A person buried by snow, typically in an avalanche, may have a brief window to breathe, but the situation rapidly becomes life-threatening. The immediate danger is not the weight of the snow but the chemical changes in the air surrounding the face. While the snowpack contains air that could sustain life, the physics of gas exchange and the body’s exhalations quickly turn the burial into a suffocating environment. Survival is measured in minutes, making immediate self-rescue actions and swift external help the only real chances for a positive outcome.
The Physics of Breathing Under Snow
The primary threat to a buried victim is not a lack of oxygen (O2) but the rapid accumulation of carbon dioxide (CO2), a process known as non-mechanical asphyxiation. When a person exhales, warm, moist breath is released into the small space around the mouth and nose. Snow is porous and contains air, but the confined space prevents the diffusion of exhaled gases away.
In the confined space of a snow burial, the CO2 concentration quickly rises as the person rebreathes their exhaust. Studies show that without a way to divert CO2, victims can become significantly hypercapnic (excess CO2) and hypoxic (low O2) in under ten minutes. The danger is compounded when the exhaled warm air melts the surrounding snow, which then refreezes into a dense, non-porous ice mask around the face. This ice layer completely seals the victim, preventing gas exchange with the snowpack and trapping the toxic CO2.
The type of snow dictates the speed of this process. Dry, powdery snow may allow for slightly better initial gas diffusion, but dense, wet snow or ice can seal the airway almost instantly. Experimental studies showed that when exhaled CO2 was completely diverted, the oxygen within the snowpack was sufficient to sustain normal breathing for over an hour. This evidence confirms that CO2 buildup, not an immediate lack of breathable air in the snow itself, causes most avalanche fatalities.
The Role of Hypothermia in Survival
While asphyxiation is the most common cause of death, cold exposure presents a secondary, serious threat. The body begins to lose heat rapidly when encased in snow, leading to hypothermia, defined as a core body temperature dropping below 95°F (35°C). In simulated snow burials, the core body temperature can drop at a rate of approximately 1.3°C per hour.
As the core temperature falls, the body’s physiological functions slow down, progressing from intense shivering in mild hypothermia to confusion and eventually a loss of consciousness. Extreme cold can sometimes offer a paradoxical extension of the survival window, especially for children, by significantly slowing the body’s metabolism and reducing the brain’s oxygen demand. This metabolic slowing can protect the brain from damage for a longer period than normally possible, provided the person is resuscitated by specialized medical teams. However, this is a rare outcome, and for most victims, the cold only exacerbates the overall crisis.
Immediate Actions for Self-Rescue
The first few seconds after being caught in an avalanche are the only window for self-rescue actions. The most important immediate action is to fight the natural instinct to panic and instead focus on creating an open air space around the mouth and nose. Using a hand or an arm to create a pocket of air immediately before the snow settles can buy precious minutes, which can make the difference between life and death.
Once the snow mass stops, it settles and hardens almost instantly, becoming dense and restrictive. Before this happens, a person should attempt to take a deep breath to expand the chest, which can provide a small amount of space to breathe once the snow sets around the body. After the snow has hardened, movement is nearly impossible, so the person must then conserve energy and oxygen. A common technique to determine which way is up is to allow saliva to drip from the mouth, as gravity will indicate the downward direction, which is the opposite of the surface.
The Critical Search Window
The timeline for a successful rescue is extremely short, with statistics showing a rapid drop in the chance of survival immediately following burial. The survival rate for completely buried victims is highest—upwards of 90%—if they are recovered within the first 10 minutes. This short period is the time before the effects of asphyxiation become overwhelming.
After the initial 10-minute mark, the survival curve drops steeply, with approximately two-thirds of asphyxiation-related deaths occurring between 10 and 35 minutes. If rescue is prolonged past 35 minutes, the probability of survival plummets to under 30%. This data underscores the importance of companion rescue, where a victim’s partners use transceivers, probes, and shovels to locate and dig out the buried person immediately, as organized rescue teams almost always take longer than the critical window.