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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.
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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.
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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.
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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,
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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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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.
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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
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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.
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Representative terms from entire chapter:
bus transit
