Experiments on the operation of sprinklers with and without permanently open roof vents have been carried out in a building approximately 50 m × 20 m × 10 m high. They were intended to validate a simple mathematical model to calculate the time of operation of sprinklers given the rates of growth of the fire before and after operation of sprinklers as an input. The fire was produced by burning hexane floating on water and grew exponentially with a time constant of 60 s until the first sprinkler operated. Thereafter the heat output remained constant; in some experiments it was reduced by 20% some 30 s after the first sprinkler operated. The first sprinkler operated when the heat output was of the order of 10 MW; the delay due to venting was about half that calculated using a simple model described in a previous report. If vents were closed or the water supply was poor then all or most of the available sprinklers operated but if vents were open and there was a good water supply then a limited number of sprinklers operated. The simple model did not predict that venting could reduce the possibility of a large number of sprinklers operating after the fire was controlled. The experiments confirmed the results of calculations using the model, that the prior opening of vents would have little effect on the operation of the first sprinkler. They also indicated that prior venting would not increase the number of sprinklers opening after control of the fire and might reduce it; when the fire growth process is completely independent of the number of sprinklers operating.
