Fires on the bus are a global concern

Technical Research Institute of Sweden leads the push for an international test standard for suppression systems

By Fredrik Rosén

SP Fire Technology is developing a new method to test the efficiency of fire suppression systems intended for bus and coach engine compartments and will submit a proposal for a standard in April 2012 at the UN Safety Group for Vehicles (GRSG) in Geneva. This photo shows the engine compartment test rig for testing fire suppression systems for buses and coaches

Statistics from the insurance sector show stricter requirements to install fire extinguishing systems in engine compartments can significantly reduce the number of total loss cases of fires in buses. The most common type of bus fire starts in the engine compartment. SP Technical Research Institute of Sweden is therefore preparing an international test standard to specify requirements for the efficacy and function of such systems.
First initiated in 2005, this work is being carried out on behalf of the National Road Authorities in Norway and Sweden. The objective is to construct a model of an engine compartment where different actors can evaluate the fire fighting performance of different suppression systems in a well defined and objective way.
Fires occur for several different reasons, and all present unique challenges for any extinguishing system. Engine components such as the manifold and turbocharger may reach temperatures high enough to cause leaking fuel or oil to ignite, electrical wiring may short-circuit, and brakes can overheat.
Ventilation fans and large openings in the engine compartment often produce high levels of airflow, which can supply oxygen to a fire and remove the suppression agent. Any suppression system must ensure the extinguishing agents can actually reach the myriad sources of a bus fire.
The study, “Bus Fire Safety” outlined areas that fell into their separate reports.
Statistics of bus fires in Norway and Sweden 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 full-scale testing shows 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), which SP finds 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.
Since 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 United Nations Economic Commission for Europe (UNECE), the Working Group on General Safety Provisions (GRSG) in Geneva, Switzerland.
U.S. research, legislation and insurance statistics
After the Wilmer bus fire in 2008 the Volpe National Transportation Systems Center carried out a study for the Federal Motor Carrier Safety Administration (FMCSA) to gather and analyze information regarding the causes, frequency and severity of motorcoach fires resulting from mechanical or electrical failure.
Based on this study the U.S. Department of Transportation issued a Motorcoach Safety Action plan in which the National Highway Traffic Safety Administration identified the upgrading of motorcoach fire safety requirements as a safety priority in its evaluation of the need for a requirement to install fire detection and suppression systems on motorcoaches.
NHTSA then initiated a two-year fire safety research program with the National Institute of Standards and Technology (NIST) and United Nations Economic Commission for Europe.
Currently U.S. Federal regulations only require a bus to carry a small fire extinguisher. While there is no national requirement or standard for automatic fire suppression systems (AFSS) the possibility is slight that a fire extinguisher can provide adequate assistance in the event of a bus fire.
Some states have gone so far as to impose their own requirements and some OEMs and operators have chosen to voluntarily install suppression systems. Florida, Georgia, Pennsylvania and New York have requirements for fire protection systems on wheelchair lift school buses and paratransit buses due to the need for additional evacuation time for these services. City transit buses have been using automatic fire suppression systems for more than 15 years.
The American Public Transportation Association (APTA) formed its Bus Safety Working Group consisting of operators, OEMs and AFSS manufacturers to develop and publish standards and recommend practices relating to bus fire safety.
Lancer Insurance Company, an insurer of buses and motorcoaches in the U.S., says the 20 to 25 bus fires on average reported each year are largely electrical, turbo or brake related. As a fire typically engulfs the engine compartment, without a fire suppression system the damages are often major. Lancer says the average cost of these fire claims is $80,000, taking into account the various ages and value of the burned vehicles.

The test rig being heated prior to a test.

Improvements in Sweden
Statistics from the Swedish insurance sector indicate that the introduction of requirements for fire suppression systems will significantly reduce number of total loss cases from bus fires.
Prior to 2004 approximately six to seven complete burnouts of buses reported each year in Sweden started in the engine compartment. In 2004 Swedish insurance companies made a concerted action to require all insured buses be equipped with a fire suppression system in the engine compartment.
Since then they say they have not received reports of any complete burnouts of insured buses due to such fires. Still, at least 40 percent of the buses in Sweden are non-insured or self-insured and lack suppression systems.

A new approach
Because no international standard presently exists for evaluating extinguishing systems in bus engine compartments, SP is preparing an international test standard on behalf of the National Road Authority in Sweden to apply when specifying requirements for the efficacy and function of such systems.
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, such as 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.
The focus is on testing the extinguishing capability and not fire detection. The testing only considers coaches with rear-mounted diesel engines and engine compartment ignition. SP will address alternative fueled buses in the near future.
The draft method used for this research simulates warm and hot surfaces, ventilation, a complex geometry and a range of fire sources. The extinguishing system under consideration in the test chamber where the fire sources ignite individually or in concert undergoes different scenarios involving various fire sources, airflows, aperture sizes, and hot-surface temperatures. The position of the extinguisher nozzles for all test scenarios is fixed. The test results indicate the strengths and weaknesses of each system and if it has met the minimum standard requirements.

Design issues and challenges
The current situation is that local transit authorities prescribe the “performance requirements.” 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 many different types of systems on the market feature different extinguishing agents such as water mist, dry agent and aerosols, which all perform differently and all with pros and cons. Certain systems have challenges concerning re-ignition protection while others may have difficulty with suppression of large 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.
NOTE: Parallel to this project, a Reference Group with representatives from the suppression manufacturers, insurance companies, bus trade associations, transit authorities and bus manufacturers will 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 – 28, 2012. For more information visit:  BR

Fredrik Rosén serves as marketing manager for SP Technical Research Institute of Sweden, Department of Fire Technology.