Standard for Road Tunnels, Bridges and Other Limited- Access Highways
2008 Edition

In recent years, road tunnel fires and subsequent international research projects have suggested that vehicle fires within tunnels are likely to develop more rapidly than expected, degrade the tenability of an environment more quickly than originally calculated, burn for longer periods of time and at higher temperatures, and resist intervention of fire-fighting operations.¹

article continues below UL/ULC listed DecoShield systems provide you with lightweight, attractive, affordable modular cover/support systems for sprinkler piping, hydronics, plumbing, cable, and conduit. DecoShield products are manufactured using an engineered resin of a Class I/A material meeting most model code requirements, and are clean, paintable, easy to install, tamper-resistant, durable, and economical. The DecoShield cover will not dent, crack, rust, or corrode. As an alternative to constructed soffits and suspended ceilings, the DecoShield systems can be installed without disturbing asbestos ceilings, and can be easily installed in occupied premises. We also offer assistance with design, installation, and anchoring problems. For more information, visit www.decoshield.com

In light of this, the NFPA Technical Committee on Road Tunnel and Highway Fire Protection determined it was timely for NFPA 502, Standard for Road Tunnels, Bridges and Other Limited-Access Highways,² to revisit a number of its provisions with respect to fires in road tunnels. The 2008 edition includes revisions that further clarify the categorization of road tunnels; a revision of 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.

In particular, there has been a broad reconsideration of the requirements and recommendations for:

• Fixed fire-suppression systems.
• Ventilation (and its effect on tenability of environment).
• Protection of structural elements.
• Hazardous goods transport.
• Design fire size.

In the past, the use and effectiveness of fixed fire-fighting systems in road tunnels were not universally accepted. One of the reasons why most countries were reluctant to use fixed fire-fighting systems in road tunnels is that many fires start in the motor compartment of a vehicle, and fixed fire-fighting systems are of limited use in suppressing the fire until the fire is out in the open. Fixed fire-fighting systems can be used, however, to cool down vehicles, to stop the fire from spreading to other vehicles (i.e., to diminish the fire area and property damage) and to stop secondary fires in tunnel lining materials. Experiences from Japan show that fixed fire-fighting systems have been extremely effective in cooling down the area around the fire, so that firefighting can be performed more effectively.³

The 2008 edition of NFPA 502 now has annex language that acknowledges the use of fixed fire-fighting systems in road tunnels. Fixed fire-fighting systems can be used as part of an integrated approach to the management of safety. To be used, the fixed fire-fighting systems must be shown by engineering analysis to provide an acceptable level of safety. Additionally, an engineering installation, inspection and maintenance schedule must be developed to maintain the level of performance intended.

Where fixed fire-fighting systems are installed in road tunnels, they must be installed, inspected and maintained in accordance with the applicable NFPA standard for the design of the system.

The addition of water-based fixed fire-fighting systems in road tunnels also protects mechanical ventilation equipment from exposure to extreme heat conditions due to fire. Currently, mechanical ventilation equipment is required to be designed to remain operational for a minimum of 1 hour in an air stream temperature of 250°C (482°F). The use of water-based fixed fire-fighting systems will control the exposure temperature to the mechanical ventilation equipment and allow for proper operation of the ventilation equipment during a high-temperature fire.

NFPA 502 now contains the following responses to the major concerns expressed by tunnel designers, engineers and authorities regarding fixed fire-fighting system use and effectiveness in road tunnels:

Concern (1) Fires in road tunnels usually occur inside vehicles or inside passenger or engine compartments designed to be waterproof from above; therefore, fixed fire-fighting systems might not have an extinguishing effect.

Response: The purpose of a fixed fire-suppression system is to prevent fire spread to other vehicles so that the fire does not grow to a size that cannot be attacked by the fire service.

Concern (2) If any delay occurs between ignition and fixed fire-fighting system activation, a thin water spray on avery hot fire could produce large quantities of superheated steam without materially suppressing the fire.

