Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?

Abstract

New measurements indicate that the public are being exposed, without their knowledge, to airborne ultrasound. Existing guidelines are insufficient for such exposures; the vast majority refers to occupational exposure only (where workers are aware of the exposure, can be monitored and can wear protection). Existing guidelines are based on an insufficient evidence base, most of which was collected over 40 years ago by researchers who themselves considered it insufficient to finalize guidelines, but which produced preliminary guidelines. This warning of inadequacy was lost as nations and organizations issued ‘new’ guidelines based on these early guidelines, and through such repetition generated a false impression of consensus. The evidence base is so slim that few reports have progressed far along the sequence from anecdote to case study, to formal scientific controlled trials and epidemiological studies. Early studies reported hearing threshold shifts, nausea, headache, fatigue, migraine and tinnitus, but there is insufficient research on human subjects, and insufficient measurement of fields, to assess what health risk current occupational and public exposures might produce. Furthermore, the assumptions underpinning audiology and physical measurements at high frequencies must be questioned: simple extrapolation of approaches used at lower frequencies does not address current unknowns. Recommendations are provided.

Comment on ‘Are some people suffering as a result of increasing mass exposure of the public to ultrasound in air?’

“…The levels are well within the MPLs quoted in fig. 3 of [1]. This makes a physical damage mechanism unlikely and suggests either that the adverse effects will not be reproducible in a double-blind trial or that they are produced by some other mechanism (note the discussion regarding birdsong in §3a(ii)).…”

“…That list (nausea, dizziness, migraine, fatigue, tinnitus and 'pressure in the ears') need not require the physical damage on which are based arguments citing the energy entering the tissue ( §3a(ii)). Indeed, the references in [1] tend to suggest that the reported adverse effects (headaches, nausea, etc.) disappear after the ultrasonic signal ceases, which is suggestive (but by no means conclusive) for the possibility of a mechanism where the response is not simply related to the absorbed energy, and certainly not one that relies on physical damage to tissue.…”

“…Such 140 dB re 20 µPa signals are far stronger than one would expect to find in approximately 20 kHz public exposures, as they exceed by 30 dB or more any of the current maximum permissible levels (MPLs) in fig. 3 of [1]. Given that such fields are then reflected by the skin ( §2a), one would not expect the fields in public places measured in [1] to cause perceptible physical effects such as radiation pressure, heating, etc.…”

“…3 of [1]. Given that such fields are then reflected by the skin ( §2a), one would not expect the fields in public places measured in [1] to cause perceptible physical effects such as radiation pressure, heating, etc. (it was only in laboratory tests that some authors reported mild to very unpleasant heating at fingers, skin clefts and nasal passages in excess of 140 dB re 20 µPa in humans [11][12][13], as reported in [1, p. 37]).…”

“…This comment is written in response to enquiries and comments asking for clarification on specific issues raised in [1], and for assistance in navigating a long paper without an index. Since publication, the paper has been cited both to open up [2,3] and to close down [4] discussion of the safety of ultrasound in air.…”