Fire and life safety systems for transportation tunnels are of paramount concern. The results of a tunnel fire can be catastrophic if the facility is not properly equipped. Not only can a fire result in loss of life, but also significant economic ramifications.
Today, tunnel owners rely on the National Fire Protection Association (NFPA) Standard 502 to provide guidance when building or rehabbing tunnels. NFPA 502 provides fire protection and fire life safety requirements for limited access highways, road tunnels, bridges, elevated highways, depressed highways, and roadways that are located beneath air-right structures.
To illustrate fire and life safety considerations, this paper explores two recent projects involving tunnels, the construction of the Elizabeth River Tunnels in Virginia, and the rehabilitation of the Hugh L. Carey Tunnel in New York. Part of the fire and life safety scope for these tunnels was to protect the tunnel structure to the NFPA 502 standard, preventing explosive spalling and progressive collapse of the tunnel lining during a 2-hour Rijkswaterstaat (RWS) fire event.
Key points of NFPA 502 edition 2011 include:
Section 7.3.1: Regardless of tunnel length, acceptable means shall be included within the design of the tunnel to protect all primary structural concrete and steel elements in accordance with this standard in order to:
- Mitigate structural damage and prevent progressive structural collapse
- Minimize economic impact due to tunnel closure
Section 7.3.2: The structure shall be capable of withstanding the RWS time/temperature curve or other recognized standard time/temperature curve that is acceptable to the authority having jurisdiction (AHJ), following an engineering analysis.
Section 7.3.3: During a 120-minute period of fire exposure, the following failure criteria shall be satisfied:
- Tunnels with concrete structural elements shall be designed or protected such that explosive spalling is prevented.
- Steel or cast-iron tunnel structural elements shall be protected such that the lining temperature shall not exceed 300 C (572 F).
Section 7.3.4: Structural fire protection material, where provided, shall satisfy the following performance criteria:
- Tunnels with cast in situ concrete structural elements protected such that:
a. The temperature of the concrete surface does not exceed 380 C (716 F).
b. The temperature of the steel reinforcement within the concrete [assuming a minimum cover of 25 mm (1 in.)] does not exceed 250 C (482 F).
- The material shall be noncombustible in accordance with ASTM E 136 or equivalent international recognized standard.
- The material shall have a minimum melting temperature of 1,350 C. (2,462 F).
- The material shall meet the fire protection requirements with less than 5 percent humidity by weight and when fully saturated with water, in accordance with the approved time/temperature curve.
Elizabeth River Tunnel
The Elizabeth River Tunnel project, located in Norfolk and Portsmouth, Virginia, included the development, design, construction, finance and operation of a new two-lane unidirectional immersed tunnel adjacent to the existing Midtown Tunnel under the Elizabeth River. The new Midtown Tunnel will relieve congestion and improve safety by eliminating bi-directional traffic in the existing Midtown Tunnel. In additional to the new Midtown Tunnel, the project included the rehabilitation of the existing Midtown and Downtown Tunnels. The Virginia Department of Transportation (VDOT) awarded the project under a P3 delivery method to Elizabeth River Concessionaire (ERC), which is responsible for all aspects of the project (design, build, finance, operate, and maintain). ERC will perform tolling, operations, and maintenance activities for a 58-year period.
With input provided by local police, fire, ambulance and first responders, the design enables enhanced emergency response and evacuation readiness. State-of-the-art safety features in the new tunnel includes a separate escape corridor, longitudinal ventilation, deluge system, fire sensors, fire alarms, motorist aid phone system, fire protection of the structural lining and video monitors for traveler safety meeting
History of Existing Tunnels
The existing Midtown Tunnel (Highway 58) opened on Sept. 6, 1962. The length of the existing Midtown Tunnel is 4,194 ft. The existing Midtown tunnel links Norfolk and Portsmouth and consists of a single bidirectional tunnel with transverse ventilation beneath the main channel of the Elizabeth River. Since the opening of the tunnel the population in the area has increased by 70% and average daily traffic has increased from 8,400 vehicles to 31,194 vehicles per day.
The existing Downtown Tunnels (I-264) carries the highest traffic volume of any tunnel in the Hampton Roads area. The first tunnel, the westbound tunnel, opened on May 23, 1952, and is 3,350 ft long. The second tunnel, the eastbound tunnel, opened on March 4, 1987, and is 3,813 ft long. Since the opening of the first tunnel, the average vehicles per day increased over 500% to an average of 67,228 vehicles per day.
