Climbers who ascend higher than 26,000 feet on Mount Everest enter the "death zone."
In the death zone, climbers' brains and lungs are starved for oxygen, their risk of heart attack and stroke is increased, and their judgment quickly becomes impaired.
In 2019, at least 11 people died on Everest, almost all of whom spent time in the death zone.
These extra, unplanned hours in the death zone might have put the 11 people who perished at higher risk, though it's hard to determine the specific causes of each death.
Temperatures in the death zone never rise above zero degrees Fahrenheit.