1、_ SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising there
2、from, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2013 SAE International All rights reserved. No part of this p
3、ublication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-497
4、0 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/AIR6036 AEROSPACE INFORMATION REPORT AIR6036 Issued 2013-05 Passenger Hypoxia Pro
5、tection Utilizing Oxygen Enriched Gas Mixtures RATIONALE There is increased interest within the aviation oxygen community in the possibility of using on-board oxygen concentration systems to supply oxygen-enriched breathable gas mixtures having less than 99.5% oxygen content. This Aerospace Informat
6、ion Report provides information that supplements standards addressing other aspects of passenger oxygen dispensing device performance, such as AS8025A. 1. SCOPE Currently, existing civil aviation standards address the design and certification of oxygen dispensing devices that utilize oxygen sources
7、supplying at least 99.5% oxygen. This Aerospace Information Report discusses issues relating to the use in the passenger cabin of oxygen enriched breathing gas mixtures having an oxygen content of less than 99.5% and describes one method of showing that passenger oxygen dispensing devices provide su
8、itable hypoxia protection when used with such mixtures. 1.1 Purpose There is no current guidance available to certify passenger oxygen dispensing devices (e.g., oxygen masks) for use with oxygen sources supplying less than 99.5% oxygen. This document is intended to provide information for use as a s
9、upplement to standards that address other aspects of passenger oxygen dispensing device performance, such as AS8025. 2. REFERENCES 2.1 Applicable Documents The following publications form a part of this document to the extent specified herein. The latest issue of SAE publications shall apply. The ap
10、plicable issue of other publications shall be the issue in effect on the date of the purchase order. In the event of conflict between the text of this document and references cited herein, the text of this document takes precedence. Nothing in this document, however, supersedes applicable laws and r
11、egulations unless a specific exemption has been obtained. SAE AIR6036 Page 2 of 6 2.1.1 SAE Publications Available from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001, Telephone: 877-606-7323 (inside USA and Canada) or 724-776-4970 (outside USA), Web address: http:/www.sae.org AIR825 Oxygen
12、Equipment for Aircraft AS8010 Aviators Breathing Oxygen Purity Standard AS 8025 Passenger Oxygen Mask 2.1.2 FAA Publications: Available from Federal Aviation Administration, 800 Independence Avenue, SW, Washington, DC 20591, Tel: 866-835-5322, www.faa.gov. 14 CFR Part 25 Airworthiness Standards: Tra
13、nsport Category Airplanes 2.1.3 U.S. Government Publications Available from Document Automation and Production Service (DAPS), Building 4/D, 700 Robbins Avenue, Philadelphia, PA 19111-5094, Tel: 215-697-6257, http:/assist.daps.dla.mil/quicksearch/. MIL-PRF-27210 Oxygen, Aviators Breathing, Liquid an
14、d Gas 2.1.4 European Aviation Regulations Available from European Aviation Safety Agency, Otto Platz 1, Koln Deutz, Postfach 101253, D-50452 Cologne Germany, Tel: +49-221-8999-000, www.easa.eu.int. CS Part 25 Certification Specifications for Large Airplanes 2.2 Definitions ALVEOLAR SPACE: The areas
15、of the lungs containing the alveoli, in which transfer of gas between the inhaled gases and the blood supply takes place. Sometimes called the respiratory zone of the respiratory tract. ARTERIAL OXYGEN SATURATION (SaO2): The ratio of the quantity of oxygen actually carried in the blood by hemoglobin
16、 to the maximum hemoglobin transport capacity of the blood. This ratio is expressed as a percentage. AVIATORS BREATHING OXYGEN (ABO): Oxygen of a quality and purity suitable for breathing use in aviation applications. Usually, ABO has a minimum oxygen content of 99.5%, although AS8010 includes certa
17、in classes for which this is not the case. DEAD SPACE: Also called Dead Volume. Portion of the respiratory tract (mouth, trachea, and bronchi) that conducts or carries inhaled gases from the mouth to the areas of the lungs in which transfer of gas between the inhaled gases and the blood supply takes
18、 place. Sometimes called the conducting zone of the respiratory tract. OXYGEN DISPENSING DEVICE: Equipment that conveys oxygen between the supply source and the respiratory tract of the user. Commonly an oxygen mask. OXYGEN ENRICHED BREATHING GAS (OEBG): A breathing gas mixture having trace impurity
