Measurements of ultrasound from public address and voice alarm systems in public places

Concerns have been raised about potential health effects of public exposure to ultrasound; however, there are few published surveys of measurements taken in public places. Results are presented of measurements taken in a selection of public places including train stations, shopping centres, galleries and museums, and the difficulties of taking measurements with conventional equipment are highlighted. Tones were identified in the 20 kHz third-octave band at 8 of the 14 locations tested; the characteristics of the tones are consistent with their source being Public Address or Voice Alarm systems. The measured results do not exceed existing interim guidelines for public exposure to ultrasound, and existing research suggests that no significant undesirable effects would be anticipated following exposure to ultrasound of this nature for short periods. The measured data may be reviewed against future public exposure guidelines which consider the variation in response across the population and between continuous and pulsed sources.