Ultrasound, human health, safe levels, and Cuba: What do we know?

While definitive statements are impossible, a slim evidence base suggests the following on weight-of-probabilities regarding ultrasonic adverse effects in humans. One study at extremely high intensities reports physical effects (notably burning between fingers/nostrils). At lower intensities, adverse psychological effects occur in only a subset of the population (susceptibility possibly decreasing with age), are restricted to frequencies below ~25 kHz, probably result from the extraordinary sensitivity of our hearing/balance systems, and can be difficult to separate from (and may be causally related to) adverse effects of anxiety and annoyance. This does not remove the need for protection, especially for increasingly common public exposures, where the exposure and exposed person are often uncharacterised. Only one interim guideline from 1984 addresses maximum permissible levels (MPLs) for public exposure. It is based on scant evidence, and may or may not be appropriate. All other guidelines relate to occupational exposure. These MPLs are a legacy of decades of copying previous guidelines, which were themselves based on inadequate sampling (usually a small cohort of adult men), and averaging practices which obscured the particular sensitivities of a subset of the population. Against this background, the likelihood, or not, of an ultrasonic weapon in Cuba will be discussed.