Fires in buses are potentially deadly

  • 19-Jul-2010 12:22 EDT
Photo 4.jpg

A full-scale fire test on a bus. The pipe from the roof is a sampling line for gas measurements.

About 1% 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 in November 2008, which killed 20 people, making it the worst bus accident in Germany for 16 years.

The results from a large project investigating bus fires will be presented at the FIVE (Fires in Vehicles) conference in Gothenburg, Sweden, in late September. The work has been carried out by SP Technical Research Institute of Sweden, Department of Fire Technology, on behalf of the National Road Authorities in Norway and Sweden.

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—This provided the background for the following sub-projects and was comprised of an investigation of bus fires between 1996 and 2004 with a focus on Norway and Sweden.

• Fire tests of interior materials used in buses—Fire tests were carried out on various interior materials, using different test methods. A comparison was made between the test methods used for interior materials in buses and other established test methods for materials for use in buildings, trains, and passenger ships and other suitable material applications.

• Fire risks in buses—This sub-project identified specific fire risks and how they are affected by design, maintenance, and cost considerations and discussed potential methods to mitigate these risks.

• Test method for fire walls—An investigation of the fire resistance of the wall dividing the engine compartment from the passenger space. The work resulted in a proposal for a test method to test the fire resistance of this fire wall.

• Test method for fire-extinguishing systems in engine compartments—A method was developed to facilitate comparable tests of different fire-extinguishing systems for use in bus engine compartments. This sub-project was in recognition of the fact that bus fires often start in the engine compartment.

• Fire simulations—Computer simulations were run to investigate the spread of smoke inside a burning bus. The results from these simulations provide groundbreaking information for this application and show that calculations of this type can be used to investigate evacuation behavior.

• Full scale trials—A complete bus was fire-tested in SP’s large fire test hall. Measurements were made of parameters including the heat release rate and the production of smoke and toxic gases. The results of this sub-project provide an understanding of flame spread in a bus and time for evacuation that has not previously been available.

• Summary and proposals for improvements—The project was summarized, and proposals for new test methods and requirement standards were put forward. Parts of these proposals are now being considered by the UN ECE Working Group on General Safety Provisions (GRSG) in Geneva.

The full-scale tests show that once flames reach the passenger space, flashover will occur within a short time. Current requirements for interior materials 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 requirements for trains and passenger ships, for example, are considerably higher. SP has been engaged internationally and, as a technical expert, has presented proposals for better test procedures for these materials.

Statistics from the insurance sector show that the number of total loss cases of fires in buses can be reduced dramatically by the introduction of requirements for fire-extinguishing systems in engine compartments. The most common type of fire on buses starts in the engine compartment. SP is, therefore, 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 Authorities in Norway and Sweden.

In response to the significant need for an international dialogue, SP is arranging the FIVE conference with the aim of exchanging knowledge concerning fires in vehicles, both road and rail. Many of the fire problems associated with these vehicles are the same, which means that solutions can be similar.

FIVE, which is sponsored by SAE International among other organizations, will bring together scientists, regulators, test engineers, industry, suppliers, insurance companies, and other organizations from the diverse field of transportation to discuss important fire issues. For example, Dr. Jeff Colwell of Exponent, who is the Chairman of the Fire Safety Committee of SAE, will have a presentation with the topic “Fire propagation in a full-scale vehicle burn test.”

Fredrik Rosen, Marketing Manager, and Michael Försth, Senior Researcher, at SP Technical Research Institute of Sweden, Department of Fire Technology, wrote this article for SAE Magazines.

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