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4 AIR QUALITY IN EMERGENCY SITUATIONS Chapter 2 describes the physical factors that influence airliner cabin air quality under normal operating conditions, and Chapter 3 describes the federal regulations and industry operating procedures that bear on air quality. This chapter focuses on the effects of emergency situations on cabin air quality. Two in-flight emergency situations affect cabin air quality: fire and cabin Repressurization. Not only can fire lead to deterioration of the structural integrity of the aircraft and its ability to remain in controlled flight, but the resulting smoke and toxic combustion products and ultimately the fire itself constitute direct hazards to passengers and crew. The main threat to passengers in sudden Repressurization is hypoxia. ONBOARD FIRES Providing protection from fire in airliners is a complicated matter. Cabin interiors are furnished and lined with potentially flammable materials, and passengers are tightly packed in a relatively small, confined enclosure. Inaccessible compartments contain potential ignition sources and combustible materials, and wing tanks carry thousands of gallons of highly flammable aviation fuel. Given these conditions, the average of 32 deaths a year from the effects of fire involving U.S. air carriers between 1965 and 1979 might seem remarkably low, compared with the figures on other modes of transport. \4 But it is a mayor concern. An estimated 15% of all deaths in domestic air carrier accidents during that period have been attributed to the effects of fire. 15 91
92 An analysis of air transport accidents in North Atlantic Treaty Organization (NATO) countries between 1964 and 1975 revealed (when such information could be determined) that injuries and deaths were due primarily to the postcrash effects of fire, smoke, and toxic fumes and only secondarily to crash impact itnelf.17 The aircraft used in NATO countries are largely of American manufacture and meet American standards, so data on accidents in these countries should be considered with the American data; that increases the apparent incidence of fire-related death. Three accidents have played an especially prominent role in increasing awareness of the importance of smoke and toxic fumes: · In 1973, a passenger aboard a Varig Airlines flight (B-707) reported smoke in the lavatory shortly before the scheduled landing at Orly Airport, near Paris. Within 6 min. thick black smoke filled the cabin and cockpit. Unable to see their instruments, the pilots opened their side windows and made a forced landing in a field 4 miles from the airport. Of 135 occupants, 10 crew members and one passenger survived, all in the cockpit. The remaining 124 died from asphyxiation or the effects of toxic gases.4 1° · In 1980, a Saudi Airlines aircraft (L-1011) with 301 passengers and crew on board made an emergency landing after reporting an in-flight fire. The aircraft landed and taxied normally for several minutes before coming to a stop. None of the doors was opened, and all on board died. · In 1983, a successful landing was made in Greater Cincinnati Airport after an in-flight fire aboard an Air Canada flight (DC-9~. Of the 46 occupants, 23 were overcome by smoke and toxic fumes, could not leave the airplane, and died in the ensuing fire.~° These incidents are part of the ample evidence that many passengers in crashes or unplanned landings in which fire is involved are unable to escape from the aircraft, even though they have not sustained injuries that would prevent escape. There is a strong presumption that these passengers have succumbed to smoke or toxic fumes in the cabin. The conditions of air quality during
93 fire emergencies are examined here, with appropriate measures that might be taken to prevent or ameliorate these conditions so as to increase the likelihood of survival and escape. INHIBITING IGNITION wayside Postcrash fires generally originate in one of six . From release of fuel caused by wing separation during impact-survivable accidents. · From release of fuel from damaged fuel tacks or fuel lines during impact-survivable accidents. · From fuel tank explosions caused by external heating and other ignition sources in the crash. ~ From ignition of materials in the cabin during the crash. · In the propulsion system. · In the landing gear system. It is generally agreed that ignition of Jet fuel constitutes the greatest potential danger in aircraft crashes.lS In accidents in which large quantities of fuel are released and ignited (pool fires) and the integrity of the fuselage is damaged to the extent that mayor portions of the cabin are directly subjected to the fuel fire, the dominance of the fuel fire is clear. But even when the fuselage remains relatively intact, the radiant energy impinging on the cabin through the window ports from the flame of the pool fire is sufficient to ignite many materials.!' Obviously, prevention of crashes and resulting fires is a major concern of the airline industry and the Federal Aviation Administration (FAA), but discussion of approaches to prevention is beyond the scope of this report. Major fuel fires are very rare, and most incidents involving fire on aircraft involve less catastrophic situations. Although they are of considerable interest, little information is available on the progress of major
