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Appendix D TRANSIT VEHICLE INTERIOR MATERIALS Over the past several decades there have been numerous changes in the design and construction of rail and bus transit vehicles. These changes have been a result of both improvements in technology and changes in the types of materials available to meet transit vehicle needs. A recent trend in the design and construction of rail and bus transit vehicles has been the increased use of synthetic nonmetallic materials such as polymers (plastics and elastomers). In rail and bus transit vehicles, these materials may be used in seats, wall and ceiling panels, windows, ducting, lighting fixtures, casketing, insulation, floor construction, floor coverings, etc. Transit vehicle procurement, construction, and arrangement; materials properties and trade-offs; and descriptions of typical materials used for rail and bus vehicle interiors are reviewed here. TRANSIT VEHICLE PROCUREMENT AND CONSTRUCTION Currently, no standard specification is used in the United States for the procurement of rail or bus transit vehicles. Procurements are generally based on the preparation by the individual transit system of specifications covering structural requirements, crashworthiness, reliability, and maintainability of subsystems such as braking, door operation, heating' ventilation, air conditioning, and other electrical and mechanical areas. In some instances the fire safety aspects of a vehicle may or may not be specified in the vehicle procurement process. 73
74 Rail Vehicles Rail transit systems typically acquire new vehicles through a detailed procurement process. A contract bid book, primarily containing design and performance specifications, is used as a basis for car builder bidding. This contract bid book specifies the various requirements expected. Included where possible are the safety requirements, including fire safety. After a contract is awarded, the car builder follows the contract bid book and contract drawings to deliver a vehicle design and then produces a certain quantity of cars tailored to the specific requirements of the particular rail transit system. In a specific instance, two transit systems have recently jointly used one basic vehicle specification, with certain modifications, to purchase vehicles built by the same car builder. Vehicles range from 48 to 75 feet long and are capable of carrying a crush load of 100 to 300 passengers. Power for propulsion is obtained from overhead wiring or a third (power) rail. Buses and Vans Various types of over-the-road vehicles are used to provide scheduled and on-demand transportation service to urban, rural, and special-needs passengers. These vehicles include full-size transit buses, small special-purpose buses, body on chassis buses, and standard and modified vans. Vehicles may be purchased by individual transit systems, groups of transit systems, or state and focal governments. Important considerations in purchasing these transit vehicles have been performance, capacity, cost, and reliability. Unlike rail vehicles, bus manufacturers offer a number of standard modem. When procuring new vehicles, transit systems or states, depending on their knowledge of safety issues and how to address them, may request changes to the standard mode! offered by a manufacturer. However, improvements in the fire safety of a transit vehicle will occur only if the transit system or state is aware of a potential safety problem or solution. A wide disparity exists among states relative to the policy and regulations concerning vehicle specifications. In most states the individual transit system prepares the specification without any state supervision; however, in a number of states, the state oversees the vehicle specifications for rural and specialized transit service and requires the use of a uniform specification guide. Other states require vehicles to be jointly purchased in pools but do not provide a specification guide. Full-Size ar'd Small Special-Purpose Buses Urban bus transit systems generally use full-size heavy-duty buses that are up to 40 feet in length and can carry up to 53 passengers. The chassis and body are often of integral (monocoque) construction. Aluminum, stainless steel, and reinforced plastics are materials used for body construction. In general, body construction is similar for all manufacturers. A rear-mounted diesel or gas engine provides the motive power for most buses. A few remaining systems operate trolley buses that receive electric power from an overhead catenary wire. In most cases, small special-purpose buses are simply small versions of full-size buses and can be equipped with many of the same heavy-duty components. They can seat 18 to 35 passengers.
