30-37 TunnelsREV[1]rev.qxd - Industrial Fire Journal

TRANSPORT: TUNNELS
Tunnel fire safety research
constructions of new challenging and complex infrastructure
systems have been the driving force for the European Commission
(EC) to finance several pan European research projects.
Haukur Ingason and Ulf Wickström, SP Technical
Research Institute of Sweden, provide an overview of
research projects into tunnel fire safety in Europe.
Figure 1: The
Runehamar fire
tests carried out in
2003 as a
collaboration
project between
SP [3] and the
European UPTUN
project [2].
Tunnels are becoming increasingly important at the same time
as they become more complex. The increase in traffic
volumes and the construction of complex underground
systems in Europe have put focus on the fire problem in tunnels.
The large and costly fire accidents that have occurred and the
increase in tunnel investments are key factors for the growing
interest in tunnel fire safety research.
European investments in tunnels are estimated to be about
150,000 million Euros between 2005 and 2010. Tunnel fires cost
up to 200 million Euros per year for the European industry. Large
economic gains could therefore be achieved by designing safety in
underground facilities in an efficient and safe manner.
The traffic volumes in Europe are estimated to increase by
approximately 50% for private transport and by 100 % for freight
traffic by 2020. At the same time public transport will increase. A
total of approximately 2,500 km of new tunnels will be built in
Europe in the coming years. This enormous expansion of traffic and
new construction requires new innovative solutions and knowledge
on how to build/safely operate these tunnels.
The tragic fire accidents that have occurred in Europe show clearly
importance reducing the impacts of a tunnel fire. Over 500 people
have died in tunnel fires in the last 15 years whereas world-wide
more than 800 people have died during the same time. In addition
to the casualties fires result in long-term halts in critical traffic
arteries. Authorities have become more and more aware of the
vulnerability of the traffic systems, eg the recent fire in the Channel
Tunnel between Britain and France on September 11, 2008, which
resulted in no fatalities, created huge disturbances in the tunnel
traffic and caused great economic losses. Major damage to the
concrete made the tunnel unsafe to operate fully for a long time, as
the reparation was very time consuming and required extensive
knowledge on concrete strength after the repair.
These severe accidents, high investment costs and the on-going
Major European projects
The research projects sponsored by the EC have all generated new
knowledge. The following projects are briefly presented here:
• Durable and Reliable Tunnel Structures (DART 2001-2004),
• Upgrading Methods for Fire Safety in Existing Tunnels (UPTUN
2001-2004),
• Innovative systems and frameworks for enhancing of traffic
safety in road tunnels (SAFE TUNNEL 2001-2004),
• Safety Improvement in Road & rail Tunnels using Advanced ICT
and Knowledge Intensive DSS (SIRTAKI 2001-2004),
• European thematic network on fire in tunnels (FIT 2001-2005),
• Thematic Network on development of European guidelines for
upgrading tunnel safety (Safe-T 2003-2006),
• Large Scale Underground Research Facility (LSURF 2005-2008).
These projects are more or less a mixture of desktop research,
small and large scale testing, product development, guidelines and
large scale demonstrations. The objectives were usually very broad,
everything from traffic management, risk analysis, construction
protection, mitigation and warning techniques as well as human
behaviour. Here follows a short summary of each project:
The DART project[1] considered tunnel design and construction.
The main objective was to develop operational methods and tools
to support operators to make the best pro-active decisions. The aim
was to select a cost optimal tunnel type and construction process in
which all decision parameters could be considered. Tools for
decision support for cost-optimal tunnelling and incorporation of
environmental, geotechnical aspects, technical qualities, and
structural life safety considerations were developed.
The UPTUN project[2] focused on upgrading methods for fire
safety in existing tunnels. Development of innovative technologies
and an assessment of existing technologies for tunnels were carried
out. Focus was on detection and monitoring, human response,
mitigating measures such as water spray systems, and protection of
structures. Numerous large scale tests were carried out, of which
the Runehamar tests[3] are the most well known (Figure 1). Other
important tests were on water spray systems in tunnels[4], which
resulted in engineering guidelines for tunnel water mist systems.