94 past in-flight fires. However, typical origins of in- flight fires have been characterized.12 Typical origins in the cockpit include malfunction of the electric equipment and oxygen supply system. Origins of fires in the cabin include failure in the oxygen supply system, liquid fuel spills, short circuits, matches, lighters, cigarettes and cigars, and carry-on luggage. The food service galley is a common source of fires, with origins including ovens and oven exhaust systems, electric equipment, food waste storage, and the oxygen system. The lavatory is one of the few areas of the cabin where, because it is enclosed and has separate ventilation, a fire can go undetected until it reaches a dangerous magnitude. Although fires resulting from smoking in the lavatories have been of considerable concern, it appears that light wiring, speaker transformers, fluorescent- light ballasts, water heaters, and the flushing motor are more likely sources of serious lavatory fires. i2 In cargo compartments, fire sources include short circuits and cargo. Movie projectors, electric motors, and control equipment are possible causes of attic fires. Unpressurized landing gear wells--containing hydraulic fuel lines, electric controls and devices, and water-line heaters--can be sources of fire. Finally, electric equipment and avionic equipment are potential sources of electric fires. Table 1-9 summarizes the incidents involving smoke or fumes in aircraft cabins or cockpits that have been recorded in the FAA Civil Aeromedical Institute (CAMI) Cabin Safety Data Bank. About 20 incidents are reported in a typical year, including about 13 emergency landings. An analysis of a different set of data, reports by Part 121 and Part 135 air carriers to FAA between 1980 and 1985 (summarized in Table 1-8), reveals that--of 138 incidents of fire, explosion, smoke, or related odors--68 involved mechanical failures, 25 involved electric malfunctions, 15 were galley incidents (of which eight involved spills of food or other material in the oven), 10 were lavatory fires (of which five were in waste-paper receptacles or otherwise involved paper products), eight were in the cabin (of which five involved cigarettes or lighters), and eight were categorized as "other" or "undetermined.' Strict adherence to servicing codes and careful examination of such codes whenever a fire results from malfunction are required. Similarly, each crew-related fire, especially
95 those involving cooking, should receive careful scrutiny from the point of view of equipment reliability, procedural safety, and crew performance. In large measure, the enforcement activities of FAA and the review and recommendation procedures of the National Transportation Safety Board described in Chapter 3 are intended to accomplish these aims. MATERIALS TESTING AND SELECTION Failing prevention or immediate extinguishing of fire, it becomes essential to decrease the rate of flame propagation and production of toxic gas through appropriate selection of structural and decorative materials in the aircraft. The mayor regulatory efforts to date have been directed toward selection of minimally flammable materials for incorporation into the aircraft cabin and cockpit, in accordance with fire testing procedures noted in the Federal Aviation Regulations.5 On October 26, 1984, FAA published new standards that would substantially reduce the flammability of foam seat cushions; 20 transport aircraft seat cushions must meet these new standards by November 26, 1987. They require exposure of specimens of seat back and bottom cushions over a limited area to a burner with temperature and heat flux typical of cabin fire. The test specifications require that the specimens simulate the intended seat configuration and allow for the burning interaction of upholstery cover, fire blocking layer, and foam cushion material.~4 Criteria for acceptance consist of 10% allowable weight loss, burn length of 17 in., and performance essentially matching that attained by two benchmark materials. On August 8, 1984, FAA announced proposed rules to upgrade the fire safety standards for cargo or baggage compartments in transport aircraft.19 FAA conducted full-scale fire tests to investigate the resistance of cargo liners to flame penetration for both compartments to which crew members have access and in which fire suppression systems are required (class C compartments) and smaller compartments without access, which are designed for fire control by oxygen starvation (class D compartments). The main conclusion drawn from the testing results was that a more realistic and severe
