Fixed Fire Fighting Systems for Road Tunnels

Issue 78: Fixed Fire Fighting Systems for Road Tunnels

By Kenneth J. Harris, P.E.

While 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 days. 

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.

	Date	Dead	Injured	Vehicles Destroyed
Holland Tunnel	1949	0	66	23
Velsen Tunnel	1978	5	3	6
Nihonzaka Tunnel	1979	7	2	173
Caldecott Tunnel	1982	7	2	8
Pecorile Tunnel	1983	8	22	10
L’Arme Tunnel	1986	3	5	5
Huguenot Tunnel	1994	1	28	1
Pfaender Tunnel	1995	3	4	4
Gotthard Tunnel	1997	0	1	1
Mont Blanc Tunnel	1999	39	14	36
Tauern	1999	8		40
Gotthard Tunnel	2001	11		23
Newhall Pass	2007	3	10	30
Burnley Tunnel	2007	3	2	3

 

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 operation.

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 addressed. 

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 objective. ⁸
• 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 water cleanliness.
• 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

References

1. 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.
2. Chiyoda Engineering Consultants. "Sprinklers in Japanese Road Tunnels," Yokohama, Japan, 2001.
3. NFPA 502, Standard for Road Tunnels, Bridges, and Other Limited Access Highways, National Fire Protection Association, Quincy, MA, 2011.
4. Tewarson, A. "Generation of Heat and Chemical Compounds in Fires." SFPE Handbook of Fire Protection Engineering. National Fire Protection Association, Quincy, MA 2008.
5. 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.
6. NFPA 15, Standard for Water Spray Fixed Systems for Fire Protection, National Fire Protection Association, Quincy, MA, 2012.
7. Rasbash, D. and Rogowski, Z. "Extinction of Fires in Liquids by Cooling with Water Sprays," Combustion and Flame. 1957, Vol. 1, pp. 453-466.
8. 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.
9. ASME B31.1, Code for Power Piping. American Society of Mechanical Engineers, New York, 2012.
10. ASME B31.3, Process Piping Code, American Society of Mechanical Engineers, New York, 2012.
11. Beard, A and Carvel, R. Handbook of Tunnel Fire Safety. Thomas Telford Publishing Ltd., London:  2005.
12. Thompson, K. "Inferno on the Interstate: What Went Wrong?" Popular Mechanics, April 2008.
13. Johnson, P. and Barber, D. "Burnley Tunnel Fire-The Arup View." Arup Fire, Melbourne, Australia, April 2, 2007.

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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

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