1、 Reference number ISO 22538-4:2007(E) ISO 2007INTERNATIONAL STANDARD ISO 22538-4 First edition 2007-09-01 Space systems Oxygen safety Part 4: Hazards analyses for oxygen systems and components Systmes spatiaux Scurit des systmes doxygne Partie 4: Analyse des dangers des systmes doxygne et leurs comp
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6、 ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web www.iso.org Published in Switzerland ii ISO 2007 All rights reservedISO 22538-4:2007(E) ISO 2
7、007 All rights reserved iii Contents Page Foreword iv 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 1 4 General. 2 5 Approach . 2 6 Procedures 3 6.1 Oxygen application and investigative scope. 3 6.2 Oxygen hazards analysis team . 4 6.3 Component/system information 4 6.4 Worst-case
8、operating conditions 4 6.5 Material flammability 4 6.6 Ignition mechanisms 5 6.7 Secondary effects analysis 6 6.8 Reaction effects analysis. 7 Annex A (informative) High-risk components . 8 Annex B (informative) Example of oxygen hazards analysis chart on a PTFE-lined flexible hose . 9 ISO 22538-4:2
9、007(E) iv ISO 2007 All rights reservedForeword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body
10、 interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotec
11、hnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by
12、the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent righ
13、ts. ISO shall not be held responsible for identifying any or all such patent rights. ISO 22538-4 was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles, Subcommittee SC 14, Space systems and operations. ISO 22538 consists of the following parts, under the general title Space syst
14、ems Oxygen safety: Part 1: Design of oxygen systems and components Part 2: Selection of metallic materials for oxygen systems and components Part 3: Selection of non-metallic materials for oxygen systems and components Part 4: Hazards analyses for oxygen systems and components The following parts ar
15、e under preparation: Part 5: Operational and emergency procedures Part 6: Facility planning and implementation INTERNATIONAL STANDARD ISO 22538-4:2007(E) ISO 2007 All rights reserved 1 Space systems Oxygen safety Part 4: Hazards analyses for oxygen systems and components 1 Scope This part of ISO 225
16、38 provides a process for conducting hazards analyses on parts, components and systems in oxygen and oxygen-enriched environments. This part of ISO 22538 identifies processes that may be used on ground support equipment, launch vehicles and spacecraft. 2 Normative references The following referenced
17、 documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. NASA TM 104823, Guide for Oxygen Hazards Analyses on Components and Syste
18、ms 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 auto-ignition temperature temperature at which a material will spontaneously ignite in oxygen under specific test conditions 3.2 hazard source of danger, which could harm property or personne
19、l 3.3 impact-ignition resistance resistance of a material to ignition when struck by an object in an oxygen atmosphere under specific test conditions 3.4 ignition temperature temperature at which a material will ignite under specific test conditions 3.5 non-metallic material any material other than
20、a metal, or any composite in which the metal is not the most easily ignited component and for which the individual constituents cannot be evaluated independently ISO 22538-4:2007(E) 2 ISO 2007 All rights reserved3.6 oxygen compatibility ability of a material to coexist with oxygen and a potential so
21、urce of ignition at an expected pressure and temperature 3.7 oxygen-enriched atmosphere any gas or liquid that contains more than 25 volume percent oxygen 3.8 risk probability of loss or injury from a hazard 4 General Since most materials will burn in oxygen-enriched atmospheres, hazards are always
22、present when using oxygen. Most materials will ignite at lower temperatures in an oxygen-enriched atmosphere than in air. Once ignited, combustion rates are greater in the oxygen-enriched atmosphere. Many metals burn violently in an oxygen-enriched atmosphere. Lubricants, tapes, gaskets, fuels and s
23、olvents can increase the probability of ignition in oxygen systems. However, these hazards do not preclude the use of oxygen. Oxygen may be used safely if all materials in the system are not flammable in the end-use environment, or if ignition sources are identified and controlled. These ignition an
24、d combustion hazards necessitate a proper hazards analysis before introducing a material or component into oxygen service. This part of ISO 22538 describes a method for analysing the hazards of components and systems exposed to oxygen-enriched environments. The oxygen hazards analysis is a useful to
25、ol for oxygen system designers, system engineers and facility managers. Problem areas shall be identified before oxygen is introduced into the system, thus preventing damage to hardware and possible injury or loss of life. Annex A provides a list of typical components particularly susceptible to ign
26、ition mechanisms that are found in oxygen systems. 5 Approach A hazards analysis of an oxygen component or system shall be approached as shown in Figure 1. The oxygen application and the scope of the investigation shall first be determined, and then a team shall be assembled to conduct the analysis.
