In a combustion safety test, if the CO reading under natural conditions is between 100 and 400 ppm, what should you do?

In a combustion safety test, if the CO reading under natural conditions is between 100 and 400 ppm, what should you do?

• A. Stop work: Work may not proceed until the system is serviced and the problem is corrected
• B. Continue operation
• C. Recheck in 15 minutes
• D. Evacuate immediately

Answer: (A)

CO readings during a combustion safety test show how safely the appliance is burning and venting. When the natural CO level is in the 100–400 ppm range, it flags a real safety concern—likely incomplete combustion or venting problems that could allow toxic CO to accumulate. Because of that risk, work should stop and the system must be serviced and corrected before continuing. This is not a situation to casually proceed or to simply recheck later; the elevated level indicates a condition that needs inspection and repair to prevent CO exposure. Continuing operation would keep occupants at risk, and rechecking after a short wait might delay necessary fixes without addressing the underlying problem. Evacuation is reserved for higher concentrations or symptoms; with 100–400 ppm, the safer, mandated step is to stop work and have the equipment repaired before proceeding.

CO readings during a combustion safety test show how safely the appliance is burning and venting. When the natural CO level is in the 100–400 ppm range, it flags a real safety concern—likely incomplete combustion or venting problems that could allow toxic CO to accumulate.

Because of that risk, work should stop and the system must be serviced and corrected before continuing. This is not a situation to casually proceed or to simply recheck later; the elevated level indicates a condition that needs inspection and repair to prevent CO exposure.

Continuing operation would keep occupants at risk, and rechecking after a short wait might delay necessary fixes without addressing the underlying problem. Evacuation is reserved for higher concentrations or symptoms; with 100–400 ppm, the safer, mandated step is to stop work and have the equipment repaired before proceeding.