Thermal sensitivity limits of residential sprinklers

Abstract

The effect of thermal sensitivity parameters on room tenability and heat release rate at first sprinkler actuation was investigated for sprinklers installed at a 3·66 m spacing in a living-room fire scenario. The thermal response was modeled using the response time index (RTI), the conduction factor (C) and the sprinkler actuation temperature. Actuation times of a bulb and a solder type of residential sprinkler were obtained in a living-room fire test in which there was no water discharge from the sprinklers. The bulb and solder models were installed at three different locations within the enclosure to verify the predictive capabilities of the response model. The living-room scenario was the same as that used to develop approval criteria for residential sprinklers in the USA. Gas velocities and temperatures in the vicinity of the sprinklers were obtained during the fire test. The sprinkler actuation times were predicted from the experimentally obtained ceiling flows. The predictions were in excellent agreement with the observed actuation times. Measurements of the gas temperature at the 1·5 m level in the room center and mass loss of a burning chair, the primary combustible in the living-room fire scenario, were also obtained as a function of time. These measurements, in conjunction with predicted actuation times for varying values of RTI and C, allowed the effect of RTI and C on room tenability and heat release rate at the time of sprinkler actuation to be predicted for a sprinkler installed at a 3·66 m spacing. The results indicate that sprinklers of the ‘fast response’ type will actuate in the living-room scenario while gas temperatures at the 1·5 m level are near ambient and before the convective heat release rate of the burning chair in the living-room fire exceeds 130 kW.