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Two different test apparatuses are used at BAM to evaluate the safety of oxygen components: First, the promoted ignition combustion test according to ASTM G 124 [1] and to EIGA IGC Doc 13/02/E [2], and second, the new metallic disk ignition test that has not been standardized yet. The standard test method ASTM G 124 allows a ranking of metallic materials for use at high pressure oxygen. However, the transfer of those test results to valves and fittings in real-life situations is rather complex. The metallic disk ignition test, developed at BAM, is more practice oriented and uses metallic disks of different thicknesses of the investigated material. A commonly used nonmetallic sealing ring is placed in front of this disk and serves as an igniter. This test array is then exposed to high pressure gaseous oxygen impacts in a standardized pneumatic impact tester according to DIN EN 1797 [3].
Self-contained underwater breathing apparatus (SCUBA) divers use different mixtures of nitrogen and oxygen as breathing gas. The so-called NITROX mixture often contains more oxygen than is contained in air and may increase the fire hazard in diving equipment. The SCUBA diving community, however, still differentiates between NITROX mixtures that contain more than 40 % oxygen or less. They consider a mixture with up to 40 % oxygen often as regular air. In filling operations of SCUBA cylinders, gas flows from high pressure to low pressure. Because of compressive heating, a sudden temperature rise in the gas occurs and nonmetallic materials, e.g., seals may ignite. BAM has used the pneumatic impact test to investigate the ignition sensitivity of ethylene propylene diene monomer (EPDM), fluorelastomer (FPM), polytetrafluorethylene (PTFE), polyetheretherketone (PEEK), and nylon (PA 6.6) to gaseous impacts in synthetic air, in various NITROX mixtures, and in pure oxygen. The test results clearly show that for nonmetallic materials, the maximum pressure of nonreaction in NITROX mixtures decreases at a content of 29 % oxygen in comparison to those in air. In addition, autoignition temperatures of the nonmetallic materials were also determined. The findings of this investigation support very well the results of other publications on oxygen enrichment. As a consequence of this study, in SCUBA diving, the same safety requirements for NITROX mixtures with more than 21 % oxygen should be applied as for pure oxygen in the industry.
The widely held incorrect belief in the self-contained underwater breathing apparatus (SCUBA) diving community, that oxygen-enriched gas mixtures, so-called NITROX, with an oxygen content of up to 40 vol. % can be considered as regular air, has already been refuted in many papers. Now, another dangerous practice has drawn the attention. In a market study, more than 60 representative SCUBA cylinder valves were examined. Sales offices claim that all of those valves can be used for oxygen-enriched gas mixtures. The fact is that some of these cylinder valves are for air use only. By exchanging the nonmetallic materials and applying additional cleaning procedures, these air valves become so-called “oxygen clean.” Then, the valves are on sale for oxygen-enriched service. This procedure is dangerous because the labeling pretends a pseudo-safety. All of the 60 SCUBA cylinder valves were tested applying the standardized oxygen pressure surge tester at BAM. As suspected, many of the cylinder valves are not burn-out safe. In addition, different test results were received for actual new valves, for so-called new but temporarily stored valves, and for used valves. This paper reveals another dangerous practice and wants to alert the SCUBA diving community.