What is the acceptable oxygen range in a manhole?

What is the acceptable oxygen range in a manhole?

• A. 19.5% to 23.0%
• B. 18% to 22%
• C. 21% to 25%
• D. 17% to 25%

Answer: (A)

Safe entry into a manhole requires the air to be close to normal atmospheric oxygen. If oxygen is too low, workers can quickly become dizzy or lose consciousness; if it’s too high, there’s a greater fire and explosion risk and it can affect equipment. The acceptable oxygen range for entry keeps the atmosphere within safe limits, roughly 19.5% to 23.0% O2. This range avoids both deficiency and enrichment, which is why it’s the best choice. The other ranges either fall below the safe minimum or exceed the safe maximum, making them unsuitable. If the O2 reading is outside this range, ventilate and re-check before entry.

Safe entry into a manhole requires the air to be close to normal atmospheric oxygen. If oxygen is too low, workers can quickly become dizzy or lose consciousness; if it’s too high, there’s a greater fire and explosion risk and it can affect equipment. The acceptable oxygen range for entry keeps the atmosphere within safe limits, roughly 19.5% to 23.0% O2. This range avoids both deficiency and enrichment, which is why it’s the best choice. The other ranges either fall below the safe minimum or exceed the safe maximum, making them unsuitable. If the O2 reading is outside this range, ventilate and re-check before entry.