What could a fluctuating high CO concentration in a sealed fire area indicate?

A fluctuating high carbon monoxide (CO) concentration in a sealed fire area suggests that there is a leakage of air into the sealed environment. In a sealed area, the goal is to limit the introduction of fresh air to control the fire's activity and prevent the spread of smoke and gases. High levels of CO can result from incomplete combustion during a fire and indicate that combustion is still happening in some form.

If there were a leak allowing fresh air to enter, it could cause the fire to intensify or change, resulting in fluctuations in CO levels as the fire responds to the changing oxygen availability. This scenario not only suggests persistent combustion but also raises significant safety concerns, as it may lead to further emissions of toxic gases and a more dangerous environment for personnel.

In contrast, if all fires were out, the CO levels would likely decrease rather than fluctuate. Excess coal burning could produce high CO readings, but a stable and continuous increase rather than fluctuation would be expected. Proper ventilation would reduce CO levels by providing fresh air, so it wouldn't cause fluctuating high CO levels. Thus, the presence of fluctuating high CO concentrations strongly indicates an unwanted air leak into the sealed area.