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Table 1. Examples of incidental or deliberate exposures from commercial devices
Incidental or Deliberate Exposure?
Commercial Source
Frequency
SPL Levels at the Possible Position of the Human Ear
Reference for Measurement
Deliberate
Pest deterrents: Used to deter birds, rodents, and insects away from locations (barns, homes, and shops)
20-kHz TOB
130 dB at 1.6 m 90 dB at 14 m
Ueda et al., 2014a,b
92 dB at 1.7 m
Dolder et al., 2018
Deliberate
Teen deterrent: Exploits high-frequency sensitiv- ity of teenagers and children to deter them from shops as age-discriminatory deterrent to make the shop more welcoming to older customers who are assumed to have greater purchasing power and be less likely to steal.
12.5-kHz TOB
72 dB at 1.5 m
Conein, 2006
16-kHz TOB
92 dB at 1.5 m
20-kHz TOB
80 dB at 1.5 m
Incidental
Public-Address-Voice-Alarm: Speakers, usually set in ceilings or high on walls in public places to alert people, e.g., to evacuate in case of bomb threat or fire; by EU law must be monitored to ensure they are functioning. Many types produce a ~20-kHz tone as a by-product of this monitoring.
~20 kHz
76 dB
Fletcher et al., 2018c
65 dB
Paxton et al., 2018
43-82 dB
Mapp, 2018
Incidental
Acoustic spotlights: Two high-intensity ultrasonic beams overlap, and the nonlinear difference fre- quency produces a low-power audible signal so that listeners to recordings who share a space do not bother one another (for museums, exhibitions, and homes). It is not known whether anecdotal reports of adverse effects, if confirmed, would be due to
the fundamental, a subharmonic produced by the source of a nonlinearity in propagation, or when the ear is driven by the signals.
~20 kHz
53 dB at 3.5 m
Dolder et al., 2019
Sapozhnikov et al., 2019
~40 kHz
118 dB at 3.5 m
Incidental
Haptic feedback: ultrasonic beams (e.g., above a computer keyboard) produce modulated radiation pressure that gives the sensation resembling “soap bubbles bursting on the skin.”
~40 kHz
125 dB at 60 cm
Battista, 2019
155 dB at 20 cm
Lieber et al., 2019
SPL, sound pressure level, TOB, third-octave band; EU, European Union. See Leighton, 2016a, for details of devices. Reproduced from Leighton et al., 2020.
centered on 25-50 kHz (i.e., from the limits of 22.4 to 56.2 kHz) and 75 dB for the TOBs centered on 8-16 kHz (i.e., having limits from 7.07 to 17.8 kHz).
After assessing the underpinning evidence, Leighton (2016a) concluded that this agreement did not result from various bodies independently validating each other but instead from each copying predecessors rather than face the prospect of funding difficult experiments to determine the MPLs for themselves. However, even without the US Occupational Safety and Health Administration (OSHA),
there was still about a 50 dB variation in MPL in the TOB centered on 20 kHz (Leighton, 2016a). Since 2004, the OSHA guideline was an outlier, permitting an extra 30 dB on MPLs for airborne ultrasound (Howard et al., 2005), a recommendation it recently dropped (Leighton, 2019).
Although occupational airborne ultrasound exposure from industrial equipment (e.g., welders, drills, cleaning baths) drove occupational MPLs for decades, public exposure was largely ignored despite the fact that it also occurred from technologies such as pest deterrents (van Wieringen and
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