Low-frequency noise from CH-53 helicopters exceeds assessment standards at NIT, Okinawa College

December 22, 2015 Ryukyu Shimpo

On December 21, Takeshi Tokashiki, Associate Professor at the University of the Ryukyus, presented the results of a low-frequency noise survey conducted at the National Institute of Technology (NIT), Okinawa College in Henoko, Nago. The survey measured the impact of U.S. military helicopters from both inside and outside the college. Low-frequency noise recorded indoors exceeded the “mental impact threshold value,” while measurements outdoors surpassed “reference values for complaints of physical discomfort,” set by the Ministry of the Environment. For the first time, over-the-threshold measurements were recorded from within the college, revealing the reality that students are exposed to low-frequency noise emitted by U.S. military aircrafts, even indoors.

Standard-exceeding levels of low-frequency noise were recorded during the flight training of two CH-53 helicopters. During training in Osprey aircraft higher levels may be recorded, since Ospreys emit louder low-frequency noise than CH-53 helicopters.

The survey was carried out on December 15. From indoors, a 76.4 dB low-frequency level was measured at 20 Hz at 4:18 p.m. This exceeds the Ministry of the Environment’s “reference values for complaints of mental and physical discomfort” by 0.4 dB. From outdoors, 83.8 dB at 20 Hz was measured at 4:16 p.m. This surpasses the mental discomfort reference values by 7.8 dB and physical discomfort reference values by 3.6 dB. Physical discomfort includes the trembling of objects, among other factors.

Tokashiki stated, “We have succeeded in measuring low-frequency noise from indoors. If the new base is relocated to Henoko, it may amplify the impact of such low-frequency noise.”

(English translation by T&CT, Kaya Doi)

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