96 test requirement was needed for cargo liners used in both class C and class D cargo compartments. The new fire test method, which measures breakthrough resistance of cargo liners, applies the maximal heat flux and temperature measured during full-acale tests under realistic ceiling and sidewall liner orientation, i.e., both vertical and horizontal. Criteria for acceptance are absence of flame penetration of ceiling and sidewall specimens and temperature above the ceiling specimen not exceeding 400°F. In 1980, the FAA Special Aviation Fire and Explosion Reduction (SAFER) Committee recommended a specific fire scenario for FAA to use in full-scale tests and expedited the development and evaluation of the Ohio State University (OSU) rate-of-heat-release apparatus as the potential standardized test for materials.25 On April 16, 1985, after full-scale tests, FAA announced a notice of proposed rule-making (NPRM 85-10) establishing new fire test criteria for type certification of transport aircraft that would apply to cabin interiors of all newly manufactured aircraft and all other aircraft that were type-certified after 1958 .22 In full-scale tests, various interior panel materials were subjected to situations simulating an external fuel pool fire with an open door, and the results were correlated with performance with the OSU test apparatus.9 A panel of phenolic-fiberglass, a state-of-the-art composite used in some applications in aircraft interiors, was used as a benchmark. It added approximately 2 min to survivability, compared with other available panels studied. Criteria of 65 kW/m2 for peak heat release rate and 65 kW-min/m2 for total heat release in 2 min were established in accordance with the performance of this benchmark panel. The Aerospace Industries Association of America (AIA), representing the airframe manufacturers, appears to have legitimate concern about the ability of the proposed NPRM 85-10 to discriminate adequately and consistently between acknowledged inferior products and molded interior components with known improved fire- resistant characteristics.2 The proposed alternative standardized testing, advocated by AIAl, so discriminates, but permits use of state-of-the-art material for aircraft interior walls, ceilings, and other components that is (from a fire-resistance
97 standpoint) only one-tenth as good as newer material, which still needs development before it can be satisfactorily used. Without some regulatory action or impetus, the use of these less developed but safer materials could be delayed until the next century. Notwithstanding a potentially adverse economic impact on airframe manufacturers, government-regulators and enforcers, airline operators, and ultimately consumer- passengers, the Committee feels (with respect to all the topics under consideration here) that improved comfort and safety deserve consideration, despite the extra time that might be required in fine-tuning the product to ensure its timely incorporation into some existing and next-generation aircraft. In general, the FAA program on flammability testing is excellent, and its research efforts to improve testing are appropriate and valuable. The Committee feels that continuing research is also needed in materials development. Although F. M standards are met by currently available materials, other materials, if developed further, would far exceed current standards and would substantially increase fire protection in aircraft. Such organizations as AIA or a similarly constituted organization of airframe manufacturers should be strongly encouraged to initiate or support programs in this field. The Secretary of Transportation is charged under the Federal Aviation Act with responsibility for regulating air commerce in such a manner as best to promote both its development and its safety, but the Committee believes that passenger safety must be paramount. Because of the extreme hazard presented by fire and the associated smoke and noxious and toxic combustion products, minimization of fire and fumes should be of highest priority. In support of the belief that a materials development program should be encouraged, we cite the example of the National Aeronautics and Space Administration's response to the 1967 pad fire. A few simple guidelines were developed for material replacement as noted in Table 4-1, and a keyed index system was initiated. The latter consisted of an index of every nonmetallic component or individual item considered for use in spacecraft or related equipment keyed to test results for a variety of atmospheric conditions, such as odor? toxicity, total emission of organic substances, and various fire tests.
98 TABLE 4-1 NASA Guidelines for Selection of Replacement Materialsa Replace all materials that burn in 100% oxygen (3.~-16.5 psia) with nonflammable substitutes. Material substitution may not affect mission function. B. All products that cannot be manufactured from nonflammable materials are to be covered with an insulating, nonflammable coating to prevent the flammable substrate from being affected by heat and fire for a specified period. If A and B cannot be accomplished in a timely fashion, institute an R&D program to achieve those aims. D. Provide a measure of fire control by the arrangement of materials in the spacecraft. Potential flame paths can be interrupted by separating from each other items that have some propensity to burn, thus creating "fire breaks." a Data from M. I. Radnofsky (personal communication). SMOKE DETECTION AND FIREFIGHTING On March 29, 1985, FAA added ~ new paragraph to the Part 121 regulations to provide thatch . Each lavatory and galley in passenger-carrying airplanes be equipped with a smoke detector system or equivalent that provides a warning light in the cockpit or an audible warning in the passenger cabin that would be readily detected by a cabin attendant. · Each lavatory be equipped with a built-in automatic fire extinguisher for each disposal receptacle for towels, paper, or waste in the lavatory.
