Cable tray fire tests in a confined and mechanically ventilated facility

Cable fires are one of the main fire hazards in nuclear power plants. As part of the cable fire spreading (CFS) campaign of the OECD PRISME‐2 programme, 3 real‐scale cable tray fire tests were performed in open atmosphere (1 CFS support test, named CFSS‐2) and in a confined and mechanically ventilated facility (2 CFS tests, named CFS‐3 and CFS‐4). This study aims at investigating the effects of confined and ventilated conditions on cable tray fires that used a halogen‐free flame retardant cable‐type. The CFS‐3 and CFS‐4 tests involved 2 ventilation renewal rates of 4 and 15 h^?1, respectively. The confined conditions lead to decrease the fire growth rate and the peaks of mass loss rate and heat release rate, compared with open atmosphere. The reductions are larger for the lower ventilation renewal rate. Furthermore, it is shown that the CFS‐4 test may be classified as a well‐ventilated fire and the CFS‐3 test as an under‐ventilated fire. For this last one, its fire characteristics and its consequences in the fire room highlight an oscillatory behaviour, with the same low frequency, for about 30 minutes. These oscillations arise from successive combustions of unburnt gases.     

Cable tray fire tests with halogenated electric cables in a confined and mechanically ventilated facility

Cable fires are one of the main fire hazards present in nuclear power plants (NPPs). Therefore, as part of the Organisation for Economic Co‐operation and Development (OECD) PRISME‐2 project, cable tray fire tests were performed both in open atmosphere conditions and in a confined and mechanically ventilated facility, called DIVA. These tests aim at showing the effects of a confined and ventilated environment on fire characteristics and consequences. This study deals with five fire tests, which used halogenated (poly [vinyl chloride] or PVC) cable types. Two tests were carried out in open atmosphere and three tests in the DIVA facility. The latter used a ventilation renewal rate (VRR) of either 4 or 15 h^?1. The confined and ventilated conditions reduced the mass loss rate and heat release rate than did those obtained in open atmosphere. Furthermore, the three confined tests produced unburnt gases, which ignited in the fire room. Two explosions were highlighted for the tests that used a VRR of 4 h^?1. These explosions indeed led to fast flame propagations over the entire upper part of the fire room and steep overpressures of almost 150 hPa. The low‐qualified PVC cables and the ventilation set‐up used in this study strongly contributed to the occurrence of these explosions.     

Horizontal cable tray fire in a well‐confined and mechanically ventilated enclosure using a two‐zone model

Electrical cable trays are used in large quantities in nuclear power plants (NPPs) and are one of the main potential sources of fire. A malfunction of electrical equipment due to thermal stress for instance may lead to the loss of important safety functions of the NPPs. The investigation of such fires in a confined and mechanically ventilated enclosure has been scarce up to now and limited to nuclear industry. In the scope of the OECD PRISME‐2 project, the Institut de Radioprotection et de Sûreté Nucléaire (IRSN) conducted more than a dozen fire tests involving horizontal electrical cable trays burning either in open atmosphere or inside mechanically ventilated compartments to investigate this topic. A semi‐empirical model of horizontal cable tray fires in a well‐confined and mechanically ventilated enclosure was developed. This model is partly based on the approach used in FLASH‐CAT and on experimental findings from IRSN cables fire tests. It was implemented in the two‐zone model SYLVIA. The major features of the compartment fire experiments could then be reproduced with acceptable error, except for combustion of unburned gases. The development of such a semi‐empirical model is a common practice in fire safety engineering concerned with complex solid fuels.