Optimizing Threshold of Line Type Optical Fiber Heat Alarm Systems for Traffic Tunnel

In order to keep a low false alarm rate of 1/year-kilometre, and in order to launch the fire alarm correctly in the initial stage of such a fire as occurred in a car, a method of threshold selection for a fire alarm system particularly applied in traffic tunnels is discussed in this thesis. Each fire alarm detector randomly collects environmental temperature rise gradients (TRG) and the probability that thus-collected TRG is higher than the lower limit of fire alarm threshold shall be lower than 3 x10-10, the upper limit of fire alarm threshold is defined as the minimum TRG corresponding to a fire with a heat release rate of no less than 1.2MW in the related tunnel. The author has given a detailed description of tunnel fire validation testing and methods for data collection, analysis and statistics in an operating tunnel. The method for rational selection of fire alarm threshold has a universal significance to the further improvement of reliability and practicality of a fire alarm system in traffic tunnels.