Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 116
117
CHAPTER FOURTEEN
CONCLUSIONS
Every tunnel is unique, which makes it very difficult to gen- would be the Memorial Tunnel program because of the large
eralize design fires in road tunnels. On average, based on the number of tests.) These observations might be used as a ref-
survey results conducted for this effort, a fire in each U.S. erence for more specific research works using appropriate
tunnel occurs 1 or 2 times a year. tools (small-scale or numerical models). Table 37 summarizes
the benefits for the research, design, and operation of tests and
A number of tunnel fire safety projects, fire tests, and models, with their advantages and disadvantages.
research work that have been initiated around the world in
the last 10 years have brought to light a significant amount of · The Memorial Tunnel Fire Ventilation test program pro-
information. This helps us to better understand tunnel fires duced much empirical data and information for future
and the safety means to prevent them and to protect tunnels. analysis. It was performed in a real tunnel with geome-
The most important documented projects are: try similar to other road tunnels. However, this test was
accomplished with fuel pans, which hindered an under-
· FHWA Prevention of Tunnel Highway Fires standing of what fire size and fire growth would result
· TRB/NCHRP Making Transportation Tunnels Safe and from real major tunnel fire events. A number of European
Secure tests with real cars, buses, and trucks were performed in
· International Technology Scanning Program sponsored tunnels of smaller cross-sectional area. Extrapolation of
by FHWA and others that data to real tunnel geometry is to be done with care.
· UPTUN, European Project (EP) Because of a lack of full-scale fire tests with real trucks
· FIT (Fire in Tunnels), EP and buses in a real geometry, confirmation of the results
· DARTS (Durable and Reliable Tunnel Structures), EP of the Runehamar tests is not possible.
· SafeT (a Thematic Network on Tunnels), EP · There are no regularity requirements in the United States
· Safe Tunnel, EP for performing hot smoke tests or burning cars when com-
· SIRTAKI, EP missioning new tunnels. The European experience allows
· Virtual Fires, EP for the verification of fire life safety systems designs, train
· EuroTAP, EP designers, operators, and first responders.
· SOLIT, EP · Small-scale tests and reduced-scale tests are in need of
· L-surF, EP further development. These tests are less expensive and
· EGSISTES, EP. are needed for scientists and designers, because they
allow for better understanding of the physics of the
Numerous fire tests were performed or analyzed as part of process and help verify the computer modeling. Such
these projects. The most important are: tests can be repeated in the design at any time and be
used for visualization of the smoke behavior in the tunnel
· The Memorial Tunnel Fire Tests (United States) depending on the system's response.
· Ofenegg tests (Switzerland) · Computational fluid dynamics (CFD) software is con-
· Zwenberg tests (Austria) sidered as the design tool of choice for obtaining an opti-
· PWRI tests (Japan) mum design. However, it requires in-depth knowledge
· Repparfjord tests (Norway) of physical processes and numerical models, and prefer-
· Benelux tests (the Netherlands) ably experience in testing from the numerical modeler.