27、 Information shall be collected on the materials, components and the worst-case operating conditions. A fire will not usually occur in any environment unless the construction materials of the system or component are flammable and a credible ignition mechanism is present. The flammability of the mate
28、rial is first reviewed to determine if any fire hazards exist under the worst-case operating conditions. If the material is flammable, then the possible ignition mechanisms are reviewed to determine which are credible. If data for the particular ignition mechanism and the material under consideratio
29、n are not available, appropriate material tests are conducted. Finally, the secondary and reaction effects are evaluated to determine what effect an ignition and possible combustion would have on the system and the facility. It is necessary that use of an oxygen hazards analysis as a tool be properl
30、y documented from the beginning. A typical oxygen hazards analysis summary (see Annex B) contains the component designation (which indicates the materials of construction including soft goods), the possible ignition mechanisms, the probability of each ignition mechanism, the results of the secondary
31、 effects analysis and the reaction effects assessment. The documentation also includes recommendations for further testing, if needed, stipulations on use and any additional safety precautions. See NASA TM 104823. ISO 22538-4:2007(E) ISO 2007 All rights reserved 3Figure 1 Approach to oxygen hazards
32、analysis 6 Procedures 6.1 Oxygen application and investigative scope The oxygen application and investigative scope are first determined to provide the basis for choosing the oxygen hazards analysis team and for conducting the analysis. ISO 22538-4:2007(E) 4 ISO 2007 All rights reserved6.2 Oxygen ha
33、zards analysis team An oxygen hazards analysis team consists of, at a minimum: personnel with expertise in mechanical design; metals ignition and combustion; non-metals ignitions and combustion; component testing (with emphasis on oxygen systems). Depending on the system, personnel with expertise in
34、 electrical design, cryogenic fluids, materials and chemistry may also be included. 6.3 Component/system information Information on each component in the system is obtained, including materials of construction (including soft goods and lubricants), drawings showing the cross-section drawings of each
35、 component, particularly fluid flow paths and the locations of the soft goods, and a fluid system schematic. The cross-section of the component shall be used to locate and identify all the soft goods. If the cross-sectional view of the component is of poor quality or unclear, a disassembled componen
36、t complete with soft goods is sometimes useful. All materials of construction shall be identified. The flow path shall also be identified, along with all oxygen-wetted materials. 6.4 Worst-case operating conditions The worst-case operating conditions that the component may undergo are determined. Th
37、is information shall be used to evaluate the materials of construction for resistance to ignition and combustion, and it includes maximum use pressures, temperatures and flow rates. Pressures and temperatures are important because materials flammability is often a function of these two parameters. F
38、low rates are important because they affect the particle impact and adiabatic compression ignition mechanisms. 6.5 Material flammability The materials used in the components and systems are evaluated to determine if they are flammable at the worst-case operating conditions. If information on a mater
39、ial for the worst-case operating conditions cannot be located, tests shall be conducted to obtain this information. If the materials and components are determined to be non-flammable, the ignition mechanisms need not be analysed for that component. The oxygen hazard analysis summary (see Annex B) is
40、 updated with the results, using “N” for non-flammable, or “F” for flammable. ISO 22538-4:2007(E) ISO 2007 All rights reserved 5 6.6 Ignition mechanisms 6.6.1 General An ignition survey is performed for each component found to have materials that are flammable under use conditions. Each ignition mec
41、hanism shall be evaluated to determine if it exists in the component and the likelihood that it will cause an ignition. The results of the analysis for each ignition mechanism are documented on the oxygen hazards analysis chart (see Annex B). Ratings for the ignition mechanism are “0” almost impossi
42、ble, “1” remotely possible, “2” possible, “3” probable, “4” highly probable. 6.6.2 Frictional heating Parts of a component or system may rub against one another with enough force or velocity to raise any one part to its ignition temperature at the given oxygen pressure and concentration. EXAMPLE Rot
43、ating or oscillating equipment and chattering relief valves. 6.6.3 Adiabatic compression High temperatures are generated if a gas is rapidly compressed. These high temperatures can readily ignite polymers or flammable contaminants. EXAMPLE Downstream valve or flexible hose with a polymer liner in a
44、dead-ended high-pressure oxygen manifold. 6.6.4 Mechanical impact An object with a large mass or momentum striking a material may cause mechanical deformation and expose fresh surfaces, thus producing ignition of the material. EXAMPLE A poppet of a solenoid-operated valve impacting the polymer seat.
45、 6.6.5 Particle impact Combustible particles impinging on materials at higher velocities in oxygen-enriched environments may cause ignition. The size of particles, flow velocity and temperature are among the variables that affect the ignition by particle impact EXAMPLE Sonic-velocity gas through an
46、orifice accelerating particles into a valve housing. 6.6.6 Mechanical stress or vibration Materials that are poor heat conductors (such as polymers) may reach their ignition temperatures when stressed or vibrated. EXAMPLE Gaskets that protrude inside piping. ISO 22538-4:2007(E) 6 ISO 2007 All rights
47、 reserved6.6.7 Static discharge Discharges of static electricity may produce high temperatures, sometimes high enough to cause a material to reach its ignition temperature. EXAMPLE The accumulation of electrostatic charges created by the friction of dry oxygen flowing over non-metallic materials. 6.
48、6.8 Electric arc Electric arcs may provide the energy to ignite materials in the presence of oxygen. EXAMPLE An insulated heater short-circuiting and arcing through its sheath to the oxygen. 6.6.9 Chemical reaction An unrelated chemical reaction can produce sufficient heat to ignite materials in the
49、 presence of oxygen. EXAMPLE A chemical process that generates elevated temperatures, oxygen-generating systems and the ignition of metals at high temperatures. 6.6.10 Resonance Acoustic oscillations within resonant cavities cause a rapid gas temperature rise. The rise is rapid and achieves higher values when particles are present. Ignition may result if the heat generated is not rapidly dissipated. EXAMPLE Gas flow into a tee and out of a branch port such that the remaining closed por
