Potential audibility of ultrasonic signal monitoring of Public Address and Life Safety Sound Systems

Validity of the 1984 Interim Guidelines on Airborne Ultrasound and Gaps in the Current Knowledge

ABSTRACT

Airborne ultrasound is used for various purposes both in industrial and public settings, as well as being produced as a by-product by a range of sources. The International Radiation Protection Association (IRPA) published interim guidelines on limiting human exposure to airborne ultrasound in 1984, based on the limited scientific evidence that was available at that time. In order to investigate whether research since 1984 requires the development of revised exposure guidelines we considered (a) within the context of ultrasound exposure the relevance to health of the biological endpoints/mechanisms listed in the IRPA guidelines, (b) the validity of the exposure limits, and (c) whether there are biological endpoints/mechanisms not covered in the guidelines. The analysis of the available evidence showed that the biological endpoints that form the basis of the guidelines are relevant to health and the guidelines provide limits of exposure based on the evidence that was available at the time. However, the IRPA limits and their associated dosimetry were based on limited evidence, which may not be considered as scientifically substantiated. Further, there is no substantiated evidence of biological endpoints/mechanisms not covered by the IRPA guidelines. These two observations could mean that IRPA's limits are too low or too high. Research since the IRPA guidelines has made some improvements in the knowledge base, but there are still significant data gaps that need to be resolved before a formal revision of the guidelines can be made by ICNIRP, including research needs related to health outcomes and improved dosimetry. This statement makes a number of recommendations for future research on airborne ultrasound.

Exposure to High-Frequency Sound and Ultrasound in Public Places: Examples from Zurich, Switzerland

The public is unknowingly exposed to very high-frequency sound (VHFS; 11.2–17.8 kHz) and ultrasound (US; >17.8 kHz) signals in air in public places, as evidenced by previously published reports. The present report provides evidence for the presence of VHFS/US signals in the air at public places in Zurich, Switzerland. The analysis of the signals measured revealed that they: (i) contain one, two or multiple frequencies; (ii) comprise frequencies ranged from 15.5 kHz to 36.0 kHz; (iii) were either quasi constant in their amplitude or exhibit a clear amplitude modulation; and (iv) were in their characteristics (frequencies, modulation, intensity) specific for each place. Based on the signal characteristic it is likely that the signals are generated by public-address voice-alarm (PAVA) systems. The work presented: (i) documents the presence of VHFS/US signals at public places in Zurich, possibly caused by PAVA systems; and should (ii) show that is easily possibly to measure the signals with an affordable measurement equipment as a “citizen scientist”, and stimulate others also to measure and analyse VHFS/US signals with this citizen scientist approach in other cities worldwide. Due to the possible negative health-related effects of a human exposure to VHFS/US signals, further research is needed to document VHFS/US signals at public places and to evaluate biological effects of this exposure with laboratory studies.

Ultrasound in air-Guidelines, applications, public exposures, and claims of attacks in Cuba and China

This editorial introduces a Special Issue of the Journal of the Acoustical Society of America, on "Ultrasound in Air." In this Special Issue, one paper covers ways of categorizing the ultrasonic regimes, and three papers cover human effects. One of those three, plus five others, constitute the six papers that report on the measured outputs of commercial devices. Two cover calibration, and the final three papers cover novel applications. This editorial outlines the context in which these papers provide individual studies, including the development of technology and guidelines for safe exposure, and ending with an analysis of what is currently known about claims of sonic attacks on embassy staff in Cuba and China.