Photovoltaic Panel Flame Spread Testing: Standards, Methods, and Compliance Requirements

Photovoltaic panel flame spread testing is a critical fire safety evaluation that measures how flames propagate across solar module surfaces and the roof assemblies on which they are installed. This testing, governed by standards such as IEC 61730-2, UL 1703, UL 790, and ASTM E84, is used to assign the Class A, B, or C fire ratings required for building permits, product certification, and insurance approval of rooftop and building-integrated PV systems. This article explains the sample requirements, measured parameters, test methodologies, and application scenarios for flame spread evaluation performed by accredited third-party laboratories.

Technical Overview

Flame spread testing evaluates the propensity of a photovoltaic (PV) panel—and the roof or building assembly on which it is installed—to propagate fire when exposed to an ignition source. Although the front glass of a typical crystalline silicon module is noncombustible, the complete product incorporates significant quantities of combustible polymeric materials, including ethylene-vinyl acetate (EVA) or polyolefin elastomer (POE) encapsulants, fluoropolymer or polyester backsheets, polymeric junction boxes, cable insulation, adhesives, and sealants. A module that contributes to fire propagation can downgrade the fire performance of an entire roof assembly, which is why building codes and product certification schemes treat rooftop PV as an integral component of the roof covering rather than as an isolated electrical device.

In North America, external fire performance is expressed as a Class A, B, or C rating, where Class A represents the highest resistance to fire exposure. The classification is determined by applying the test methods of UL 790 (technically equivalent to ASTM E108) to the combined module–mounting–roof deck assembly, as mandated by UL 1703, UL 61730 (the harmonized North American edition of IEC 61730), and UL 2703 for mounting systems. Internationally, IEC 61730-2 specifies fire test requirements referencing applicable installation codes, while building-integrated PV products in Europe are typically classified under EN 13501-1 using EN ISO 11925-2 and EN 13823. In the Chinese market, reaction-to-fire classification is performed under GB 8624.

The principal standards governing PV flame spread evaluation include:

• IEC 61730-1 / IEC 61730-2 — Photovoltaic (PV) module safety qualification, including fire test requirements
• UL 1703 and UL 61730 — Flat-plate PV module and panel safety with North American fire classification requirements
• UL 790 / ASTM E108 — Standard test methods for fire tests of roof coverings (spread of flame, burning brand, fire penetration)
• UL 723 / ASTM E84 — Surface burning characteristics of building materials (Steiner tunnel test)
• UL 2703 — Mounting, mounting-disconnection, grounding, and bonding devices for PV systems
• ISO 5660-1 — Reaction-to-fire tests using the cone calorimeter (heat release rate measurement)
• IEC 60695-11-5 and IEC 60695-11-10 — Needle-flame and 50 W horizontal/vertical flame tests for polymeric components
• EN 13501-1, EN ISO 11925-2, and EN 13823 — European reaction-to-fire classification for construction products
• GB 8624 — Chinese classification for burning behavior of building materials and products

Testing Samples

Complete PV Modules and Panels

Full-size, production-representative modules are required, complete with front glass, cells, encapsulant, backsheet, frame, junction box, and cabling as shipped to the field. Sample quantities typically range from three to ten units depending on the test method and the number of configurations being evaluated. Any deviation between the test specimen and series production, such as substitute encapsulants or backsheets, may invalidate the classification.

Module-and-Mounting System Assemblies

Under UL 1703 and UL 2703, the fire classification applies to the module installed on a specific racking system over a representative roof deck, not to the module in isolation. Assemblies are constructed in end-use configuration over both noncombustible and combustible decks, and at both steep-slope and low-slope inclinations, because the resulting classification is valid only for the tested combination. Test decks may extend several meters in length to permit evaluation of flame propagation across multiple modules.

Building-Integrated Photovoltaic (BIPV) Products

Solar shingles, tiles, curtain-wall laminates, facade elements, and flexible PV laminates intended for direct integration into the building envelope are tested as installed systems. These products are evaluated against construction-product reaction-to-fire frameworks such as EN 13501-1 or GB 8624 in addition to PV-specific safety standards, since they replace rather than supplement conventional building materials.

Polymeric Component Materials

Individual materials—backsheets, encapsulant films, junction box housings, connectors, cable insulation, adhesives, and frame sealants—are subjected to small-scale flammability screening using UL 94 or IEC 60695-11-10 ratings such as V-0, V-1, V-2, 5VA, and 5VB. These component-level results support material qualification, design documentation, and research and development activities.

Testing Items

Depending on the applicable standard and product configuration, accredited third-party laboratories measure and report the following parameters:

• Flame spread index (FSI) relative to the calibrated red oak reference in the Steiner tunnel test
• Smoke developed index (SDI) based on optical density of combustion products
• Maximum flame spread distance and rate of propagation across the assembly
• Time to ignition under a defined radiant heat flux
• Peak heat release rate (kW/m²) and total heat released (MJ/m²) via oxygen consumption calorimetry
• Mass loss rate during combustion
• Afterflame time and afterglow duration following removal of the ignition source
• Production of flaming droplets, debris, or particles that ignite materials below the assembly
• Fire penetration through the module or underlying roof deck
• Resistance to burning brands of standardized dimensions and mass
• Damage length and affected area of the specimen after test completion

Testing Methods

Steiner Tunnel Test (ASTM E84 / UL 723)

The specimen, approximately 7.3 meters in length and faced downward in a ceiling orientation, is exposed to a controlled gas burner flame for ten minutes under forced ventilation. The flame front position is recorded optically over time, and the flame spread index is calculated using the historical calibration in which select-grade red oak is assigned a value of 100 and inorganic cement board a value of 0. Commonly adopted classification limits are FSI 0–25 for Class A, 26–75 for Class B, and 76–200 for Class C, with a smoke developed index generally limited to 450 or below. This method is most often applied to PV laminates, BIPV products, and backing or insulation materials.

