Fire Dynamics

Unique Metro Tunnel Fire Tests Conducted in Sweden

By Haukur Ingason and Anders Lönnermark, SP Technical Research Institute of Sweden, Department of Fire Technology
Photographs by Per Rohlén

Large-scale fire tests of commuter railcars were carried out in Sweden as a part of the Metro project. These tests were carried out with full-scale cars in a tunnel. The objective is to obtain better information about the differences in fire behavior between older- and newer-type wagons. Explosion tests were also carried out as a part of the test program.

Metro Project
The Metro project (see bottom of article) was involved in the staging of unique, full-scale fire tests carried out in commuter train cars in a Swedish tunnel in September 2011. Mälardalen University in Västerås is leading the project, in cooperation with eight other organizations: the SP Technical Research Institute of Sweden, Lund University, the Greater Stockholm Fire Service, SL (the Greater Stockholm Area Transportation Company), the FOI Swedish Defence Research Agency, the CRISMART (Swedish National Defence College), the Swedish Fortifications Agency, and the University of Gävle.

SP Fire Technology is responsible for the large-scale tests, where the aim is to determine an appropriate fire design for metro/commuter trains. The commuter trains used were transported from Stockholm to Arvika, a distance of more than 400km. On the way to Arvika, the three commuter trains, which comprised one motor wagon and two passenger wagons, made a halt at Västerås, where they were equipped with the necessary measuring instruments and the internal lining of one of the cars was changed from combustible to non-combustible material. This was done by installing aluminium profiles on walls and ceilings. The seats in the same wagon were also replaced with more modern ones. The aim was to see if there was any difference in the fire behavior of the railcar types. Another parameter applied was the amount of luggage used in the tests. The amount used, approximately 5.4 kg/m2, was the same as was found in a survey carried out on the Stockholm metro.

Full-Scale Fire Tests
The work on design fires (a specific heat release rate as a function of time) involves investigating which parameters will affect the spread and progress of a fire and the nature of the conditions both inside and outside a burning car. The work includes comparing test results at various reduced scales with those of full-scale tests carried out in a railway tunnel, which is the culmination of the work.

With access to three commuter train cars, the main purpose of the tests is to investigate how a fire develops and what are the consequences of an explosion are inside a railcar. This work was carried out with two different types of interior standards: the normal interior standard of a commuter train car and an interior that is more similar to that of an underground metro carriage in Stockholm. Mälardalen University was also involved in the work to determine the design fires and to carry out the tests.

The full-scale tests were performed in the old Brunsberg tunnel (see photos), located between Kil and Arvika in western Sweden. This abandoned, 276m tunnel lies on a siding about 1km long. It was taken out of service when a new tunnel was constructed close by to reduce the sharpness of a bend in the route.

Performing fire tests such as these requires major resources, and so data acquisition was extremely comprehensive. Gas temperatures at numerous positions, heat release rates, gas concentrations, and smoke inside the car and the tunnel, as well as radiant fluxes and gas velocities, were measured. The tests were also filmed from several different angles using both ordinary video and infrared cameras.

Fire and rescue personnel from Greater Stockholm, Arvika, and Höga Kusten-Ådalen areas were involved to investigate ways of tackling such fires. Also investigated were the behavior and determination of thermal loads to which personnel are exposed during this sort of firefighting. The results will be of value in a number of areas, including the following:

  • Input for fire design rating;
  • Investigating evacuation methods;
  • Assessment of effects of fire exposure on people in the tunnel;
  • Assessment of effects of fire exposure on equipment and infrastructure in the tunnel;
  • Investigating methods of tackling such fires;
  • Scaling model development, and
  • Validation of simulation calculations.

Two-Day Seminar
A two-day seminar was staged on September 13-14, 2011, in connection with the large-scale tests; it was attended by more than 170 participants from 18 countries. On the first day, participants were given the option of visiting the tunnel; buses were available to transfer them from the conference center to the tunnel. The group was divided into subsets and was shuttled at different times to the tunnel to avoid congestion.

At the test site, the groups disembarked and boarded trolleys for the final leg of the journey, since the buses could not get closer than 300m from the portal. Visitors were allowed to enter the tunnel and walk past the commuter train that was to be tested. This opportunity for a site visit was much appreciated: visitors were given the opportunity to smell, feel, and touch the test object prior to the actual test and to get a feel for the confined space and its relevance to the metro scenario.

Once back at the conference center, they were able to watch a live broadcast of the tests on television screens in the auditorium. They could also listen in to the live radio communications between the fire brigades and testing personnel.

A few presentations about the project and other related subjects were given to the attendees while they waited the start of the tests. The following day, presentations were given about various fire safety aspects in metro systems, as well as about the test results. This offered a workshop-style atmosphere for open discussion of tunnel fire safety together with the aim of the tests and the utility of the results developed.

Lessons Learned So Far
It is clear that this type of large-scale testing is very complicated and difficult to undertake. Because of the few tests that were possible, there was limited potential to vary the different parameters and conditions. However, what became clear was the importance of the choice of lining materials inside the car on the fire behavior. Further, the importance of luggage and its contribution to the overall fire load was clearly demonstrated, as its involvement in a fire can lead to a very rapid fire spread. On the other hand, high-performance lining materials can considerably delay the onset of flashover.

A phenomenon seen in tests carried out by SP in 2003 in the Runehamar tunnel was observed once again. The bulk of air in the tunnel started to pulsate, resulting in flames and smoke traveling backward and forward at a very precise frequency. The control of back-layering was shown to be very important. When the mobile ventilator used could no longer maintain the set speed because of the size of the fire, a rapid development of backlayering occurred. This surprised the firefighters inside the tunnel. The heat release rate was most likely higher than that obtained in other similar tests, but the final results of the analysis will be given at the ISTSS conference in New York, March 14-16, 2012. More information about ISTSS can be found at The Metro project has already produced much new information on fire development, evacuation, and firefighting. SP will post more information as it emerges.

About the Metro Project

The Metro project ( is a three-year undertaking, running until the end of 2012, with Mälardalen University ( in charge. Its objective is to conduct comprehensive research to improve the safety of travel, work, and rescue in underground railways. The project is unique in Sweden, given that it examines the fire performance of underground public transport.

Testing was performed in the old Brunsberg tunnel between Kil and Arvika in western Sweden. The abandoned tunnel is 276m long and is situated on a 1km-long siding.

The project is divided into seven work packages; subjects under investigation include design fires, evacuation, technical and organizational solutions, control of fire gases, extraordinary loads on structures, and rescue work.

The chief financer of the project is the Greater Stockholm Area Transportation Company (SL), which financed the majority of the full scale tests and also provided the commuter train carriages used. Other financers are the Swedish Civil Contingencies Agency (MSB), Swedish Fortifications Agency (FORTV), Swedish Fire Research Board and the Swedish Transport Administration. The total budget for the project amounts to more than U.S. $2 million (SEK14m).