Microwaves in fire detection

Abstract

In this contribution the issue of fire detection by means of thermal radiation in the microwave region of the electromagnetic spectrum is addressed. The aim of this work is to show that microwave radiation is a useful quantity to detect fires, which is confirmed by measurements. Some of the results even indicate that it could be possible to detect smoldering fires with microwaves earlier than with smoke or with gas detectors. The first part is a short summary of the basic concept of our previous paper [Kaiser T, Kempka T. Is microwave radiation useful for fire detection? Proceedings of 12th international conference on automatic fire detection AUBE ’01, vol. 965, 26–28 March 2001. Gaithersburg: NIST Special Publication; 2001.] published at AUBE ‘01, along with a short revisit of the physical fundamentals of thermal radiation, of electromagnetic wave propagation, and of attenuation. In the second part, the microwave receiver will be presented, which is used to conduct experiments in Duisburg's fire detection lab. The receiver is able to measure thermal radiation in the frequency region from 2 to 40 GHz, and the superheterodyne technique used by the receiver enables a rather flexible measurement range among arbitrary frequency bands with individual widths of 100 MHz. The receiver is controlled by a normal PC, which makes the measurement setup configurable, i.e. one can choose any combination of 380 × 100 MHz frequency bands for a single measurement. Some measurement results for the standardized European test fires TF1 and TF2 according to ISO 7240 (EN 54 Part 9) are shown in the last part of this contribution. The gathered data is discussed and compared to ionization chamber (MIC), to extinction light sensor (MIREX), and to gas-concentration measurements.