Fire Resistance Testing of Fire Protection Wrapping Systems for Metro Engineering Projects

Fire protection wrapping systems—including rigid fireproof boards, flexible fire-resistant blankets, and sprayed coatings—are critical passive fire protection measures in metro tunnels, stations, and ancillary structures. Fire resistance testing verifies that these systems can maintain structural integrity, insulation, and operational function under standardized and tunnel-specific fire conditions. This article outlines the sample types, testing items, test methods, and applicable standards for fire resistance testing of fireproof wrapping systems used in metro engineering projects.

Technical Overview

Metro systems operate in confined underground environments where heat, smoke, and toxic gases accumulate rapidly and evacuation paths are limited. A train fire can produce peak gas temperatures of 1,100°C to 1,350°C within minutes, a scenario far more severe than a standard building fire. To mitigate this risk, fire protection wrapping—also referred to as fireproof cladding or encasement—is applied to steel structures, tunnel linings, ventilation and smoke exhaust ducts, cable trays, and pipelines to delay heat transfer, prevent premature structural failure, and keep life-safety systems functional during evacuation and firefighting operations.

Fire resistance testing subjects full-scale protected specimens to controlled furnace exposure following defined temperature–time curves, measuring whether the assembly continues to carry load, remain intact, and limit heat transfer for a required duration. In China, GB 51298 (Standard for Fire Protection Design of Metro) and GB 50157 (Code for Design of Metro) establish the fire safety design basis, while testing is performed by accredited third-party laboratories against standards such as GB/T 9978.1, ISO 834, EN 1363, UL 1709, and ASTM E119. Depending on the exposure scenario, several fire curves may apply:

• Standard heating curve (ISO 834 / GB/T 9978.1) for station building elements and general structural members
• Hydrocarbon curve (HC) for fuel-rich fire scenarios involving rolling stock and cables
• Modified hydrocarbon curve (HCM) with elevated peak temperature for severe tunnel scenarios
• RABT curve with forced cooling phase, reflecting typical road and rail tunnel fire development
• RWS curve representing an extreme, long-duration hydrocarbon fire event

Testing Samples

Rigid Fireproof Boards

Board-type wrapping materials include fiber-reinforced calcium silicate boards, vermiculite boards, and magnesium-based boards. These are mechanically fixed with pins, clips, and framing to encase steel columns and beams or to form protective liners on tunnel surfaces. Test specimens are prepared at the certified system thickness, including all joints, fixings, and edge details used in actual installation.

Flexible Fire Wrapping Systems

Flexible systems consist of needled ceramic or inorganic fiber blankets, often foil-faced and layered, secured with stainless steel pins and straps. They are widely used on ventilation ducts, smoke exhaust ducts, cable trays, and irregularly shaped penetrations because they conform to complex geometries. Specimens must reproduce the field-applied layer count, overlap arrangement, and fastener spacing.

Fireproof Coatings

Sprayed and troweled coatings include thick cementitious (Portland cement or gypsum-based) formulations and thin intumescent coatings for steel substrates. Coated specimens are prepared on steel plates or structural sections at representative dry-film thickness, with primer and topcoat included where specified in the system, and are conditioned to constant mass before testing.

Full-Scale Protected Assemblies

System-level specimens include loaded and unloaded steel columns, beams, duct sections, cable trays, and pipe assemblies protected with the complete wrapping system. These full-scale specimens are the primary basis for assigning fire resistance ratings, because performance depends on the interaction between the protective material, substrate, joints, and fixing hardware rather than on material properties alone.

Testing Items

Testing programs for metro fire protection wrapping typically combine system-level fire resistance evaluation with material-level performance characterization:

• Load-bearing capacity (R): ability of the protected member to sustain design load throughout the fire exposure
• Integrity (E): resistance to flame passage, gaps, cracks, and ignition of cotton pads on the unexposed side
• Insulation (I): limitation of temperature rise on the unexposed surface, generally to 140°C average and 180°C maximum above ambient
• Fire resistance duration ratings: 30, 45, 60, 90, 120, 150, 180, or 240 minutes as required by design
• Critical steel temperature criteria: for protected steelwork, average steel temperature not exceeding 550°C and maximum single-point temperature not exceeding 630°C in accordance with GB 14907 and GB/T 9978
• Combustion performance classification to GB 8624 (Class A1/A2 non-combustible requirements are typical for underground applications) and EN 13501-1
• Smoke production and toxicity, including smoke density per GB/T 8627 and smoke toxicity classification per GB/T 20285
• Physical and mechanical properties: dry density, thermal conductivity, compressive and flexural strength, bond or adhesion strength, and water absorption
• Durability assessment: freeze–thaw cycling, damp-heat exposure, chemical corrosion resistance, and long-term aging behavior relevant to the tunnel service environment

