title: Ultrasonically triggered ignition at liquid surfaces.
abstract: Ultrasound is considered to be an ignition source according to international standards, setting a threshold value of 1mW/mm(2) [1] which is based on theoretical estimations but which lacks experimental verification. Therefore, it is assumed that this threshold includes a large safety margin. At the same time, ultrasound is used in a variety of industrial applications where it can come into contact with explosive atmospheres. However, until now, no explosion accidents have been reported in connection with ultrasound, so it has been unclear if the current threshold value is reasonable. Within this paper, it is shown that focused ultrasound coupled into a liquid can in fact ignite explosive atmospheres if a specific target positioned at a liquid's surface converts the acoustic energy into a hot spot. Based on ignition tests, conditions could be derived that are necessary for an ultrasonically triggered explosion. These conditions show that the current threshold value can be significantly augmented.
authors: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany. Electronic address: Lars.H.Simon@PTB.de.
authors: Lars Hendrik
authors: LH
authors: Simon
authors: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany.
authors: Lennart
authors: L
authors: Meyer
authors: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany.
authors: Volker
authors: V
authors: Wilkens
authors: Physikalisch-Technische Bundesanstalt (PTB), Bundesallee 100, 38116 Braunschweig, Germany.
authors: Michael
authors: M
authors: Beyer
keywords: Focused ultrasound; Ignition source; Ultrasonic bath