· Runehamar tests (the Netherlands) The strengths and weaknesses of each program are to be
· Other tests as part of UPTUN project. investigated beforehand, while validation of the results
against experimental data or another equivalent program
The full-scale experiments generally provide interesting is encouraged. Good experimental data are required. New
qualitative observations. For example, some opaque situations small- or large-scale experiments are to be undertaken
appear clearly as a combination of the heat release rate (HRR), with the priority objective of validating and calibrating
the nature of the burning object (smoke density), and the lon- physical models. It may include the understanding of
gitudinal air velocity. The relatively low number of experi- flow generated by fire as well as measurements of some
ments does not lead to general conclusions. (An exception physical smoke properties, which are critical for models
OCR for page 117
118
TABLE 37
FIRE TESTS AND FIRE MODELING FOR RESEARCHES, DESIGNERS AND OPERATORS
Means Use for: Research Use for: Design Use for: Operation
Full-scale Advantages: Advantages: Advantages:
Fire Test - Direct interpretation - Direct interpretation - Direct interpretation
Programs - Complete results - Possibility of using real Disadvantages:
Disadvantages: road vehicles - Cost
- Cost Disadvantages: - Limited number of
- Limited number of tests - Cost tests
Conclusions: - Limited number of tests Conclusions:
- Well suited - Geometry of the test - Unrealistic if not
facility associated with other
Conclusions: objectives
- This solution depends on
the importance and
specific problems of the
project
(e.g., Memorial Tunnel)
Tunnel Fire Advantages: Advantages: Advantages:
Tests Before - Partial results with full-scale - Accumulation of - Shows to the operators
or Under facilities experience useful to choose how the ventilation
Operation - Numerous different a system reacts
(aimed at situations - Test performed with real - Fire departments are
optimizing Disadvantages: ventilation systems very interested in
ventilation - Lack of information due to Disadvantages: expected situation
responses in the limited number of - Limited number of tests Disadvantages:
fire event) sensors Conclusions: - No operation possible
Conclusions: - Useful during the tests
- Useful but partial results Conclusions:
- Well suited
Tunnel Fire Advantages: Advantages: Advantages:
Tests Before - Visual observations possible - Test performed with real - Representative
or Under Disadvantages: ventilation systems situation
Operation - Lack of information due to Disadvantages: Disadvantages:
(aimed the absence of sensors - Limited analysis due to the - No operation possible
at operators Conclusions: lack of measurements during the tests
and fire - Not suited Conclusions: Conclusions:
department - Not well suited - Well suited
training)
Reduced Advantages: Advantages: Advantages:
Scale - Many tests possible - Cost lower than full-scale - Cost
Models - Possible to study global tests Disadvantages:
laws governing specific Disadvantages: - Linked to the
situations - Linked to the limitations limitations induced by
Disadvantages: induced by the similarity the similarity laws
- Needs full-scale reference laws - No respect of time
tests for transposition to real Conclusions: basis
situations - Very difficult to conclude Conclusions:
Conclusions: that the results are - Possibly unrealistic but
- Useful method for research representative of demonstrative
full-scale situations
Numerical Advantages: Advantages: Advantages:
Models - Possible to study many - Possible to get an - Possible to describe
(CFD) different situations optimization by the use of the physical conditions
- Information on flow different assumptions in several locations of
structures unattainable with Disadvantages: the tunnel
other methods - The model requires Disadvantages:
Disadvantages: qualification - Theoretical results lead
- The conclusions must be Conclusions: to theoretical
correlated to existing - Useful method for projects, conclusions
experimental references if validated Conclusions:
Conclusions: - The adaptation
- Useful method for research depends on the use of
the model
Source: PIARC (21).
OCR for page 118
119
(i.e., radiative smoke properties, generation of soot, and Safety is a result of the integration of infrastructural mea-
turbulence models). sures, operation of the tunnel, and user behavior, as well as
preparedness and incident management. The assessment of
Several statements can be made based on the studies, tunnel fire safety in tunnels is a complex issue, where broad multi-
fire events statistics, experience, and tunnel fire tests: disciplinary knowledge and application of different physical
models are necessary to explore the causes and development
· A tunnel by nature is a highly risky environment. No tun- of fires and evaluate measures to prevent and reduce their
nel is absolutely safe regardless of how it was designed consequences.
and what types of fire life safety systems were installed.
The goal of the design, operation, and maintenance is to A design fire is an idealization of a real fire that might
make a tunnel as safe as possible based on previous expe- occur. A design fire scenario is the interaction of the design fire
rience, on present knowledge, and on the development of with its environment, which includes the impact of the fire on
technical equipment. The key element is prevention of the geometrical features of the tunnel, the ventilation and other
tunnel fire. fire safety systems in the tunnel, occupants, and other factors.
