According to NFPA standards, when should an SCBA low-air alarm sound?

The correct response is based on the NFPA standards, which stipulate that an SCBA's low-air alarm should activate when the cylinder pressure drops to 25 percent of its full capacity. This feature serves as a critical safety mechanism for firefighters, alerting them to the depletion of air supply and prompting them to exit hazardous environments before their air supply runs critically low. Setting the alarm at 25 percent ensures that firefighters have sufficient time to respond to the alert and take action to preserve their safety during operations.

This standard is established to provide a balance between adequate time to escape and the realistic depletion rates that can occur during firefighting activities, making it essential for maintaining safety in potentially life-threatening situations.