Fire whirl induced smoke hazard in vertical shafts repaired with aramid fiber reinforced polymer: Experimental and numerical investigation

Aramid fiber-reinforced polymers are commonly used for repairing concrete structures such as shafts, but these applications pose significant fire safety challenges. This is due to the flammability of the epoxy resin matrix, as well as the exacerbated smoke diffusion within vertical shafts driven by internal fire whirls. This study systematically evaluates the coupled fire hazards of aramid fiber-reinforced polymers through an integrated approach combining cone calorimeter tests, laboratory-scale (1:10) fire whirl experiments, and Fire Dynamic Simulator simulations. Three key fire risk indicators, namely flashover propensity, total heat release, and toxic hazard were employed to assess the fire risk of aramid fiber-reinforced polymers. The results showed that the incorporation of the epoxy matrix significantly increased the fire risk and the emission of toxic gases. Approximately 80 % of aramid fiber-reinforced polymers exhibited high flashover propensity, whereas untreated aramid fibers showed mainly low to medium levels. The most notable aramid fiber-reinforced polymers test group exhibited toxicity approximately seven times higher than the corresponding aramid fiber group. Fire Dynamic Simulator simulations further indicate that compared to pool fires, fire whirls generate low-pressure cores and strong buoyant plumes, resulting in higher temperatures, greater flame heights, and significantly altered smoke dynamics. These findings suggest that the potential fire hazards of aramid fiber-reinforced polymer materials must be thoroughly considered in performance-based fire protection design, as well as complex fire phenomena such as fire whirls, to prevent underestimating the potential fire risks within structures like shafts. © 2025 Elsevier Ltd.