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Fire- and Smoke-Resistant Interior Materials for Commercial Transport Aircraft Executive Summary The Aviation Safety Research Act of 1988 (Public Law 100–591) provides the Federal Aviation Administration (FAA) with a mandate to conduct long-term investigations concerned with fire safety, including fire containment and the fire resistance of cabin materials. As part of their response to this legislation, the FAA Technical Center established a program to investigate improved fire-resistant materials for aircraft interiors, with the objective ''to discover the fundamental relationships between the composition and structure of materials and their behavior in fires to enable the design of a totally fire-resistant cabin for future commercial aircraft.'' The Committee on Fire-and Smoke-Resistant Materials for Commercial Aircraft Interiors was established to provide guidance for this effort. The two principal objectives of the committee's task were (1) to identify promising materials technologies, design issues (both overall and for individual components), and fire performance parameters (both full scale and for individual components) that, if properly optimized, would lead to improved fire and smoke resistance of materials and components used in aircraft interiors; and (2) to identify long-range research directions that hold the most promise for producing predictive modeling capability, new advanced materials, and the required product development to achieve totally fire-resistant interiors in future aircraft. The emphasis of the resulting study is on long-term innovation leading to impacts on fireworthiness of aircraft interiors 10–20 years hence. CONCLUSIONS AND RECOMMENDATIONS Aircraft interiors are complex systems that include visible items such as flooring, seats, lavatories, ceilings, sidewalls, stowage bins, bag racks, closets, and windows, and items that are not visible to passengers such as ducting, wiring, insulation blankets, and supporting structures. Polymeric materials are predominant, appearing in a wide range of product forms including molded sheet or shapes, composite-faced honeycomb sandwich, textile fibers (fabrics or carpets), foams, sealants, and adhesives. Interiors currently contain materials of varying fire resistance, selected for their particular application and a variety of additional factors such as availability, cost, producibility, and a balance of other useful properties. The committee believes that long-term, focused research in fire-resistant polymeric materials can lead to significant improvements in fire performance and safety. To support the development of such materials, advances are required in the understanding and analytical modeling of aircraft fire scenarios, polymer combustion, small-scale characterization tests, and fire-hazard assessments. In addition to the materials' properties, the development process must address the needs of users of the materials. These needs include the processing and production capabilities of the materials suppliers and aircraft manufacturers; the ability to meet the design, performance, comfort, and aesthetic demands of aircraft interior applications; and compliance with environmental, health, and safety regulations and practices in the manufacture, use, and disposal of aircraft interior components. The committee focus was on materials technology and enabling design, manufacturing, testing, and modeling capabilities. A comprehensive research program with the goal of improving survival of aircraft accidents would also include aspects of fire-safety and-suppression systems, human factors and behavior in emergencies, and sensor and control development for accident avoidance. While the committee is confident that significant improvements can be realized in materials performance, the FAA goal of an "order-of-magnitude" improvement in fire resistance is difficult to define because of the multitude of performance metrics and fire scenarios that need to be considered and evaluated. Establishing specific performance goals for materials research based on the current understanding of materials combustion and aircraft fire scenarios is problematic because the data needed to relate materials performance and configurations to observed fire scenarios are not available. The committee recommends that materials performance goals for long-term research be established using hazard and risk assessment techniques. These techniques require experimental data from appropriate small-scale tests in conjunction with fire models to predict the expected fire performance and assess the probability of occurrence under realistic conditions, followed by validation tests in the intermediate-and full-scale regime.
