Airborne ultrasound might be undetectable to us as we go about our lives, but a new study by University of Southampton researchers claims that the public is being exposed to damaging levels of it without their knowledge. The study found that in locations such as railway stations, museums and libraries, airborne ultrasound levels are high enough that people have complained about nausea, dizziness, fatigue and other negative effects. This ultrasound could stem from numerous sources such as door sensors and public address systems.
Over years, many workers regularly exposed to ultrasound due to proximity to industrial devices have reported similar negative effects as those mentioned above, but thus far, there has not been enough research to prove the link between the two variables. Regardless of a concrete link being unearthed, Tim Leighton, who participated in the current research, doesn't believe that current guidelines are adequate to ensure safe levels.
"Existing guidelines are insufficient for such large public exposures as the vast majority refer to occupational exposure, where workers are aware of the exposure, can be monitored and can wear protection," Leighton said in a press release. "Furthermore, the guidelines are based on the average response of small group, often of adult males."
"The guidelines are also based on an insufficient evidence base, most of which was collected over 40 years ago by researchers who considered it insufficient to finalize guidelines, but which produced preliminary guidelines," he added.
Leighton and his team used smart phones and tablets in conjunction with an app that could produce a spectrogram of what they detected with their microphones, leading to the discovery of very high frequency/ultrasonic fields (VHF/US) in numerous public buildings that contained hundreds of people at the time of the study. They found that numerous members of the public were being exposed to levels above 20 kHz, which is the safety threshold in the current guidelines.
"Individuals who are unlikely to be aware of such exposures are complaining, for themselves and their children, of a number of negative conditions," he said. "The lack of research means that it is not possible to prove or disprove the public health risk or discomfort. However, it is important that sufferers are able to identify the true cause of their symptoms, whether they result from VHF/US exposure or not."
The findings will be published in the Proceedings of the Royal Society A.
