ASTM G 175 is a standard test method for evaluating the ignition sensitivity and fault tolerance of oxygen regulators used for medical and emergency applications. To show the ASTM G 175 test method was repeatable at different laboratories, a series of interlaboratory tests were performed on medical oxygen regulators in late 2002. These tests were performed on six regulator designs at three laboratories. Three of the regulator models employed a compressed gas association (CGA) 870-style connection and the other three regulator models used a CGA 540-style connection. Five of the regulators were commercially available and the other one was a CGA 870-style regulator that was intentionally designed to tail the test. The results of the round robin tests are presented and discussed.

Revelations of excessive property variation in polychlorotrifluoroethylene (PCTFE) semifinished and finished parts led to concerns that leaks or part failure could occur in service, possibly leading to catastrophic component or system failure by flow friction and/or kindling chain mechanisms. Such concerns led to the issuances of an internal Kennedy Space Center (KSC) Problem Advisory and a Government-Industry Data Exchange Program Materials Advisory on PCTFE. The advisories led to an engineering analysis review of PCTFE-containing ground support equipment used in “at-risk” high-pressure oxygen and air systems at KSC Representative PCTFE replacement parts used in “at-risk” systems were removed from inventory and tested. Tests included determination of (1) dimensional stability by thermomechanical analysis and metrology, (2) percent crystallinity by specific gravity, and (3) the effect of annealing on engineering tolerances. While dimensional instability was determined not to be a major issue in existing inventories, establishing traceability back to the semifinished article (starting rod or sheet stock) was often not possible. Percent crystallinity varied widely depending on part origin and thickness. Annealing was found to lead occasionally to out-of-tolerance parts. The pneumatic impact ignition threshold of PCTFE in enriched air was also determined at pressures up to 41.4 MPa. Results show that ignition does not occur at ambient oxygen concentrations. Last, hazard analyses were performed on “at-risk” systems. Two problematic designs were discovered, but based on operational histories, a recommendation was made to redesign or repair and replace on a noninterference basis.

ASTM G175 is a standard test method for evaluating the ignition sensitivity and fault tolerance of oxygen regulators used for medical and emergency applications. During its development, interlaboratory testing was conducted to assess whether the standard could be performed reproducibly and repeatably. Specifically, this testing examined ignition pill production and the performance of different test systems using test articles manufactured specifically for this testing. Five laboratories used materials provided from single batch lots to manufacture ignition pills, and their heat of combustion was determined and compared to G175 requirements. To determine whether the performance of different test systems would affect upcoming interlaboratory testing, four laboratories tested CGA 870-style test articles manufactured to examine the flame jet resulting from pill ignition. Still photography was used to capture the ignition events; these photos were used to compare test system performance. This paper discusses these results in relation to the repeatability and reproducibility of G175 and the possible effect on future interlaboratory testing, which will involve actual off-the-shelf regulators.