Which atmospheric zone is considered extremely hazardous for the human body?

The Space Equivalent Zone is recognized as extremely hazardous for the human body primarily due to the lack of atmospheric pressure and the absence of breathable air, as well as exposure to high levels of radiation. In this zone, the conditions are so hostile that human survival without protective spacecraft or life-support systems is impossible.

In the Space Equivalent Zone, factors such as microgravity can lead to rapid physiological changes, including fluid shifts and muscle atrophy, while the exposure to vacuum can induce ebullism, a condition where bodily fluids vaporize due to low pressure. Additionally, without proper shielding, humans are susceptible to harmful cosmic and solar radiation, increasing the risk of cancer and acute radiation sickness.

In contrast, the other atmospheric zones mentioned either still provide some amount of breathable atmosphere or do not subject the body to the extreme conditions faced in space. For example, the Physiological Zone contains adequate atmosphere that allows human beings to function normally, while the Physiological Deficient Zone may present challenges, such as reduced oxygen levels, it still permits survival for limited periods without immediate life-threatening consequences. The Tropospheric Zone, while variable in weather and altitude, supports normal physiological functions and is where most human activities occur safely.