What is the minimum oxygen level that can lead to severe health complications?

Severe health complications can occur at various reduced oxygen levels, but typically, levels around 6% or below are particularly critical. At this concentration, the human body cannot sustain adequate metabolic functions. Oxygen levels below 6% can lead to unconsciousness within minutes and pose a significant risk of suffocation and death.

The body's oxygen requirement for normal functioning is generally about 19.5% to 23.5%, which is considered the safe range in the atmosphere. When oxygen levels fall to around 6%, vital organs become starved for oxygen, resulting in severe physical and cognitive impairments, potential loss of consciousness, and ultimately life-threatening conditions. Therefore, the choice indicating 6% accurately reflects the threshold at which oxygen deprivation causes critical health issues, making it the correct answer.