Photovoltaic (PV) module fire resistance testing evaluates how solar modules behave when installed on roof assemblies and exposed to flames, burning brands, and radiant heat, establishing the fire classification required by building codes and product certification schemes. This article explains the governing standards—IEC 61730-2, UL 790 / ASTM E108, EN 13501-1, and GB 8624—along with sample requirements, test items, and evaluation methods. It is a practical reference for manufacturers of rooftop modules, building-integrated photovoltaic (BIPV) products, and utility-scale systems seeking market access and safe deployment.
Technical Overview
A photovoltaic module combines polymeric materials such as encapsulant films, backsheets, and junction-box housings with live electrical circuits that can act as ignition sources through hot spots, series arcs, or overcurrent faults. When modules are mounted on rooftops or integrated directly into the building envelope, their fire behavior becomes part of the building's overall fire performance. Fire resistance testing therefore evaluates the module as installed on a representative roof assembly rather than as an isolated product.
The principal frameworks governing PV module fire performance include:
- IEC 61730-2: PV module safety qualification, which includes a fire test for modules intended for mounting on building surfaces.
- UL 61730 and UL 1703: North American safety standards for flat-plate PV modules, which reference the fire test methods of UL 790 / ASTM E108.
- UL 790 / ASTM E108: standard test methods for fire tests of roof coverings, covering spread of flame, burning brand, intermittent flame exposure, and flying brand evaluations.
- EN 13501-1, together with EN ISO 11925-2, EN 13823, EN ISO 1182, and EN ISO 1716: the European reaction-to-fire classification system (Euroclasses A1 to F) applied to construction products, including BIPV elements.
- GB 8624: the Chinese classification standard for the burning behavior of building materials and products, relevant to BIPV approvals in the Chinese market.
- IEC 63226: guidance on fire risk reduction for ground-mounted and utility-scale PV power plants at the system level.
Under the UL 790 / ASTM E108 methodology, assemblies are classified as Class A, Class B, or Class C, with Class A representing the most severe external fire exposure conditions and the most demanding acceptance limits.
Testing Samples
Complete Modules
Full-size production modules are required, typically covering glass-backsheet crystalline silicon designs, glass-glass bifacial laminates, thin-film products, and lightweight or flexible modules. Because testing is performed at multiple deck slopes and exposure conditions, several identical modules of each construction are usually consumed in a single classification program.
Material and Component Specimens
Polymeric parts are additionally evaluated at the material level. These include backsheets, encapsulant films, junction-box housings, connector bodies, and cable insulation, which are subjected to flammability ratings such as UL 94 vertical burning classes and glow-wire ignition assessments.
Installed Roof Assemblies
Because the fire class applies to the module-roof assembly, test samples must reproduce the actual installation. This includes the representative roof deck construction, underlayment, standoffs, rails, and clamps at the design spacing and orientation used in the field. A change to the racking hardware or roofing materials can invalidate the original classification.
Specimen Conditioning
Test decks and specimens are conditioned to the temperature and humidity requirements of the applicable standard, and wooden test brands are dried to a specified moisture condition before ignition, ensuring reproducible and comparable results between test runs.
Testing Items
Typical fire performance evaluation items for PV modules and related materials include:
- Roof covering fire classification: determination of Class A, Class B, or Class C for the module-roof assembly.
- Spread of flame along and across the module and deck surface.
- Resistance to burning brands of varying sizes and severities.
- Endurance under intermittent flame exposure cycles.
- Propensity to generate flying brands carried by the air stream.
- Verification of no flame penetration through the roof deck and no sustained structural ignition.
- Reaction-to-fire classification for BIPV products, including ignitability, lateral flame spread, heat release rate (FIGRA), total heat release, and smoke production (SMOGRA).
- Material flammability ratings: UL 94 classes, glow-wire flammability and ignition indices (GWFI / GWIT), needle-flame test, and limiting oxygen index (LOI).
Testing Methods
Spread-of-Flame Test
The module assembly is mounted on an inclined deck at the selected roof slope. A gas burner flame is applied to the lower edge of the assembly while a forced air current of approximately 5.3 m/s (12 mph) flows across the surface, simulating wind-assisted fire exposure. The flame application duration depends on the target class, for example 10 minutes for Classes A and B and 4 minutes for Class C. Acceptance is based on maximum flame spread distance: no more than 1.8 m (6 ft) for Class A, 2.4 m (8 ft) for Class B, and 4.0 m (13 ft) for Class C, with no significant lateral spread, glowing embers, or flaming debris beyond the permitted limits.
