Thermal Characteristics of Vertically Spreading Cable Fires in Confined Compartments

Fire risk analysis for cables in a vertical cable tray is important for fire protection design in nuclear power plants. One important characteristic of vertical cable tray fires is the upward spreading of the cable flame along the cable tray, which should be considered as a time-varying fire source. Experiments involving vertical cable tray fires with a spacing of 0 and 8 mm between cable lines were conducted in confined compartments with dimensions of 3 m × 3 m × 3 m (length × width × height). The cable in a 0.3 m wide × 2 m long vertical cable tray was ignited using a line-source gas burner of a 20-kW premixed flame system. The experiments indicate that a room with a vertical cable tray fire could be divided into three zones with respect to thermal characteristics. Notably, a middle zone having reduced temperature was observed, even though the intensity of burning did not decrease. By considering the effect of a time-varying fire source, an expression for predicting the ceiling jet temperature was proposed. For the prediction of the maximum ceiling jet temperature, the relative errors were less than 18.8%; for the entire cable fire process, the normalized Euclidean distances were less than 20.4%. The available literature data concerning a vertical cable tray fire in a confined room were used to validate this expression. It is further confirmed that the proposed expression predicts well the literature data for vertical cable tray fires in a confined space. This new expression can be used for estimating the hazards from a vertically spreading fire in a compartment in nuclear power plants.