The SAFE TUNNEL project[5]. The main objective was to reduce
the number of accidents in road tunnels by preventive
measurements. An ”intelligent tunnel" and an "intelligent vehicle"
interacted, so that information about the vehicle's operational status
could be fully exploited. Tunnel operators can then determine
whether and how the vehicle is allowed to use the tunnel
depending on the vehicle status. This feature can reduce the
number of stops in the tunnel.
The SIRTAKI project[6]. The main objective was to create an
advanced decision support system for tunnel operators when
responding to/dealing with incidents. The system is innovative in
respect to key aspects of tunnel management including tunnel
operator support, integrated management of the network as a
whole, improved sensors and improved surveillance. The benefits
were mainly enhanced tunnel safety, reduced stress for the
operators and others involved in an incident.
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in Europe
The FIT[7] was a European network project which coordinated
and optimised tunnel fire safety research. It resulted in very good
overviews of standards and regulations for tunnels and in a
collection of data from real tunnel fires and other data, in particular
fire temperatures and heat release rates to be used for design
purposes, so-called “design” fires. The overview included road,
railway as well as subway tunnels. The project report contains basic
principles for fire design, underground fire statistics and consequences
of fire/smoke spread on people, equipment and structures.
The Safe-T[8]. The main objective was to develop good practices
for making optimal decisions with respect to security in European
tunnels, primarily for road tunnels, but also railway tunnels; to find
practical solutions for preventing/avoiding accidents in existing
tunnels, to limit the range of possible accidents; and to ensure a
high level of safety in European tunnels.
L-SURF[9] is a joint initiative by five European leading institutes on
safety and security of underground spaces (VSH in Switzerland,
STUVA in Germany, SP in Sweden, Ineris in France and TNO in the
Netherlands). The initial project included surveying existing test
facilities, identifying research needs, outlining lay-out and geometry
of a future research facility, defining measurement techniques
suitable to use in the facility, and defining activities in terms of R&D.
Technical results of European projects
The technical results from the above mentioned European projects
are very broad and comprehensive. Below we have summarised
the most important results from four main topics (design fires,
active fire protection, passive fire protection, egress).
Tunnel design fires
Design fires were discussed and investigated in many of the
projects. A design fire is not necessarily the worst fire that may
occur, but a conscious choice between the probability that it may
arise and the ability to achieve practical solutions. Therefore,
different design scenarios are often used for various safety systems.
In the FIT and UPTUN projects’ literature compilations were
carried out and overviews of heat release rates as a function of
time for several types of vehicles. These compilations show that the
peak heat release rates of various commonly used design fires
differ a lot, especially with regard to heavy goods vehicles.
Documented heat release rates from real accidents differs greatly as
well. For other types of vehicles, the difference is not as great.
Literature suggests that the peak heat release rates for single
passenger cars (small and large) lies between 1.5 MW and 8 MW,
although the majority of the real tests show heat release rate values
less than 5 MW. When two cars are involved the peak heat release
rate varies between 3.5 MW and 10 MW. Time to peak heat
releaser rate is between 10 and 55 minutes. The peak heat release
rates for the HGV trailers vary from 13 MW to more than 200 MW,
depending on the fire load of the goods. The time to reach the
peak HRR is in the range 10-20 minutes. The Runehamar tests[3]
of UPTUN were very significant as they showed that very high HRR
could develop from HGVs. For rolling stocks (train, subway etc) the
heat release rates vary from 7 MW to 43 MW and the time to
reach the peak heat release rate varies from 5 to 80 minutes.
The UPTUN project[10] recommended two sets of design fire
scenarios based on data obtained mainly from Runehamar tests:
A) Fire scenarios where tunnel users, rescue teams and installed
Risk to life
HRR MW vehicles
vehicles
Road, examples Rail, examples
Risk to construction
equipment necessary to provide safe evacuation and rescue
operations (human safety) are at risk, and
∫B) fire scenarios where the protection of the tunnel boundary
structure is at risk or where unwanted spread of fire and smoke
by ventilation ducts or through fire doors may occur.
