Safety-related conclusions for the application of ultrasound in explosive atmospheres

Abstract

a b s t r a c tInternational safety regulations such as EN 1127-1 consider ultrasound to be an ignition source. Currently, applications of ultrasound in explosive atmospheres have to comply with a threshold value of 1 mW/mm 2 . However, it is unclear as to how this intensity has to be measured and, therefore, this threshold value is poorly defined. Moreover, it is based on theoretical estimations in analogy to other ignition sources and there are no publications or significant records on these estimations. Within a research project at PTB, it has now been investigated experimentally in relation to worst-case considerations including airborne ultrasound, focused MHz ultrasound in liquids and acoustic cavitation. On the basis of the results of the research it is now possible to revise the current regulations and to specify measures for safe operation of ultrasonic applications in explosive atmospheres. In this context, for ultrasound coupled directly to gaseous atmospheres a new threshold value of 170 dB (re. 20 mPa) can be suggested, and for ultrasonic applications in liquids, an augmentation can be made to the threshold to 400 mW/mm 2 .

Transformerless Ultrasonic Ranging System with the Feature of Intrinsic Safety for Explosive Environment

“…Therefore, this paper focuses on the ignition caused by electric sparks. Moreover, Reference [10] even suggested a new safety threshold value of 170 dB for ultrasound coupled directly to gaseous atmospheres. Actually, in normal or fault conditions, when the energy released in the equipment circuit is higher than the minimum ignition energy of the material in the environment, it may ignite the surrounding dust or gas [11,12].…”