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Eingeladener Vortrag
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In oxygen components, even for high pressure oxygen service, it is possible to use organic seals, lubricants, or filling liquids, provided their oxygen compatibility has been checked. However, fire incidents in oxygen systems still occur because these materials ignite and burn. There are many reasons, such as incorrect design, contamination, faulty operation, unsuitable materials, etc., why this happens. Another cause that is overseen very often is proper maintenance on the user´s side. It is very important to replace in a component a worn out seal by the same one with identical oxygen compatibility properties. On the part of the producer or distributor of materials, batch testing and also a quality assurance system play a key role in the safety of an oxygen component. Any change in the manufacturing process of a material, or in its composition, and even its further processing may have an impact on its oxygen compatibility and finally on the component in which it is used. Numerous investigations by BAM over decades reveal the influence of minor constituents and fillers on a material´s oxygen compatibility. The test results in this paper show how important it is to regularly perform batch testing on nonmetallic materials used for oxygen service and to have a quality assurance system that helps minimize incidents where unsuitable materials are chosen by accident.
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.
Adiabatic compression testing of components in gaseous oxygen is a test method that is utilized worldwide and is commonly required to qualify a component for ignition tolerance under its intended service. This testing is required by many industry standards organizations and government agencies; however, a thorough evaluation of the test parameters and test system influences on the thermal energy produced during the test has not yet been performed. This paper presents a background for adiabatic compression testing and discusses an approach to estimating potential differences in the thermal profiles produced by different test laboratories. A "thermal profile test fixture" (TPTF) is described that is capable of measuring and characterizing the thermal energy for a typical pressure shock by any test system. The test systems at Wendell Hull and Associates, Inc., in the United States and at the BAM Federal Institute for Materials Research and Testing in Germany are compared in this manner and some of the data obtained are presented. The paper also introduces a new way of comparing the test method to idealized processes to perform system-by-system comparisons. Thus, the paper introduces an "idealized severity index" (ISI) of the thermal energy to characterize a rapid pressure surge. From the TPTF data a "test severity index" can also be calculated so that the thermal energies developed by different test systems can be compared to each other and to the ISI for the equivalent isentropic process. Finally, a "service severity index" is introduced to characterize the thermal energy of actual service conditions. This paper is the second in a series of publications planned on the subject of adiabatic compression testing.
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.
Die meisten Sauerstoffarmaturen und -anlagenteile bestehen aus Metallen und enthalten nichtmetallische Materialen als Sitz- und Dichtungswerkstoffe. Die Gefahr eines Ausbrands ist grundsätzlich vorhanden, jedoch relativ gering, wenn neben der richtigen Konstruktion geeignete metallische und nichtmetallische Materialien für die vorgesehenen Betriebsbedingungen gewählt werden. Aus sicherheitstechnischer Sicht sollten Sauerstoffarmaturen und -anlagenteile, die komplett aus metallischen Materialien gefertigt und abgedichtet werden, ein noch geringeres Risiko eines Ausbrands aufweisen. Bei einer Versuchsreihe auf dem BAM-TTS-Freiversuchsgelände brannte unerwartet ein rein metallisches Anlagenteil komplett ab. Bei dieser Versuchsanordnung platzt eine metallische Berstscheibe bei einem bestimmten Sauerstoffdruck auf. Die anschließenden Untersuchungen konzentrierten sich auf die Frage, wie es bei diesem Versuch zu einem Ausbrand des massiven Anlagenteils kommen konnte. Im Vortrag werden die Ergebnisse der Untersuchungen diskutiert und die Sauerstoffverträglichkeit der verwendeten Metalle auf Grundlage des Abbrandverhaltens nach ASTM G 124-95 verglichen. Es wird versucht, die Frage zu beantworten, ob der Einsatz metallischer Berstscheiben zu einer Erhöhung der Brandgefahr in Sauerstoffanlagen führen kann.
Oxygen Compatible Materials & Burn-Out Safe Oxygen Components Approach and Test Methods by BAM
(2013)
Cylinder valves for oxygen service that meet the standard DIN EN ISO 10297 should be safe, if properly handled by the user. In the last few years, however, the number of incidents with oxygen valves that has been reported to Federal Institute for Materials Research and Testing (BAM) has increased. According to the incident reports, incorrect handling can be ruled out. People were seriously injured and in most cases, the causes of these incidents were not clear. Very often, such incidents occurred during opening and closing of the valves. Therefore, the technical-scientific community has put the existing test methods for type testing more and more into question. Besides other mandatory tests, the above-mentioned standard allows to perform the endurance test with air or with nitrogen. This is appropriate for all other gases but not for oxygen. Up to now, this test does not consider the fact that cylinder valves also contain nonmetallic seat materials and lubricants that may react with oxygen in a dangerous way. Because of this unsatisfactory situation, BAM initiated a research project to perform endurance testing of cylinder valves for oxygen service much more practice related with oxygen. This test simulates very well real life situations when the cylinder valve is opened or closed. The first part of this project was the development of a new oxygen operated endurance tester in accordance with DIN EN ISO 10297. In a second part, endurance testing of valves with air and with oxygen was performed and the results were compared. In addition, another mandatory test of the standard, the oxygen pressure surge test was carried out on new valves and on valves that had undergone endurance tests with air or oxygen, to see the influence on the burn-out safety of such pre-stressed valves. This paper presents the main results of the project. The findings clearly speak for implementing the oxygen endurance test not only to DIN EN ISO 10297 but also to various other standards to increase the burn-out safety of oxygen cylinder valves.