Assessing the sprinkler activation predictive capability of the BRANZFIRE fire model

Abstract

This paper describes an investigation into the sprinkler response time predictive capability of the BRANZFIRE fire model. A set of 22 fire/sprinkler experiments are simulated where the sprinkler activation time and the heat release rate (HRR) for each individual experiment had been determined. The experiments provided data for use in validating the sprinkler activation prediction algorithms in the BRANZFIRE zone model. A set of base case values were chosen and input files constructed for the simulations. The experiments were then simulated by the fire model using both the NIST/ JET ceiling jet and Alpert’s ceiling jet options (which are the two ceiling jet correlations available in the BRANZFIRE zone model). The fire model included a heat transfer calculation for the temperature of the heat sensitive sprinkler element. Different sprinkler operational parameters such as the conduction factor, response time index (RTI) and the sprinkler depth below ceiling were also varied to assess the sensitivity of their effect on the activation time. Results showed that using the NIST/JET ceiling jet algorithm gave a closer prediction of the sprinkler response time in a small room than Alpert’s correlation. This was expected, since the former includes the effect of a hot upper layer while the latter applies to unconfined ceilings. The experiments available for comparison had been conducted inside an enclosure with a developing hot upper layer. The findings also signified that changing the sprinkler operational parameters can change the predicted sprinkler activation time significantly.