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Fire- and Smoke-Resistant Interior Materials for Commercial Transport Aircraft Materials Materials used in the production of current aircraft interiors, with some exceptions, tend to have better tire resistance than materials used in other transportation systems. Regulatory requirements have been significant driving forces in the optimization of fire-resistant polymers and the development of required product forms for aircraft interior applications. Independent programs pursued by industry have also resulted in essentially a new generation of materials that found application in the 747, DC-10, and L-1011, and then a second generation of materials used for the 767, 757, and A300-600/A310. The FAA's heat and smoke release regulations drove improvements to the second-generation materials and to the application of new materials such as more fire-resistant thermoplastics to satisfy specific application needs. The committee has identified three approaches to provide further improvements in tire-resistant materials: Modification of specialty polymers including thermoplastics such as polyetheretherketone, polyetherimide, polyphenylene sulfide, and polysulfone and thermosets such as cyanate ester, bismaleimide, polyimide, and polybenzimidizole. This approach may provide the best performance in the near term (< 10 years). Development of new, high-performance, thermally stable materials including organic/inorganic polymer systems, copolymers, polymer blends and alloys, and glasses and ceramics. These materials have the potential for the best performance in the long term (> 10 years). Modification of existing engineering polymers including thermoplastics such as polycarbonates, nylons, and polyethyleneterephthalate and thermosets such as phenolics and polyesters. While it is not clear that this approach would lead to the significant improvement in performance sought, this approach may result in significant cost reductions. A basic scientific understanding of char and intumescence (swelling, foaming) is crucial to the development of improved materials. Research in char formation should include structural characterization and mechanical behavior (durability) and its relationships to ambient environment, heating rate, chemical derivatization, additives, and coatings. The two general technical directions identified by the committee for polymeric materials development to improve fire and smoke resistance are incorporation of additives in polymers and synthesis of thermally stable, fire-resistant polymers. Particularly promising approaches are discussed in detail in Chapter 4. These include thin laminated or co-extruded films and blends, coatings and additives (including intumescents), phase-change or temperature sensitive materials, organic/inorganic polymer blends, polymer blends utilizing a high char-forming polymer as an additive, and polymer modifications. Additive approaches include volatile-phase active flame retardants that inhibit the combustion process, condensed-phase active flame retardant that lead to char or intumescence, flame retardants that endothermically lose volatile components, heat-sink additives, toxicant suppressants, and combinations of additives that take advantage of synergistic effects (i.e., multiple additives with differing but cooperative modes of activity in optimized combinations). Recommendations: Perform research to improve the fundamental understanding of polymer combustion, including thermal degradation, char formation, intumescence, toxic gas production, and heat effects. Place special emphasis on the characterization of char and intumescence processes. Investigate new additive approaches that allow for significant improvements in fire resistance and reduced toxic gas production in current materials. Facilitate the development of new or modified polymers with significantly improved resistance to ignition and flame spread. Emphasize the modification of existing specialty polymers to obtain desired properties and the development of new thermally stable polymers or blends. Evaluate and prioritize research and technological development efforts to ensure that the new materials will meet end-use requirements. Issues to be considered include costs; the contemporaneous processing and production capabilities of the materials and aircraft industries; ability to meet the design, performance, comfort, and aesthetic demands of aircraft interior applications; and compliance with environmental and health and safety regulations and practices. Component Design and Manufacturing New fire-resistant materials are of little practical value for aircraft interior use if the industrial processing technologies required to manufacture parts are not fully developed and broad-based. Short-and long-term strategies should be developed to characterize new material opportunities for compatibility with existing processes, as well as determining needs for future designs and manufacturing technologies. Short-to mid-range strategies should focus on researching materials that can be produced with existing tooling and manufacturing processes. Long-term strategies should evaluate both materials that can be processed with today's technologies as well as with future technologies. Where improved tire performance can only be achieved with materials requiring new manufacturing processes, materials research and manufacturing process development should be conducted concurrently to ensure smooth implementation.
