Direct gas fired Industrial Air Heaters may not be utilized unless manufacturer states that there is no more than how many ppm of carbon monoxide in total volume discharged from unit?

• A. 0 ppm
• B. 10 ppm
• C. 50 ppm
• D. 100 ppm

Answer: (C)

Direct gas-fired industrial air heaters add combustion products to the air they discharge, so the CO level in that discharged air must be kept within safe limits. The manufacturer’s certification for these units typically specifies a maximum carbon monoxide concentration in the total volume discharged, and that limit is 50 ppm. If the discharge air is at or below 50 ppm CO, the unit is considered acceptable under NFPA 54, assuming other installation requirements are met. If CO in the discharge exceeded this value, the unit should not be operated until the issue is addressed (e.g., by a different burner configuration or a compliant unit). The other options are not the standard limit used for these appliances.