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

• We test the suitability of ultrasounds in firefighting safety devices and robots.
• Experimental investigation of reflected ultrasounds traveling through fire and hot air
• We examine changes in the level of received signal for a variety of conditions
• Ultrasounds devices for location at small distances require an attenuation margin of more than 40 dB.

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, 10–40 dB), highly variable attenuations of the ultrasounds, with variations of less than 1 ms, 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 40 dB 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.

Histogram of the received ultrasound impulses and approximation of the experimental data by a power law (middle bars) and by mixed exponential-power law distributions.Figure optionsDownload as PowerPoint slide