Ultrasound independent Advisory Group on Non-ionising Radiation (AGNIR) produced a report in 2010, which was published by the UK Health Protection Agency (HPA). This report recommended an exposure limit for the general public to airborne ultrasound sound pressure levels (SPL) of 70 dB (at 20 kHz), and 100 dB (at 25 kHz and above). Ultrasound Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000
6955 kHz 6955 kHz "6955 kHz" is the sixth episode of the third season of the American science fiction drama television series "Fringe". It first aired on November 11, 2010 in the United States. The third season spent much of its time alternating between the prime and parallel universes, and "6955 kHz" was set in the former. The storyline followed the Fringe team's investigation into a numbers station that mysteriously gave its listeners amnesia, a case that ultimately ties to a doomsday device. The episode was written by story editors Robert Chiappetta and Glen Whitman, and was directed by Joe Chappelle. Its