Abstract
Background: Mountaineers must control and regulate their thermal comfort and heat balance to survive the rigors of high altitude environment. High altitudes feature low air pressure and temperatures, strong winds and intense solar radiation, key factors affecting an expedition’s success. All these climatic elements stress human heat balance and survival. We assess components of human heat balance while climbing Mt. Everest.Materials and Methods: We calculated climbers’ heat balance using the Man-ENvironment heat EXchange model (MENEX-2005) and derived meteorological data from the National Geographic Expedition’s in situ dataset. Three weather stations sited between 3810 and 7945 m a.s.l. provided data with hourly resolution. We used data for summer (1 May–15 August 2019) and winter (16 October 2019–6 January 2020) seasons to analyze heat balance elements of convection, evaporation, respiration and radiation (solar and thermal).Results: Meteorological and other factors affecting physiology—such as clothing insulation of 3.5–5.5 clo and activity levels of 3–5 MET—regulate human heat balance. Elevation above sea level is the main element affecting heat balance. In summer two to three times more solar radiation can be absorbed at the summit of the mountain than at the foot. Low air pressure reduces air density, which reduces convective heat loss at high altitude by up to half of the loss at lower locations with the same wind speed and air temperature.Conclusion: 1. Alpinists face little risk of overheating or overcooling while actively climbing Mt. Everest, despite the potential risk of overcooling at extreme altitudes on Mt. Everest in winter. 2. Convection and evaporation are responsible for most of the heat lost at altitude. 3. Levels of physical activity and clothing insulation play the greatest role in counteracting heat loss at high altitude.
Highlights
High-altitude tourism and mountaineering is becoming ever more popular, especially on the world’s highest mountains in the Himalayas
Given the average values of the characteristic human heat balance for the observation period (1 May 2019 to 6 January 2020) that we calculated for various combinations of metabolic heat production and clothing insulation, the largest statistically significant differences between the stations involved convective heat loss, which increased with altitude
Altitude had no significant effect on the intensity of evaporative heat loss and the amount of water lost to sweating: these variables depended on the level of physical activity
Summary
High-altitude tourism and mountaineering is becoming ever more popular, especially on the world’s highest mountains in the Himalayas. Heat Balance on Everest century (Salisbury and Hawley, 2007). Commercial climbing gained popularity in the early 1990s, when commercial expeditions contributed about 20% of all climbers attempting peaks over 6,000 meters; by 2006 climbers in commercial expeditions constituted almost 75% of attempts (Salisbury and Hawley, 2007). Two of the four most popular commercial climbing routes are on Mt. Everest and the number of climbers attempting this peak has risen 60% over the past 15 climbing seasons (Huey et al, 2020). High altitudes feature low air pressure and temperatures, strong winds and intense solar radiation, key factors affecting an expedition’s success. All these climatic elements stress human heat balance and survival.
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