99 Smoke detectors are to be installed by October 26, 1986, and automatic fire extinguishers, by April 29, 1987. The rifle also increases the number of hand- operated fire extinguishers that must be carried and provides that at least two must contain Halon 1211 (bromochlorodifluoromethane) or equivalent as the extinguishing agent. On October 10, 1985, FAA announced a proposed addition to the Part 121 regulations to require portable breathing equipment for at least one flight-attendant station in each passenger compartment and to require crew members to participate in approved firefighting drills with the portable breathing equipment .2 3 REMOVAL OF TOXIC FUMES . . . . .. In at least two incidents involving onboard fires, air-conditioning equipment was turned off, or engine power cut, before or after landing, and that exacerbated a serious situation with respect to toxic smoke. Smoke and toxic fumes are the principal problem in noncrash aircraft fires. Industry practice, according to the results of the Committee's review, is to specify using maximal outside- air ventilation if smoke is present in the cabin or cockpit and turning off recirculation systems if the equipment includes this option. However, the details of the emergency procedures are inconsistent, and in some cases they cover only electric smoke or air-conditioning smoke and are not explicit regarding cabin smoke. All procedures that the Committee reviewed specified increasing cabin altitude to 10,000 ft "to increase ventilation." Although that will increase the volume of air flowing through the cabin, the lower pressure will also increase the volume of smoke produced by a given fire, and there would be little or no reduction in smoke concentration. Any reduction in burning rate due to the decrease in partial pressure of oxygen in the cabin is insignificant. Deployment of oxygen masks in a fire is not recommended by the airline procedures, because current passenger oxygen masks only increase the oxygen
100 concentrations in the air provided to passengers and do not reduce the hazard of toxic fumes. The use of oxygen masks could thus lead to an unwarranted sense of security. Details of the use of ventilation and pressurization during an emergency descent due to a cabin fire were not found in any of the procedures reviewed. In the Air Canada incident near Cincinnati, in which air- conditioning was turned off, air entering the cabin during descent probably forced smoke into the cockpit. During an unpressurized rapid descent, air enters the cabin through the negative relief valves, which are installed to prevent crushing of the fuselage. On the DC-9, which was involved in the Air Canada incident, the negative relief valves are above the ceiling in the aft pressure bulkhead. Air entering through these valves would have been forced over the fire and would have carried smoke forward through the area above the ceiling and caused it to enter the forward cabin and the cockpit. As discussed in Appendix A, the steady-mate concentration of fumes in an aircraft cabin is the effective volume production rate, P. divided by the loss frequency, L. L is found by dividing the outside-air ventilation rate by the cabin volume. Both decreasing P (by inhibiting ignition, extinguishing a fire, and improving materials) and increasing L (by using the maximal available outside-air ventilation rate) reduce fume concentration. The Committee strongly recommends that cabin-fire instructional material emphasize the need to turn on all available air packs to full volume if a cabin fire or smoke is present. That should reduce the possibility of smoke in the cabin and increase the likelihood of passenger survival. All recirculation should be turned off if the equipment includes this option. FAA, manufacturers, and the airlines should conduct further analyses aimed at developing detailed procedures for optimal crew management of pressurization, ventilation, auxiliary ventilation (if available), and exhaust systems to control smoke during an emergency descent. Because current supplemental oxygen masks are designed to substitute cabin air for oxygen automatically whenever the cabin pressure is below the equivalent altitude of about 18,000 ft. even attaching the oxygen
