Toxic concentrations of carbon monoxide ___ be detected by persons with a normal sense of smell.

• A. can not
• B. can
• C. sometimes
• D. always

Answer: (A)

Toxic concentrations of carbon monoxide cannot be detected by persons with a normal sense of smell. CO is odorless and colorless, so a leak won’t be noticed by smell, and by the time symptoms appear, dangerous levels may already be present. Carbon monoxide binds to hemoglobin more readily than oxygen, reducing the blood’s ability to deliver oxygen to tissues, which is why exposure can escalate quickly and be life-threatening. Because smell isn’t a reliable warning, relying on it is dangerous; the safe practice is to use dedicated carbon monoxide detectors and ensure proper ventilation and maintenance of fuel-burning appliances.