75 Body on Chassis Buses These buses are built on mass-produced commercial chassis of light-duty trucks, motor homes, or school buses. The framework and body are constructed around the steel chassis frame. The bus manufacturer is essentially a body builder and assembler. A gasoline or diesel engine is located in the front of the vehicle. Passenger capacity is 12 to 30 persons. These vehicles are used primarily by rural and specialized transit systems. Standard and Modified Vans Standard vans that can carry 9 to 15 passengers can be purchased from automobile dealers and are produced as part of the manufacturer's standard production line. Modified vans may be slightly longer, wider, and higher than standard vans and may have a raised roof, heavy duty electrical systems, additional seating, etc. A common modification for rural and specialized transit systems is the addition of lifts and ramps for elderly and disabled passengers. FIRE SAFETY CONSIDERATIONS Providing transit system passengers with the highest practical degree of safety requires that an effort be made to prevent the occurrence of fires. This may be accomplished through a design process that is directed at eliminating potential ignition sources, providing for early detection, containing fires should they occur, and limiting fire propagation through vehicle configuration and proper materials selection. Existing Rail Transit Vehicle Materials Selection Guidance Currently, the fire safety guidance available from the Urban Mass Transportation Administration (UMTA) consists only of the unrecommended Practices for Rail Transit Materials Selection." These recommended practices present flammability and smoke emission performance criteria for rail vehicles. The performance criteria are intended to be included in rail transit system vehicle specifications. Car builders are then required to use materials that meet these performance criteria. At least one transit system specifies more extensive fire safety requirements. However, because of its complexity, smoke toxicity is not currently addressed by the recommended practices. Limited guidance for flammability and smoke toxicity characteristics of electrical insulation Is available in other UMTA documents. Existing Bus Transit Vehicle Materials Selection Guidance Many bus transit systems specify the use of fire-retardant or fire-res~stant materials for component such as seats, interior panels, and undercoating. But the fire safety performance of the materials is not defined in the specifications. Buses and vans are required to comply with Federal Motor Vehicle Safety Standard (FMVSS) 302, which addresses vehicle materials. However, this standard provides only limited guidance for bus material flammability and does not address smoke emission or toxicity. The National Transportation Safety Board has concluded that FMVSS 302 Is inadequate for use in screening out any but the most obviously unsatisfactory materials. FMVSS 302 is currently under consideration by the National Highway Traffic Safety Administration for revision.
76 MATERIAL PROPERTIES AND TRADE-OFFS In many instances, interior materials used in newer transit vehicles are more attractive to transit riders and provide lighter component weight while maintaining necessary strength characteristics. Use of these materials may also result in less or easier fabrication, installation, and maintenance operations. Other considerations for materials selection include durability, comfort, resistance to vandalism, and cost. For synthetic materials, the modification of these materials (e.g., with fire retardants or smoke suppressants) to decrease flammability and smoke emission could lead to changes in other materials properties. As an example, one property that may increase is the toxicity of the combustion gases. Materials substitutions in ~ given application also require consideration of properties other than fire safety and compromises or trade-offs are inevitable. The properties of importance are the material, · those requiring processing modifications in the manufacture and/or installation of · properties that affect performance and wear life, · properties that affect aesthetics and comfort, and · availability and cost factors. The evaluation of materials according to predetermined specifications or criteria may be more easily implemented than an evaluation of the processing changes needed. Ultimately the results obtained in all of these evaluations, including fire behavior, guide the decision of the designer in specifying the materials for a particular application. The following sections describe the typical interior materials used and note associated important design properties. RAIL VEHICLE INTERIOR MATERIALS A major part of the specification development process Is the consideration of fire prevention, detection, and materiab fire performance. Currently, no single federal agency has codified the design requirements necessary for fire safety of transit vehicles. Some guidance is available to the designer, however, such as the UMTA Flammability Guidelines and the National Fire Protection Association's Standard 130, Fixed Guideway Transit Systems. It ~ generally left to the designer to ensure that appropriate design requirements are specified to eliminate ignition sources, contain fires should they occur, and limit propagation through proper material selection. Potential ignition sources may be classified as either intentionally caused (arson) or related to equipment failure. Arson fires have occurred on most U.S. and Canadian rapid transit systems, causing extensive damage in some instances. Available materials found on the vehicles, such as newspapers, are generally used by arsonists although use of flammable liquids is known to have occurred. Arson fires are generally set on or underneath car seats. There are a number of potential ignition sources in the car equipment, such as the current collection system, traction motors, braking systems, dynamic brake resistor grids,
