CO detectors alert occupants when backdrafting has allowed carbon monoxide to rise above what threshold?

• A. 70
• B. 50
• C. 90
• D. 110

Answer: (A)

Backdrafting spreads combustion byproducts into the living space, so CO detectors are tuned to warn when indoor carbon monoxide reaches a level that poses a real risk. The alert level of 70 parts per million provides a practical balance: it’s high enough to indicate a genuine buildup from poor venting but low enough to give occupants time to leave or ventilate before exposure becomes dangerous. Lower thresholds would lead to more frequent alarms, while higher thresholds could delay warning into harmful levels. So the detector activates when CO reaches about 70 ppm.