Oxygen must be between what percent?

Oxygen must be between what percent?

• A. 18-21%
• B. 21-25%
• C. 19-23%
• D. 19.2-22%

Answer: (D)

Maintaining a safe breathing atmosphere hinges on keeping oxygen at a precise level. While normal air is about 21 percent oxygen, safety practice uses a narrower band to balance enough oxygen for crew activity with a reduced fire risk. The range 19.2 to 22 percent provides that balance: the lower bound helps prevent hypoxia during duties, and the upper bound limits oxygen enrichment that could accelerate combustion. Other options either drop too low for safe breathing or push into enrichment zones that increase fire hazards, or fall outside the established safety band.

Maintaining a safe breathing atmosphere hinges on keeping oxygen at a precise level. While normal air is about 21 percent oxygen, safety practice uses a narrower band to balance enough oxygen for crew activity with a reduced fire risk. The range 19.2 to 22 percent provides that balance: the lower bound helps prevent hypoxia during duties, and the upper bound limits oxygen enrichment that could accelerate combustion. Other options either drop too low for safe breathing or push into enrichment zones that increase fire hazards, or fall outside the established safety band.