According to OSHA, what is the lowest safe concentration of oxygen in air for humans?

The correct answer is based on OSHA's standards regarding oxygen concentration in the air. OSHA recognizes that the normal atmospheric oxygen level is approximately 20.9%. To ensure safety in environments where oxygen levels may be lower, OSHA has set a guideline where a concentration of at least 19.5% oxygen is considered the minimum safe level for human health. Concentrations below this threshold can lead to impaired cognitive and physical functions and can pose serious health risks.

Therefore, a concentration of 19.5% is established as the lowest acceptable level for human safety, as it ensures that individuals have enough oxygen for proper physiological function while minimizing the risk of oxygen deficiency.