1、BS 5N 100-5:2006Aircraft oxygen systems and equipment Part 5: Guide to fire and explosion hazards associated with oxygen, including handling, storage and replenishmentICS 49.090NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBRITISH STANDARD AEROSPACE SERIESPublishing and copyr
2、ight informationThe BSI copyright notice displayed in this document indicates when the document was last issued. BSI 2006ISBN 0 580 49312 1The following BSI references relate to the work on this standard:Committee reference ACE/38Draft for comment 06/30140682 DCPublication historyFirst published as
3、BS N 100:1967Second edition BS 2N 100:1973Third edition BS 3N 100:1985Revised as BS 4N 100-5:1999This publication BS 5N 100-5:2006Amendments issued since publicationAmd. no. Date Text affectedBS 5N 100-5:2006 BSI 2006 iBS 5N 100-5:2006ContentsForeword ii1 Scope 12 Normative references 13 General 14
4、Factors affecting an incident 25 Illustrative case histories 66 Common incident causes 97 Summary 12AnnexesAnnex A (normative) Liquid and gaseous oxygen handling, storage and aircraft replenishment 13Bibliography 17Summary of pagesThis document comprises a front cover, an inside front cover, pages i
5、 and ii, pages 1 to 17 and a back cover.BS 5N 100-5:2006ii BSI 2006ForewordPublishing informationThis part of BS 5N 100 was published by BSI and came into effect on 31 October 2006. It was prepared by Technical Committee ACE/38, Aircraft oxygen equipment. A list of organizations represented on this
6、committee can be obtained on request to its secretary.SupersessionThis part of BS N 100 supersedes BS 4N 100-5:1999, which is withdrawn.Information about this documentThis new edition of BS 5N 100 incorporates technical changes only. It does not represent a full review or revision of the standard, w
7、hich will be undertaken in due course.BS N 100 consists of the following parts: Part 1: Design and installation Part 2: Tests for the compatibility of materials in the presence of oxygen Part 3: Testing of equipment and systems Part 4: Guide to the physiological factors Part 5: Guide to fire and exp
8、losion hazards associated with oxygen, including handling, storage and replenishment Part 6: Guidance and recommendations on the selection of materials for use with oxygen Part 7: Guide to cleaning, labelling and packagingNOTE The latest revision of an aerospace series standard is indicated by a pre
9、fix number.Hazard warningsWARNING. This British Standard calls for the use of substances and/or procedures that can be injurious to health if adequate precautions are not taken. It refers only to technical suitability and does not absolve the user from legal obligations relating to health and safety
10、 at any stage.Use of this documentIt has been assumed in the preparation of this British Standard that the execution of its provisions will be entrusted to appropriately qualified and experienced people, for whose use it has been produced.Presentational conventionsCommentary, explanation and general
11、 informative material is presented in smaller italic type, and does not constitute a normative element.Contractual and legal considerationsThis publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a Brit
12、ish Standard cannot confer immunity from legal obligations. BSI 2006 1BS 5N 100-5:20061 ScopeThis part of BS N 100 provides guidance on the dangers, and avoidance of, fire and explosion hazards associated with oxygen. Annex A provides additional guidance and recommendations on liquid and gaseous oxy
13、gen handling, storage and aircraft replenishment.2 Normative referencesThe following referenced 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
14、 amendments) applies.BS N 100-1, Aircraft oxygen systems and equipment Part 1: Design and installationBS N 100-2, Aircraft oxygen systems and equipment Part 2: Tests for the compatibility of materials in the presence of oxygenBS N 100-6, Aircraft oxygen systems and equipment Part 6: Guidance and rec
15、ommendations on the selection of materials for use with oxygenBS N 100-7, Aircraft oxygen systems and equipment Part 7: Guide to cleaning, labelling and packaging3 General3.1 With few exceptions, metallic and non-metallic materials continue to burn in oxygen-rich atmospheres when once ignited. The r
16、esulting release of energy can cause very high local pressures and temperature and weakening of the surrounding materials, with resultant explosive failure of the pressure-containing envelope.3.2 Ignition conditions can result from the internal or external application of sufficient heat energy and s
17、pontaneous combustion can be caused by the adiabatic compression of oxygen in the vicinity of certain non-metallic materials. Friction rubbing, certain gas flow phenomena (e.g. gas and material resonance), impact of particles (e.g. contamination) and electrostatic discharge are also possible causes