Under the first point A) design scenarios were recommended for
human safety in terms of heat release rate, while under B) design
fires were recommended for fire resistance estimations in terms of
time-temperature curves. This approach follows how fire safety is
expressed in the building regulations and allows the application of
some commonly accepted methods for the documentation of fire
resistance. In general, UPTUN recommends several fire scenarios
are used for risk analysis of tunnels, as it is significant to know how
any possible scenarios may contribute to the overall hazard. Small
fires might cause problems other than larger fires. For A) human
safety, all proposed scenarios from 5MW up to the actual design
fire are recommended to be considered in risk analyses (Table 1).
UPTUN proposes that the duration of a fire is determined by the
amount of combustible material, assuming that all the fuel is
consumed at a combustion efficiency of 80%. The amount of fuel
depending on the type vehicles, load and traffic pattern should
always be evaluated for each study. In particular traffic at standstill
can increase the amount of available combustible material.
Under the second point B) design scenarios were recommended
for fire resistance. Three curves are recommended, ISO 834,
Hydrocarbon Curve (HC) and RWS-curve, see Figure 2. The same
rule for duration applies as for type A) scenarios.
Active fire protection in tunnels
Within the UPTUN project, extensive analysis and testing of water
spray systems in tunnels were carried out[4] to find new, innovative
and optimal solutions for fire protection in existing tunnels. Various
automatic water spray systems were described and evaluated in
different large scale tests. The focus was on controlling the fire
development and fire spread, and not necessarily to suppress
them. Effects of ventilation together with water spray systems were
not considered specifically.
Metro, examples
vehicles
At the
fire
boundary
(Figure 2)
5 1-2 cars ISO 834
10 Small van, 2-3 cars,
++
20 Big van, public bus,
multiple vehicles
Electric
locomotive
30 Bus, empty HGV Passengers
carriage
50 Combustibles load
on truck
70 HGV load with
combustibles
(approx. 4 tonne)
Open freight
wagons with
lorries
Low combustible
passengers
carriage
Normal
combust i ble
passengers
carriage
ISO 834
ISO 834
Two Carriages ISO 834
Multiple carriages
(more than two)
ISO 834
100 HGV (average) HC
150 Loaded with easy
comb. HGV (approx.
10 tons)
200 or
higher
Limited by oxygen,
petrol tanker,
multiple HGVs
Limited by
oxygen
The following fire growth rate ( α
g, L
) were recommended by UPTUN:
Peak HRR of fire ≤ 30MW, => α
g, L
= 10 MW/min
Peak HRR of fire > 30MW, => α = 20 MW/min
g, L
HC
RWS
RWS
Table 1:
fire scenario
recommendation,
see UPTUN WP2
[10].
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TRANSPORT: TUNNELS
Figure 2:
recommended
time temperature
curves for fire
resistance design.
Temperature [ o C]
1400
1200
1000
800
600
400
200
One important conclusion from UPTUN is that every system is
unique, and therefore testing and documentation is important to
ensure the desired function and quality of the system. It must be
able to operate in conjunction with other mitigation measures (eg
ventilation systems). Installation of automatic systems is associated
with significant investment costs and it is essential to have control
of the operating and maintenance costs. Water spray systems will in
general improve ventilation conditions and the ability to escape
from a tunnel fire. In particular, such systems are valuable for saving
people who are for some reason unable to evacuate themselves.
Water spray also reduces the thermal exposure to tunnel structures
and therefore eg reduce the risk of explosive spalling of concrete.
In heavily trafficked urban tunnels extinguishing and ventilation
systems may be very useful. They may prevent rapid fire spread
and reduce the effects of fire on people, and provide better tunnel
access and rescue conditions for first responders. As water spray
systems are very effective for reducing the thermal exposure level
on the tunnel construction and equipment, they could considerably
reduce the total costs in case of fire in tunnels.
