When does the EOSTI or low-air alarm activate in an SCBA cylinder?

The EOSTI (End of Service Time Indicator) or low-air alarm in a self-contained breathing apparatus (SCBA) is designed to provide a safety measure for firefighters when they are using the equipment in potentially hazardous environments. The activation of the EOSTI typically occurs at approximately 35% of the cylinder's capacity. This is crucial because it gives the firefighter an early warning that the air supply is becoming low, allowing them to exit the hazardous area before running out of air.

By activating at this threshold, the EOSTI ensures that users can safely manage their air supply during operations. Using an alarm at 35% rather than a lower threshold minimizes the risk of unexpectedly running out of air while still ensuring the firefighter has sufficient time to react and evacuate if necessary. This safety feature is vital in emergency situations where time and air supply management can be critical to the safety of the firefighter.