Why might a lack of odor in a manhole not guarantee safety?

• A. Some dangerous gases have no odor
• B. Oxygen may still be lacking
• C. Some gases deaden the sense of smell
• D. All of the above

Answer: (D)

Relying on odor to judge safety in a manhole is risky because several hazards don’t rely on smell. Some dangerous gases are odorless, so you can be exposed without noticing a warning scent. Oxygen may still be lacking even if nothing smells wrong, which means the air could be unsafe to breathe. And some gases deaden the sense of smell, so the odor can fade as concentrations rise. Because any of these can occur, a lack of odor does not guarantee safety. Use proper gas detectors, ventilate the space, and follow confined-space entry procedures to test and control the atmosphere before entering.