Response: Fire tests have now shown this concern not to be valid.⁴ A properly design fixed fire-fighting system suppresses the fire and cools the tunnel environment. Since a heavy-goods vehicle fire only needs 10 minutes to exceed 100 MW and1200°C,¹ which are fatal conditions, it is important to operate the fire-suppression system as quickly as possible.

Concern (3) Tunnels are very long and narrow, often sloped laterally and longitudinally, vigorously ventilated and never sub-divided, so heat normally will not be localized over a fire.

Response: Advances in fire detection technology have now made it possible to pinpoint the location of a fire in a tunnel with sufficient accuracy to operate a zoned fixed fire-fighting system.

Concern (4) Because of stratification along the tunnel ceiling, a number of the activated sprinklers would not, in all probability, be located over the fire. A large number of the activated sprinklers would be located away from the fire source, producing a cooling effect that would tend to draw this stratified layer of smoke down toward the roadway level,thus impeding the rescue and fire-fighting effort.

Response: Any activated fixed fire-fighting system not over the fire would cool the tunnel to help rescue services to intervene. Zoned systems are released by a detection system that is accurate even with forced ventilation.

Concern (5) Water spraying from the ceiling of a sub-aqueous tunnel could suggest tunnel failure and induce panic in motorists.

Response: This was a hypothetical concern not borne out in practice. In the event of fire, motorists are likely to recognize water spraying from nozzles as a fire safety measure. Behavioral studies have shown that people do not panic in afire, even when they are unable to see.⁵

Concern (6) The use of sprinklers could cause the disruption of the smoke layer and induce turbulence and mixing of the air and smoke, thus further threatening the safety of persons in the tunnel.

Response: This has been shown not to be a valid concern. Fire tests have demonstrated that smoke does not usually form a layer at the top of the tunnel but quickly fills the cross-section. Normal air movement in the tunnel accelerates this process.⁶ A fixed fire-fighting fire-suppression system reduces temperatures and the risk of fire spread to other vehicles.

Concern (7) Testing of a fixed fire-fighting system on a periodic basis to determine its state of readiness could be impractical and costly. Inspection can be performed when other facilities are inspected.

Response: A full discharge test is normally only performed at system commissioning. During routine testing, the system can be configured to discharge flow to the drainage system.

PROTECTION OF STRUCTURAL ELEMENTS

The 2004 edition of NFPA 502 introduced new requirements for the protection of structural elements. In the2008 edition, several requirements were added to further support this important function of the tunnel as it pertains to user safety.

Regardless of tunnel length, all primary structural con-crete and steel elements are required to be protected in accordance with this standard in order to:

• Maintain life safety and provide a tenable environment.
• Mitigate structural damage and prevent progressive t structural collapse.
• Minimize economic impact.

The time/temperature development is shown in Table 1. After a 120-minute period of fire exposure, the following failure criteria must be satisfied:

(1) Tunnels with cast in-situ concrete structural elements shall be protected such that:

• The temperature of the concrete surface does not exceed 380°C (716°F).
• The temperature of the steel reinforcement within the concrete [assuming a minimum cover of 25mm (1 in)]does not exceed 250°C (482°F).

(3) Steel or cast iron tunnel linings shall be protected such that the lining temperature does not exceed 300°C (572°F).

(4) Structural fire protection materials shall satisfy the following performance criteria:

• They shall be noncombustible in accordance with ASTM E 136⁸ or equal international standard.
• They shall have a minimum melting temperature of 1350°C (2462°F).
• They shall not produce toxic smoke or fumes under a t fire exposure in accordance with ASTM E 84⁹ or equal international standard.
• They shall meet the fire protection requirements with <5% humidity by weight and also when fully saturated with water in accordance with RWS Fire Test Procedure1998-CVB-R1161 (Rev 1).⁷

• Be resistant to freezing and thawing;
• Withstand dynamic suction and pressure loads;
• Withstand both hot and cold thermal shock from fire exposure and hose streams;
• Meet all applicable health and safety standards;
• Not itself become a hazard during a fire; and
• Be resistant to water ingress.