· Most tunnels experience fires. However, most of the tun-
nel events are generally small in scale and involve cars Given the range of variables and human behavior nobody
and vans. can precisely predict every fire scenario. The key design fire
· Major tunnel fires that involve heavy goods vehicles scenarios relevant to fire safety in tunnels are:
(HGVs) with dangerous goods and fuel tankers, although
rare, can be severe in the tunnel environment. Conse- · For ventilation and other systems (e.g., fixed fire suppres-
quences of tunnel fires can be disastrous for occupants, sions) design and assessment;
tunnel structures, and the economy. · For egress analysis;
· Severe tunnel fires are rare and happen less often than · For thermal action on structures;
fires on open roads. Cumulatively, the number of people · For the safety of tunnel fire equipment; and
killed in road tunnels worldwide is fewer than 200, · For work on tunnel construction, refurbishment, repair,
including those killed in collisions. Fewer than 20 tunnels and maintenance.
worldwide have suffered substantial structural damages
as the result of a fire emergency. A design fire scenario represents a particular combination
· Road tunnel fires cannot be completely eliminated until of events associated with:
vehicle fires are eliminated.
· Type, size, and location of ignition source;
Analysis of the catastrophic tunnel fire events resulted in · Type of fuel;
the following conclusions: · Fuel load density and fuel arrangement;
· Type of fire;
· Fires develop much more quickly than expected. Many · Fire growth rate;
known actual tunnel fires and fire curves show a very fast · Fire's peak HRR;
development during the first 5 to 10 (sometimes 15) min. · Tunnel ventilation system;
The gradient of temperature is steep and the emission of · External environmental conditions;
heat and smoke are very important. · Fire suppression; and
· Fire temperatures in excess of 1000°C (1832°F) can be · Human intervention(s).
achieved.
· Smoke volumes are higher than expected from an early Design fires in tunnels are usually given as the peak fire
stage of the fire growth. HRR, although it has become more common for engineers to
· Fire spread between vehicles occurs over a much greater combine the peak HRR with the fire growth rate. Some esti-
distance than had been expected previously (e.g., more mates of the HRR use weighting of the burning components of
than 200 m or 656 ft in the Mont Blanc Tunnel). a vehicle to incorporate burning efficiency, which implies that
· The road tunnel users behaved unexpectedly, such as: the fire may not consume the entire heat load available. The
Did not realize the danger to which they were exposed. leftover content is typically in the form of either a char residue
Failed to use the safety infrastructure provided for or as soot and smoke particles displaced by the combustion
self-rescue. gas stream.
Wrongfully believed that they were safer in their cars
than if they used the self-rescue safety systems. The magnitude and development of fire depends on:
Chose to stay in their vehicles during the early stages
of a fire because they did not want to leave their · Vehicle combustion load (often called the fuel load)
property. · Source of ignition
Realized too late the danger they had placed them- · Intensity of ignition source
selves in, by which time it was too late to self-rescue. · Distribution of fuel load in the vehicle
OCR for page 119
120
· Fire propagation rate The development of fires inside vehicles depends on a num-
· Tunnel and its environment. ber of factors including:
Table 38 summarizes the main design fire variables and · Fire performance of interior materials and features,
provides the ranges for these variables. The table illustrates · Fire performance of vehicle cargo,
that time-dependent design fire variables depend on a num- · Size and location of the initiating fire event or ignition
ber of factors to be studied. The table was developed for this scenario,
effort based on the literature review. · Size of the enclosure where the fire is located, and
· Ventilation into the enclosure.
New energy carriers can lead to explosions with cata-
strophic consequences when there is a fire. Although they do Specification of a design fire may include the following
not necessarily mean higher risks, they do represent a new sit- phases:
uation and imply new risks. Systems, not only components,
need to be tested to study different possible scenarios and to · The Incipient Phase is characterized by the initiating
develop models for these scenarios. When the scenarios are source, such as smoldering or flaming fire.
described in a representative way, technical safety solutions, · The Growth Phase is the period of propagation spread,
mitigation systems, and rescue service tactics can be devel- potentially leading to flashover or full fuel involvement.
oped. It is also important to study how the different systems · The Fully Developed Phase is the nominally steady ven-
(detection, ventilation, mitigation) interact and how the mod- tilation or fuel-controlled burning.
els developed are altered depending on the scenario. The field · The Decay Phase is the period of declining fire severity.
of new energy carriers is very diverse and constitutes many · The Extinction Phase is the point at which no more heat
different fields of research. More research is needed concern- energy is being released.
ing how safety in tunnels is affected by the introduction and
development of new energy carriers. Simple heat transfer equations do not allow for the making
of a direct correlation between the timetemperature curve and
Fires can develop inside vehicles or outside in a cargo con- the timeheat release curve. It appears that the known fire
tainer. As fires develop inside a vehicle heat builds up, leading growth rates follow the super fast (highest increasing rate mea-
to elevated gas temperatures within the enclosure. The ele- sured) temperature rise in the timetemperature curves. How-
vated temperatures will in turn have a significant impact on the ever, ultrafast HRR curves are often allowed for the design.
growth rate of the fire. Elevated gas temperatures will pre-heat
materials that have not been ignited and potentially accelerate Tunnel ventilation systems are still the primary tunnel fire
flame spread. Gas temperatures in an enclosure can be affected life safety system for controlling smoke and providing a tenable
by the size of the enclosure, the ventilation into the enclosure, environment for evacuation. There are many types of tunnel
and the fire HRR. ventilation systems.
TABLE 38
MAIN DESIGN FIRE VARIABLES
Time Dependent Design Design fire variables are
Fire Variables Values Range a function of:
Fire Size--Maximum (1.5 MW300 MW) Type of vehicle (cars, buses,
FHRR HGVs, tankers; alternative fuel)
Fire Growth Rate (slow, 0.0020.178 kW/s2 as high as Type of cargo including bulk
medium, fast, ultra fast) 0.331 kW/s2 measured at one transport of fuel
test
Fire Decay Rate 0.0420.06 (min-1) Fire detection system and delay in
activation of FLS systems
Perimeter of Fire Car--truck perimeter Ventilation profile
Maximum Gas 110ºC1350ºC Fire suppression system
Temperature at Ceiling (212ºF2462ºF)
(higher with FCV)
Fire Duration 10 min2 days Tunnel geometry
Smoke and Toxic Species 20300 m3/sec - tunnel width, height, cross
Production Rate section, length
Radiation From 0.25 to 0.4 of total heat - volume (available oxygen)
flux up to 5,125 W/m2
(1,625 Btu/hr/ft2)
Flame Length - shape of tunnel, grade
- location of exits
Tunnel drainage system
OCR for page 120
121
· Although longitudinal ventilation controls smoke, it may A fire suppression industry offers to control the fire size,
increase the fire HRR and fire growth rate once air veloc- reducing the maximum HRR and fire growth by applying a
ities are high. It may also increase the flame length and fixed fire suppression system. Once a fire is detected early by
help the fire to spread farther. However, recent fire tests a reliable fire-detection system, the fire protection system
concluded that the affect of longitudinal ventilation on could be activated within several minutes, taking the fire under
fire growth and fire HRR was previously significantly control and not allowing it to grow further or spread to other
overestimated. vehicles. It may also suppress a small fire.
· A single-point extraction system supported by jet fans
(or other longitudinal ventilation, such as Saccardo noz- · It is essential that the detection system be capable of
zles) is considered the most effective in smoke control detecting a small fire (in the order of 15 MW). If this
for bi-directional traffic tunnels or when vehicles are is not achieved and the fire is not detected until it
trapped on both sides of the fire. This system relies on enters its rapid growth phase, the resultant fire will, in
smoke stratification and smoke capture, produces low all likelihood, be well beyond the capabilities of a fixed
longitudinal air velocities, and does not impact the fire fire suppression system. The fire may continue grow-
growth and HRR as much. However, this system is com- ing, resulting in the production of dangerous steam
plicated and requires air velocity controls on both sides and may cause concrete spalling. Sprinklers must not
of the fire. It also needs coordination with sprinkler sys- be turned off before the fire is completely extinguished
tem activation. Additional means for providing protec- or being suppressed by the fire department. Early sprin-
tion of ventilation ducts, such as sprinkler protection of kler deactivation may lead to explosions and structural
vent duct, may be needed to avoid structural collapse. collapse.
