Evaluation of Empirical Evidence Against Zone Models for Smoke Detector Activation Prediction

A series of experiments were conducted in a large room to generate data to assess the accuracy of computer fire model predictions of detector activation time. A comparison between experimental measurements and zone model predictions of the detector activation in the Consolidated Fire and Smoke Transport model (CFAST) version 7.4.3 were made. The experimental room was 11.0 m by 7.3 m by 3.7 m high with a single opening 2.44 m high and 1.83 m wide centered in a short wall. Two ceiling configurations were examined, a flat ceiling and a flat ceiling with two 0.30 m wide and 0.30 m deep solid beams. The fire source was a gaseous fuel burner fed with different mixtures of propane and propene that produced soot yields ranging from 0.010 g(soot)/g(fuel) to 0.072 g(soot)/g(fuel) and a fuel flow ramp time that ranged from 30 s to 1800 s. The heat release rate profile reached a nominal maximum value of 30 kW. The activations of two different models of photoelectric smoke detectors and a single ionization smoke detector, each with a range of alarm set points and installed at various locations on the ceiling, were recorded. Predictions of the various smoke detector activation times were made in CFAST with the temperature approximation method, and a fixed smoke detector concentration method for photoelectric detector activations. Predictions with the smoke detection method were better than the temperature approximation method over the range of fire scenarios examined. Predictions of smooth ceiling experiments were generally better than the beamed ceiling experiments.