18、of oxygen fires.3.3 In any oxygen system, materials should be selected to withstand the maximum temperature and pressure likely to be experienced under the most adverse operating conditions. The tests described in BS N 100-2 should be used for the selection and quality control of all non-metallic ma
19、terials. However, consideration should be given to the possible interaction between two relatively “safe” materials, for example the reaction between aluminium and fluorinated greases.3.4 Despite the most careful attention given to the selection of the materials, and of the construction of component
20、s, there remains a potential risk that combustion will occur. The possibility of sustained combustion can be greatly reduced by selecting materials in accordance with BS N 100-6 and employing designs in accordance with BS N 100-1.BS 5N 100-5:20062 BSI 20063.5 The effects of combustion can be minimiz
21、ed by ensuring that it is contained, and heat generated is rapidly dissipated, before the adjacent metals reach ignition temperature.3.6 From data reported to HSE under the Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995 1 (RIDDOR) over a five year period (1990 to 1994), 9
22、5 incidents involved gaseous oxygen (see 5.4).4 Factors affecting an incidentNOTE See ASTM Standard Guide for Studying Fire Incidents in Oxygen Systems 2 for further information.4.1 Local area enrichmentOxygen is not a flammable gas but supports combustion. Most materials, including those normally r
23、egarded as fire resistant, burn vigorously in an oxygen enriched atmosphere. They are also more easily ignited. These effects are evident even if the enrichment is only a few per cent. Oxygen enrichment of the atmosphere is generally the result of leakage from damaged pipes, hoses, valves, connectio
24、ns, etc.4.2 Contamination4.2.1 Low level contaminationWhen contamination is present in an oxygen system, the contaminant might serve to start the incident. Then, the ensuing fire involving the polymers, metals, non-metals and contaminant can consume the contaminant fully, leaving no indication of it
25、s original presence.4.2.2 High level contaminationWhen the contamination level is high, it can produce so large and explosive an event that the system integrity can be breached, and the fire extinguished without complete combustion of the contaminant, thus leaving evidence of its presence.In these i
26、nstances, the flammability of the contaminant can be so much greater than that of the metals and non-metals that there might be only scant damage to the system materials.4.2.3 “Carbon” or black dustIn many incidents, a black powder is present on many surfaces. The powder could be unreacted carbon fr
27、om incomplete combustion of organic materials either inside or outside the components. However, some powders that look like carbon are not. For example, fires involving aluminium in gaseous or liquid oxygen produce a black (and in some cases grey) powder that is largely unreacted aluminium. Indeed,
28、such dust might be present as a result of a fire involving aluminium or because of fabrication processes. In metal inert gas (MIG) welding, aluminium is vaporized and condenses as a black dust in the region of the bead. BSI 2006 3BS 5N 100-5:2006If this powder is present in an oxygen system, it coul
29、d be the cause of ignition, because it is very flammable and has even been observed burning in air.4.2.4 OilOil in oxygen systems can be a severe hazard. Many oils, hydrocarbons in particular, are relatively volatile in comparison to metals and polymers, especially in aerosol form. Their spontaneous
30、 ignition temperatures are much lower than those of most other materials (metals and non-metals) used to fabricate oxygen systems, including many materials not generally regarded as oxygen compatible. Therefore, heat of compression can ignite oils much more easily. Furthermore, many oils burn very r
31、apidly, even explosively, and they are often the likely cause of an oxygen incident. Obvious presence of oil near an oxygen incident is a strong indicator of probable contamination.4.3 Particle impactImpact and subsequent ignition of particles in oxygen systems have been demonstrated to have been th
32、e cause of several fires. This ignition mechanism is especially likely at, and just downstream of, locations where the velocity of the oxygen is sonic (any location across which there is a 2:1 absolute pressure drop), and has been demonstrated at velocities as low as 150 ft/s (50 m/s).4.4 Debris sum
33、psMany systems contain regions where debris tends to collect. Particle debris can accumulate at low points or stagnant side branches. If the piping for a by-pass valve is connected to the bottom region of a horizontal run of pipe, debris that passes through the system could drop into the stagnant up
34、stream legs of the by-pass run. If this valve is then opened, accumulated debris is injected into the high-velocity valve and could possibly cause a fire either in the by-pass run or further downstream.4.5 Heat of compressionWhen a gas is compressed rapidly, its temperature rises. The pressurization