Spread of Flame Test (UL 790 / ASTM E108 per UL 1703)

The module-mounting-roof deck assembly is mounted on an inclined frame at the slope specified by the target classification and exposed to a gas burner flame at its lower edge with defined airflow. Flame application durations, air velocity, and pass criteria depend on the classification sought. The assembly passes if flame propagation and glowing combustion remain within the limits specified by the standard, with no sustained flaming debris. Because results are configuration-dependent, separate tests are performed for each roof deck type and slope, and the listed classification is restricted accordingly.

Burning Brand and Fire Penetration Tests

In the burning brand test, wooden brands of standardized size and mass are ignited and placed on the assembly surface while the test frame is subjected to the required air supply. The assembly must prevent sustained flame spread and must not allow the brand to burn through to the deck. In the fire penetration test, a more severe exposure is applied to determine whether flames or glowing combustion penetrate the module and roof construction. Class A assemblies must withstand the largest brand; correspondingly smaller brands apply to Class B and Class C evaluations.

Cone Calorimeter Testing (ISO 5660-1)

Square specimens of 100 mm × 100 mm are exposed horizontally to radiant fluxes typically between 25 and 50 kW/m², simulating exposure conditions in a developing fire. Using the oxygen consumption principle, the apparatus measures time to ignition, peak and total heat release rate, mass loss, smoke production rate, and effective heat of combustion. Cone calorimetry is widely used for material screening, comparative evaluation of encapsulants and backsheets, and fire modeling input data.

Small-Scale Ignition Tests (UL 94 / IEC 60695-11-5)

Component materials are evaluated with a 50 W premixed flame applied under horizontal or vertical orientation to determine ratings such as HB, V-0, V-1, V-2, 5VA, and 5VB, based on afterflame time, ignition of cotton indicators by flaming droplets, and glowing duration. The needle-flame test of IEC 60695-11-5 applies a small gas flame to junction boxes, connectors, and insulation parts for durations of 5 to 60 seconds to verify that a small ignition source does not cause sustained burning.

Applications

Flame spread test reports and classifications are used throughout the PV industry value chain:

• Certification and market access for rooftop modules under IEC 61730, UL 1703, and UL 61730, enabling listing and labeling of modules with defined mounting systems
• Building permit submissions and approval by authorities having jurisdiction, which typically require the PV system fire class to match or exceed that of the underlying roof covering
• Qualification of building-integrated PV envelope products such as solar facades, curtain walls, roof tiles, and flexible laminates under EN 13501-1 or GB 8624
• Insurance underwriting, project due diligence, and fire risk assessment for commercial, residential, and utility-scale installations
• Research and development support for material selection, including flame-retardant backsheets, halogen-free encapsulants, and thermally stable junction box compounds
• Supply chain verification and incoming material control for module manufacturers and EPC contractors

FAQ

What fire classification is required for rooftop PV systems?

Requirements are set by the authority having jurisdiction, but most modern building codes require the PV system to carry a fire classification equal to or higher than that of the roof covering on which it is installed. Class A is commonly specified for commercial buildings, multifamily dwellings, and low-slope roofs, while Class B or C may be acceptable for certain residential steep-slope applications.

Is the fire rating assigned to the module alone?

No. Under UL 1703, UL 2703, and UL 61730, the classification applies to the complete assembly of module, mounting system, and roof deck type as tested. A Class A module rating is therefore valid only in combination with the specific racking hardware and roof construction listed in the certification documentation, and installers must verify that the field configuration matches the listed combination.

How does ASTM E84 differ from UL 790?

ASTM E84 (UL 723) is a tunnel test that measures the surface burning characteristics of a material specimen and yields a flame spread index and smoke developed index. UL 790 (ASTM E108) evaluates the external fire exposure performance of complete roof covering assemblies through spread of flame, burning brand, and fire penetration tests. PV roof products are typically classified under UL 790 methods, while E84 data is more common for BIPV components and construction materials.

Do glass-glass modules still require flame spread testing?

Yes. Even when both outer layers are glass, the assembly contains combustible encapsulant, junction boxes, cables, adhesives, and edge sealants, and the interaction between the module and the mounting system governs the assembly behavior under fire exposure. Certification therefore requires evaluation of the full end-use assembly regardless of front-sheet material.

How many samples and how much time are needed for a test program?

Small-scale component tests may require only a handful of specimens and a few days of laboratory time. Full assembly testing under UL 790 requires multiple complete test decks several meters in length, one per deck type, slope, and exposure condition, plus contingency specimens for repeat testing. A typical program covering spread of flame, burning brand, and penetration tests across two deck types generally spans several weeks, including assembly construction, conditioning, testing, and reporting.

Can test results from one module type be extended to a similar product family?

Extension is possible only within the limits defined by the applicable standard and certification scheme. Variations in encapsulant, backsheet, frame design, junction box, glass thickness, or mounting geometry can materially alter flame spread behavior, and such changes normally trigger additional testing or an engineering evaluation by the accredited third-party laboratory before the classification can be extended.