Characterisation of Smoke Hazards Due to Fire Whirl in Shafts of Tall Green Buildings Repaired Using Aromatic Polyamide Fibre Composite Materials

Description

Polyamide (aramid) fibre composite materials (AFCMs) are commonly used to repair structures, such as vertical shafts in green buildings that allow entry of daylight or fresh air. However, the polymer matrix materials, adhesives and aramid fibres in AFCMs arecombustible, and fires in vertical shafts create fire whirls (FWs; i.e., elongated swirling flames) that generate three main smoke hazards in the presence of AFCMs. First, the strong thermal radiation of an FW rapidly ignites AFCM surfaces, generating muchsmoke. Second, FWs mix smoke rapidly with air to swiftly fill a shaft with smoke. Third, smoke accumulated in a shaft can attenuate radiofrequency signals and thus hinder wireless communication between firefighters. The proposed project will study these threesmoke hazards in vertical shafts repaired with AFCMs.Samples of two common AFCMs will be applied to a large-scale (15 m × 3 m (height × square cross-section)) vertical shaft model and a 1/10-scale model, both of which will be ventilated via a sidewall gap to generate circulating airflow. The samples will be appliedat different locations on shaft walls, and the effect of an FW on the samples will be studied, first in the small-scale model and then in a large-scale model. The thermal radiation from an FW upon ignition of the AFCMs will be investigated, and the smokefillingof the shaft caused by the FW mixing effect will be experimentally examined, with the results compared with those of computational fluid dynamics models. A mathematical model of the thermal ignition of AFCMs will be developed by considering how high temperatures affect their structures. In addition, RAD-NNET, a model based on a neural network, will be used to mathematically characterise theabsorption and emission characteristics (i.e., thermal radiation) of burning AFCMs. Furthermore, cone-calorimeter experiments will be conducted on the small-scale model under high heat fluxes, with the results used as inputs for CFD modelling.The smoke-based attenuation of various radiofrequency signals from handheld communication devices will be investigated in a 1 m × 1 m × 1 m smoke chamber, and the relationship between signal attenuation and the optical density of smoke therebyderived. Thereafter, fire tests will be performed in the large-scale model to confirm the small-scale model results on FW-driven AFCM ignition, the smoke-filling of a shaft, and smoke’s hindrance of wireless communications. All results will be integrated into areport containing recommendations on appropriate methods for fire-fighting in vertical shafts.