When should a new POB be obtained?

A new Portable Oxygen Bottle (POB) should be obtained when the gauge reaches approximately 500 psi to ensure that you have enough breathable oxygen available. This threshold is crucial because it indicates that the pressure in the tank is approaching a level where the amount of oxygen may be insufficient for safe operation, particularly in an emergency situation. By obtaining a new POB at this point, you can ensure that there is a reliable and adequate supply of oxygen available for use, maintaining safety for personnel, especially in scenarios where high altitudes or other factors may deplete oxygen levels.

The other options suggest inappropriate times to replace the POB. Waiting until the gauge is below 100 psi is risky, as this could lead to a complete depletion of oxygen during critical operations. Replacing the POB after every flight or every hour of operation may lead to unnecessary use of resources and is not aligned with standard practice, which bases replacement on the actual pressure readings indicating the safety and reliability of the equipment.