What should be totally absent from air samples before unsealing a mine fire?

Before unsealing a mine fire, the presence of carbon monoxide in air samples must be totally absent due to its toxic nature and association with combustion processes. Carbon monoxide is a byproduct of incomplete combustion and can indicate the presence of fire or smoldering materials in a mine. If carbon monoxide is detected, it poses a serious health risk to personnel entering the area and suggests that the fire is still active or could reignite. Thus, ensuring that carbon monoxide levels are zero is crucial for safety.

While dust particles, humidity levels, and nitrogen levels can all have their implications in a mining environment, they do not directly indicate the presence or potential threat of a fire in the way that carbon monoxide does. Dust and humidity can be managed and are not as urgent as the presence of carbon monoxide when addressing mine safety in the context of a fire scenario.