During flight at higher altitudes, the risk of carbon monoxide poisoning increases due to

• A. Altitude increases
• B. Temperature decreases
• C. Humidity increases
• D. Airspeed increases

Answer: (A)

As altitude increases, the amount of oxygen available in each breath drops because the air is thinner. Carbon monoxide binds to hemoglobin far more readily than oxygen, forming carboxyhemoglobin and reducing the blood’s ability to deliver oxygen to tissues. When there’s less oxygen available to begin with, any level of CO becomes more effective at causing hypoxia, so the risk of CO poisoning rises with higher altitude. The other factors listed don’t change how CO binds to hemoglobin or the body’s oxygen needs in the same direct way, so they don’t explain the increased risk.