77 motor control equipment, heating, ventilation, air-conditioning systems, and batteries (Figure Den. An optimal design will minimize the probability of equipment-caused ignition, minimize the possibility of any undercar fires entering the passenger compartment, and lastly, minimize fire growth in a car's interior. The design must ensure that should a fire occur, despite the best effort to prevent it, the passengers will have sufficient time to evacuate to a place of safety. Car Design and Material Selection Considerations Floor Assembly The floor assembly provides the load-bearing surface within the car as well as the barrier between the undercar equipment and the interior compartment. An example is shown in Figure D-2. The design must consider fire resistance, weight, structural rigidity, thermal and acoustical insulation, and cost. Typical transit car floor assemblies are as follows: · plymetal - steel or aluminum-faced plywood core sandwich panels; · honeycomb - may be fabricated from a variety of materials in different combinations, i.e., phenolic faced with Nomex core; and · balsa core - metal-faced end-grain balsa sandwich. Interior Liners The side and ceiling liner panels (e.g., Figure D-3) provide the decorative interior finish. The design features that should be considered are resistance to fire, nondirectional appearance, large pane! size, resistance to graffiti and vandalism, weight, maintenance, formability to desired shapes, and cost. Plastics have gained wide usage as transit vehicle liners because highly suitable components can be economically produced, usually at reduced weight. Some examples are polyester/fiberglass; phenolic, sheet; phenolic, molded; polyetherimide; and melamine on aluminum. Seat Materials Seat assemblies can represent a significant amount of combustible material in a transit vehicle. Factors considered in seat selection include aesthetics, weight, durability and maintainability, structural adequacy, cost, and replacement. Typical types of transit seating are metal, fiberglass-reinforced polyester, fiberglass-reinforced polyester (fire-retardant), and cushion and cover over various frame types. Sidewall Insulation Insulation of the car sidewall is accomplished with both glass fiber bats and elastomeric foam. Thermal and acoustical properties are important considerations.
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81 Miscellaneous Components While the floor liners, seats, and sidewall insulation represent the areas of major concern from flammability considerations, the designer must consider a number of other components, such as air-conditioning ducting, light diffusers, windscreens, trim, glazing, armrests, seat pans, and floor coverings. . In summary, there is considerable variation in the materials used in rail vehicles. A tabulation of materials found in various rapid transit and commuter rail cars is shown in Table Do 1. TABLE D- 1. Tabulation of materials used in various rapid transit and commuter cars. 1 ~ |TRANS"SYST~ ~ B C D ~ F InsideLinin" ~ | Side K Roy Nor MLF ACR-PVC MB MLP MAL | Side ceiling MB MAL ACR-PVC MB MUL MAL Ceiling center VAL MNPM MHC MB MPM MAIL End MPM MPM ACR-PVC MLP MPM MAL Floor ~ 3/4 AHPM i3/4APM ~5/8APM ~3/4SPM1 ~3/4APM ~3/4P~ FBGLS Red UR Fr UR | Insulation | FBGLS | FBGLS | | F~BGLS I 0 Seat ~ NED | UR ~ ~ UR ~ jUR | Back | ROY |ROY |ROY? |8S | KYDEX | SS ~ LeRend:ACR-acrylic;~/~AHPM-~PM-ithhon~combcorc(~/~-~.t~ck);~-~u~n~m;~/~APM-~PM S/~-in.thick;FBGL8~1~;K-Kyd-;M~m~a~eon~; ~ b~-dmel ~ e;MHC-m~"nmeon -f""honeycomb;MLP-mel-mnconl"mnat~pl~tic;MNPM-melM=neon novaplymet~; MPM--lun=e onplymet~;NEOm~p~ne;NOR-No~l;PM-l~met~;PVC--ly(~mylcMonde);PW-lyw=~;ROY-~y~te; S/dSPMI-~/~-in.plyw=~ with SS on top f"~;~_t-~st-;UR~"th~e (Fm-fo"~,~d-n~d); V~vinylon~. BUS AND VAN INTERIOR MATERIALS As discussed earlier' the only fire safety guidance available to the designer is FMVSS 302. This creates a situation, coupled with the desire to be competitive, that has resulted in vehicle manufacturers selecting materials that are low cost, durable, and attractive. Unfortunately, fire safety often has not been adequately considered in these vehicles, and their interior materials are likely to burn vigorously once ignited. The following sections identify and describe vehicle interior materials by material function. Seating Bus transit vehicles are equipped with various types of seats. Selection of seating materials may result in soft-cushionecl or hard-shell seats. Upholstered seats are comprised of seat cushions that consist of a foam padding covered by fabric mounted on a seat frame.
