NFPA 130, Standard for Fixed Guideway and Transit Systems, is an international fire safety standard widely used for design of transit systems.1 First published in 1983, it applies a holistic approach to life safety from fire and fire protection requirements to include stations, trainway, emergency ventilation systems, vehicles, emergency procedures, communications, and control systems. NFPA 130 regulates, through design selection, type of materials, material fire safety properties (flammability, combustibility, and smoke production), and potential fire hazards. These regulations are intended to control and/or limit the likelihood of a fire’s occurrence, its growth rate, and severity. NFPA 130 applies to new systems, to extensions of existing systems, to new rolling stock, and to retrofitting existing rolling stock and equipment. The portion of the standard dealing with emergency procedures applies to new and existing systems.

Vehicle Fire Safety


Passenger vehicles (rolling stock) represent the greatest single combustible fuel load within a fixed guideway and passenger rail transit system. Several significant fires in the 1970s involving fixed guideway transit systems, including the BART trans-bay tunnel fire, revealed the magnitude of risk to passenger life safety in a fire event.2 Consequent fire hazard evaluation, full-scale fire testing, and the fire hardening program of the BART passenger vehicles and studies performed by U.S. federal government agencies on transit vehicle fire safety influenced the basis of the vehicle fire safety strategy in NFPA 130.3,4,5,6

Figure 1: NFPA 130 strategy to achieving passenger vehicle fire safety


NFPA 130 attempts to achieve its fire safety goal by focusing on both preventing fire ignition and managing the fire impact within passenger vehicles. For electric propulsion vehicles, performance requirements apply to controlling heat-energy sources from electrical components and wiring to minimize the potential of electrical component and wiring failure contributing to fire ignition. Figure 1 illustrates the relationship of the various NFPA 130 requirements associated with vehicle fire safety performance as viewed in the context of NFPA 550, Fire Safety Concepts Tree.7


Insulation, isolation, and electric power control are the primary methods prescribed by NFPA 130 as a means to prevent fire ignition by minimizing the potential of equipment or component failure as a contributor to fire. Segregating electrical equipment (including the propulsion system and propulsion and breaking system resistors and equipment with a high energy heat source potential) from the vehicle’s exterior and separating the equipment from the passenger compartment via fire-resistance-rated floor and roof assemblies serves to manage the fire impact by inhibiting fire spread beyond the failed component or piece of equipment.

The passenger vehicle interior has a significant influence on overall vehicle fire safety. It is possible to mitigate potential fire growth and spread from likely ignition sources by regulating the flammability, combustibility, and flame spread of the vehicle’s interior, including seating, flooring, wall and ceiling lining materials, and vehicle insulation. Internal event ignition sources, including electrical failure, and external event ignition sources such as a burning bag of trash with paper and plastic, each pose differing levels of point-source ignition heat flux on the vehicle’s interior. Full-scale fire tests evaluating the vehicle interior’s fire safety performance when exposed to various probable internal and external fire scenario events provide the best understanding of the expected fire performance.


Full-scale testing is cost prohibitive and rarely performed during the design, specification, and procurement process of new passenger vehicles. Fire test standards adopted by NFPA 130 are individual material tests and apply point-ignition heat fluxes for both internal and external event scenarios. A reasonable degree of vehicle fire safety is achieved when all materials and assemblies comply with the performance criteria prescribed by NFPA 130.

NFPA 130 allows the use of an optional fire hazard analysis process to establish the fire performance of vehicle materials and assemblies in the context of actual use in lieu of compliance with the prescriptive requirements for equipment arrangement, flammability and smoke emission, fire performance, and electrical fire safety.

The fire hazard analysis is designed to understand the role of materials, geometry, and other factors in the development of fire within the vehicle that might not otherwise be ascertained through individual material tests. The fire hazards analysis process is intended to achieve the fire safety goals and objectives established by NFPA 130. These goals and objectives are to provide an environment that is safe from fire and similar emergencies for the passengers not intimate with the initial fire development and maximize the survivability of passengers intimate with the initial fire development – and to protect occupants who are not intimate with the initial fire development for the time needed to evacuate, relocate, or defend-in-place during a fire or fire-related emergency.

