What occurs when the SCBA bottle pressure drops to 1825 psi or lower?

When the SCBA bottle pressure drops to 1825 psi or lower, it signals the activation of safety mechanisms built into the system to ensure user safety. In this scenario, the low cylinder transfer valve and secondary reducer open. This is a safety feature designed to provide a more stable air supply under low-pressure conditions.

As the primary cylinder pressure decreases, the SCBA system allows for a seamless transition to maintain adequate airflow. This action prevents sudden loss of air supply and ensures that the user continues to receive breathable air, even as the primary air source depletes.

The other options do not accurately describe the actions taken when the pressure reaches this critical level. For instance, the primary reducer does not remain open to avoid the risk of running out of air since it only operates effectively while there is sufficient pressure. Additionally, the Vibralert—a warning device meant to alert the user of low air supply—remains active to warn the user that they are approaching the critical pressure threshold. Lastly, stating that the air supply remains constant does not reflect the reality of decreasing pressure in the SCBA, as the system is designed to adjust to ensure safety when experiencing low air pressure conditions.