101 masks to a clean-air intake would not eliminate the hazard of breathing smoke and toxic fumes. Detailed procedures should also be developed for engine and air pack shutdown and for use of an auxiliary power unit after landing, to continue to provide ventilation and prevent buildup of heat and flammable fumes that could produce flashover during evacuation. INDIVIDUAL SMOKE AND FUME PROTECTION Because smoke and toxic fumes are principal causes of death in survivable crashes, smoke hoods and other passenger breathing devices have been proposed as a way of protecting passengers and increasing the likelihood of their survival. The studies referred to below suggest that some protection could be gained through their use, but there are limitations and difficulties. After a crash in 196S, CAMI embarked on a program to develop passenger smoke hoods.1 7 The program led to announcement of an amendment to FAR Part 121 in 1969 that would have required protective smoke hoods to be available on all civil air carrier.24 A number of critical comments were received, mostly involving hood safety, practicality, slowing of evacuation, and Justification of the specifications. In response to these comments9 and over the strong objection of the medical and regulatory arms of FAA, the proposed rule was withdrawn in September 1969.' 7 Several protective devices have been developed, ranging from a simple moist multilayer cloth large enough to cover the mouth and nose and held to the mouth and nose by hand or by an elastic band around the head (the North American Rockwell smoke mask) to hoods incorporating compressed-air or oxygen generators (e.g., the experimental FAA-Sheldahl hood with self-contained air supply, the Lear-Siegler air capsule, and the Scott aviation emergency smoke hood and breathing device). In addition, devices developed for other purposes, such as escape from mines, have been examined for their applicability as passenger protective devices. \7 It was widely publicized that cabin attendants passed out wet towels during the Air Canada in-flight fire aboard a DC-9. However, that was probably not
102 effective--only a small percentage of the passengers who were given wet towels survived.3 The relative advantages and disadvantages of passenger smoke hoods and other protective breathing devices have been assessed. In 1969, the Air Transport Association appended to its comments on the proposed rule the concerns of Richard L. Riley and Solbert Permutt, of the Johns Hopkins University Department of Environmental Medicine, about the hazard of hypoxia created by the configuration of the smoke hood itself. They were especially concerned about prolonged breath-holding and were uncertain about whether all passengers would remove their hoods when the carbon dioxide in the hoods exceeded the generally accepted safe concentration. In 1970, FAA asked the National Research Council Space Science Board to evaluate the smoke hood.13 The Board pointed out several potential hazards, including the narcotic effect of high concentrations of carbon dioxide (9.2%), the impossibility of effecting resuscitation once respiratory failure has been brought about by inhalation of pure carbon dioxide, and the possibility of hypoxia. It raised the legal question regarding a lethally injured person who is found wearing a smoke hood after a fire when cause of death is difficult to determine. And it raised questions about the use of the hood by people with cardiac disease or pulmonary dysfunction and about the fitting of the device for infants, children, and people with an abnormal neck size. In 1976, several smoke hoods were reviewed in a report of the NATO Advisory Group for Aerospace Research and Development.l 7 The report examined leakage, effectiveness in toxic environments, vision, acoustic attenuation, effectiveness in dense smoke environments, and effectiveness of safety briefings. It concluded that the available Sheldahl rebreathing smoke hood with septal neck seal (Type S) "can provide protection from smoke, toxic fumes, and flame in postcrash fire emergency egress" and stated that "its demonstrated merits far outweigh any potential risks or problems." That Judgment appears to have considered all the problems noted above, except the issues of legal responsibility and liability.
