Photovoltaic modules installed on roofs and building skins are exposed to external fire sources and internal heating faults, and their fire behaviour directly affects the structure beneath them. Photovoltaic panel and module fire resistance testing evaluates this behaviour through standardized external flame exposure applied to a complete module assembly. The test object covers rigid flat-plate modules, framed or frameless, crystalline-silicon or thin-film, together with the mounting hardware and roof covering used in service. The sections below set out the scope and principle of the method, sample and deck preparation, and the spread-of-flame and burning brand procedures. They continue with fire classification criteria, co-testable hot-spot and bypass diode parameters, and compliance requirements for rooftop and building-integrated applications. Accredited laboratories, manufacturers and code authorities rely on these results for certification, system selection and fire-risk control.
module fire resistance testing — scope and principle
Fire resistance testing of photovoltaic modules is specified in IEC 61730-2 and, for roof-mounted assemblies, in roof-covering fire test procedures such as UL 790 and ASTM E108. The scope covers the module together with its frame, junction box, cables, connectors and the support structure. Fire performance depends on the installed configuration rather than on the laminate alone, which is why the assembly is treated as the test unit. The operating principle is comparative exposure. A representative assembly is fixed to an inclined deck. Gas flames, burning brands, or a combination of both are applied under a controlled airflow that simulates wind-driven fire conditions. Trained observers record flame travel, brand behaviour, penetration of the deck and the generation of embers, and classification follows from these observations. Because results are configuration-specific, each combination of module type, mounting system and roof covering is evaluated as a discrete assembly.
Sample and test deck preparation
Sample preparation begins with production-representative modules drawn from normal manufacturing, complete with frames, glazing, encapsulant, backsheet and junction boxes as shipped. Conditioning in a controlled atmosphere precedes the fire exposure, and any electrical or climatic conditioning required earlier in the test sequence is completed first. The test deck reproduces the intended roof build-up. It combines a substrate of the specified thickness, underlayment, and any battens, spacers or rails from the mounting system. The inclination is set to the slope defined for the classification sought. The air-supply duct is aligned with the deck, and the airflow velocity is verified at reference points with a calibrated anemometer. The gas feed to the burner is adjusted until the flame temperature, measured by thermocouples at designated positions, falls within the tolerance band of the method. Gauge marks along the deck surface define the ignition zone and the measurement path for flame travel.
Spread-of-flame and burning brand test methods
Two exposure procedures form the core of the assessment. In the spread-of-flame test, the gas burner is positioned so that its flame plays on the lower portion of the module and the deck edge. The wind tunnel supplies the calibrated airflow, and the burner operates for the exposure time stated for the class under evaluation. The observer tracks the furthest advance of the flame front in both surface and lateral directions and records the time to extinction after the source is shut off. In the burning brand test, a wooden crib brand of the size assigned to the severity class is ignited until glowing. It is then placed at the designated position on the module and exposed to the same airflow. Observations cover brand consumption, flame spread from the brand footprint, penetration through the module or deck, and the release of burning or glowing fragments capable of igniting material downwind.
Fire classification ratings and acceptance criteria
Rooftop photovoltaic assemblies are graded into fire classes, with Class A corresponding to the most severe exposure conditions and lower classes to progressively lighter exposures. Acceptance is judged against the limits written into the standard for each class. Typical criteria limit flame travel beyond the ignition zone to a permitted distance. Flaming and glowing must cease within a defined period after removal of the source, and lateral spread along assembly edges must stay within stated limits. The burning brand exposure must not cause sustained flaming on the underside, penetration of the deck, or release of burning brands carried beyond a stated distance. A failure is recorded when any criterion is breached, when the deck is damaged through its thickness, or when flaming debris ignites receptacles placed downwind. A reported class therefore applies only to the exact module, mounting and roof combination tested, and this configuration is documented in the test report.
Co-testable parameters — hot spot and bypass diode
External flame exposure does not address internal ignition mechanisms, so module safety programmes usually schedule electrical heating tests within the same campaign. The hot-spot endurance test shades the worst-case cell or cell group and drives the module at its rated current for the specified duration. Thermography and post-test inspection then reveal localized overheating, delamination or backsheet degradation. The bypass diode tests proceed in two steps. A functional check verifies that each diode conducts under reverse bias. A thermal measurement then records diode temperature under worst-case forward current and assesses the margin against thermal runaway. Both mechanisms are recognized contributors to field fires, since sustained shading, failed diodes or cracked cells can raise local temperatures until polymeric layers degrade or ignite. Running these tests alongside the fire classification sequence saves sample procurement and conditioning effort and produces a single report covering external and internal hazards.
Application scenarios — rooftop and BIPV compliance
Rooftop and building-integrated installations follow different compliance logic. For rack-mounted systems on pitched or low-slope roofs, building codes assign the roof covering a fire class. The photovoltaic assembly installed over it must demonstrate an equivalent class through system-level testing, so designers select module, rail and roof combinations that hold a valid classification. Field crews must reproduce the tested configuration, since changes to standoff height, rail orientation or flashing can invalidate the rating. Building-integrated photovoltaics, where modules replace roofing, façade or skylight elements, are treated as building components. They must meet the reaction-to-fire requirements applicable to the envelope element they replace, in addition to the module fire tests. Specifiers should also review junction box placement, cable routing and connector quality, because these details govern behaviour in realistic fire scenarios. Documentation of the tested configuration, maintained from design through installation, closes the compliance chain between laboratory and finished roof.