Firefighters use air-monitoring devices to:

• A. Control ventilation fans.
• B. Measure humidity levels.
• C. Track firefighter location.
• D. Detect oxygen levels and hazardous substances.

Answer: (D)

Continuous air monitoring at a fire scene centers on ensuring a breathable atmosphere and identifying dangerous conditions. Air-monitoring devices provide real-time readings of oxygen levels and the presence of hazardous substances, such as toxic gases or volatile compounds. This information is crucial for deciding whether it’s safe to enter a space, what PPE or SCBA to use, whether ventilation should be increased, and when conditions have deteriorated enough to warrant retreat. While other tools might assess related factors, the primary purpose of air-monitoring equipment is to detect oxygen concentrations and hazardous substances, ensuring crew safety in dynamic environments. Humidity is not the main safety determinant here, and locating firefighters uses other systems, not these monitors.