Heat Balance When Climbing Mount Everest

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.

Simulations of the human heat balance during Mount Everest summit attempts in spring and winter

“…The data represent the hourly values of the measured meteorological parameters—Supplementary Materials (SM) (Table SM1 ). The characterization of the meteorological data was done by Szymczak and Błażejczyk ( 2021 ).…”

“…Mountaineers, especially in the Himalayas, must face harsh weather conditions that can be compared to polar ones (Havenith 2010 ; Szymczak and Błażejczyk 2021 ). These conditions are characterized by low air temperature (Ta) and high wind speed (v) (Szymczak et al 2021a ).…”

“…These conditions are characterized by low air temperature (Ta) and high wind speed (v) (Szymczak et al 2021a ). Additional climate features specific to the high mountain environments are the air pressure (ap)—which results in reduced air density and oxygen content that decrease with altitude (Huey et al 2001 ; Kandjov 1997 ) and the increasing intensity of solar radiation (due to low optical mass and high transparency of the atmosphere and a large share of radiation reflected from snowy slopes) (Błażejczyk et al 2013 ; Szymczak and Błażejczyk 2021 ).…”

“…Szymczak et al ( 2021b ) investigated deaths >8000 m potentially associated with body cooling. Szymczak and Błażejczyk ( 2021 ) assessed how meteorological conditions at different altitudes affect heat transfer flows in individuals in different seasons while climbing Everest. They also examined how various wind speeds and clothing insulation levels influenced human heat balance.…”

The effect of the lowest heat stress limit conditions on psychomotor fatigue threshold in soccer players

“…The Man-ENvironment heat EXchange model (MENEX) of Błażejczyk (1994) was applied for this purpose. Detail equation of above measures are done in Błażejczyk and Matzarakis (2007), Błażejczyk and Kunert (2011), Szymczak and Błażejczyk (2021). The calculations were made using the BioKlima 2.6 software package.…”