Ignition of dust-air atmospheres by ultrasonic waves

•The verification of the incendivity of the ignition source ultrasound.•Identification of conditions critical for ignitions triggered by ultrasound.•Identification of a threshold sound pressure level for ignitions of sulfur dust at 20 kHz.•Worst-case consideration of airborne ultrasound with respect to an ignition.

This paper shows the results of our investigations on the ignition source ultrasound in dust-air atmospheres. Ultrasound is, on the one hand, considered to be an ignition source according to international safety standards (EN 1127–1 (2011)). On the other hand, though, ultrasound is used for various applications in gases and air, such as level and flow measurement, or in the process industry, but no explosion accidents have yet been reported. Our research now shows that it is indeed possible to ignite dust-air mixtures in ultrasound fields under certain conditions. We conducted our experiments in an ultrasound standing wave field and used maize starch, calcium stearate and sulfur dust. For ignitions, an absorbing target was needed to convert the acoustic energy into heat. From theoretical estimations and experiments critical conditions that provoke ultrasonically triggered explosions are identified.