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Fire- and Smoke-Resistant Interior Materials for Commercial Transport Aircraft Innovative design and processing concepts could facilitate additional fire-resistant materials research options while allowing for reduced manufacturing costs. New modular design technologies should be pursued to reduce part count by integrating components. Minor changes to component designs may also yield improved fire performance. Lightweight films and coatings with improved fire resistance that can be easily integrated into current component constructions, such as interior sandwich panels or insulation blankets, should be investigated. The development of manufacturing processes for future aircraft interiors will emphasize cost reduction. Process developments likely in future interior applications include increased automation of cutting and ply location processes; reduction in the number of process steps and decreased cycle times in molding and decorating processes; low-temperature-curing and quick-cure thermoset polymers; and net-(or near-net-) shape molding processes to reduce machining and trimming operations. Developing continuous-fiber-reinforced thermoplastic composites to take advantage of thermoplastic processing advantages could provide significant savings in manufacturing costs in future aircraft. Thermoplastic composites could offer the advantages of less expensive tooling, more versatile production methods, short production cycle times, elimination of hand finishing, increased durability, the ability to integrate decoration or texture, and the potential for recycling. Development of manufacturing processes and compatible materials for co-bonding, secondary bonding, and decorative processes are required before the full potential of thermoplastic composites can be realized. Recommendations: Prioritize materials research opportunities in terms of compatibility with existing tooling and manufacturing processes. Short-to mid-range programs should focus on materials systems highly compatible with existing manufacturing technologies for a smoother introduction into production. In long-range development where new manufacturing processes are needed, materials research and manufacturing process development should be conducted concurrently to ensure smooth implementation. Investigate innovative design and processing concepts such as modular design, fire-resistant films and coatings, new thermoset composite materials and manufacturing approaches to reduce the number of processing steps and cycle times, and expanded use of thermoplastics. These concepts could provide improved fire resistance while reducing manufacturing costs. Fire Testing, Evaluation, and Modeling To perform an adequate fire-hazard analysis or flammability assessment of a material, several materials characteristics must be integrated. Experimental data from appropriate small-scale tests should be used in conjunction with fire models to predict the expected fire performance and the probability of occurrence under realistic conditions, followed by validation tests in intermediate-and full-scale regimes. This type of assessment is sensitive to the end-use application, type of material, and actual fire threats. A complete understanding of aircraft fires and the responses of materials and components in these fires is required to establish appropriate performance goals and evaluation criteria for new fire-resistant materials. Based on prior experience, two basic aircraft fire scenarios have been identified: post-crash fires involving (potentially large) quantities of aviation fuel from ruptured fuel tanks and in-flight fires involving only interior cabin components and passenger-specific items. These scenarios provide the basis for establishing fire performance behavior and criteria for new materials. However, new aircraft configurations may be significantly different from past designs, and the response of aircraft interiors in these fire scenarios depends on the details of the design. Thus, each aircraft configuration must be analyzed to assess its response. In the past, in-flight interior fires have very rarely developed into accident scenarios. Those fires within the passenger compartment have been detected and extinguished before posing a significant threat, and most that began in or around lavatories either were detected and extinguished or self-extinguished. Therefore, in-flight fires in accessible areas within the aircraft interior were not considered in this study. However, in-flight fires in inaccessible areas can be a serious concern because of the potentially long periods (up to three hours) before passengers can be evacuated. The number of accidents that began as a fire in a cargo compartment is, relatively speaking, extremely small. Nevertheless, recent regulatory upgrades of cargo compartment liners require them to perform as a substantial fire barrier to contain possible fires from spreading into the passenger compartment. Adaptation of current test methods, and, in many cases, new small-scale test methods, are needed to evaluate fire performance characteristics of materials for specified aircraft interior situations and to provide property data for use by modelers to predict component fire performance in expected large-scale fire scenarios. Rather than being used exclusively as pass/fail screening tests, small-scale tests should be used to measure flammability properties of the materials that can be used as input to theoretical models to predict fire hazard. This process requires enhanced interaction between the experimentalist and the modeler to establish that the test procedures are designed to obtain the parameters that the models require. A better understanding of the performance, limitations, and operating principles of existing test equipment and the development of new and better test methods are needed. The development of a materials fire-test database would provide a framework to establish performance criteria, evaluate