Trainway Fire Safety

The trainway typically serves as the means of egress for passengers in the event it becomes necessary to evacuate a train. In an enclosed trainway/tunnel, the means of egress includes enclosed exits and cross passageways that serve as points of safety. The maximum distance between exits and cross passageways permitted by NFPA 130 is 2,500 ft.  (762m) and 800 ft. (244m), respectively. In an urban transit system or intercity passenger rail system, the train population during peak period can be as many as 1,200 passengers. The expected required safe egress time to evacuate all passengers from the tunnel into an exit or cross passage can be one hour or longer. Accordingly, evacuation of passengers via trainway is considered the last option in a fire and emergency event.

Figure 2: NFPA 130 strategy to achieving trainway fire safety


Figure 2 illustrates the relationship of the NFPA 130 requirements associated with trainway fire safety performance. Trainway fire safety is achieved by preventing fire ignition and managing fire impact. NFPA 130 restricts combustible components in the enclosed trainway to minimize its potential contribution to the fire load and creation of potential fire hazards.

Rail ties and walking surfaces are required to be noncombustible. Combustible contents are limited to essential equipment including cover boards serving to protect exposure to traction power contact (third) rail and wood rail ties at switches and crossovers. Cover boards are required to comply with maximum flame spread, smoke development, and peak heat release rates in accordance with specific fire test standards.

Wooden rail ties are required to be fire-retardant-treated. Power, communication, and signal wiring and cables installed within the trainway are required to be fire-resistant and have reduced smoke emissions. All conductors, except radio antennas, are required to be in armor sheaths, conduits, or enclosed raceways, boxes, or cabinets except in ancillary areas. Ancillary areas are required to be separated from trainway areas by two-hour fire-resistance-rated construction and three-hour-rated construction when within underwater trainway sections.

NFPA 130 requires that an enclosed or tunnel trainway 200 ft. (61m) or more in length be provided with emergency ventilation to maintain a tenable environment along the path of egress from a fire incident. The emergency ventilation system is required to maintain tenable egress conditions for minimum duration of one hour, but not less than the required safe egress time.

Station Fire Safety

Modern transit station design is a single volume space formed by the passenger platform and contiguous trainway, possible intermediate mezzanine level(s), and continuous connection to the street level above. Modern stations often include extensive use of escalators and elevators for efficient passenger movement.

NFPA 130 station fire strategy is to manage fire impact. Controlling the fire in ancillary spaces by means of fire barriers and automatic sprinkler systems and installation of emergency ventilation in enclosed stations serves to manage the fire and manage the exposed.

The basis of station platform design is the NFPA 130 requirement to evacuate all passengers from the platform in four minutes and to reach a point of safety within six minutes. Escalators are permitted to serve more than half of the required means of egress from a platform and station when, for enclosed stations, at least one enclosed exit stair or exit passageway provides continuous access from the platforms to the public way.

The egress calculation procedure included in NFPA 130 is a simple hydraulic model. For stations with multiple passenger platforms, platforms on multiple levels, or converging egress routes, the use of a more robust model is often necessary to analyze variations that influence the required safe egress time.

In deep-tunnel stations, passenger elevators serve as the primary means of platform access and means of egress. The passenger elevator lobby holding area must be separated from the station platform by a fire barrier having a fire resistance rating of at least one hour but not less than the time required to evacuate the holding area occupant load. When elevators serve as the means of egress, at least one enclosed exit stair must be accessible from and enclosed in the holding area.

In enclosed stations, an emergency ventilation system is required to maintain tenable egress conditions for a minimum of one hour, but not less than the required safe egress time.

NFPA 130 requirements for station fire safety performance are similar to that of the trainway illustrated in Figure 2.


Emergency Ventilation

The basis for the emergency ventilation system’s design is the expected fire severity, including heat release rate and fire smoke release rate produced by the combustible load of a vehicle and any combustible materials that could contribute to the fire load at the incident site. Fire heat release rate, heat release rate profile, peak heat release rate, and decay are significant contributors to the expected fire severity.

