August 2011

Improving Fire Safety of Buses and Coaches

by Fredrik Rosén

About 1 percent of all buses suffer some form of fire incident each year. Some of these fires have serious consequences. A recent example of a tragic accident is the bus fire near Hannover, Germany in November 2008, which killed 20 people, making it the worst bus accident to occur in Germany for 16 years. Another example is the Wilmer, Texas bus fire, in September 2005, where 23 nursing home passengers were fatally injured.

In Sweden alone, an average of three fires in buses and coaches are reported each week. Most of these fires occur in the vehicle's engine compartment, which is often located at the rear of the bus or coach making it difficult for the driver to discover a fire. Experience from Sweden, where the installation of detection and fire suppressions systems is actively encouraged by the insurance industry, shows that the installation of an active fire protection system is an important safety measure.

Fires may occur for several different reasons. Some engine parts, e.g. manifold and turbocharger, may reach temperatures high enough to cause leaking fuel or oil to ignite. Fires may also occur due to electrical wiring short-circuits or overheating of engine components or the brake system — disc or drum. The conditions in the engine compartment are challenging for any extinguishing system, — ventilation fans in the engine compartment often produce high levels of airflow and many compartments have large openings. This can lead to efficient oxygen supply to a fire, and the suppression agent may be rapidly removed with the air flow. Furthermore, bus engine compartments are often geometrically complex and/or very compact, making it difficult to ensure that extinguishing agents actually reach the fire source. Finally, fuel and lubricants are not the only flammable materials present. Fires may also reach solids, like plastics, rubber and insulation materials, which can be more difficult to extinguish than liquid fuels.

Nordic research
Due to the large potential risk for catastrophic fires with many casualties, the Norwegian and the Swedish Road Administrations initiated a bus research project, "Bus Fire Safety," together with SP Technical Research Institute of Sweden in 2005.

The overall objective of the project was to investigate the fire safety of buses and to produce recommendations for improvements. The project was divided into the following sub-projects, each of which resulted in a separate report:

  • Statistics of bus fires in Norway and Sweden based on fires between 1996 and 2004.
  • Fire tests of interior materials used in buses.
  • Fire risks in buses.
  • Test method for fire walls.
  • Test method for fire-suppression systems in engine compartments.
  • Fire simulations.
  • Full scale trials.

The reports are all published in English and can be downloaded at www.firesinvehicles.com/en/about/research/Sidor/default.aspx.

The full-scale tests show that once flames reach the passenger space, flashover will occur within a short time. Current requirements for interior materials (UNECE regulation 118) only require them to pass a simple horizontal spread of flame test (FMVSS 302). This is clearly insufficient, as even materials with poor fire performance can be approved. The fire safety requirements for other means of mass transportation, such as trains, passenger ships and airplanes, are considerably more stringent. After the completion of the Bus Fire Safety research project, SP has been engaged internationally as Swedish technical expert to present proposals for better test procedures for these materials at the UN ECE (United Nations Economic Commission for Europe) Working Group on General Safety Provisions (GRSG) in Geneva. The work of introduction of relevant levels of safety into regulations is ongoing.

Research, legislation and stats
Following the Wilmer, Texas bus fire, the Volpe National Transportation Systems Center carried out a study for the Federal Motor Carrier Safety Administration (FMCSA). The objective was to gather and analyze information regarding the causes, frequency and severity of motorcoach fires that are caused by mechanical or electrical failure. Based on this study, the U.S. Department of Transportation issued a Motorcoach Safety Action plan. In this plan, the National Highway Transportation Safety Administration (NHTSA) identified upgrading motorcoach fire safety requirements as a priority safety area, and as part of this, to evaluate the need for a Federal Motor Vehicle Safety Standard (FMVSS) that would require installation of fire detection and suppression systems on motorcoaches.

In 2008, NHTSA initiated a two-year fire safety research program with the  National Institute of Standards and Technology (NIST). The objectives were to better understand wheelwell fires, their propagation into the passenger compartment and tenability of the passenger compartment, due to such fires as well as and countermeasures and detection systems.

Although there is no national requirement or standard for Automatic Fire Suppression Systems (AFSS) on buses, there are some individual requirements at the state level. In addition, some OEMs and operators have chosen to voluntarily install automatic fire suppression systems. The over-the-road coach market began making AFSSs standard on wheelchair lift-equipped buses and optional on some buses more than five years ago.

Its use has grown steadily. Several states, including Florida, Georgia, Pennsylvania and New York, have requirements for fire protection systems on wheelchair lift school buses and paratransit buses. This is mostly due to the need for additional evacuation time in these cases.

City transit buses have been using AFSS for more than 15 years. Early adoption was driven by concerns over risks associated with alternate fuels, such as methanol. Today a vast majority of the transit operators are specifying AFSS on their buses. The American Public Transportation Association (APTA) formed a "Bus Safety Working Group" in recent years, which consists of operators, OEMs and AFSS manufacturers. The group has developed and published four standards and recommended practices relating to bus fire safety.

U.S. federal regulations only require that a bus carry a small fire extinguisher. There is little possibility that a fire extinguisher will assist in any bus fire. On average, 20 to 25 bus fires are reported each year, according to Lancer Insurance Co. The majority of these fires are electrical, turbo or brake related. They generally engulf the engine compartment, and without a fire suppression system, these fires often result in serious physical damage to the bus. The average cost of these fire claims is $80,000. This takes into account the variety of ages and value of the buses involved in the fires. Clearly, fire suppression systems are more effective in managing bus fires. They also allow precious time for passengers to evacuate the bus. Bus fires remain a serious issue in the U.S. and will remain so until there are efficient tools to fight the fire, better engine maintenance and adoption of recommended safety measures.


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