103 The Ontario Research Foundation, in Canada, recently completed an evaluation of over 20 devices and extensive tenting of six, all of which include filtration or absorption. 6 Test criteria included edge leakage, smoke and toxic gas penetration of filtration units, condition of inhaled air (carbon dioxide, oxygen, and temperature), comforts ease of donning, breathing resistance resistance _ ~ ~ ~. ~. of filtration units, vision and communication, to flame, cost, size and weight, and compactly warn current passenger supplemental oxygen systems. The report concluded that a compact device providing both Repressurization and protection from toxic smoke and gas for airline passengers in feasible and that the devices tested can provide several extra minutes of escape time. However, although the study considered use of the devices under several different conditions (sitting, walking, talking, and light exercise), it did not evaluate their use under conditions corresponding to the evacuation of an aircraft during a fire. The FAA position is that efforts to reduce the likelihood of ignition or smoldering fire have diminished the need for individual passenger smoke and fume protection dulcet. FAA bases its position on the relative merits of four basic types of passenger emergency breathing devices: simple smoke hoods with neck seal and no oxygen supply, hoods or masks that connect to the individual ventilation outlets (gaspers), modifications of current oxygen masks, and hoods or masks with individual self-contained oxygen supplies. · FAA concluded that simple smoke hoods are of limited utility, because of the restrictions on the length of time they can be worn before effects of hypoxia, carbon dioxide poisoning, etc., set in. The time involved in a typical incident associated with an in-flight fire at cruise altitude--including emergency descent, landing at the (possibly unscheduled) airport, stopping, and evacuation--is sufficient to make adverse behavioral and physiologic effects likely. In one study in which smoke hoods were donned in a darkened cabin and the aircraft was evacuated, the use of smoke hoods reportedly increased evacuation times by 50% (T. E. McSweeny, personal communication, 1986~. · It all aircraft have Raspers, and they are not commonly selected by airlines for current aircraft
104 models. Thus, the connection of hoods or masks to gaspers cannot be considered a general solution. More important, most ventilation systems on current aircraft involve at leant some recirculation of air in the cabin. Connection of hoods or masks to gaspers thus presents the possibility of introducing smoke or toxic fumes directly into the passengers' air supply. · F. M considers modification of current supplemental oxygen masks to be the most promising of the options examined. However 9 the current diluter demand mask operates as a function of cabin altitude. Below a cabin altitude of about 20,000 ft. no oxygen is introduced, and the system relies on air from the standard ventilation system, so it is also subject to possible contamination with smoke and fumes, as are gaspers. Modification of the oxygen supply system to cover the time required for descent, landing, stopping, and evacuation would require re-engineering of the oxygen supply systems and considerable extension of the oxygen supply. Careful thought must be given to the addition of large amounts of oxygen in an extensive network of overhead tubes, because it would be in the same portion of the cabin that is typically subjected to the greatest temperatures and to flashover conditions. · FAA has given less attention to self-contained breathing devices, mostly because of their greater cost. Furthermore, passengers have found it difficult to don and use current oxygen masks and life vests properly and would probably have even more trouble with more complicated breathing devices. For these reasons, FAA hen chosen to pursue engineering solutions involving selection of materials, fire detection and extinguishing, evacuation and development of a method of purging the aircraft of smoke and toxic fumes in flight, rather than passenger protective breathing device. The FAA policy, however, is based on the premises that flashover is not survivable and that the primary concern in pontcrash fires or in-flight fires once the aircraft has landed and stopped is rapid evacuation. Although this initially appears valid, some people have survived flashover. For example, two passengers and an attendant hid in the aft stairwell of a B-737 involved
105 in a large postcrash fire in 1965 until rescued 25 min later. \6 They survived, one on top of the other, by breathing through a small crack in the fuselage. The one on top, a 61-yr-old man, died of burn injuries on the seventh postcrash day. In the recent British Airtours accident in Manchester, England, a B-737 caught fire and burned. A 14-yr-old boy was removed from the aircraft approximately S min after flashover and survived. An older man was rescued from the same aircraft 30 min after flashover and survived for 6 d before succumbing (E. J. Trimbell, personal communication, 1986~. On the basin of that incident, the Accident Investigation Branch of the U.K. Department of Transport has strongly recommended that the Civil Aviation Authority require passenger breathing devices in that country. The Committee feels that passenger smoke hoods and breathing devices should be evaluated in terms of their potential contribution to survival and their effect on such factors as evacuation time. In case toxic fumes are the reason for a need for quick escape, protection at the slight expense of speed might save many lives. This needs to be critically examined. Despite the incompleteness of data on the effectiveness of passenger protective breathing devices under realistic conditions, the Committee recommends that such systems be studied. Published reports suggest that one passenger could be saved for each second added to the time available for escape in an emergency evacuation of an aircraft on which a fire is generating toxic smoke.7 It might be worth while to reinvestigate this life-sustaining protective breathing equipment in light of recent developments in contaminant absorption and self-contained sources of air or oxygen for such units. EMERGENCY ESCAPE On October 269 1984, FAA published a new requirement for floor-proximity emergency escape-path marking that provides visual guidance for emergency escape when all sources of cabin lighting more than 4 ft above the floor are totally obscured. 2 ~ Although this standard does not affect cabin air quality, it is designed to deal with a situation of severely degenerated air quality.