19、 levels equivalent to ABO and containing a higher percentage of oxygen than ambient air but a lower percentage of oxygen than is present in Aviators Breathing Oxygen. SAE AIR6036 Page 3 of 6 OXYGEN ENRICHED GAS (OEG): A gas mixture containing a higher percentage of oxygen than ambient air. PHASE-DIL
20、UTION EFFECT: The phenomenon in which a higher degree of blood oxygenation is achieved by dispensing supplemental oxygen non-homogeneously, such that the gas that penetrates deepest into the respiratory tract contains a higher percentage oxygen than the average value for the entire inhaled volume. 3
21、. BACKGROUND Historically, when civil aircraft operational altitudes were high enough that supplemental oxygen was necessary, the source has usually been greater than 99.5% oxygen content, typically meeting the purity requirements of “Aviators Breathing Oxygen“ or “ABO.“ Designs for oxygen dispensin
22、g devices as well as certification requirements reflected the use of this type of gas. In 14 CFR 25.1443 (c) (1) and (2), mean trachael oxygen partial pressure is used as the defining standard for passenger supplemental oxygen dosage. Developments in civil aviation have led to a situation in which i
23、t may be technically feasible and operationally desirable to meet the need of cabin occupants for supplemental oxygen by using oxygen enriched gas mixtures that have an oxygen content greater than ambient air but less than 99.5%. Such a condition could occur if an oxygen concentration system were us
24、ed to supply oxygen-enriched breathing gas (OEBG). If it is necessary for an airplane to fly a considerable distance at an altitude where the passengers will need supplemental oxygen, the use of equipment that generates an oxygen-enriched gas mixture may offer advantages, compared to the use of stor
25、ed compressed oxygen. Present standards such as AS8025 do not consider the use of OEBG. There is no clear guidance as to how one might show that the performance of a dispensing device is satisfactory for use by cabin occupants when some of the supplemental oxygen needs are met by use of oxygen enric
26、hed gas mixtures. 4. PROPOSED APPROACH An oxygen-dispensing device under consideration for use with OEBG may have previously been shown to perform satisfactorily when used with 99.5% oxygen. In that case, issues such as materials of construction, mechanical strength, and performance across a suitabl
27、e range of ground survival environments and operating environments would already have been adequately addressed, for instance by showing the device conforms to AS8025. Other means of addressing these issues could also be acceptable if they properly consider the range of performance attributes needed
28、 for a given application. Given that satisfactory hypoxia-protective performance with 99.5% oxygen has been established, it remains necessary to evaluate the performance that will be achieved by the dispensing device when a supplemental oxygen source having lower oxygen content is used. In evaluatin
29、g the performance of a dispensing device when a supplemental oxygen source other than 99.5% oxygen is used, the objective is to show that the combination of device and source can provide an equivalent respiratory performance to that provided when 99.5% oxygen is used to supply the mean inspired trac
30、heal partial pressure of oxygen that is mandated by Airworthiness requirements for a given pressure altitude. 5. EQUIVALENT PERFORMANCE CONCEPTS It must be recognized that airplane cabin occupants are not generally supplied with a sufficient flow of supplemental oxygen to provide 100% of their inhal
31、ed volume during a decompression event. A combination of some oxygen and some ambient air is delivered in most cases. SAE AIR6036 Page 4 of 6 5.1 Mass Balance Equivalence When a known quantity of 99.5% oxygen is dispensed in combination with a known quantity of ambient air at a known ambient pressur
32、e, the result can be analyzed in terms of the average percent oxygen that would result from homogeneously mixing these quantities of gas at the prevailing ambient pressure. The total volume of the homogeneous mixture would be equal to the sum of the volumes of ambient air and 99.5% oxygen that were
33、dispensed. In principle, a gas mixture having any desired oxygen concentration between ambient air and 99.5% oxygen can be produced, if the proper fraction of 99.5% oxygen is employed in the process. Alternatively, one can analyze the result in terms of the oxygen partial pressure rather than oxygen
34、 concentration, under a similar set of arguments. If a second mixture were prepared combining suitable (different) volumes of OEBG and ambient air, an identical homogeneous mixture could be produced, so long as the oxygen concentration in the OEBG were not less than the final target oxygen concentra
