With the growing use of photovoltaic panels in buildings, concerns over their fire safety have increased. However, the influence of front-glass type and its fracture behaviour in fires remains insufficiently understood. This study examines the combustion characteristics of monocrystalline silicon photovoltaic panels using both annealed (non-tempered) and tempered glass surfaces, with a specific focus on the interaction between glass fracture and ignition development. A total of 17 cone calorimeter tests were conducted under heat fluxes of 50, 60, and 65 kW/m2. Thermal decomposition behaviours were further characterised using TG-IR-GC-MS analyses. Results showed that annealed glass fractured earlier under thermal stress, while tempered glass fractured later or remained intact, depending on the heat flux. At 65 kW/m2, annealed panels fractured significantly earlier ((38 ± 16) s) but ignited later at (330 ± 33) s. In contrast, tempered panels fractured at (177 ± 36) s and ignited earlier at (228 ± 9) s. Ignition was most delayed (353 s) when the glass surface remained fully intact. This is due to the dense network of cracks that forms in tempered glass after fracture, which enhances fuel–air mixing and accelerates ignition. Thermal analysis further revealed that combustion of photovoltaic panels produces toxic volatiles, including acetic acid, carbon monoxide, carbon dioxide, and hydrogen fluoride. The toxic emissions appeared above the temperature of 300 °C and intensified above the temperature of 500 °C, which were linked to the staged decomposition of the EVA and TPT layers. These findings highlight that the timing and pattern of glass fracture critically influence heat accumulation and vapour release, thereby affecting ignition location and intensity.