UPTUN showed that tests with both low and high pressure water
mist systems required significantly less water than ordinary water
spraying systems in tunnels. The efficiency was strongly dependent
on the size of the fire, nozzle type, location and water discharge
rates. A rapid reduction of the temperatures downstream of the fire
was noticed after activation of the water spray system. The visibility
was, however, not improved during the first minutes after activation,
but later on as the fire size and the heat release rate were reduced.
The problem of back layering (ie smoke spreading upstream) and
the visibility upstream were also significantly improved after
activation of water mist systems.
One part of UPTUN was to carry out demonstration tests in a
large scale tunnel. Thus a section of a high pressure water mist
system was installed in the Virgolo tunnel in Italy and used to
demonstrate the effectiveness of such a system in a fire. As a result
of the successful tests, a complete high pressure water mist system
was later permanently installed as part of the upgrading of Virgolo.
Protection of concrete structures
Researchers in Europe have worked on methods to reduce
explosive "spalling" in structures of high performance/strength and
self-compacting concrete. In most cases structures made of these
types of concrete need to be protected with a passive fire
protection barrier such as shotcrete (sprayed concrete), or boards
of mineral wool or ceramic materials. Alternatively polypropylene
0
0 20 40 60 80 100 120
Time [min]
ISO 834
Hydrocarbon (HC)
RWS
fibres may be mixed into high performance or self-compacting
concrete. The risk for spalling in case of fire is then reduced
considerably. Another possible approach that has been suggested is
to expand the dimensions of the concrete cross section so that
some spalling may occur without causing unacceptable damage. All
the European research projects that dealt with the problem of
spalling (DART, UPTUN and FIT) recommend similar technical
solutions for protecting tunnel constructions[11].
The surface insulation must be so thick that the temperature at
the surface or just inside the concrete structure must not exceed
certain values depending on the concrete strength. In the DART
project it is stated that if the surface temperature is kept under a
level of 380 o C and the temperature at 25 mm inside the concrete
is lower than 250 o C, the risk for spalling is deemed insignificant.
The European projects recommend that the quantity of
polypropylene should be between 1-3 kg/m 3 depending on
assumed design fire and type of concrete eg in the FIT project a
mixture of 2-3 kg/m 3 of polypropylene is recommended whereas
in the DART project the recommended amount of polypropylene is
stated to depend on the design fire curve assumed:
• 1-2 kg/m 3 for ISO 834 fire.
• 3 kg/m 3 for RABT curve (German curve).
In the UPTUN project the following recommendations and
methods for the design of concrete structures were given[11]:
• Insulate tunnel surfaces with eg sprayed concrete, theramic or
mineral boards.
• Mix polypropylene fibres into concrete in appropriate quantities.
• Assure that protective layers of shotcrete have aggregates with
maximum size of 8 mm. The minimum thickness of the
shotcrete should be 20 mm.
• Test fire resistance for 2 hours at 1,200 0 C.
• Fastened protective boards properly into the concrete.
• Assure that the concrete surface temperature does not exceed
350 0 C and that the temperature at 40 mm depth does not
exceed 250 0 C.
Egress from tunnels
Numerous studies and demonstrations carried out in the European
tunnel fire safety research projects show how difficult and
unpredictable human behaviour is in case of a tunnel fire. From real
incidents, it has been observed that people react too slowly and
therefore they have not enough time to reach escape routes.
Important observations and recommendations from the European
research projects are[11]:
• Alarm alone rarely leads to evacuation without additional
information.
• The self-assessment of individual determines which actions will
be carried out.
• People rarely panic unless they fear they are unable to evacuate.
• Individuals tend to follow the action pattern of the majority.
• Trustworthy/authoritarian people usually facilitate an emergency.
• Tunnel occupants are reluctant to use unfamiliar escape routes.
• Instructions in foreign languages increase the uncertainties.
• Tunnel occupants must understand or be aware of seriousness
of a possible critical situation.
• Instructions on how to act in case of emergency must be clear.
• Extremely long tunnels must be avoided.
• Designers must rely on self-evacuation.
Key to improving the situation in critical situations is:
• The tunnel operator has an overview/understands the incident.
• There must be relevant communications to the tunnel
occupants so that they themselves understand the seriousness
and ultimately make the right decisions.
