Frostbite … ?

It was a chilly one this morning. The grass was crackling under my feet and the puddles were frozen as I got the bikes out of the garage.

Readers from elsewhere in the world may have the notion that Australia is a land of never ending sunshine and warmth. Not so. South-east Australia even has some ski resorts. The Victorian goldfields are on the inland side of the Great Dividing Range away from the moderating influence of the sea. We have some knockout frosts. The last couple of mornings -2° C.

Having said that, though, it’s the cloudless nights that produce the lowest temperatures. Cloud cover helps to hold the warmth in. Snow (below 1000) meters is therefore unusual.

Plugging away at 25 kph into a 5 km headwind made the fingers numb after a while. I haven’t solved the problem of the appropriate gloves yet – I’m on to my third pair presently. Do avoid neoprene it doesn’t keep out the cold but sure does a good job of keeping in the sweat. Anyway, the mind turned to consideration of frostbite. Is the wind that is generated by the forward motion of the bike sufficient to turn an uncomfortable experience into a dangerous one?

Once home again and thawed out I consulted the internet. I found a couple of windchill calculators that talk metric after a fashion. One at calculator.net can be persuaded to accept metric input. It then calculates a metric answer and also a Fahrenheit answer which you can look up in a nice graphic.

Another at  romseyaustralia.com is very informative but having got your answer you consult a table to discover the likely outcome for your fingers and toes which is not quite as intuitive as the graphic. It was at this site that I learnt …

Twelve volunteers (six men and six women) participated in the clinical trials. These consisted in four walks, at 4.8 km/h, on a treadmill in a refrigerated wind tunnel at the Defence and Civil Institute of Environmental Medicine in Toronto, Canada: one walk at each of -10, 0 and +10 deg C, plus a “wet trial” at +10 deg C during which participants received, every 15 seconds, a light one-second splash of water in their faces. During each 90-minute walk, the volunteers were walking while facing a wind of 2 metres per second (m/s) for 30 minutes, followed by 30 minutes at 5 m/s, and 30 minutes at 8 m/s (or about 4, 10 and 16 mph, respectively). Sensors were fixed to participants’ forehead, cheeks, chin and nose, as well as to the inside of one cheek, to measure skin temperature and heat loss. The results from these trials were used to determine the various thresholds for frostbite, as seen on the new wind chill chart.

The new wind chill equation is now in use in both Canada and the United States. Therefore, there is now a consistent wind chill formula across North America.

Where would we be without volunteers?

Should you distrust the calculator and prefer to compute your own here’s the formula …

Twind_chill = 13.12 + 0.6215*T – 11.37*(v0.16) + 0.3965*T*(v0.16)

If you were surprised to discover that Australia has ski resorts you probably won’t be surprised to discover that my fingers and toes were in no danger whatever. At -2° C. the wind would be uprooting trees before it caused sufficient chilling to freeze my extremities. Hypothermia, though, is another issue.

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