Snow poses a wide range of threats that can indeed be fatal, extending far beyond simple cold exposure. While often viewed as a picturesque winter phenomenon, this frozen precipitation can become lethal through biological, mechanical, and indirect mechanisms. The danger comes not only from the direct impact of the snow itself but also from the secondary hazards created by winter conditions. Understanding these specific risks, from the immediate strain on the human body to the failure of infrastructure, is the first step in recognizing the true lethality of a severe winter storm.
Fatal Threat of Hypothermia
Hypothermia, defined as a core body temperature dropping below 95°F (35°C), is the most direct biological threat posed by prolonged exposure to snow and cold. The body loses heat through mechanisms significantly accelerated when snow is involved. Direct contact with snow or wet clothing causes rapid heat transfer via conduction, which can be up to 25 times faster than heat loss to cold air alone.
The body attempts to counteract this loss through shivering, a muscular contraction designed to generate metabolic heat. As the core temperature drops further, the central nervous system begins to fail. Shivering eventually ceases in the moderate stage of hypothermia, typically below 89.6°F (32°C). This cessation removes the body’s last automatic defense, leading to a faster temperature decline.
As the core temperature approaches the severe stage, falling below 82.4°F (28°C), the cardiovascular system becomes profoundly impaired. The heart rate slows, blood pressure drops, and the heart muscle becomes unstable and highly irritable. Death most commonly results from a lethal cardiac arrhythmia, such as ventricular fibrillation, which causes the heart to stop beating effectively. The metabolic slowdown ultimately leads to organ failure and death.
Lethality of Snow Mass Movement
Moving masses of snow, primarily avalanches, cause death through physical trauma and asphyxiation. The sheer force of a large, fast-moving snow slide can be immense, subjecting a victim to blunt force trauma from being slammed into trees, rocks, or the ground. Studies show that trauma alone accounts for a significant percentage of avalanche deaths, sometimes up to 24%.
For most victims, the cause of death is asphyxiation as the snow mass comes to rest and hardens around them. Once completely buried, the snow quickly restricts chest movement, making breathing difficult even if an air pocket exists. The critical time for survival is short, with roughly two-thirds of asphyxia deaths occurring within the first 35 minutes of burial.
The primary danger is not a lack of oxygen in the porous snow, but the buildup of exhaled carbon dioxide (hypercapnia). When a person breathes into a confined space, the exhaled carbon dioxide rapidly contaminates the limited air supply. This process, combined with the body’s consumption of available oxygen, quickly renders any small air pocket unusable, leading to unconsciousness and death within minutes.
The Danger of Stationary Snow Load
The cumulative weight of stationary snow on roofs and structures presents a mechanical threat capable of causing catastrophic collapse. The danger is magnified by snow density, which varies based on its water content. While fresh, dry snow might weigh as little as four to seven pounds per cubic foot (lb/ft³), wet, compacted, or rain-soaked snow can weigh over 20 to 30 lb/ft³.
This immense, concentrated load can exceed the structural capacity of buildings, particularly those with low-pitched or flat roofs or older structures. The resulting failure often occurs without warning, leading to a sudden roof or structural collapse. Fatalities are typically caused by crush injuries, blunt force trauma from falling debris, or prolonged entrapment under the rubble.
Secondary and Indirect Fatalities
Indirectly, snow events lead to fatalities through hazards created by infrastructure failure and human exertion. A particularly insidious risk is carbon monoxide (CO) poisoning, a colorless, odorless gas produced by combustion appliances. Heavy snowfall can block the exhaust vents for furnaces, water heaters, and clothes dryers, forcing the deadly gas back into the home.
Carbon Monoxide Poisoning
Lethal CO concentrations can also accumulate rapidly inside vehicles when the tailpipe is blocked by snow while the engine is idling. Lethal levels have been recorded in a car cabin in as little as 2.5 minutes if the exhaust is completely obstructed and the windows are closed. This danger is compounded because CO poisoning symptoms, such as headache and dizziness, are easily mistaken for the flu or common cold.
Physical Strain of Snow Removal
Another significant cause of death is the physical strain of snow removal. The exertion required for shoveling heavy, wet snow, especially in cold air that constricts blood vessels, places extreme stress on the cardiovascular system. Research indicates that ten minutes of intense shoveling can involve moving nearly a ton of snow. The resulting heart rate can equal or exceed that achieved during a vigorous treadmill stress test. This combination leads to hundreds of sudden cardiac events, such as heart attacks, each year, particularly among individuals with underlying heart conditions.
Travel-Related Fatalities
Snow and ice dramatically increase the risk of travel-related fatalities. Snowy and icy road conditions reduce tire friction and driver control, significantly increasing the braking distance required to stop a vehicle. Annually, an average of over 1,800 deaths and 136,000 injuries in the United States are attributed to accidents on snow- or ice-covered roads. The presence of ice, particularly black ice, poses a major hazard because it is virtually invisible to drivers, leading to sudden loss of traction and control.