediately.  Otherwise get indoors or to a warm shelter ASAP. Take off any constricting jewelry (flesh may expand and rings are sometimes cut off a swollen finger). Take off wet clothing. Never rub or massage frostbitten skin, but do use your armpits or the body heat of a warm companion.

If possible, immerse the affected area of your body in warm -- NOT HOT -- water, or apply warm cloths to affected areas of your ears, nose, or cheeks for 20-30 minutes. Try to move the area of your body that is affected as little as possible to decrease doing additional damage.

You should not use hot water or a heating pad, heat lamp, hair dryer, or the heat from a stove, fireplace, or radiator to warm yourself. This because your frostbitten area may be numb and you won't be able to feel if you're overdoing the heat and burning yourself.

As you warm up your frostbitten skin will become red and swollen, and you'll feel like it's on fire. You may develop blisters. Don't break the blisters. It could cause scarring.