Rehabilitation of the Existing Midtown & Downtown Tunnels
The rehabilitation of the existing Midtown and Downtown tunnels included the removal of the ceiling divider slab, inspection and repair of structural lining, addressing leaks and concrete degradation, tunnel structural fireproofing protection, new electrical with LED tunnel lighting, tile and concrete repair, exit and safety signage. The existing ventilation was a transverse ventilation system which was replaced by longitudinal ventilation system.
The contract documents allowed either board or spray fire protection solutions to be installed during nightly single lane closures and full tunnel closures over the weekend.
The board solution considered was a calcium silicate matrix engineered board with a minimum thickness of 22 mm to meet the 2-hour RWS time/temperature curve. This type of board can be post-curved and post fixed directly to the existing concrete lining using stainless steel mechanical anchors. No specialty installation contractor or special preparation of the tunnel lining is required prior to installation.
The spray fire protection solution considered was a high-density cementitious spray material with a minimum thickness of 30 mm. The spray solution requires a specialty spray fire protection installation contractor. The lining of the tunnel also requires power washing to remove all contamination as spray fire protection solution relies on the chemical bond to the tunnel structure to stay in place. The spray solution also requires a reinforcement mesh anchored with stainless steel anchors. Because of 15 mm being the maximum thickness that can be applied in one pass, the spray solution required two passes. Another consideration in the evaluation was the spray fire protection is temperature and humidity sensitive, which limited the time of year it could be applied without special control measures.
After evaluation of the cost of installation and special preparations, the design-build team chose Promat T calcium silicate matrix engineered board solution using the post curved-post fixed method.
There are limitations to the flexibility of the calcium silicate boards, however, and the existing tunnel’s radii were too severe to post curve one layer of 22 mm, so the contractor chose the minimum thickness the manufacture could make, which was 15 mm. The additional 8 mm of fire protection above the minimum required was a thermal value added to the solution. All calcium silicate boards are manufactured in a 1,200 x 2,500 mm format. For ease of handling and post curving, half size boards (1,200 x 1,250 mm) were chosen for light weight (32 lbs).
The first layer was post curved and temporarily anchored using a type of flat head spike anchors (0.25 x 2 in.) with six required per sheet. The second layer was post curved and staggered over the first layer, so joints are not in line. This second layer was permanently anchored with 9 each 0.25 x 3.25 in. 316 stainless mechanical expansion anchors (non-cut back anchors), including stainless steel nut with nylon insert and 30 mm (1.125 in.) washers.
The permanent anchors go through both layers of boards anchoring directly into the concrete lining to a depth specified by the anchor manufacturer. The number and spacing of anchors required are determined not on the live and dead load the boards will experience during daily operations of the tunnel, but determined from full scale fire testing for a 2-hour RWS fire event. Because of the closer spacing required during a fire event, the possibility of the boards detaching from the ceiling during operation is negligible.
Thermal justification of the Post Curved/Post Fixed System
To comply with the requirements of NFPA 502-2011, existing fire test data provided sufficient thermal information on the proposed system thermal performance. In addition, a thermal FEM calculation was provided from software developed and validated for the manufacture by an independent testing laboratory.
Because of the double layer of boards and staggering the joints between the first and second layer, gaps were not a critical part of the thermal justification. Due to the “Buy America Act” contract requirement for steel components, the U.S.-manufactured anchors selected were fire tested to 2-hour RWS time/temperature curve to satisfy the thermal performance for the double layer of fire protection boards and anchors as a system. A full-scale fire test for validation of any fire protection system is always highly recommended.
Experiences Existing Midtown and Downtown Tunnels
After the ceiling divider slabs were removed, the ceilings were inspected. Several areas in the tunnels had leaks with localized concrete degradation. The leaking areas were sealed and grouted, and the degraded concrete was removed and patched. The aggregate used in the original tunnel lining was locally available river aggregate quartz varying in size. The quartz aggregate was very abrasive which increased the drill bit usage. The fire protection overlapped onto the existing tile. Void areas were filled with a trowel grade fire protection mortar.
In areas where leaks could not be stopped, a stainless-steel channeling system was installed to direct the water around the tunnel structure to the storm drain on the sides. These channels were overlapped as shingles on a roof. The calcium silicate boards were boxed around drainage channel sections, providing fire protection in this area.
In areas where new jet fan ventilation and signage systems were to be installed, the areas were left blank until equipment was installed. The fire protection boards were then built up around and over the mounting plates to protect the mounting plates from localized heating sink into the concrete during a fire event.
At each end of the tunnel, the portal ceiling areas transitioned from a curved ceiling into a flat tunnel ceiling. These areas were easily custom fit by a carpenter crew. New electrical utility conduits were relocated on the side walls of the tunnel as a part of the electrical and communication upgrade package.