Tunnel trainway emergency ventilation systems typically exhaust smoke in one direction along the length of the tunnel while maintaining tenable conditions on the opposite/upstream side of the train. Required airflow rates are a function of the critical velocity to move smoke in one direction while preventing smoke back-layering from occurring. NFPA 130 acknowledges that, depending on the fire location within the train, a portion of the train will be exposed to smoke.

Enclosed station emergency ventilation is typically provided via the tunnel trainway ventilation system. In this design scheme, the station means of egress paths typically serve as a conduit for ventilation make-up air, thus maintaining tenable conditions for occupant evacuation. Other design schemes include point extract ventilation within the station to maintain tenable conditions in the means of egress.

Figure 3: Overall Fire Incident Data Sorted by Fire Location8


Emergency ventilation is a significant contributor to achieving fire safety in a tunnel trainway and enclosed station during a fire condition. NFPA 130 recognizes that ventilation system reliability and operability are essential and require a reliability analysis of the electrical, mechanical, and supervisory control subsystems. Emergency ventilation fans, their motors, and all related components exposed to the exhaust airflow must be designed to operate at the fan inlet airflow hot temperature condition of not less than 302°F (150°C) for a minimum of one hour, but not less than the required safe egress time.

NFPA 130 emergency ventilation system requirements apply to new fixed guideway transit and passenger rail systems and to extensions of existing systems.

Fire Risk

Fire incident data obtained from eight of the world’s top 12 transit agencies in North America and Europe over the period of 1998 to 2009 revealed that 88 percent of fires occur in the trainway or the station and 12 percent of the reported fires involved the passenger vehicle.8 (See Figure 3) No passenger deaths were reported. None of the vehicle fires reported were fully engulfed in fire. Fire events where the passenger vehicle was fully engulfed in fire, involving passenger vehicles complying with NFPA 130 are rare and extraordinary events.

The average life span of a passenger vehicle is approximately 40 years, and a vehicle will typically undergo complete overhaul near its mid-life. NFPA 130 requires new work and equipment on existing vehicles undergoing overhaul and retrofit to comply with the standard. Transit agencies, associated with the referenced fire incident data, adopt NFPA 130 or enforce fire safety requirements that are similar in scope and performance. These agencies operating vehicle fleets are compliant with at least the early editions of NFPA 130.

Improvements in passenger vehicle material fire safety mitigate the potential for extraordinary fire events. Diligence of transit agencies in maintaining tunnels and stations clear of potential fire hazards and combustible fuel loading lessens the likelihood of death from fire in transit systems whose tunnels and enclosed stations were constructed without emergency ventilation. Overall passenger risk of death from fire is low in fixed guideway transit systems.

John F. Devlin is with Aon Fire Protection Engineering Corporation.


References:

  1. NFPA 130, Standard for Fixed Guideway and Passenger Rail Systems, National Fire Protection Association, Quincy, MA, 2014.
  2. "Railroad Accident Report – Bay Area Rapid Transit District Fire on Train #117 and Evacuation of Passengers While in the Transbay Tube, San Francisco, CA, Jan. 17, 1979,” NTSB-RAR-79-5, Washington, DC, 1979.
  3. Braun, E., "Fire Hazard Evaluation of BART Vehicles,” Center for Fire Research, National Bureau of Standards, NBSIR 78-1421, Gaithersburg, MD, 1978.
  4. McDonnell – Douglass Corporation, "BART Transit Vehicle Full-Scale Test – Final Report,” McDonnell – Douglass Report #MDCJ4670, Feb. 27, 1981.
  5. Hathaway, W. & Litant, I., "Analysis of BART Fire Hardening Program,” Urban Mass Transportation Administration, Washington, DC, 1982.
  6. Hathaway, W. & Flores, A., "Identification of the Fire Threat in Urban Transit Vehicles,” J.A. Volpe National Transportation Center, Cambridge, MA, 1980.
  7. NFPA 550, Guide to the Fire Safety Concepts Tree, National Fire Protection Association, Quincy, MA, 2012.
  8. Aon Fire Protection Engineering Corporation, "Fire Ventilation Upgrade Program Risk Assessment Report,” Contract No. G85-269, Toronto Transit Commission, 2011.