Sergeant, it’s cold outside! How the Army is revising its wind chill rules
An Army officer invented the chart that forecasters everywhere use to measures wind chill. But it's never been perfect.
How cold is too cold? Army researchers want to find out.
For soldiers in arctic conditions, cold injuries are a constant threat. According to the Army’s Prevention and Management of Cold Weather Injuries manual, keeping a finger on the steel trigger of an M-16 rifle in 14-degree cold can “cause the finger skin temperature to reach 32°F in just 15 seconds.”
Scientists at the Army Research Institute of Environmental Medicine are taking aim at another constant reality of cold operations: the wind chill. Army researchers are looking to update the rules that govern Army training and operations in cold weather environments, according to John W. Castellani, deputy division chief of Thermal & Mountain Medicine Division at the institute.
“Wars are not fought indoors,” Castellani said. “Our soldiers and sailors and marines and all are subjected to the environment and that’s why the military has always been very interested in environmental physiology and looking at how the body responds to extreme environments.”
Most people think they know what “wind chill” is but Castellani and his Army researchers want to add data that specifically examines how soldiers work in cold, windy conditions.
Wind chill is caused by the effect of wind on heat loss from bare human skin. Wind-chill indices, based on temperatures and wind speeds, have long warned people headed into the cold how fast they can develop frostbite with their skin exposed to wind.
But Castellani, who is leading the study, said the National Weather Service’s wind chill chart doesn’t take physical activity into account, which is key for the military.
The current Army advisory for cold weather injuries cites the NWS chart to calculate the risk of frostbite. As that risk goes up, soldiers are required to do more frequent buddy checks, wear specific cold-weather gear, and adjust the time they handle weapons.
Castellani’s work will examine if the Army’s current cold rules should be adjusted.
The Army has long had a primary, if little-known, role in setting wind chill standards, including the official chart used for nearly all daily weather forecasts and relied upon by millions across the U.S. The first widely used version of the wind chill index was invented by Army Maj. Paul Siple, who also helped develop cold weather gear for the U.S. Army.
Today’s NWS chart was developed in 2001 by a group of Canadian and American scientists who wanted a more accurate measurement of wind chill compared to the previous iteration. In November of that year, the military services adopted the new chart, distributed it to bases, and revised relevant guidance and publications.
The new Army study is the first major study to revisit those standards.
The wind chill study is one of many efforts across the service to update policies for troops in the Arctic and cold weather environments as the region becomes more important for strategic competition with Russia and China.
Army Pacific Command has ramped up its cold weather and Arctic training scenarios and service-wide, the Army has begun developing its first Arctic-focused doctrine in more than 50 years. The manual is set to be released this year and will provide information and techniques for handling the Arctic environment and temperatures as low as – 40 degrees Fahrenheit.
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The study
One of the goals of Castellani’s study is to see how physical activity and movement outdoors affect frostbite risk.
“When we think about the military or other people going out and doing things, you start to move and then you get an increase in blood flow to these different regions,” he said. “Well, that’s definitely going to change your risk.”
In Alaska, for example, there aren’t any specific rules that say “No, we can’t go out today,” Castellani said. Instead, they leave it up to the whim of commanders and leadership to make those decisions, he said. The purpose of their study is to develop more refined guidance that considers the risks of training, operating and just being outside in very cold temperatures.
In Alaska, every soldier completes an annual training program referred to as the “Cold Weather Indoctrination Course” which consists of classroom and field instruction on “common core cold weather tasks.” The training is designed to familiarize soldiers with the terrain, weather, uniforms, and equipment for extreme cold weather and high altitude environments, according to Maj. Taylor Lee, commandant for the Northern Warfare Training Center.
During the program, they also focus on risk management with blocks of instructions for unit leaders based on various environmental conditions and temperature zones. The five temp zones when assessing and making decisions to mitigate cold weather risk are:
-Temp Zone 1: 39 to 20 Degrees (Wet Cold)
-Temp Zone 2: 19 to -4 Degrees (Dry Cold)
-Temp Zone 3: -5 to -25 Degrees (Intense Cold)
-Temp Zone 4: -25 to -40 Degrees (Extreme Cold)
-Temp Zone 5: -40 degrees and colder (Hazardous Cold)
Each zone has required and recommended actions for personal equipment (uniform configuration), pre-requisite training requirements, nutrition, and shelter and heat requirements. It also includes control measures like the frequency that buddy/medic checks must be conducted for cold weather injuries to the type of operations that can/should be conducted.
“Everything we’re doing is trying to prevent the injury from occurring in the first place through scientifically valid guidance that you can use to help figure out what you should or shouldn’t do or at least know what the risks are so then you can have the right controls in place,” Castellani said.
For example, with the current chart, 15 degrees fahrenheit and 15 mph winds have a windchill temperature around zero degrees fahrenheit which has a relatively moderate risk of frostbite with around 30 minutes of risk, he said.
“We expect the wind chill to be shifted to the right. You’re at a relatively lower risk if you’re exercising. That’s what we expect,” he said.
As temperatures drop, cold injuries and cold-related injuries historically rise, including hypothermia, frostbite, trench foot, carbon monoxide poisoning, snow blindness, sunburn, altitude sickness, and muscle strains.
With the study, researchers are looking to pinpoint more susceptible areas on the body for frostbite like the nose, ears, and fingers. They’re also going to study how frostbite risk differs between males and females because of factors like body composition and skin thickness.
“The peripheral cold injury rate for female soldiers is two times higher than the rate for males,” according to the Army’s cold weather manual.
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