106 PASSENGER SAFETY BRIEFINGS In-flight or postcrash fires are never mentioned by cabin crew in their passenger safety instructions. Toxic, noxious, and blinding gaseous products and particulate matter resulting from fire stratify in the aircraft in such a way that the best air is closest to the floor, but this potentially vital information is not given to passengers. However, when speed is critical for evacuation, staying close to the floor under conditions of limited visibility might be counterproductive. DEPRESSURIZATION The primary threat to the passenger in depressurization is hypoxia. The main problem is in inducing passengers to don their oxygen masks correctly and quickly. Records in the CAMI Cabin Safety Data Bank show a total of 355 incidents involving Repressurization in 1974-1983 (Table 4-2~. Of these, 43% were classified as "significant" incidents--i.e., cabin pressure decreased to an equivalent altitude above 14,000 ft. passenger masks were deployed, or an injury resulted.8 Only one death occurred: that of a passenger with a history of heart problems. There were three serious injuries: one cockpit crew member had a broken arm, one passenger had a nonfatal heart attack, and one passenger had a collapsed lung. Sixty-six passengers and two cockpit crew members reported minor ear pain; 55 passengers and two cockpit crew members reported intense ear pain; 11 passengers incurred serious ear damage, including eight with bleeding ears; and three passengers suffered nosebleeds. No flight attendants reported any of these problems. Seventeen cases of hypoxia were reported: seven passengers and five flight attendants suffered mild hypoxia, and one passenger and four flight attendants suffered loss of consciousness. No cockpit crew members reported symptoms of hypoxia, perhaps because they are usually the first to be aware that Repressurization has occurred and have ready access to masks with demand regulators.
107 TABLE 4-2 Ten-Year History of Reported Depressurizations, 1974-1983a No. No. No. Total Significantb Minor Undefined No. Year IncidentsIncidents Incidents Incidents 197418 24 12 54 197515 22 1 38 197617 10 6 33 197716 13 2 31 197816 17 6 39 197920 18 7 45 198019 20 5 44 198118 12 4 34 19828 8 2 18 19837 6 6 19 Total154 150 51 355 a Data from Higgins.8 b See text for definition of "significant." In studies conducted at CAMI in 1976, it was determined that the physical activity typical of a flight attendants duties reduces the time of useful consciousness (amount of time until mental functioning deteriorates) by about 40% compared with that of an inactive passenger. If rapid d enrenn''r! 7= ~ ~ ^- ^~- ~ _% ~ _ _ ~ ~ "~` "~cenuanc nas only 15-20 a, depending on altitude and final cabin pressure, to don a mask before adverse effects, such as mental sluggishness, begin. The continuous-flow passenger mask has Q 9 t" ~ ~ ¢^ ~_.. =~ ~ ~ _ ~ . · . ~ ~ ~ -~v ~ ~ our canon a'c~tuces up to 40,000 ft. when properly used. Most of the problems with this type of mask appear to be associated with the lack of timely or proper donning--for example, failure to pull the mask down to activate the oxygen flow, failure to ensure that the mask covers both nose and mouth, and failure to tighten the straps to ensure a good fit.8
108 The problem of depressurization thus has to do essentially with passenger retention of safety instructions and quickness of response. Issues involving cabin safety procedures and information presentation are dealt with in Chapter 3. CONCLUSIONS AND RECOMMENDATIONS The Committee concludes that, although the ignition and propagation of fires and the resulting generation of combustion products aboard commercial airliners is complex, much can be accomplished toward alleviating the associated hazards. The use of materials that have high resistance to burning, that will not propagate a flame, and that will not generate toxic products when subjected to heat loads sufficient to cause currently used materials to degenerate would constitute a distinct improvement in passenger safety and air quality in the event of an in-flight, postcrash, or landing fire. The Committee recommends that FAA review current airline operating procedures and flight crew instructions for emergencies involving cabin fire or smoke; this