Non-avalanche-related snow immersion deaths: tree well and deep snow immersion asphyxiation.

Non-avalanche-related snow immersion death (NARSID), or snow immersion asphyxiation, is a significant winter mountain hazard for skiers and snowboarders. This phenomenon occurs predominately in western North America, where large tree wells and deep snowpacks develop. Although statistics are difficult to procure, snow immersion asphyxiation has resulted in more than 70 documented deaths in the past 2 decades. The primary purpose of this review is to examine the existing literature on NARSID to help prevent such dangerous accidents through educating wilderness medicine professionals and fostering public awareness. The exact duration of burial to time of death and the cause of death are not precisely known but can be postulated from accident reports, experimental snow burial studies, and avalanche literature. In most cases, death probably occurs within 15 to 30 minutes from the time of burial. However, survival after prolonged burial in a tree well and deep snow is possible. The cause of death is asphyxiation, probably due to one of the mechanisms that produce asphyxia in avalanche burial victims: positional asphyxia, airway obstruction, or carbon dioxide displacement asphyxia. Prevention of snow immersion asphyxiation begins with skiers and snowboarders staying within the limits of their skills, using the proper tools for deep powder, staying in control at all times, and employing a buddy system. A skier or snowboarder who falls near or into a tree well should tuck, roll, and try to land upright, grab the tree trunk or a branch, and yell or blow a whistle to alert partners. If buried upside down, the person should stay calm and create an air pocket, which is probably of paramount importance. Skiers and snowboarders should use avalanche safety equipment to lessen the risk of snow submersion asphyxiation.