Flame Retardancy Testing of Photovoltaic Carport Materials: Standards, Methods and Compliance

Flame retardancy testing of photovoltaic carport materials evaluates how PV module components, canopy sheets, cables, and coatings resist ignition, flame spread, heat release, and smoke generation under standardized laboratory conditions. This technical article explains the key test items, sample requirements, and internationally recognized methods, including UL 94, ISO 4589-2, GB 8624, EN 13501-1, and IEC 61730-2, used by accredited third-party laboratories to classify the fire performance of solar carport materials. It serves as a practical reference for specifiers, EPC contractors, and quality engineers responsible for PV carport fire safety compliance.

Technical Overview

A photovoltaic (PV) carport combines electricity generation with an occupied, semi-enclosed parking structure. Unlike rooftop systems, the space beneath a PV canopy shelters vehicles, EV charging equipment, and people, so fire behavior cannot be assessed at the module level alone. Potential ignition sources include DC arc faults, hot-spot heating in modules, failed connectors, cable insulation faults, and vehicle fires occurring directly under the canopy. Because a large share of carport materials, including backsheets, encapsulants, junction box housings, polycarbonate or FRP canopy sheets, membranes, and cable insulation, are polymeric and inherently combustible, flame retardancy testing is the primary means of demonstrating that these materials will not readily ignite, spread flame, or produce dangerous smoke.

Flame retardancy testing measures a defined set of fire performance properties: ignitability, burning rate, flame spread, heat release rate, flaming droplets, smoke density, and combustion gas toxicity. The results are mapped to classification frameworks such as GB 8624 in China, EN 13501-1 in Europe, and UL 94 for polymeric materials, while complete canopy and module assemblies are further assessed using roof covering fire test methods such as UL 790 and ASTM E108 and the module safety requirements of IEC 61730-2. Accredited third-party laboratories conduct these tests on representative material samples and issue classification reports that support design approval, tender compliance, insurance review, and factory quality control.

Testing Samples

PV Module Polymeric Components

Representative samples are taken from the module laminate and electrical components: fluoropolymer or PET-based backsheets, EVA or POE encapsulant films, junction box housings (typically PBT, PA, or PPO compounds), potting compounds, and connector bodies. These thin, small components are tested as materials at their end-use thickness, and junction box plastics are typically required to meet UL 94 V-0 in procurement specifications.

Canopy and Cladding Materials

Canopy samples include polycarbonate hollow and solid sheets, fiber-reinforced polyester (FRP) corrugated sheets, PVC and PVDF tensile membranes, and any polymer edge trims or seals used with glass-glazed roofs. Sheet thickness, color, and any protective UV coating layers must match the commercial product, because burning rate and dripping behavior are strongly thickness-dependent. These products are usually classified at product level under GB 8624 or EN 13501-1.

Cables, Connectors, and Electrical Enclosures

DC string cables, AC wiring, inverters, combiner boxes, and charging equipment enclosures are sampled as complete cable cross-sections or molded parts. Cable samples are evaluated for vertical flame propagation and, where low-smoke zero-halogen grades are specified, for smoke emission and acidic gas release.

Coatings, Adhesives, and Sealants

Structural paints, anti-corrosion coatings, PU or silicone sealants, gaskets, and mounting pads are tested as applied films or free films, since a combustible coating applied over a steel frame can contribute to early flame spread if not properly formulated.

Sample Preparation and Conditioning

All specimens are cut to the dimensions prescribed by each method and conditioned before testing, typically at 23 ± 2 °C and 50 ± 10% relative humidity for a minimum of 48 to 88 hours depending on the standard. Thickness is recorded for every specimen, and testing is normally performed at the minimum and maximum commercial thicknesses to establish the worst case.

