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 Office of Special Investigations.To test for any potential leakage and therefore an inadequate quantity of oxygen, EPOS units were collected from Air Force bases and submitted by the manufacturer for a series of tests. The primary indicator in the testing was the mass (weight) of oxygen in the cylinder. A total of 92 oxygen cylinders that were manufactured for assembly into EPOS or similar models of PBE were evaluated. Estimated dates of manufacture were between January 1989 and November of 2003. Four tests were conducted.The first measurement was the oxygen concentration in the vacuum-packaged PBE. The oxygen cylinders were then removed from the PBE and any difference between the current cylinder weight and the cylinder weight at manufacture was recorded. The cylinders were then exposed to 40,000 feet altitude in a hypobaric chamber for 4 hours. Weights before and after the chamber exposure were recorded. Finally, the cylinders were emptied of oxygen and the empty cylinder weight recorded. Two oxygen cylinders had large oxygen deficits (>11 grams).Based on the results of the altitude testing, the loss did not appear to be related to diffusion out of the cylinder. Therefore, other explanations need to be examined as to why these two cylinder shortages existed.
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