New Midtown Immersed Tunnel Fire Protection System
The contract documents for the New Midtown Tunnel specified a fire board protection system. Spray fire protection was not allowed as the owner required the fire protection to be easily removed for inspection on a routine basis, especially considering the fact that is an underwater immersed tunnel.
The contractor explored two options of means and methods of installation – “Lost Formwork” method and the “Post Fixed” method.
“Lost Formwork” method is the placement of fire protection boards on top of the concrete formwork, simply butt jointed. After the boards are in place, stainless steel 316 deck screws – 0.25 x 2 in. – are inserted into the back side of the board for additional concrete anchorage. Once the boards are in place on the concrete forms, the reinforcement steel is installed and concrete cast in place. After the concrete cures, the forms are removed, and the fire protection boards are in place. No cleaning of forms or demolding grease is required. There is a chemical bond between the boards and tunnel structure during the curing process, but experience has found that it is not reliably consistent, thus the requirement of the stainless steel deck screws for additional anchorage.
The Lost Formwork method is a simple and quick method for installing fire protection boards on a rectangular tunnel sections or cut-and-cover sections. However, the chemical bond and anchors on the back side of the board combine to make removal of the fire protection difficult. For this reason, the Post Fixed method was chosen.
The contractor/designer chose to use calcium silicate boards specifically used for immersed tunnels. The thickness requirement is 27.5 mm to meet the 2-hour RWS time/temperature curve. The initial design was to fire protect the ceiling and 1 m down the side walls. These fire protections boards are butt jointed and placed directly against the concrete. The standard board format for this type of board is 1,250 x 2,500 mm and weighs 168 lbs. To facilitate ease of handling, the contractor chose to use half size boards, 1,250 x 1,250 mm and weighing 84 lbs. These boards were anchored using 9 each 0.25 x 3.25 in. mechanical expansion anchor with nut, nylon insert and 30 mm (1.125 in.) washers, all 316 stainless steel.
The initial design did not have fire protection on the walls. During the design process, the design team decided to add additional fire protection on the walls. For the walls, the team chose a different type of board. The board chosen was a calcium silicate aluminate matrix engineered board, 22 mm thickness, in a half board format (1,200 x 1,250 mm). These boards were also anchored direct post fixed to the concrete surface with 9 each 0.25 x 3.25 in. mechanical expansion anchor with nut, nylon insert and 30 mm (1.125 in.) washers, all 316 stainless steel.
Since these boards are in the reflective zone, they were pre-coated: three coats front side and two coats back side. The color was an off-white two-part water-based epoxy coating to facilitate mechanically washing the fire protection panels on a routine basis. The top coating also increases the light reflection in the tunnel.
Thermal Justification of the System
As in the existing tunnels, test data provided sufficient thermal information on system performance of the proposed system along with FEM calculation to comply with the requirements of NFPA 502-2011.
As in the existing tunnels, the fire protection system was fire tested to 2-hour RWS time/temperature curve to confirm the thermal performance.
Experiences New Midtown Immersed Tunnel
To secure the transverse mechanical metal framework to the ceiling, stainless steel mechanical struts were cast in the ceiling slab running longitudinally to the tunnel alignment. To install the mechanical metal framework, a 3-in. circular coupon was removed, exposing the embedded mechanical struts. Half-inch diameter stainless steel hanging rods were installed in to the exposed mechanical strut to hang the mechanical framework. A 6 x 6-in. cover piece of 22 mm fire protection board covered the exposed area in the ceiling. This cover ensured the interface temperature did not exceed 380 C. This cover was held in place with a stainless steel lock nut and washer.
A thermal simulation for the connection of the hanging rods and mechanical strut was prepared by PRTC (Promat Research Technology Center) to determine the thickness required to thermally protect the concrete tunnel substrate and limit the heat sink into the metal strut. Based on the testing, the conclusion was that the concrete temperature is not negatively influenced by the strut-rod-connection.
Restoration of the Hugh L. Carey Tunnel
In 2012, Hurricane Sandy devastated the New York City metropolitan area. Sandy’s impact included major flooding of all highway tunnels except the Lincoln Tunnel. Among those flooded was the Hugh L. Carey Tunnel (formerly known as the Brooklyn-Battery Tunnel), which crosses under the East River connecting Manhattan and Brooklyn. The brackish floodwaters affected all tunnel services, requiring major FEMA-funded repairs to the concrete liner, ceiling slab dividing the roadway and the ventilation plenum, air ducts, tunnel wall tiles, ceiling finishes, LED lighting, traffic control communication, CCTV, fiber-optics, lead and asbestos abatement, and upgrade fire-life safety to NFPA 502. The project was delivered by design-bid-build method.
