Issue 83: Current Concerns and Associated Research on Fires in Tunnels
By Haukur Ingason
recent years, there has been much focus on tunnel fire safety, partly
due to some spectacular incidents that have occurred and partly because
of the increase in construction of tunnel systems worldwide. There is a
clear connection between solving the traffic problems in large urban
cities and the need for more tunnels. Interruptions in the traffic
through such tunnels creates economic losses and delays that may have
severe impacts such as transportation of merchandise and people.
Fires are major risks that can create devastating effects. Expansion
in the transportation sector and the ensuing pressure on traffic systems
forces construction of more complex and complicated underground
systems. This, in turn, requires new fire safety engineering solutions
that need support and validation before being put into use.
Recent developments in water spray techniques (sprinkler, water mist
etc.) for protection of tunnels is of course a positive reaction to the
need to minimize the risks and the consequences of fires in tunnels. In
urban road tunnels, there is a new type of hazard, namely constantly
increasing queues, which has forced searching for new solutions to
existing safety problems.
Previously, systems were designed assuming a continuous traffic flow
throughout the tunnels. A longitudinal ventilation system with jet fans
in the ceiling could solve most of the problems associated with control
of heat and smoke, assuming that the traffic on the downstream side of
the accident site could simply drive out of the tunnel. Through
prevention of smoke backlayering, tunnel users on the upstream side of
the accident could easily escape from the tunnel through a smoke free
Semi-transverse ventilation systems, where the heat and smoke are
extracted from the ceiling, or transverse ventilation systems where
fresh air is evenly supplied and hot smoke extracted along the tunnel,
are not as common today as they were some decades ago. Properly designed
semi-transverse systems can solve the fire problem related to the queue
situation, as they confine the region where the smoke may exist in the
tunnel, and thereby increase the opportunity for evacuation on both
sides of the accident site.
Using both a semi-transverse ventilation system and a water spray
system is a very safe solution, but of course rather expensive,
especially for long tunnels. Therefore, a longitudinal ventilation
system in combination with a water spray system is a more frequent
The large scale testing of water spray systems and the research that
has been performed in relation to such testing has improved our
understanding of these issues and helped to debunk many of the myths
associated with the use of water spray systems in tunnels. The main
questions today concern technical trade-offs and maintenance costs
together with reliability issues.
Traffic control issues and detection of fires in relation to the use
of water spray systems still need to be resolved properly. The
challenging issue for the fire safety engineering community is
associated with technical trade-offs when installing these systems.
Should the design fire for the ventilation system to be lowered from say
100 MW to 50 MW, if a water spray system is installed? This would
reduce the investment costs of the ventilation system considerably. An
example of such a decision is found in the new Stockholm Bypass project
where millions of dollars have been saved in initial costs.
Further, should the required structural fire load be reduced if a
water spray system is used? The tendency at present is to pose that it
should, but many are of the opinion that one must guarantee the
reliability of water spray systems before such technical trade-offs can
be allowed. An additional trade-off which is discussed is a reduction in
number of escape routes used in a tunnel when a water spray system is
Each of these questions is very important, but neither of them has
been explicitly explored in large scale research projects. Design fires
for tunnels with water spray fires have not been dealt with in
guidelines or regulations to date.1, 2 The effect of water
spray on fires related to new energy sources (electrical, hydrogen etc.)
has not been tested. There is clearly a need for research dealing with
these issues in the near future.
In rail and metro tunnels, the situation is different. The
requirements for materials used in rolling stock makes it easier to deal
with fire safety issues, although the latest large-scale testing
carried out in Sweden3 and Canada4 indicate very high heat release rates from burning trains.
Properly designed carriages can minimize the consequences of a fire,
but the consequences can be large in mass transport systems. The
interior lining material, luggage and ignition sources are very
important parameters in determining the fire development. Also, the
compartmentation and quality of outer compartmentation like windows or
the steel body play important roles in the risk of a fully developed
The trend towards open gangway trains, with no separations between
three, six or more carriages, has created new challenges for the fire
safety authorities. There are no large scale tests performed that
address the impact of open gangways on the fire development. Future
research should focus on new type of carriages with long open gangway
and trains with other types of bodies than steel, such as glass fiber or
other lightweight materials.
Fire safety in road tunnels and rail tunnels require completely
different approaches as the material and the fire performance
requirements of the vehicles, as well as the number of users, are very
different. The fire dynamics, however, are very similar. The challenges
in future fire safety design require better education of fire safety
engineers in the fire dynamics in tunnels. Lund University in Sweden
gives courses in this field, and this important issue will increasingly
become an important part of the education of future fire safety
engineers around the world.
Haukur Ingason is with SP Technical Research Institute of Sweden
NFPA 502, Standard for Road Tunnels, Bridges, and Other Limited Access Highways, National Fire Protection Association, Quincy, MA, 2014.
Road Tunnels Manual, World Road Association (PIARC), La Défense cedex, France, 2011.
Lönnermark, A., Lindström, J., Li, Y., Ingason, H., and Kumm, M.,
"Large-scale Commuter Train Tests - Results from the METRO Project",
Proceedings from the Fifth International Symposium on Tunnel Safety and
Security (ISTSS 2012), SP,Boras, Sweden, 2012.
Hadjisophocleous, G., Lee, D., and Park, W., "Full-scale Experiments
for Heat Release Rate Measurements of Railcar Fires", International
Symposium on Tunnel Safety and Security (ISTSS), SP,Boras, Sweden, 2012.
1st Quarter 2011 – Fixed Fire Fighting Systems in Road Tunnels – Andreas Haggkvist, Lulea University of Technology
The use of Fixed Fire Fighting Systems (FFFS) in road tunnels is a
controversial issue in many parts of the world. This article presents an
overview of the current research, standards, debates, and attitudes
regarding FFFS in road tunnels. Negative attitudes, the author contends,
are often not based in reality. READ MORE
Spring 2008 – Changes to NFPA 502: Standard for Road Tunnels, Bridges and Other Limited- Access Highways, 2008 Edition – Jason R. Gamache
The author discusses the 2008 edition of NFPA 502, pointing out
revisions that further clarify the categorization of road tunnels;
changes to the discussion topics in the Annex on fixed fire-suppression
systems; and revisions regarding ventilation and tenable environments,
protection of structural elements, hazardous goods transport and design
fire size. READ MORE
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