How would an air analysis indicate that a fire was extinguished?

An air analysis indicating that a fire was extinguished is characterized by low oxygen levels and the absence of carbon monoxide (CO). When a fire is burning, it consumes oxygen and produces carbon monoxide as a byproduct of incomplete combustion. Therefore, if the air analysis shows that oxygen levels are lower than normal and there is no detection of carbon monoxide, it strongly suggests that the fire has been suffocated or extinguished, effectively ceasing combustion processes.

In contrast, high levels of nitrogen, presence of water vapor, or stable temperature with high humidity do not directly indicate that a fire has been extinguished. While water vapor may increase if water is used to combat a fire, its mere presence is not definitive evidence of extinguishment. High humidity or stable temperature measurements also do not provide conclusive evidence regarding combustion activity. Thus, low oxygen and absence of carbon monoxide are critical markers confirming that a fire has been successfully put out.