Comments on the Article “Negative Effect of High-level Infrasound on Human Myocardial Contractility: in Vitro Controlled Experiment” by Chaban R. et al. (Noise Health 2021;23:57-66)

In their paper, Chaban et al.[1] show that the contraction force in a small sample of live heart tissue is significantly less when exposed to 16 Hz infrasound of 120 dB compared to no infrasound exposure; the difference at 110 dB is not significant. In their discussion, the authors relate this to possible effects of infrasound from wind turbines on residents, although at the same time declining responsibility for making this connection by stating “Whether or not wind turbines are, or will be, able to produce harmfully high levels of infrasound (….) remains out of the scope of this paper.” From a modest literature search, they could have concluded that it is not necessary to cause worry to residents near wind farms as their results simply do not apply to wind farm infrasound. One reason for this is that wind turbine infrasound levels are too low, and another is that their understanding of the impact of sound on the human body is incorrect.

In 2005, Jakobsen[2] concluded from available measurement data of wind turbines up to 4.2 MW that the infrasound pressure level from an upwind turbine at 100 m istance is about 70 db (G) or lower. In 2016, Keith et al.[3] reported that at a 10-m wind speed of 8 m/s, the measured maximum sound power level from nine different wind turbine types of 1.5 to 3 MW was 120 dB; from their results, it can be calculated that this corresponds to a total (0.5 to 16 Hz octaves) infrasound power level of 125 dB. Just taking spherical spreading into account to a point at a 100 m distance, this gives a sound pressure level of 73 dB or about 69 db (G). Herrmann et al.[4] measured infrasound pressure levels at 150 m from a wind turbine ranging from 55 to 80 db (G). At distances of 650 m and more, the wind turbine infrasound level was 55 to 75 db (G), irrespective of whether the wind turbines were operational or not: the specific wind turbine sound disappeared in the general environmental presence of infrasound.

Chaban et al. state that “the human body itself does not shield against infrasound”. In fact, sound does not easily penetrate the body: because both the density of and sound velocity in the human body tissues are rather higher than in the air, the acoustic impedance is much higher. As a consequence, sound predominantly reflects on the body and is not readily absorbed, similar to the high reflection of sound on the water. Thus the body already “protects” internal organs from outside noise, which has not been taken into account by the authors. For a possible amplification due to resonance, Chaban et al. give two references, one concerning maintenance personnel near military jet engines[5] and the other about subjects standing on a vibrating horizontal beam.[6] Both studies do not support their arguments. Smith showed that chest vibrations occurred at 60 to 100 Hz and stated as the main conclusion that “infrasound occurring at 40 Hz and below did not appear to be a problem.” The effect of standing on a horizontal beam vibrating in the vertical direction, as reported by Randall et al., is quite different from being exposed to more or less horizontally propagating airborne sound pressure waves because of differences in direction and magnitude of the forces exerted on the body. Chest vibration is unlikely to be a result of pressure exerted by a sound wave as the pressure difference over ≈30 cm (chest size) in an infrasound wave is very low (<1 Pa). Chest vibration is most likely driven by expansion and compression from the changing air pressure[7] (personal communication with Wijnant t. from the University of Twente) and is strongest when this coincides with the chest resonance frequency. Takahashi[8,9] has shown that there is no sensation of vibration from infrasound/low-frequency sound when the level is below the hearing threshold. Although a chest vibration may be transmitted weakly to the heart, even at very high exposure levels near aircraft engines, heart problems have not been reported in studies by Smith[5] and Jensen et al.[9] Direct effects on the heart are thus far from plausible near wind turbines where the (infra)sound level is much lower and even below the perception threshold. There are a number of other reasons for reports of ill health[10] and these can be understood without speculative reference to the effects of infrasound at far higher and clearly perceptible levels.