A general conclusion is that tunnel occupants cannot rely on any
active support from the rescue services in case of fire.
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Discussion
Pan-European projects have created new and useful information for
authorities, researchers and engineers working with tunnel fire
safety eg the Runehamar tests, the large scale demonstration tests,
human behaviour tests and water spray tests. Traffic management,
risk analysis as well as human behaviour are also examples of
research areas where new and important knowledge were
obtained. The understanding developed on spalling of high
performance concrete has lead to valuable practical
recommendations on how to protect tunnels. All this new
knowledge about tunnel construction will in the long term find its
way into standardisation and will increase the safety level in tunnels.
None of the projects focused on smoke ventilation or smoke
control, which is still a very interesting research area, as the EC was
of the opinion that therE was no need for further research in this
area[11]. The International Tunnel Association ITA created in May
2005 following a joint initiative of eight European research projects
the Committee on Operational Safety of Underground Facilities
COSUF[12]. The COSUF scope concerns the operational safety of
tunnels and underground facilities in general but included also the
aspects of security. The creation of COSUF was a natural step in the
development of closer ties between the different research groups.
Another good example of what these projects can lead to is the
establishment of L-surF [9], which aims to be a leading player in
European tunnel research activities. SP is one of the founders of
this organisation together with VSH in Switzerland, STUVA in
Germany, INERIS in France, and TNO in the Netherlands.
Conclusion
The pan-European projects sponsored by the EC have raised the
level of knowledge on tunnel fire safety. The success varies
depending on the field. Within traffic management and risk analysis
many interesting projects and models were developed. UPTUN’s
work on human behaviour is a good example of useful research.
The large scale tests in the Runehamar have already been widely
used for comparison/validation by several researchers around the
world, and served as a basis for the development of design fires in
standards such as NFPA 502[13] for road tunnels. A
recommendation on avoiding explosive spalling is also a good
example of useful information. The water spray tests and the large
scale demonstration tests have all given basic knowledge that have
pushed the technological development within the area forward.
References
1. DARTS, Durable and Reliable Tunnel Structures – The reports (CD Rom)
2004, : CUR Gouda, The Netherlands.
2. UPTUN - Final Technical Report - Document UPTUN FTR v10 20061204. 2006.
3. Ingason, H. and A. Lönnermark, Heat Release Rates from Heavy Goods Vehicle
Trailers in Tunnels. Fire Safety Journal, 2005. 40: p. 646-668.
4. K. Opstad, J.P. Stensaas, and A.W. Brandt. Fire mitigation in tunnels, experimental
results obtained in the Uptun project. in 2nd Int. Symp. on Tunnel Safety and
Security. 2006. March 15-17, Madrid, Spain.
5. R. Brignolo, et al., SAFE TUNNEL in Safety ITS congress. 2002: Lyon, France.
6. SIRTAKI Safety Improvements in Road&Rail Tunnels using Advance ICT and
Knowledge Intensive DSS - Final Report 2001 - 2004. 2004.
7. FIT – Fire in Tunnels - Thematic Network - General report 2006: www.etnfit.net.
8. SAFET-T www.crfproject-eu.org.
9. Felix Amberg and M. Wietek, L-surF: Large Scale Underground Research Facility
on Safety and Security, in Proceedings from the 3rd International Symposium on
Tunnel Safety and Security. 2008: Stockholm, Sweden.
10. Opstad, K., Fire scenarios to be recommended by UPTUN WP2 Task leader
meeting of WP2. 2005.
11. Høj, N.-P., et al., NordFoU samarbetet - Utvärdering av EU-projekt om
vägtunnelsäkerhet, Report nr. H-SE-011 2009: (in Swedish).
12. Amberg, F., ITA COSUF – SCOPE, ACTIVITIES, STRUCTURE The Committee on
Operational Safety of Underground Facilities of the International Tunneling and
underground space Association, in Think Deep. 2008: Amsterdam.
13. NFPA 502 - Standard for Road Tunnels, Bridges, and Other Limited Access
Highways. 2011 Edition, National Fire Protection Association.
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