History of Hugh L. Carey Tunnel
The Hugh L Carey Tunnel opened on May 25, 1950, and is 9,117 ft long, making it the longest continuous underwater vehicular tunnel in North America. The first month of operation the tunnel carried approximately 41,000 vehicles. Today, traffic averages over 60,000 vehicles per day. The tunnel consists of twin-unidirectional roadways with transverse ventilation beneath the East River connecting via Governor’s Island.
Sandy Hurricane Restoration of Hugh L Carey Tunnel Fire Protection System
The contract documents required the fire protection to protect the precast reinforced concrete divider slab separating the ventilation plenum and the roadway surface from progressive collapse. The fire protection also needed to be easily removed for inspection of the tunnel structure and to withstand routine cleaning and maintenance with a power scrubbing brush machine.
The existing tunnel ceiling was covered with a ceramic coated steel architectural panel. These panels were removed before the fire protection was installed. The existing ceiling slab has ventilation and lighting recesses. These recesses vary throughout the tunnel, but there is a repeating pattern through more than 80% of the tunnel. The contract documents provided an example layout for fire protection boards, but it was the contractor’s responsibility to do the final fire protection panel layout with approval by the owner. The contractor chose to do a 3-D scan survey of the tunnel to develop accurate data for all of the recesses and to help determine an overall layout pattern.
The tunnels had several horizontal curves and compound curves ranging from 1,885 to 3,000 ft radii. The placement of the boards through the curves were negotiated in tangent sections. The layout in the curves required a tapered course to be cut-to-fit every 22 ft length of tunnel.
Because of clearance issues and the maximum fire protection thickness was limited to less than 22 mm (0.875 in.). Due to the need for routine mechanical washing of the ceiling, a two-part epoxy based top coating was required to protect the fire protection boards. Initially, a dark gray ceiling was chosen to keep the ceiling dark and reduce the claustrophobic feeling of being in an enclosed space. By the ceiling being dark in color, the height of the tunnel is not easily recognized. After coating the boards gray, the owner decided to change the portal areas color to “New York Blue” to match the new blue, yellow and cream-colored wall tiles.
The coating was a two-part epoxy water-based coating. The coating specification was of one coat primer plus two coats of colored epoxy water-based coating and one coat primer plus three coats colored epoxy water-based coating. The coating selected was from a U.K. manufacturer who had served the tunneling sector for over 40 years.
The contractor chose a 22-mm matrix engineered calcium silicate aluminate board (Promat H) utilizing the Post Fixed method. The boards were pre-cut at the factory to fit the layout of the tunnel then shipped to the U.K. for coating. The coated fire protection boards were butt jointed and placed directly against the concrete on the tunnel ceiling and anchored using mechanical anchors.
The owner looked at the U.S. manufactured stainless steel anchors available and determined along with the contractor to us a “nail head” type anchor. The anchor chosen was specifically designed for anchoring fire protection boards to tunnel ceilings and walls. This anchor at this time is only made in Europe. These anchors have a closer profile to the board and the owner liked the aesthetic look by not having the nuts protruding into the tunnel profile. The owner did require a larger anchor 0.375 in. (10 mm) diameter in each corner with a nut with nylon insert and washer to ensure a conservative approach and a small tradeoff on the aesthetic look. All mechanical anchors including 1.125 in. (30 mm) were stainless steel Grade 316.
Thermal Justification of the System
Existing test data provided sufficient thermal information on system performance of the proposed system along with Promat’s FEM software, developed and validated by Efectis, to comply with the requirements of NFPA 502-2011.
The intended anchors including the 0.375 in. (10 mm) were fire tested to RWS time/temperature curve prior to this project per NFPA-502 requirements and satisfied the thermal performance for the Promat T 22 mm boards and anchors as a system.
Experiences Sandy Restoration of the Hugh L Carey Tunnel
The biggest challenge on the project was ensuring the boards could be cut to size and coated prior to installation. Even though the 3-D scan survey was detailed, verification in the field after the board layout was required to ensure the boards would fit. The portal areas, approximately 600 ft at each end, was built by open-cut construction. These areas had large light recesses and vent areas all varied in spacing. The portal areas required the fire protection panels to be cut to fit in the field. The balance of the tunnel, which was constructed using a TBM shield, the vents and light recesses were in line and had a repetitious pattern with only a few anomalies.
The main part of the tunnel used four different sized boards (A,B,C,D). The A panels ran along the outside of the tunnel to the edge of the recessed light. The B panels were placed between the lights. The C panels were placed between the vents. This left two rows of D panels running down the centerline of the tunnel. The lengths of the panels in the longitudinal direction of the tunnel were 1,200 mm (47.25 in.), the standard width of the fire protection boards selected.
This article was submitted by Promat, a leading supplier of fire protection products. For information, click here.