82 Seat cushion materials used have included polyurethane, neoprene, and fire-retardant polyurethane. Neoprene, although harder to ignite, does give off hydrogen chloride gas. In an attempt to lessen costs resulting from vandalism, molded fiberglass-reinforced polyester (hard-shell) seats, which do not contain cushions, have been specified by a number of rail transit systems. Finally, some systems use a hard-shell seat with a small cushion (pad) insert. Seat frame and shroud materials used have been metal and fiberglass-reinforced polyester and polyvinyl chIoride-acrylic). In bus transit the primary selection factors for seating include resistance to vandalism, maintainability, structural adequacy, cost of replacement, comfort, and aesthetics. Interior Linings Plastics have gained wide usage as vehicle liners because they may be formed to a variety of desired shapes, and can be produced economically usually with a reduction in weight. Examples of materials used include molded fiberglass-reinforced polyester, phenolic sheet, molded phenolic, polyetherimide, melamine plymetal (a sandwich of plywood and steel or aluminum), and stainless steel sheets. Ceiling panels are usually made of sheet metal but may also be constructed of plastic. Important design considerations include ease of fabrication' formability, resistance to graffiti, size, and weight. Floors As noted in Table C-2, bus fires occur predominantly in the wheel well and under the floor. Accordingly, it is important in these cases to contain the fire to the area of origin. To accomplish this, bus floor construction has utilized steel plating' plymetal, or a sandwich of steel. The design should consider weight, structural rigidity' and thermal and acoustical insulation properties. Wheel well covers are considered to be part of the flooring construction. In the past, fiberglass-reinforced polymers were substituted for metal materials to reduce cost, corrosion, and weight. However, when brake and tire fires occurred, the wheel well covers contributed to fire propagation. Metal is again the preferred material. Floor coverings used have included woo! or synthetic carpeting and rubber tiles or mats. Durability and resistance to slipping are important design factors. Insulation Insulation materials are used to control occupant compartment noise and to minimize heat input or heat loss to the occupant compartment and thereby provide a comfortable ride. Fiberglass batting and sprayed-on polyurethane foam have commonly been used as bus insulation materials. Along with cost, thermal and acoustical properties are important factors to be considered. Ducting Air-conditioning and heating ducting and plenums in older Vehicles were generally of metal construction, but new vehicles are equipped with ducting made of polymers with a wide range of composition, combinations, and finishes. t
83 Light Diffusers Light diffusers are often made of acrylic materials. This material, although having a high flame-spread rate, is durable and less costly than other materials. Windows Glass and acrylic plastic have been the most common materials used for windows. Acrylic materials, although having a high flame-spread rate, are durable and less costly than other materials such as polycarbonates, which are an alternative window material. Important design considerations are clarity of viewing, impact resistance, and resistance to scratching and to discoloring due to sunlight. In most instances, buses use either safety glass or plastics (acrylic or polycarbonate). However, a glass and acrylic sandwich may be specified in some cases. Miscellaneous Door edges and window seals are made of elastomeric materials such as neoprene. Urethane foam has been used for armrests and padding for stanchions and grab rails.