Experimental investigation of the reliability of reception of ultrasound signals in fire conditions

Abstract

We are concerned with the reliability of ultrasound location through beams reflected or propagating along the line of sight in fire conditions. For this purpose, we experimentally investigate the propagation of ultrasounds under hot air and fire environment, in a laboratory setting, in view of assessing the reliability of ultrasound-based safety devices and equipment for use in fire combat, and the limits of the ultrasounds in this type of application. Effects of hot air flows and fires on the ultrasound attenuation and on the attenuation variability are determined. The main finding is that hot air and fire induce strong (up to two orders of magnitude, 10–40dB), highly variable attenuations of the ultrasounds, with variations of less than 1ms, while the amplitude of the transmitted pulses through fire environment has a power-type law distribution. The main conclusion is that low frequency ultrasounds can be dependably used for localization and for robot guidance in fire environments for distances of a few meters, provided that a minimum of 40dB attenuation is allowed due to fire and that appropriate detection methods, as time diversity, are used. We derive the probability distribution for the amplitude of the transmitted ultrasound pulses and develop design equations for ultrasound equipment for fire environments.