Two series of experiments have been carried out on the effect of roof vents on the operation of sprinklers in a building approximately 50 m × 20 m × 10 m high. This paper describes experiments in which measurements were made of temperature and velocity distributions produced by a 2 m square hexane fire with a controlled theoretical heat output of 5 MW. Combinations of 0, 10 or 20 vents, each having an area of 1.64 m
2, and 0, 1 or 5 sprinklers were investigated.
The plume was generally deflected from the vertical and estimates were made of the position of the centre of the plume at ceiling level. The deflection was increased by the sprinkler spray but was not increased by venting.
The results have been compared with the distributions calculated by a previously-described simple zone model of the effects of venting on sprinkler operation with a growing fire. The model makes a good approximation for the radial temperature distribution beyond the 'turning region' of the plume when there are no sprinklers. Within the turning region the assumption of a temperature plateau is valid when there is a deep layer of hot gases but not otherwise.
With the vents used, local effects of vents on temperatures 100 mm beneath the ceiling were small compared with the 'global' effects calculated by the model.
The model generally underestimates the maximum velocity of the ceiling jet but the mean velocity is predicted more closely.
The model requires better information on the cooling of the hot gases by the sprinkler spray. There is some evidence that cooling by the water droplets may not in itself be sufficient to explain the observed temperatures and that there may be some additional cooling. This may be by increased entrainment of hot gases into the ceiling jet caused by the sprinkler spray.
The work provides evidence that calculations using the model overestimate the effect of venting on the operation of the first sprinkler and may underestimate the reduction by venting of the number of sprinklers operating beyond the turning region of the fire plume.
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