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Fire- and Smoke-Resistant Interior Materials for Commercial Transport Aircraft new materials, and predict materials behavior in-service. The steps involved in database development are (1) categorizing and cross-referencing test methods and characteristics, identifying the fire parameters needed for hazard assessment and modeling; (2) compiling existing fire characterization data; (3) obtaining relevant fire-test data through testing programs as they become available; and (4) developing new test methods where needed to provide additional data not available from current methods. An integrated modeling capability for aircraft interior designers could allow the estimation of the performance benefit of various choices of fire-resistant materials and components in aircraft interior applications. Analytical models, ranging in scale from molecular to full scale, are needed to support the development and evaluation of new fire-resistant materials. Models could be used to predict materials performance in fires, to assess the fire hazard, and to establish performance goals for new materials. Thermal degradation models that include crosslinking, cyclization, aromatization, and network formation could be used as tools to determine ways to enhance the thermal stability of polymers and to promote char formation during polymer degradation. Intumescent char models based on the formation and growth of bubbles, swelling, polymer melt behavior, and carbonization may be used as tools in optimization of intumescent materials or coatings. The models should be applicable to engineering polymers, specialty polymers, polymers with fire-retardant additives, and polymer blends. To provide an understanding of how materials and components contribute to development of a full-scale fire, largerscale fire models need to be improved for the specific needs of aircraft interior designers. Fire-growth models, compartment fire models (zone and field models), hazard assessment models, and toxicity models need to be developed or modified to address the aircraft interior configuration and relevant fire scenarios. Finally, the models under development must be validated to gain the confidence of the design community. This requires a closely coordinated research effort between theoretical model development and intermediate and large-scale validation testing. More emphasis needs to be placed on requiring intermediate and large-scale testing to verify small-scale data and to refine the effects of size and configuration on the fire performance. Recommendations: Develop the science base for small-scale fire performance and toxicity tests, based on expected fire scenarios and verified with full-scale tests, to provide meaningful property data for modeling and materials evaluation. Develop a database of materials fire performance properties to provide a means to establish performance criteria, evaluate new materials, and predict materials behavior in aircraft applications correlatable with expected fire scenarios. Support technology scale-up through testing on an increasing scale, from small-scale through full-scale testing. Develop basic thermal degradation models that are applicable to engineering and specialty polymers and include crosslinking, cyclization, aromatization, and network formation to aid the understanding of polymer stability and char formation. Include both char characteristics and evolved gaseous product properties as key model parameters. Develop intumescent char models based on the formation and growth of bubbles, swelling, polymer melt behavior, and carbonization. Develop an integrated modeling capability that will allow the estimation of the performance benefit of various choices of fire-resistant materials and components in aircraft interior applications. Work is needed to develop fire-growth, toxicity, and hazard assessment models relating to aircraft fire scenarios. Long-Term Research Program The committee believes that the goals of the FAA's research program to develop order-of-magnitude improvements in materials fire performance cannot be met with incremental advances or near-term regulatory activity. Rather, what is required are substantial advances based on a fundamental understanding of polymer combustion, on accurate aircraft fire scenarios, and on the systematic development of materials technology improvements. These advances in turn require a long-term commitment on the part of the FAA working with the aircraft and materials industries and research laboratories. The uncertainty of new commercial programs, the cost of qualification and certification, and the long time-to-market for new materials tends to discourage suppliers from embarking on materials development efforts. The size of the potential market for materials for use in aircraft interior components often does not justify the expense to the suppliers of development and qualification. Thus, it is important to develop alternate markets for new materials and to apply technological developments from other industries. Many of the developments that arise from this research will be unique to the issue of commercial aircraft interior fire safety. However, advances in the understanding of polymer combustion, new materials and additive technology, and testing and modeling methods may have applicability to fire safety in other transportation systems such as ships, trains, automobiles, and buses, as well as commercial and residential buildings. If this long-term research effort is sustained and a
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Fire- and Smoke-Resistant Interior Materials for Commercial Transport Aircraft coordinated, parallel effort persists in these related areas, significant advances will be made in the understanding of materials fire safety not only for commercial aircraft interiors but also in many other areas where fire safety is a concern. Recommendations: Sustain the effort to develop significantly improved fire-resistant materials as a long-term research program, with clearly stated goals, plans for systematic technology development, and stable financial commitment. Continue to follow developments in fire safety in the materials and aerospace industries, as well as in related industries. Coordinate within the U.S. Department of Transportation and with other federal agencies conducting related research, including the National Aeronautics and Space Administration, the departments of Defense, Energy, Transportation, Commerce, and the National Science Foundation. REPORT ORGANIZATION The findings of the committee have been organized into five chapters, with relevant background information included in the appendices. Chapter 1 introduces the study task and report objectives. Chapter 2 describes the array of design criteria that influence the selection and use of aircraft interior materials. Chapter 3 focuses on the evaluation and prediction of how aircraft materials perform in fires. Chapter 4 addresses the goal of developing substantially improved fire-resistant materials. Chapter 5 presents the committee's conclusions and recommendations for long-term research in fire-resistant materials development. Appendix A is a glossary of fire-related terms. Appendix B provides a description of FAA research and developmental mandates in aviation safety and fire-research program plans. Appendix C discusses current fire-modeling capabilities. Appendix D provides a discussion of toxicity models and testing methods, and Appendix E contains biographical sketches of committee members.
Representative terms from entire chapter: