Issue 78: Fixed Fire Fighting Systems for Road Tunnels
By Kenneth J. Harris, P.E.
the benefits of water-based suppression systems have been recognized by
fire protection professionals for many years in many different types of
structures, their incorporation into road tunnels in North America has
been very slow. That trend is now changing. Two incidents, both
occurring in 2007, helped spur this change.
The Newhall Pass Tunnel Fire in Santa Clarita, CA1 started
as a three-vehicle incident and grew to 30 trucks. The tunnel, a
critical truck bypass on I-5 near Los Angeles, was closed six weeks for
repairs. By contrast, the Burnley Tunnel2 in Australia also
suffered a three-car incident. However, this tunnel had a deluge spray
system that was activated by tunnel operators, confining the fire
effects to the initial incident. That tunnel was reopened in four
After that, the California Department of Transportation (Caltrans)
began to look seriously at fixed fire fighting systems (FFFS) for their
new tunnels. The next one in the process, Presidio Parkway, which is
the southern approach to the Golden Gate Bridge, had four tunnels and
Caltrans included FFFS in all of them. A test of this system is shown
in Figure 1.
Figure 1. Deluge fixed fire fighting system for the Presidio Parkway.
This was well received by both the local fire agencies and the state
fire marshal, and involved some significant education in the design
basis and the reduction of the design fire scenario.
Currently, the Colorado Department of Transportation (CDOT) is
preparing to solicit for an FFFS for the Eisenhower/Johnson Tunnels near
Denver, CO. Much of the pressure for this is coming from the trucking
industry, which would like to take all cargoes through the tunnel.
Presently, hazardous cargoes are required to take a more circuitous
route over the pass. New tunnels in Miami and Virginia are being
equipped with FFFS and the Federal Highway Administration (FHWA) is
supporting this as they learn more about it.
In general, the objective of an FFFS is to prevent the spread of fire
from the initial incident to other vehicles. In most cases, nothing
can be done about the initial incident. However, tunnel fire history,
as shown in Table 1, has shown that the most significant damage and loss
of life occurs not from the initial incident, but the later involvement
of other vehicles.3 In addition, the fire may be shielded
from the water spray; so again, the mitigation of the initial incident
may be less effective.
Table 1. Tunnel Fires.
Mont Blanc Tunnel
Determination of water application rate is the most difficult and
controversial aspect of system engineering at this time. Harris4 delineated
the range (large) and justification (little) for the rates currently
used. Unlike most structures, the requirements for water-based
suppression systems are not codified. There is no clearly defined
occupancy and hazard classifications for road tunnels. To complicate
matters further, many road tunnels are in remote areas, so water supply
is a critical factor.
History has shown that the duration of water application is probably a
more important factor than the rate itself, so minimizing water
application rates is extremely important. The best example of this was
the Nihonzaka Tunnel in Japan.5 This tunnel was equipped
with a deluge spray system that controlled the fire until the water
supply was depleted, with the results noted in Table 1.
Since many tunnels are in remote areas, the water supply is often
from tank storage rather than a municipal supply. In these cases, the
optimization of the water supply is a key consideration. Water supply
is determined by application rate, deluge zone(s) length and duration of
The length and number of deluge zones to be operated is usually an
economic trade-off between valve costs and storage costs. Each zone
requires a valve. The length of deluge zone(s) must at least cover the
longest expected vehicle and allow for that vehicle to span multiple
zones. Truck lengths are usually taken as 15 meters.
In municipal areas, zone lengths of 30 meters are often used, and two
zones are considered the design condition. If the cost of storage is
significant, it may pay to decrease zone lengths to 15 meters and allow
for three zones to activate. This obviously doubles the valve cost, but
may reduce storage costs.
The cargoes carried by large trucks, or heavy goods vehicles (HGVs)
are typically considered the design fire hazard because they represent
the largest fuel load carried in road tunnels. There is another
category of large truck cargo: flammable liquid tankers (FLTs) that are
usually prohibited or severely restricted from tunnels.
In some cases, the alternate routes that FLTs can take have their own
hazards, such as increased population centers, or more dangerous roads
than the tunnel corridor route. The I-90 tunnels in Seattle, Washington
allow FLTs when the installed deluge foam system is operational. This
system requires more time and money to maintain than a plain water
system and increases the operational complexity by requiring a decision
to dump foam.
Road tunnel environments are often corrosive to metals used in fire
protection piping. These corrosives include products used for snow and
ice removal as well as weak acids formed from vehicle exhaust. These
conditions often mandate the use of corrosion-resistant materials that
are more commonly seen in the process industries.
When new tunnels are constructed, FFFS can be implemented into the
new design. This means that space can be allocated for the required
piping and controls. Structural components for supporting the piping
can be included where necessary. Freeze protection can be appropriately
The situation for existing tunnels can be quite different. In many
cases, there is barely space for current truck clearance in existing
tunnels. The ceilings that would normally be used to support piping may
be structurally marginal, meaning additional loads cannot be added.
For tunnels in climates subject to freezing, heat tracing and insulation
for freeze protection is costly.