Testing Items

A complete flame retardancy evaluation for a PV carport project typically covers the following items, selected according to the material type and the target market:

• Limiting oxygen index (LOI) — ISO 4589-2 / GB/T 2406.2
• Horizontal and vertical burning of plastics — UL 94 / GB/T 2408 / IEC 60695-11-10 (HB, V-2, V-1, V-0, 5VA, 5VB)
• Single-flame-source ignitability — ISO 11925-2
• Single Burning Item (SBI) heat release and smoke parameters (FIGRA, THR600s, LFS, SMOGRA) — GB/T 20284 / EN 13823
• Gross heat of combustion and non-combustibility for Class A assessment — ISO 1716 / ISO 1182
• Smoke density rating — GB/T 8627, or smoke opacity under ISO 5659-2
• Combustion gas toxicity classification — GB/T 20285
• Glow-wire ignition and flammability temperatures — IEC 60695-2 series / GB/T 5169
• Roof covering fire classification (spread of flame, burning brand, flying brand) — UL 790 / ASTM E108
• Fire test of the PV module assembly — IEC 61730-2
• Cable vertical flame propagation, smoke density, and halogen acid gas — IEC 60332, IEC 61034, IEC 60754 series
• Cone calorimetry for R&D heat release characterization — ISO 5660-1

Testing Methods

Limiting Oxygen Index (ISO 4589-2 / GB/T 2406.2)

A specimen is clamped vertically inside a glass chimney and ignited at its top edge in a flowing mixture of oxygen and nitrogen. The LOI is the minimum oxygen concentration, expressed as a percentage, at which candle-like burning is sustained for at least 3 minutes or over at least 50 mm of specimen length. Since ambient air contains approximately 21% oxygen, materials with an LOI above 27% are regarded as flame retarded, and typical carport procurement specifications require LOI of 28% minimum, with 32% or higher preferred for polycarbonate sheets and membranes. JIS K 7201 provides an equivalent method accepted in the Japanese market.

Horizontal and Vertical Burning (UL 94 / GB/T 2408 / IEC 60695-11-10)

In the 20 mm vertical burn test, a small gas flame is applied twice for 10 seconds to the lower end of each of five bar specimens. For a V-0 rating, individual afterflame times must not exceed 10 seconds, the total afterflame time for all ten ignitions must not exceed 50 seconds, and no flaming drips may ignite the cotton indicator placed below the specimen. V-1 permits longer afterflame times with no flaming drips, while V-2 permits flaming drips that ignite cotton. The 5VA and 5VB ratings apply a more severe 127 mm (5-inch) flame to horizontal and vertical plaques for five applications and are the strictest levels, commonly required for electrical enclosures. The horizontal HB test limits burning rate to 40 mm/min or 75 mm/min depending on thickness, or requires self-extinguishment before the 100 mm gauge mark.

Building Products Classification (GB 8624-2012 / EN 13501-1)

For canopy sheets and membranes sold as building products, classification combines several methods. ISO 11925-2 applies a small propane flame for 15 seconds to the surface and edge of the specimen; a pass requires that the flame tip does not reach the 150 mm gauge within 20 seconds and that flaming droplets do not ignite filter paper. Higher classifications (B1 in GB 8624, or classes B and C under EN 13501-1) additionally require the SBI test, in which a specimen corner is exposed to a 30 kW propane burner and the heat release rate and smoke production are measured continuously. Typical grade B thresholds include FIGRA not exceeding 120 W/s, THR600s not exceeding 7.5 MJ, flame spread (LFS) not reaching the specimen edge, and SMOGRA not exceeding 30 m²/s² for the s1 smoke class, while grade C allows FIGRA up to 250 W/s and THR600s up to 15 MJ. Class A1/A2 assessment adds non-combustibility furnace testing per ISO 1182 or gross heat of combustion per ISO 1716. Smoke density rating under GB/T 8627 (SDR ≤ 75) and smoke toxicity grading under GB/T 20285 are frequently specified alongside the classification for enclosed or semi-enclosed carports.

Roof Assembly and Module Fire Tests (UL 790 / ASTM E108 / IEC 61730-2)

Because a carport canopy functions as a roof, the assembled system, module, mounting rails, and deck, is tested as a complete covering rather than as discrete materials. Under UL 790 and ASTM E108, the assembly on an inclined test deck is subjected to a spreading flame, intermittent flame exposure, burning brand, and flying brand tests. Class A, the most severe rating, limits flame spread to approximately 1.8 m (6 ft) and requires resistance to the largest brand class, while Class B and Class C allow progressively greater spread. IEC 61730-2 applies corresponding fire test requirements to PV modules so that the module construction can be matched to the fire class of the roof or canopy structure on which it is installed.