Fire tests must meet the following requirements:

• Concrete slabs used for the application of fire protection t materials for fire testing purposes have dimensions of at least 1400x1400 mm and a nominal thickness of 150 mm.
• The exposed surface will be approximately 1200x1200 mm.
• The fire protection material must be fixed to the concrete t slab using the same fixation material (anchors, wire mesh, etc.) as will be used during the actual installation in the tunnel.
• In the case of board protection, a minimum of one joint in t between two panels must be created to judge if any thermal leaks will occur in the case of a real fire in the tunnel.
• In case of spray materials, the number of applications (amount of layers) must be recorded when preparing the test specimen. The same number of layers must be used when applying the spray material in a real tunnel.
• Temperature recordings must be made by thermocouples located at the interface in between the concrete and the fire protection material, at the bottom of the reinforcement and on the non exposed face of the con-crete slab.

• The diameter should be limited to maximum of 6 mm t (0.25") in order to reduce the heat sink effect through the steel anchor into the concrete. It is reported that thicker anchors can create a local spalling effect of theconcrete.6 This local effect is only temporary because the spalling can spread over the surface once a small part of the concrete is directly exposed to fire.
• The use of stainless steel anchors is recommended. Types that can be used are A4, 316, 1.4401 and 1.4571. In some countries, even higher requirements are applied, such as 1.4529.
• If necessary, a washer must be used to avoid a t pull-through effect when the system is exposed to dynamic loads.
• The anchors should be suitable for use in the tension t zone of concrete (cracked concrete).
• The anchors should be suitable for use under t dynamic loads.

The 2008 edition includes a complete revision to the Annex material relating to tenable environment. This is intended to correlate with the material in NFPA 130, Standard on Fixed Guideway Transit and Passenger Rail Systems.¹⁰ The purpose of the Annex is to provide guidelines for the evaluation of tenability within the tunnel evacuation paths. Current technology is capable of analyzing and evaluating conditions to provide proper ventilation for emergency conditions.

The same ventilating devices might or might not serve both normal operating conditions and emergency requirements. The goals of the ventilation system, in addition to addressing fire and smoke emergencies,are to assist in the containment and purging of hazardous gases and aerosols, such as those that could result from a chemical/biological release.

Environmental conditions, geometric considerations and time considerations should be taken into account.Some factors that should be considered in maintaining a tenable environment for periods of short duration are:

Heat Effects. Exposure to heat can lead to life threat three basic ways:

• Hyperthermia,
• Body surface burns, and
• Respiratory tract burns.

Air Carbon Monoxide Content. Air carbon monoxide(CO) content should be as follows:

• Maximum of 2000 ppm for a few seconds;
• Averaging 1150 ppm or less for the first six minutes t of the exposure;
• Averaging 450 ppm or less for the first 15 minutes t of the exposure;
• Averaging 225 ppm or less for the first 30 minutes t of the exposure;/
• Averaging 50 ppm or less for the remainder t of the exposure; and
• These values should be adjusted for altitudes above 1000 m (3000 ft).

Air Velocities. Air velocities in the enclosed tramway should be ~ 0.76 m/s (150 fpm) and ˚11.0 m/s (2200 fpm).

Noise Levels. Noise levels should be a maximum of 115 dBA for a few seconds and a maximum of 92 dBA for the remainder of the exposure.

REGULATED AND UNREGULATED CARGOES

Recent road tunnel fires suggest that goods traditionally not characterized as "hazardous," e.g., flour and margarine (1999 Mont Blanc Tunnel), paint (1999 Gothard Tunnel) and tires (2005 Frejus Tunnel), may constitute a greater risk to tunnel users and tunnel structures than expected. As a result, Chapter13, "Control of Hazardous Materials," has been retitled "Regulated and Unregulated Cargoes" to provide guidance on developing rules regarding any and all cargoes traveling through the tunnel.

