The protective breathing equipment (PBE) procured by the U.S. Air Force as Emergency Passenger Oxygen System (EPOS; Fig. 1) was alleged to have significant numbers of inadequate oxygen cylinders. In theory, this could prevent the PBE from providing the required time of protection for the user. The Civil Aerospace Medical Institute was requested to participate in the testing for the possibility of inadequate oxygen cylinders through the U.S. Air Force ...