Smoke Density and Combustion Gas Toxicity

Smoke behavior is critical in carports because smoke accumulating under a canopy can obscure escape routes and hinder firefighting. Smoke density is measured either gravimetrically and optically under GB/T 8627 or in a sealed chamber under ISO 5659-2, which reports specific optical density across transmittance data. Toxicity testing under GB/T 20285 analyzes the combustion atmosphere for CO, HCN, HCl, HF, and other gases from a smoldering and flaming decomposition stage, producing a hazard classification used to restrict high-toxicity materials.

Glow-Wire Tests (IEC 60695-2 Series)

Electrical parts that cannot be evaluated by the needle-flame or 50 W flame methods, such as junction boxes, terminal blocks, and enclosure walls, are tested with a glowing wire at 550 °C to 960 °C. Glow-wire flammability index (GWFI) and glow-wire ignition temperature (GWIT) results, commonly 960 °C GWFI and 750 to 800 °C GWIT for unattended equipment, confirm that a glowing component or overload fault will not ignite adjacent plastics.

Applications

Flame retardancy test reports for PV carport materials are used throughout the project lifecycle:

• Building permit and fire design review, demonstrating that canopy sheets and membranes meet GB 8624 B1 or the applicable national classification before construction approval.
• Tender and procurement compliance, with LOI, UL 94, and cable flame propagation requirements written into material submittals and enforced through witnessed sampling.
• EV charging hub risk management, where low-smoke, low-toxicity materials are prioritized because charging faults and battery thermal events add ignition scenarios beneath the canopy.
• Insurance and risk engineering assessments supporting underwriting of commercial and industrial solar carport portfolios.
• Material development, comparing halogen-free phosphorus, nitrogen, ATH, and magnesium hydroxide flame retardant systems using LOI, UL 94, and ISO 5660-1 cone calorimeter data.
• Factory quality control and batch conformity verification, ensuring that production compounds remain consistent with the certified flame retardant formulation.
• Export market mapping, correlating GB 8624 results with EN 13501-1 Euroclasses, UL classifications, and JIS equivalents for international projects.

FAQ

What fire classification should PV carport canopy materials achieve?

For most jurisdictions, polymer canopy sheets and membranes are specified at GB 8624 B1 (with smoke class s1 to s2 and droplet class d0 where possible) or Euroclass B-s1,d0 under EN 13501-1. Metal and glass-gazed systems can reach A2 or Class A roof covering levels when tested as assemblies under UL 790 or ASTM E108.

Is a UL 94 V-0 rating equivalent to GB 8624 B1?

No. UL 94 is a small-scale material test on plastic bars and plaques, while GB 8624 is a product-level classification built from ignitability, SBI heat release, and smoke data. Many specifications require both: UL 94 V-0 for discrete plastic components such as junction boxes, and GB 8624 B1 for the finished canopy product.

What LOI value is considered acceptable for carport sheeting?

An LOI of 28% is generally accepted as the baseline for flame-retarded material, 32% is the common acceptance threshold in carport procurement, and values of 35% or higher indicate strong flame retardancy suitable for high-risk installations such as EV charging areas.

Do glass-fronted PV modules still require fire testing?

Yes. Although tempered glass front covers are non-combustible, the backsheet, encapsulant, junction box, cables, and the mounting assembly as a whole determine system fire behavior. IEC 61730-2 includes fire tests on the module mounted over a representative deck so the assembly can be assigned a roof covering fire class.

How many specimens are needed and how long does testing take?

Specimen counts vary by method: UL 94 vertical testing uses five bars per set, LOI requires a series of specimens across oxygen concentrations, and SBI testing uses three replicate corner specimens. Simple material tests can be completed within one to two weeks, while a full GB 8624 B1 classification including conditioning, SBI, smoke, and toxicity testing typically takes three to six weeks at an accredited third-party laboratory.