The authority having jurisdiction must adopt rules and regulations that apply to the transportation of regulated and unregulated cargoes. Design and planning of the facility must address the potential risk presented by regulated and unregulated cargoes.

When developing rules and regulations, fire, accident and research experience of the vehicles and car goof the type expected within the tunnel, particularly of goods and vehicles not normally characterized as hazardous or otherwise regulated, should be considered.Some types of cargos not normally considered hazardous may, in certain circumstances, in confined spaces within tunnels behave as,or equivalent to, hazardous materials in terms of the rate of fire growth, the intensity of the fire,discharge of noxious materials, destruction to infrastructure and threat to users' safety.

In developing regulations, the following must be addressed:

1. Population density.
2. Type of highway.
3. Types and quantities of hazardous materials.
4. Emergency response capabilities.
5. Results of consultation with affected persons.
6. Exposure and other risk factors.
7. Terrain considerations.
8. Continuity of routes.
9. Alternative routes.
10. Effects on commerce.
11. Delays in transportation.
12. Climatic conditions.
13. Congestion and accident history.

DESIGN FIRE SIZE

Large-scale fire tests¹¹ have shown that vehicle fires within tunnels are likely to develop more rapidly and have higher peak heat release rates than expected. The results of these tests have led to the revision of Table A.10.5.1, "Fire Data for Typical Vehicles," which now reads as follows:

Car	5-10 MW
Multiple passenger cars (2-4 vehicles)	10-20 MW
Bus	20-30 MW
Heavy goods truck	70-200 MW
Tanker	200-300 MW

There are substantial increases over the 2004 edition values of 20 MW for buses, 20-30 MW for heavy goods trucks and 100 MW for tankers. In addition, a value has been added for multiple passenger car fires.

Jason R. Gamache is with the National Fire Protection Association.

References:

1. Ingason, H., Ed. "Recent Achievements Regarding Measuring of Time-Heat and Time-Temperature Development in Tunnels," SP Technical Research Institute of Sweden, Borås, Sweden, 2004.
2. NFPA 502, Standard for Road Tunnels, Bridges and Other Limited Access Highways, National Fire Protection Association, Quincy, MA, 2008.
3. Mashimo, H., and Mizutani, T., "Current State of Road Tunnel Safety in Japan," Advanced Construction Technology Center, Tokyo, Japan, 2003.
4. Kashef, A., Kim, A.K., Liu, Z.G., and Loughseed, G., "Challenges for Use of Fixed Fire-Suppression Systems in Road Tunnel Fire Protection," National Research Council of Canada, Ottawa, Canada, 2007.
5. Jennsen, G., "Way Finding, Signage, and Human Factors in Tunnels" Proceedings of the NCHRP Workshop on Safety and Security in Roadway Tunnels, Irvine, CA, 28-29 November, 2007.
6. Carvel, R., and Marlair, G., "Experimental Tunnel Fires," The Handbook of Tunnel Fire Safety (R. O. Carvel and A. N. Beard, Eds.), Thomas Telford Publishing, 201-230, London, 2005.
7. "Fire Protection for Tunnels," TNO Report 1998-CVB-R1161 (Rev. 1), TNO Building and Construction, Delft, Netherlands, 2000.
8. ASTM E 136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750°C, ASTM International, West Conshohocken, PA, 2004.
9. ASTM E 84, Standard Test Method for Surface Burning Characteristics of Building Materials, ASTM International, West Conshohocken, PA, 2008.
10. NFPA 130, Standard on Fixed Guideway Transit and Passenger Rail Systems, National Fire Protection Association, Quincy, MA, 2007.
11. Ingason, H., and Lönnermark, A., "Heat Release Rates from Heavy Goods Vehicle Trailers in Tunnels," Fire Safety Journal, 40, 646-668, 2005.