Before entering a confined space, you should check for oxygen levels no less than 19.5% or greater than 23.5%.

• A. 20.9% & 23.0%
• B. 18% & 25%
• C. 19.5% & 23.5%
• D. 21% & 24%

Answer: (C)

Maintaining a safe atmosphere in a confined space means verifying the oxygen content stays within a specific range so you can breathe safely and reduce fire risk. The allowable range is 19.5% to 23.5% oxygen by volume. Checking for 19.5% as the lower bound and 23.5% as the upper bound ensures you’re not entering an oxygen-deficient environment, which can cause dizziness, loss of consciousness, or death, and not entering an oxygen-enriched environment, which raises the chance of ignition and explosions. The other options either fall outside this range or use values that don’t define the exact boundaries of safe entry. In practice, you’d use an calibrated detector to confirm the atmosphere is within 19.5%–23.5% before entry.