For safe working conditions, the oxygen level by volume must range between which?

For safe working conditions, the oxygen level by volume must range between which?

• A. 18.0 to 22.0 percent
• B. 19.5 to 23.5 percent
• C. 21.0 to 25.0 percent
• D. 20.0 to 24.0 percent

Answer: (B)

Oxygen in the work environment should be kept within 19.5% to 23.5% by volume. This range balances safe breathing with lower fire risk: below 19.5% can cause hypoxia and impairment, while above 23.5% makes the environment more flammable and can affect safety controls. Normal outdoor air is about 21%, so this window stays near normal but provides a safety buffer. The other ranges either dip into deficient levels or exceed the upper limit, which is why they aren’t appropriate.

Oxygen in the work environment should be kept within 19.5% to 23.5% by volume. This range balances safe breathing with lower fire risk: below 19.5% can cause hypoxia and impairment, while above 23.5% makes the environment more flammable and can affect safety controls. Normal outdoor air is about 21%, so this window stays near normal but provides a safety buffer. The other ranges either dip into deficient levels or exceed the upper limit, which is why they aren’t appropriate.