Testing Methods

The core method is the full-scale furnace test. Vertical or horizontal furnaces heat the protected specimen following the specified temperature–time curve, with furnace pressure controlled relative to the ambient environment. Specimens are instrumented with thermocouples on the steel substrate and on unexposed surfaces; structural specimens such as columns and beams are tested under applied mechanical load to verify simultaneous load-bearing performance. The test continues until a failure criterion is reached or the required rating period is exceeded, and behavior during any cooling phase—particularly important for RABT-curve tunnel tests—is also evaluated.

Supporting small-scale and bench tests establish the material baseline. Non-combustibility is determined per GB/T 5464 and ISO 1182 or ASTM E136; reaction-to-fire behavior is assessed with the single burning item test per GB/T 20284 or EN ISO 11925-2; heat release is characterized by cone calorimeter testing per ISO 5660; and thermal conductivity is measured by guarded hot plate methods per GB/T 10294, ISO 8302, or ASTM C177. Hydrocarbon and rapid temperature rise exposures may be conducted in accordance with UL 1709 or the special exposure procedures of EN 1363-2.

Upon completion, accredited third-party laboratories issue test reports documenting the system description, material thickness, fixing details, exposure curve, measured temperatures, observed failure modes, and the achieved fire resistance classification. Reports serve as the technical basis for design compliance, product certification, and construction acceptance.

Applications

Fire resistance testing of fire protection wrapping systems directly supports fire safety delivery across the full scope of metro engineering:

• Tunnel works: protection of shield tunnel segments, lining reinforcement, cross passages, and contact channel structures against hydrocarbon and RABT-curve fire scenarios
• Stations: fireproof encasement of structural steel columns, roof trusses, and mezzanine framing in station halls and platform levels
• Mechanical systems: wrapped ventilation and smoke exhaust ducts that must remain leak-tight and functional throughout the required rating period
• Electrical systems: protection of high-voltage cable trays, cable routes, and busway runs to prevent fire propagation and preserve emergency power supply
• Utilities: wrapping of water, drainage, and fire main piping, including fire-rated penetration sealing at wall and slab openings
• Depots, parking areas, and elevated sections: fire protection of steel structures in workshop halls and elevated station frameworks

FAQ

Q: What fire resistance ratings are typically required for metro fire protection wrapping?

A: Ratings of 1.0 to 2.0 hours are most common for structural members and smoke control systems, with exact values determined by the design standard applied to the project. Tunnel lining protection may additionally be assessed under tunnel-specific curves such as RABT or RWS, including the cooling phase.

Q: Which fire curve should be used for testing?

A: The standard ISO 834 curve generally applies to station building elements, while hydrocarbon (HC), modified hydrocarbon (HCM), RABT, or RWS curves are used for tunnel and rolling-stock fire scenarios. The selection is defined by the project fire safety design and applicable metro fire codes.

Q: Can test results for a fireproof coating be transferred to a board wrapping system?

A: No. Fire resistance performance is system-specific and depends on material type, thickness, substrate configuration, joints, and fixings. Each protective system must be tested and certified in the configuration intended for installation.

Q: What specimen sizes are involved?

A: Full-scale specimens are required—for example, protected steel columns approximately three meters in height tested vertically, or beam and duct assemblies tested horizontally at representative span dimensions. Specimen dimensions and quantities follow the requirements of the applicable test standard and laboratory protocol.

Q: How long does the testing process take?

A: Beyond the furnace exposure itself, the timeline includes specimen fabrication, system curing or conditioning to stable mass, instrumentation, and report preparation. A complete program covering fire resistance testing and supporting material characterization typically requires several weeks, depending on scope and laboratory scheduling.