What role do fire protection engineers have in this? Tunnel
ventilation engineers have traditionally been the voice of fire and
life-safety in the tunnel world. In fact until fairly recently,
suppression systems were not recommended by NFPA 502.6 With
their broader understanding of fire physics, fire protection engineers
can provide a key role in the implementation of FFFS road tunnels.
Fire protection engineers can help evaluate the water/fire
interaction. When analysis is done on the fuel surface, showing the
amount of water really necessary to prevent fuel vaporization, a water
application rate can be calculated, rather than reading from a graph,
where the assumptions are not articulated.7
Fire protection engineers can help evaluate the significance of
droplet penetration through the fire plume. If the maximum benefit is
obtained by preventing fuel vaporization, the water must get to the fuel
surface. If it is evaporated in the plume, it cannot accomplish this
Fire protection engineers can help evaluate how water alone can
control flammable liquid fires. This is already prescriptively allowed
by NFPA 15,9 and tests by Rasbash showed that water controls
the fire heat release rate almost immediately while the water
application rate controls how quickly the fire is suppressed.10,11
Fire protection engineers can help evaluate how risk assessment can be
used to evaluate FLT alternatives and that the addition of a FFFS may
significantly alter the probability factors used for tunnels.
All of these issues are within the subject matter practiced by fire protection engineers.
What else do fire protection engineers need to do to optimize FFFS in road tunnels?
Fire protection engineers need to consider other piping codes for the
design and installation of these piping systems. Other Standards such
as the ASME Code for Power Piping (B31.1)12 and Code for Process Piping (B31.3)13
provide a comprehensive treatment for design, installation and testing
of piping systems including allowable stresses, allowable loadings,
welding and testing. The service requirements for power and chemical
plants are more stringent than fire protection. These codes also offer
more flexibility for alternative supporting designs than the
prescriptive tables used in most codes. In fact, high pressure mist
systems use these codes for their piping design, which is often welded
stainless steel pipe because of the requirement for high pressure and
Fire protection engineers need to consider transient heat conduction
for freeze protection. In many cases the mains can be installed in
places that will not freeze. The ground provides significant heat that
can mitigate the air temperatures. The cost of analysis is usually five
to ten percent of the cost of freeze protection.
While FFFS have been used sparingly in the past, transportation
agencies are seeing its benefits, particularly in minimizing disruptions
to major transportation corridors. New tunnels are including them in
the original plans. Agencies are looking seriously at adding them to
existing critical corridors. Fire protection engineers have the
understanding of fire science that can allow for optimizing the system
for each tunnel. This perspective is new to the tunnel industry. Fire
protection engineers will need to add some additional skills to address
situations in the tunnel environment that are different than the
building environment in which they traditionally operate.
Kenneth Harris is with Parsons Brinckerhoff
Harris, K. "Water Application Rates for Fixed Fire Fighting Systems in Road Tunnels." Proceedings from the Fourth International Symposium on Tunnel Safety and Security, SP Technical Research Institute, Borås, Sweden, March 2010.
Chiyoda Engineering Consultants. "Sprinklers in Japanese Road Tunnels," Yokohama, Japan, 2001.
NFPA 502, Standard for Road Tunnels, Bridges, and Other Limited Access Highways, National Fire Protection Association, Quincy, MA, 2011.
Tewarson, A. "Generation of Heat and Chemical Compounds in Fires." SFPE Handbook of Fire Protection Engineering. National Fire Protection Association, Quincy, MA 2008.
Arvidson, M." Large-scale Water Spray and Water Mist Fire Suppression System Tests,". Proceedings from the Fourth International Symposium on Tunnel Safety and Security, SP Technical Research Institute, Borås , Sweden, March 2010.
NFPA 15, Standard for Water Spray Fixed Systems for Fire Protection, National Fire Protection Association, Quincy, MA, 2012.
Rasbash, D. and Rogowski, Z. "Extinction of Fires in Liquids by Cooling with Water Sprays," Combustion and Flame. 1957, Vol. 1, pp. 453-466.
Rasbash, D., Rogowski, Z. and Stark, G. "Mechanisms of Extinction of Liquid Fires with Water Sprays," Combustion and Flame. 1960, Vol. 4, pp. 223-234.
ASME B31.1, Code for Power Piping. American Society of Mechanical Engineers, New York, 2012.
ASME B31.3, Process Piping Code, American Society of Mechanical Engineers, New York, 2012.
Beard, A and Carvel, R. Handbook of Tunnel Fire Safety. Thomas Telford Publishing Ltd., London: 2005.
Thompson, K. "Inferno on the Interstate: What Went Wrong?" Popular Mechanics, April 2008.
Johnson, P. and Barber, D. "Burnley Tunnel Fire-The Arup View." Arup Fire, Melbourne, Australia, April 2, 2007.
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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The Society of Fire Protection Engineers (SFPE) was established in 1950 and incorporated as an independent organization in 1971. It is the professional society representing those practicing the field of fire protection engineering. The Society has over 4,600 members and 100 chapters, including 21 student chapters worldwide.