NFPA 54 National Fuel Gas Code Practice Test

CO in the discharge air from a direct gas-fired industrial air heater must be kept very low to protect anyone in the space from exposure. Because the heater directly vents combustion products into the heated air, the amount of carbon monoxide in that discharge becomes part of the supply air, so controlling it is essential. The required limit is 50 ppm or less in the discharged air, ensuring reasonably safe indoor air quality while the unit operates. If the measured CO is above this level, the heater should not be used until adjustments (burner tuning, adequate combustion air, proper venting, and fuel pressure) bring CO down. Higher values like 75 or 100 ppm exceed the allowable safety threshold, and 0 ppm, while ideal, is not practical in typical operation.