· Water droplets will be affected by ventilation. Longitu-
Ventilation has an influence on the fire development that dinal airflow must be selected to ensure an appropriate
does not always conform to expectations: droplet spread and mass flow. Ventilation system perfor-
mance is also affected by sprinkler operation. The main
· Owing to increased ventilation the fire development for idea is to acquire a well-designed system with a reliable
a car can be slowed if the fire is ignited at the front of the quick fire-detection system to start these systems before
car. This is in contrast to the accepted view of supposed the fire gets too large.
accelerated development resulting from ventilation. · Additional considerations need to be given to the impact
· The influence of increased ventilation on the observed fire of a fixed fire suppression system on smoke stratification,
behavior depends on the ignition location. Note that 95% visibility, and steam generation during the evacuation
of fires begin in the engine compartment (i.e., at the front). phase.
· Under the influence of a high-ventilation velocity, the · If the sprinkler system is activated early enough, can
fire development accelerates for a covered load at a rate ventilation be reduced or eliminated and what will be the
2 to 3 times faster. The fire size was 20% to 50% higher impact on smoke production? Additional studies may be
owing to a high-ventilation speed. required.
· There could be a negative effect of ventilation because · There is still a lack of experience in the United States
forced ventilation may cause significant flame deflec- with tunnel fire suppression systems. This system has
tion, which leads to the chance that the fire might spread pros and cons and its benefits need to be evaluated for
to other vehicles and threaten the integrity of the tunnel each tunnel because every tunnel is unique.
structure on a larger surface, assuming the ventilation · A structural protection industry offers coatings and pro-
cooling effect and reduction in radiation at the source are tection materials to protect the tunnel structure from
insignificant. damage. However, what will this do to the safety of the
tunnel environment by not allowing heat to dissipate
Tenable environment is well-defined by NFPA 502 and through the tunnel walls? What will happen to the tun-
other standards. To develop a time-of-tenability curve, the nel temperatures and the ability of first responders to
project must develop: enter the tunnel?
· A fire heat release curve as a function of time, Major progress has recently been made in fire-detection
· A design evacuation (egress) curve as a function of time, technology. Listed and approved video flame and smoke
and detectors that have been tested in the tunnel environment are
· A design systems response curve as a function of time. now available. Tunnel safety starts with fire detection, which
will cause all systems to activate and notify people to evacu-
A tenability map indicates all time steps and the resulting ate. Every second is accounted for in the major tunnel fire
impact on casualties and tunnel structure. It allows for pre- event, especially during evacuation and the initial phase
dicting how long the environment will be tenable in the tun- of fire development. Several countries provide standard
nel and helps to decide what needs to be done to achieve fire requirements for detection time and maximum fire size for
life safety goals. detection.
OCR for page 121
122
The survey conducted for this effort proved that fires in road management scenarios and procedures must take
tunnels are rare events. Here are some findings and lessons human behavior into account to be fully effective in
learned from the survey: saving lives.
2. Operation and commissioning
· More fires occur in the busiest tunnels. In most of the · International practice of commissioning tunnel fire
U.S. tunnels, fires happen 1 or 2 times a year; however, life safety equipment and fire fighting procedures
most of them are small and do not result in any signifi- using hot smoke tests and burning actual vehicles in
cant losses. The most significant fires occur with trucks the tunnels needs to be evaluated for future national
(HGVs). In these cases, casualties are likely. standards' considerations. The best international prac-
· Many agencies would consider protection tunnels with tice of commissioning tunnel life safety systems
the fixed fire suppression system, if proven effective. using hot smoke tests is not (or seldom) used in
Future studies are required to address this area of tunnel national practice. With the exception of several juris-
technology. dictions, cold smoke is commonly used to evaluate
· Most of the agencies rely on closed circuit television ventilation system performance simulating tunnel
(CCTV) for fire detection and incident detection. This fires. Unfortunately, cold smoke tests cannot replace
technology needs to be further developed for heat and hot smoke tests. The national standards do not
smoke detection, as well as be tested and listed for fire- require that systems commissioning hot smoke tests
detection applications in tunnels. use hot smoke tests.
