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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Safety improvements
<p>An engine compartment mock-up has been built at SP for testing of fire suppression systems.  The aim has been to design an enclosure with Statistics from the Swedish insurance sector indicate that the number of total loss cases of fires in buses can be reduced dramatically by the introduction of requirements for fire-suppression systems in engine compartments.

Before 2004, there were approximately six to seven complete burnouts of buses each year in Sweden due to fires that started in the engine compartment. In 2004, Swedish insurance companies made a concerted action requiring that all (insured) buses be equipped with a fire suppression system in the engine compartment. Since then, there have not been any complete burnouts of insured buses due to such fires.

Still, it should be noted that at least 40 percent of the buses in Sweden are not equipped with suppression systems as they are non-insured or self-insured. The reason for the significant decrease in complete burnouts is therefore most likely more complex than simply the introduction of suppression system requirements. In 2001, the Swedish Motor Vehicle Inspection introduced compulsory fire safety inspection of buses, which has almost certainly led to improved overall bus maintenance, and therefore, a reduced number of bus fires.  

International standards
Presently, there is no international standard for evaluating extinguishing systems in bus engine compartments. In response to this, SP is preparing an international test standard that can be used when specifying requirements for the efficacy and function of such systems. This work is being carried out on behalf of the National Road Authority in Sweden.
The objectives of this project are to:

  • Create a safer environment for passengers and bus drivers worldwide, in particular with respect to safe escape for vulnerable passengers i.e. those with disabilities, the elderly and children.
  • Reduce the loss of property.
  • Design a standard that will evaluate the firefighting performance of different suppression systems in a well-defined, objective and comparable way.

Some of the system boundaries in the project are that the focus will be on testing the extinguishing capability. Further, only diesel-fueled buses — 89 percent of Swedish buses — and engine compartment ignition — approximately 70 percent of all fires start in the engine compartment — will be considred. In addition, only rear-mounted engine compartments will be covered. In the future, buses run on alternative fuels will be considered.
The draft method developed thus far simulates warm and hot surfaces, ventilation, a complex geometry and a range of fire sources. The extinguishing system being tested is installed in the test chamber, after which the fire sources are ignited, individually or in concert. Several different scenarios are set up and studied with various fire sources, airflows, aperture sizes and hot-surface temperatures, but with a fixed position of the system's extinguisher nozzles for all test scenarios. The test results indicate the strengths and weaknesses of the system, as well as whether or not the minimum standard requirements have been met.

[PAGEBREAK]Design issues, challenges
When designing a fire suppression system for buses and coaches there are some critical aspects that need to be considered. Presently, there is no existing international standard, and consequently, suppression manufacturers must verify and authenticate their systems using systems defined by relevant local or national transit authorities and insurance companies. This can be extremely difficult, and results today do not typically allow the comparison of different suppression systems. Unresolved issues include whether the engine should be shut down during a test, whether the fuel system and fan should be shut off, and whether the system activation should be delayed to give the vehicle operator the opportunity to move to the side of the road or out of a tunnel if a fire is detected while the bus is rolling. The current situation is that "performance requirements" are prescribed by the local transit authorities in their contract with transport providers.

Clearly, a standardized approach with broad acceptance would simplify the situation. Ideally, this would be in the form of a UN ECE regulation. Alternatively, an international standard with broad market acceptance could provide a basis for a level playing field for manufacturers.

The robustness of the system and its components is also critical. The discharge system, with included components, should not fail before it is activated and discharged so that the system remains operational after being exposed to heat, cold, vibrations, temperature changes, corrosion, stress, dirt, soot and road dust.

Finally, there are many different types of systems on the market with different extinguishing agents, including water mist, dry agent, aerosols and gas. These systems all behave differently in terms of their firefighting performance and they all have their pros and cons when it comes to their mode of extinguishment. Certain systems have challenges concerning re-ignition protection while others may have difficulty with suppression of large and/or small hidden fires. Most systems work well in confined spaces, where the concentration of the extinguishing agent remains high for a long period of time but have difficulty maintaining performance under the high airflow conditions, often present in bus engine compartments.

What now?
During 2010, SP carried out a pilot study (Phase 1) concerning the development of a test method for fire suppression systems in engine compartments in buses and coaches. All results from the study and a first draft of a test protocol were presented in SP Report 2011:22.
The release of the report signified the start of Phase 2 of the project in which a more in-depth analysis of the proposed methodology has been conducted. An engine compartment mock-up has been built where the impact of various parameters is being examined. The aim has been to design an enclosure with "typical" bus engine compartment characteristics, — enclosure size, hot surfaces, obstructions, ventilation, and openings — rather than to create a replica of a specific engine type. In the generic enclosure, different petrol-based fires will be initiated that will test the ability of an extinguishment system.

Phase 3 started early June and entails running tests with different fire suppression systems, including dry systems, water mist and aerosols.
Parallel to this project, a "Reference Group" has been created, with representatives from the suppression manufacturers, insurance companies, bus associations, transit authorities and bus manufacturers. APTA, American Bus Association, United Motorcoach Association, Commercial Vehicle Safety Alliance and Lancer Insurance are examples of U.S.-based representatives in the group. The main objective is to present a draft proposal of a standard at the spring meeting of the GRSG group at UN ECE in 2012, with the intention to produce a revised updated international UN ECE Regulation No 107.

All results will be presented next year at the FIVE (Fires in Vehicles) conference in Chicago Sept. 27 to 28, 2012. For more information, visit www.firesinvehicles.com

 

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