35、tion. In terms of a simple mass balance, these two homogeneous mixtures could be considered identical. The most basic mathematical analysis of breathing oxygen requirements, as found in AIR825, implicitly assumes that dispensing these two mixtures would produce the same results. A simple mass balanc
36、e analysis would also indicate that these two mixtures would produce the same mean inspired tracheal partial pressures under the tidal volume and breathing rate assumptions used in 14 CFR/CS 25.1443(c). However, state-of-the-art dispensing devices utilize the phase dilution principle, in which the i
37、nspired gas is intentionally transferred in a non-homogeneous manner to improve SaO2. It is demonstrated that in some cases, the simple mass balance equivalence may not equate to equivalent respiratory performance under phase dilution conditions. 5.2 Phase Dilution and SaO2Benefit When a human inhal
38、es under nominal conditions, about two thirds of the inspired volume enters the alveolar space (containing the alveolar sacs) where gas transfer occurs. The other one third of the inspired volume progresses no further than the structures of the dead space (including the mouth, trachea, and bronchi),
39、 which essentially function as plumbing, with little or no gas transfer to and from the blood occurring in that region. A simple example can illustrate the significance of this fact. Consider two hypothetical oxygen dispensing cases. (The effects of water vapor are neglected in this example.) In the
40、 first case, the subject inhales his full inspired volume as a perfectly homogeneous mixture containing 66.7% oxygen and 33.3% nitrogen. In the second case, the subject inhales 100% oxygen for the first 2/3 of his inspired volume and 100% nitrogen for the final 1/3. For simplicity, imagine that no m
41、ixing occurs within the respiratory tract during the inhalation process in either of these hypothetical cases. In the first case, this means that the partial pressure of oxygen in the alveoli is only 66.7% of the ambient pressure. In the second case, the partial pressure of oxygen in the alveoli is
42、equal to 100% of the ambient pressure. The higher partial pressure of oxygen in the alveoli would be expected to produce better oxygenation in the second case. In these two hypothetical cases, one would anticipate different oxygenation effectiveness, even though the overall mass balance is the same
43、and the same mass of oxygen has been delivered to the user. The designs of phase dilution oxygen masks are intended to exploit this effect. The mask is equipped with valves arranged so that the first valve to open during inhalation supplies the user with gas that had been delivered directly from the
44、 oxygen source to the reservoir bag since the end of the previous inhalation. When the reservoir bag is emptied, another valve opens and the gas making up the remainder of the inhalation volume is a mixture of ambient air entering from the dilution port and additional gas arriving from the oxygen so
45、urce at the moment of inhalation. As a result, the first gas inhaled has the highest oxygen content. While some mixing is presumed to occur in the respiratory tract, it is believed that a homogeneous composition is not achieved. Thus, the gas penetrating into the alveoli contains a greater-than-aver
46、age oxygen content. More effective oxygenation of users is expected to result from this dispensing strategy. SAE AIR6036 Page 5 of 6 The apparatus used in breathing machine tests is designed to mix the gases and does not simulate the phased dilution performance. Thus, it is standard practice to util
47、ize human subject testing as a means of validating the results from breathing machine tests. 5.3 Physiological Equivalence The purpose of equipping aircraft with supplemental oxygen systems is to ensure occupants are adequately oxygenated in the event of decompression at high altitude. The primary i
48、ndicator of an individuals degree of oxygenation is SaO2. Accordingly, if two means of dispensing oxygen result in the same degree of oxygen saturation, they can be considered equivalent in a physiological sense. In AS8025, measurement of SaO2is considered a suitable alternate to determining trachea
49、l oxygen partial pressure, as a method of assessing performance of an oxygen mask used by human subject tests in an altitude chamber. Pulse oximetery is an established technique that can measure SaO2 in human subjects. Pulse oximetery is used in clinical situations to monitor patients that are receiving anesthesia during surgery, or that are undergoing oxygen therapy. It is a non-invasive method that is widely accepted in the medical com
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