· There is a need to continue developing tunnel ventilation · It is advisable to study the experience of the road
systems and ventilation response in conjunction with tunnel operations managing fuel tankers and other
other systems such as fixed fire suppression systems. dangerous goods. Such experience exists and best
· Specifications for the devices need to be developed fur- practice could be studied for both design and opera-
ther. Reliable and maintainable devices could become tion. Categorically banning dangerous goods from
commercially available that are designed for a particular tunnels may create an adverse economic impact.
tunnel environment, considering the typical tunnel clean- 3. Physics, numerical modeling, and testing:
ing and washing operation, chemicals and pollutants pres- · Correlation between a timetemperature curve and a
ent, and dirt and debris build up. One example is locating HRR curve.
a commercially available pull station system for a road- · The impact of passive fire protection materials on the
way tunnel that has long-time reliability. fire HRR and resultant temperatures in the tunnel
environment.
One item for future study that was expressed by many of · Verifications through the performance of additional
the national and international tunnel agencies is the need to vehicle tunnel fire tests with the special aim of mea-
develop a tunnel fire system computer simulator for opera- suring the production rates for smoke and toxic gases
tors to manage fires. Similar research programs have been (e.g., CO, CO2, and HCN) and factors related to the
successfully accomplished in Sweden and Austria. Learning light absorption by smoke (e.g., mass optical densi-
from their experience might help tunnel operators, first respon- ties). Full-scale fire tests may need multi-agency sup-
ders, and tunnel agencies to better understand their tunnels and port and possibly international collaboration.
train their personal accordingly. · Evaluation of the state of the art of numerical fire
and evacuation simulations. Capabilities of captur-
Many research works and studies have been done in the ing the effects of mitigating measures, such as early
United States and worldwide on the development of design or delayed suppression (e.g., water-based, foam, fixed,
for tunnel fires. However, there are still knowledge gaps in and mobile), ventilation, insulation, smoke compart-
many areas including: mentation, operator interventions, and so forth, need
to be included.
1. Training and education · Post-cooling spalling mechanism and structural pro-
· Training of tunnel operators and first responders tection of tunnel walls by means of a fixed fire sup-
by developing, for example, a virtual fire/systems pression system. This also requires a review of the
simulator. experiences with the use of fixed fire suppression
· Better understanding of the human behavior of tun- systems in managing tunnel fires and additional test-
nel users and operators, as well as providing a means ing of the systems.
of public education. During emergency situations, · Harmonization of the design parameters for numer-
human behavior is even harder to predict, as the stress ical fire and evacuation simulations.
of the situation replaces intellect with curiosity, fear, · Numerical modeling of sprinkler system impact on
or even panic. Unfortunately, in general, people are flame and fire size needs CFD code development and
inclined to do the wrong thing in the event of a tun- validation.
nel fire, such as staying inside their cars instead of · Development of uniform methods of assessment and
heading for the emergency exits. Tunnel emergency the validation of numerical modeling results.
OCR for page 122
123
· Coupling of numerical aerodynamic and fire simu- commercially available that are designed for the tun-
lation with structural calculation methods and even- nel environment, considering the typical tunnel clean-
tually with evacuation models. ing and washing operations, chemicals and pollutants
· Additional studies and analytical modeling is needed present, and dirt and debris build up.
on alternative fuel vehicle fires in the tunnel envi- 5. Risk of tunnel fires:
ronment. · It is important that the frequency of tunnel fires be
4. Development of specifications, regulations, and tech- evaluated against their consequences for developing
nology: a weighted risk impact.
· Further development of CCTV-based fire-detection · Risk of fires in combined use tunnels need to be eval-
technology tested and listed for tunnel applications. uated and special recommendations be provided on
· Further development of tunnel ventilation systems, design approach of combined use tunnel fire safety
and the ventilation response in conjunction with other design.
systems, such as fixed fire suppression systems. · The field of new energy carriers is very diverse and
· Regulations and guidance need to provide better con- new types of energy carriers are being introduced. The
sideration of the activity of all systems that interact safety of tunnels that allow alternative fuel vehicles
in a tunnel. Integrated approaches shall be applied to might not rely on component tests of such vehicles,
tunnel fire safety. but on the testing of entire systems using realistic sce-
· Consideration shall be given for technical innova- narios. Such aspects as possible gas detonations with
tions that allow for more ambitious safety objectives. low ventilation require systematic research. Risk to
· Specifications for the tunnel fire life safety devices. the tunnel structure as the result of alternative energy
Reliable and maintainable devices could become carriers' fires requires additional research work.
