At what percentage of the cylinder's capacity does the end-of-service-time indicator (EOSTI) alarm on an SCBA typically activate?

The correct answer is that the end-of-service-time indicator (EOSTI) typically activates at 33 percent of the cylinder's capacity. The EOSTI is a critical safety feature designed to alert firefighters when they have reached a certain level of air supply in their self-contained breathing apparatus (SCBA). Activating the alarm at 33 percent allows firefighters an adequate margin of safety to exit hazardous environments before the air supply runs critically low.

This proactive measure helps ensure that firefighters can safely retreat and avoid becoming trapped or incapacitated due to an empty air supply. The timing of the alarm is crucial in emergency situations where every second counts, and having this notification helps in planning an escape route while ensuring that the firefighter can continue to perform necessary tasks without immediate concern for air supply as they approach the end of their operational time.