Fire behaviour of compartments with combustible ceilings: Unveiling risks in temperature-time vs. HRR-time fire curve testing

This work investigates the influence of ISO 834 temperature-time and heat release rate (HRR)-time fire curves on compartments featuring inert or exposed cross-laminated timber (CLT) ceilings. A series of tests was performed in a scaled compartment, aiming to investigate the observed effects on the temperature distribution, heat flux values and the overall fire behaviour. Under the standard ISO 834 temperature-time curve, the CLT-equipped compartment required 55% less fuel to replicate temperature profiles compared to an inert configuration, reflecting the timber’s contribution to fuel load. In contrast, when an HRR-time curve was used, an 80% increase in HRR for the CLT-equipped compartment was observed, due to sustained combustion of the exposed timber; also, HRR-based testing elevated compartment temperatures by 20% on average, with transient deviations exceeding 80% during early fire stages. The results underscore the limitations of temperature-time curves, which impose fixed thermal profiles and neglect fuel contributions from combustible materials, potentially underestimating fire risks, thus highlighting the need for fire testing methodologies that incorporate HRR as a key parameter when assessing the fire performance of combustible construction materials.