In fresh air, what should be the O2 reading on the multi-gas detector?

In fresh air, what should be the O2 reading on the multi-gas detector?

• A. 19.5% to 20.0%
• B. 21.5% to 22.0%
• C. 20.0% to 20.5%
• D. 20.8% to 21.0%

Answer: (D)

Oxygen in fresh air is about 21 percent. A well-calibrated multi-gas detector will show roughly 20.8 to 21.0 percent O2 when the air is normal and not depleted or enriched. This range indicates safe, breathable conditions and proper ventilation. Values much lower than this signal a hypoxic risk (dangerous for workers and may trigger a low-O2 alarm), while readings significantly higher indicate oxygen enrichment, which also poses hazards such as increased fire risk. So, the reading around 20.8–21.0% best reflects fresh air conditions.

Oxygen in fresh air is about 21 percent. A well-calibrated multi-gas detector will show roughly 20.8 to 21.0 percent O2 when the air is normal and not depleted or enriched. This range indicates safe, breathable conditions and proper ventilation. Values much lower than this signal a hypoxic risk (dangerous for workers and may trigger a low-O2 alarm), while readings significantly higher indicate oxygen enrichment, which also poses hazards such as increased fire risk. So, the reading around 20.8–21.0% best reflects fresh air conditions.