35、 of a system tends to produce the greatest temperatures within the gas initially in the system. The increase in temperature can cause spontaneous ignition of some system components. This compression is nearly adiabatic and typically occurs at system end points or trapped volumes. In extreme cases, h
36、eat of compression has produced some of the most explosive (rupturing and fragmenting components) and most probable mechanisms of oxygen fires. In severe cases, a heat of compression fire might occur on the very first pressurization of a system. Every incident should be examined for a mechanism that
37、 could have enabled rapid gas compression and for where the compressed gas might have been located relative to the fire damage.BS 5N 100-5:20064 BSI 20064.6 Over-pressure4.6.1 Loss of containmentA fire in an oxygen system can produce over-pressurization leading to possible loss of containment of the
38、 oxygen. Among the characteristics that can be seen are bulging (see 4.6.2), bursting (see 4.6.3), venting, explosion, and fragmentation (see 4.6.4).4.6.2 BulgingBulging or swelling of components can occur at the site of explosions, at weak regions of the system, or both. In brazed copper systems, i
39、t is common to see over-pressure effects at annealed regions, such as just outside brazed joints, where hardened tubing is annealed and therefore be of lower strength. The presence of such bulging in brazed copper joints in a local region only suggests a localized explosive event. Bulging at copper
40、joints throughout the system can also indicate a systematic pressure increase.4.6.3 BurstingVessels that burst into several large pieces typically have failed along weak regions or flaws and have been exposed to either a small explosive event or to a general systematic pressure rise that has been re
41、latively slow. In some metal alloys, such as aluminium, piping is extruded with dies and mandrels in a way that can produce weak longitudinal seams. Over-pressurization, either slow or fast, can cause tears along these seams, yielding several similar pieces. This can occur at pressures much lower th
42、an those normally expected to cause fragmentation.4.6.4 FragmentationWhen a vessel is fragmented into many small pieces of dissimilar shapes and sizes, it usually suggests a very fast combustion that produced pressures well above the burst pressure of the vessel, before the vessel actually fails. Th
43、is type of failure is also commonly known as a “brittle” failure.Fragmentation can be associated with detonations where the propagation velocities are greater than the speed of sound and this makes the presence of relief valves and vents ineffective.4.7 Time delaysTransient events, e.g. the operatio
44、n of a valve, can lead to the unexpected consequence of an oxygen fire. Most of the time the fire occurs almost simultaneously with the event, but there can be appreciable delays between its cause and effect. BSI 2006 5BS 5N 100-5:20064.8 Crevices and cavitiesA crevice can be a potential ignition si
45、te in liquid oxygen (LOX) systems if it fills with liquid, especially through a narrow passage or pore. When the vessel is drained and warmed, high pressure and high velocity develops in the liquid, if the passage is small, as it tries to escape. If the crevice is in a weld of a metal that produced
46、MIG weld dust, it could contain fine, easily ignited particles that might become entrained in the flow and impact a piping inter-section or valve seat, causing ignition (see also 6.2).4.9 Surface discolorationDuring a fire, brass alloys might be exposed to brief, intense temperature or to corrosive
47、chemicals, resulting in a surface depletion of the volatile zinc constituent known as “pink brass”. The result can be a pink hue on the brass surface that is not contamination and that is also not likely to be associated with the cause of the incident.4.10 Flash fire4.10.1 There are often two distin
48、ct phases in an oxygen incident: an initial flash fire of the most flammable portion of the system followed by slower, more enduring general combustion.4.10.2 The prospect of an initial flash fire involving surface contaminants is one reason that low levels of oil in an oxygen system might not be di
49、scovered after an incident, despite the possibility of having played a crucial role either in ignition or in the related kindling chain.4.11 Gas permeationWhen a gas permeates or dissolves into a material at high pressure and the pressure is suddenly released, the material can behave like a pressure vessel. If the material is an elastomer, it can swell like a balloon, sometimes more than doubling its apparent size. The internal pressure can cause the elastomer to exceed its tensile strength, and it can burst. Consequent leakage of oxygen