Burning Brand Test
Wooden brands of defined geometry are ignited to a glowing state and placed on the test assembly. Brand size scales with severity, for example approximately 300 mm (12 in) square for Class A, 150 mm (6 in) for Class B, and 75 mm (3 in) for Class C. The assembly passes if flames and glowing combustion die out within the standard's limits, with no burn-through of the roof deck and no unacceptable flame spread.
Intermittent Flame Exposure
The assembly is subjected to repeated short-duration flame applications in cycles, evaluating resilience against recurring external ignition sources. This method is commonly applied in Class C evaluations and, depending on the standard's provisions, may substitute for certain brand test requirements when the results justify it.
Flying Brand Test
This test determines whether the assembly produces burning or glowing fragments that are lifted and carried by the air stream beyond the distances allowed by the standard. Controlling flying brands is critical where adjacent structures or vegetation could be ignited during a roof fire.
Reaction-to-Fire Testing for BIPV
For building-integrated products, classification under EN 13501-1 uses EN ISO 11925-2 for single-flame-source ignitability, EN 13823 (Single Burning Item) for heat release and smoke parameters, and EN ISO 1182 and EN ISO 1716 for non-combustibility and gross heat of combustion at the higher Euroclasses. Equivalent classification in China is performed under GB 8624 using the corresponding national test methods, resulting in classes A, B1, B2, or B3.
Material-Level Fire Tests
Polymeric components are qualified through UL 94 or IEC 60695-11-10 and IEC 60695-11-20 horizontal and vertical burning tests, IEC 60695-2-10, -2-11, and -2-12 glow-wire tests, IEC 60695-11-5 needle-flame testing, and ISO 4589-2 limiting oxygen index determinations. These results support component acceptability within the module safety evaluation.
Applications
Fire resistance testing results are used across the PV industry value chain:
- Product certification for rooftop PV systems under the IEC 61730 CB Scheme and North American listing programs, where building codes frequently require Class A assemblies on steep-slope residential roofs.
- Market access for BIPV products such as façade modules, curtain-wall laminates, and solar roof tiles, which require Euroclass or GB 8624 reaction-to-fire classifications under construction product regulations.
- Fire-risk assessments for utility-scale and agrivoltaic plants, providing documented input to the system-level mitigation guidance of IEC 63226 for insurers, owners, and engineering firms.
- Research and development support, enabling comparative evaluation of backsheets, encapsulants, and module constructions during design optimization.
- Quality control, market surveillance, and technical root-cause analysis following field fire incidents or material substitution claims.
FAQ
Is fire resistance testing mandatory for every PV module?
Fire evaluation is required for modules intended for building-mounted applications, classified as Application Class A under IEC 61730. Ground-mounted utility modules are generally not subject to roof-covering classification, but system-level fire-risk management in accordance with IEC 63226 is increasingly expected by owners and insurers.
What is the difference between Class A, Class B, and Class C?
The classes rank resistance to external fire exposure in decreasing severity. Class A permits the shortest flame spread distance and requires resistance to the largest burning brand, Class B applies intermediate limits, and Class C allows the longest spread distance with the mildest brand exposure. Many jurisdictions mandate Class A for residential steep-slope roof installations.
Does the fire class belong to the module alone?
No. The classification is assigned to the combination of the module, roof deck, underlayment, and mounting hardware as tested. If the racking system, standoffs, or roofing materials change, the assembly must be re-evaluated before the original class can be claimed.
How many samples are needed and how long does testing take?
Sample quantity depends on the scope, since spread-of-flame and brand tests at multiple slopes and class severities each consume full-size modules. Programs typically require several modules plus material specimens, and the overall timeline, including deck fabrication, conditioning, and testing, generally spans several weeks. Accredited third-party laboratories provide project-specific sampling plans and schedules.
How is BIPV fire performance assessed differently from rack-mounted modules?
BIPV elements are treated as construction products and must satisfy reaction-to-fire classifications based on ignitability, flame spread, heat release, and smoke production under EN 13501-1 in Europe or GB 8624 in China. These methods measure the material's contribution to fire growth, complementing rather than replacing the roof-covering style assessments used for rack-mounted systems.