review should cover every type of aircraft, regardless of size, in commercial service in the United States. The Committee recommends that the Aerospace Industries Association of America, a similarly constituted organization of airframe manufacturers, or even an individual manufacturer be encouraged to fund and initiate a program to develop a more fire-resistant set of materials from which to fabricate fully functional interior materials for aircraft. The Committee concludes that smoke hoods or other protective breathing and vision devices would provide additional passenger survival time in an otherwise debilitating situation that might normally preclude survival. FAA should re-evaluate smoke hoods or special breathing devices for passenger use. The Committee recommends immediate implementation of directions to turn on all air packs and to turn off internal recirculation systems in case of onboard fire. The Committee recommends that air contamination modeling studies and confirmatory live testing in aircraft be performed as soon as possible, by properly constituted FAA-industry teams, to determine conclusively the
109 advantages of turning on all packs to full volume when there is an in-flight fire. The Committee recommends that FAA require information on proper response to fire emergencies to be included in oral and written passenger safety briefings. REFERENCES 1. Aerospace Industries Association of America, Inc. Comments to NPRM 85-lOa, "Improved Flammability Standards for Materials Used in the Interiors of Transport Category Airplane Cabins," Docket No. 24594. (unpublished communication, October 16, 1985) 2. Aerospace Industries Annociation of America, Inc. Final AIA comments to NPRM 85-1OA, "Improved Flammability Standards for Materials Used in the Interiors of Transport Category Airplane Cabins," Docket No. 24594. (unpublished communication, January 8 9 1986) Barthelmess, S. Flight 797: A h~man-factors perspective. Part II. FSF Flight Safe. Dig. (Aug.~:12-17, 1984. 4. Bulloch, C. Survivability in aircraft fires: New standards are needed. Interavia 34:557-558, 1979 5. Compartment interiors. Code of Federal Regulations, Title 14, Pt. 25.853. Washington, D.C.: U.S. Government Printing Office, 1985. 6. Dranitsaris, P. An Evaluation of Candidate Smoke Masks for Passenger Use in Airplane Fires. Draft Report P-4612/G. Mississauga, Ontario: Ontario Research Foundation, 1986. Hall, J. R., and S. W. Stiefel. Decision Analysis Model for Passenger Aircraft Fire Safety with Application to Fire-Blocking of Seats: Interim Report' November 1982-December 1983. NBSIR 84-2817, DOT/FAA/CT-84/8. Atlantic City, N.J. U.S. Federal Aviation Administration Technical Center, 1984.
110 8. Higgins, E. A. Protective breathing: Oxygen mask use/problems, pp. 61-65. In Flight Safety Foundation, Inc. Proceedings of Cabin Safety Conference and Workshop, December 11-14, 1984. Washington, D.C.: U.S. Federal Aviation Administration, Office of Aviation Safety, 1985. 9. Hill, R. G., T. I. Eklund, and C. P. Sarkos. Aircraft Interior Panel Test Criteria Derived from Full-Scale Fire Tests. DOB/FAA/CT-85/23. Atlantic City, N.J.: U.S. Federal Aviation Administration, Technical Center, 1985. 10. Johnston, W. L., and P. T. Cahalane. Examination of fire safety of commercial aircraft cabins. SAFE J. 15(2):4-9, 1985. 11. McSweeny, T. E. FAA cabin safety activities, pp. 30-44. In Flight Safety Foundation, Inc. Proceedings of Cabin Safety Conference and Workshop, December 11-14, 1984. Washington, D.C.: U.S. Federal Aviation Administration, Office of Aviation Safety, 1985. 12. Miniazewski, K. R., T. E. Waterman, J. A. Campbell, and F. Salzberg. Fire Management/Suppression Systems/Concepts Relating to Aircraft Cabin Fire Safety: Final Report. DOT/FAA/CT-82/134. Atlantic City, NeJ. UeS. Federal Aviation Administration Technical Center, 1983. 13. National Research Council, Space Science Board. Evaluation of Smoke Hoods. 1970. (unpublished document) 14. Sarkos, C. P. New FAA regulations improve aircraft fire safety. ASTM Standardization News 13~12~:33-39, 1985. 15. Sarkos, C. P., R. G. Hill, and W. D. Howell. Full-scale wide-body test article employed to study post crash fuel fires. ICAO Bull. 37~10~:30-39, 1982.
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