Stepanov,V. Health Risk Factors of Low Frequency Noise Oscillation Below 20 Hz
Dr Vladimir Stepanov
State Research Center of Russia
Biological Effects of Low frequency Acoustic Oscillations and Their Hygienic Regulation
Basic physical concepts
According to the adopted classification, the infrasound is defined as sound oscillations of frequencies below 20 Hz (some researchers sometimes note the upper limit of 16 Hz). The adopted subdivision is determined by the peculiarities of the human hearing apparatus perceptiveness of the specific frequency range only. The limits of the hearing are conditional. It is known that they depend on the individual sensitivity of the sound perceptive apparatus and age dependent peculiarities of the human hearing function. Lower infrasound frequency is not specified; at present it is investigated to 0.001 Hz, i.e. infrasound range covers- 15 octaves.
The infrasound or low frequency oscillations of the infrasound band (< 20 Hz) are widely disseminated in the environment. The infrasound is the persistent factor of noises and vibrations naturally occurred due to the turbulence of fluids and gases, at sea storms, tide waves, air flow above mountain areas, earthquakes, volcano eruptions, bolide explosions, polar auroras, strong thunderstorms and seismic events.
Though the physical nature of the infrasound is similar to that for sound waves of any frequency bands, it was already noted that it has a number of peculiarities giving the long distance propagation and far distance exposure abilities. These peculiarities are basically caused by low frequencies and large wavelengths. In case of infrasound frequencies, wavelengths in the air are 17 m to 34 km, 75 m to 150 km in the water, and 150 m to 300 km in the ground surface. The infrasound attenuation in the environment occurs at the distance from the source and is caused by the energy absorption in the atmosphere for less than 1%. It is supposed that average constant infrasound background is specific to the sound pressure of 0.001-0.0035 Pa (35-40 dB) in the frequency band of 1-0.02 Hz.
Hurricanes and oceanic storms are powerful infrasound sources. They occur due the turbulence of fluid and gas flows occurred at sea storms, tide waves (tsunami) (up to 140-145 dB, “linear scale”), air movements above the mountain areas.
The seismic activity is correlated to the solar activity. It is very probable, that the same solar activity correlation exists for infrasound noise intensification. Infrasound signals generated by polar aurora are tightly correlated to the solar activity. The polar aurora creates LSP of – 100-110 dB “linear scale”. Magnet storms are accompanied by acoustic infrasound storm with 100% probability and its signals cover the band of 0.05-0.01 Hz.
The infrasound pressure was detected in the aircraft pathways, inside automobiles, trains and vessels, during the operation of the vessel engines, compressors, vibration instruments, fans, air conditioners, powerful turbines of diesel electric supplies, gas turbine installations, Martin furnaces.
It is established that infrasound of high intensity (>120 dB) is able to inflict health harm. Infrasound vibrations are more harmful because of dangerous resonance phenomena in some organs. The powerful infrasound can destroy or damage constructions and equipment too. At the same time, the infrasound (due to the long distance propagation) can be usefully applied to investigate ocean, upper atmosphere; the eruption or explosion site can be infrasound detected, when solving different problems of communication and detection. Infrasound waves emitted in case of underwater eruptions can predict tsunami.
The infrasound research is most frequently elaborated applying the explosion to generate infrasound, because emitters of routine type are high sized and low effective; they also have large reactive power. To receive infrasound, they use microphon , hydrophones and geophones, which design and amplifier electronics are adjusted to large amplitudes, low frequencies and large input resistance of the detecting element. Specialized low frequency receivers of electronic-chemical, thermistor and optical type are also used.
Natural and artificial (man-made) sources of the infrasound and low frequency acoustic oscillations
The range of natural and artificial (man-made) sources of the infrasound and low frequency acoustic oscillations is 2-10-5 Pa to … 105 Pa. Sound pressure levels are O dB to 194 dB.
The sound pressure level of …105 Pa was recorded near missile engines. Common life noise is usually less than 100-110 dB. Basic value of the sound pressure (PO = 2·10- 5 Pa) is the limit of aural perception of human and average pain threshold is 120-125 dB.
The development of modern technologies, transportation and improvements of technological processes and equipment accompanied by the increase of power and sizes of machines has resulted to the significant increase of infrasound components of the environment and their intensity growth. These components are generated at the time of reciprocating movement of parts of different mechanisms and inside operated installations: blast furnaces, diesel motors, forge presses, reactors. Low frequency acoustic oscillations are also generated by the aircraft, space missiles, artillery shots and such powerful sources like nuclear explosions. The option to detect nuclear explosions at far distances using long distance propagation in the atmosphere was the start point of the development of the infrasound measurements and theoretical studies on infrasound radiation propagation.
Inside the helicopter, the level is 110-120 dB at < 20 Hz. At the time of the supersonic barrier crossing, the jet results to the shock wave of maximal spectral density at 1-10 Hz. The infrasound pressure in jet trajectories (-140 dB), inside railroad trains and sea vessels, near compressors, vibration units, fans, air conditioners, power turbines of the electric power plants, and Martin furnaces was found. In such case the maximal sound pressure levels (SPLs) are found at octaval bands of average geometric frequencies of 8, 16 and 31.5 Hz; most maximal levels are 90 to 118 dB; so, that in case of sound levels of 70 to 100 dB “A scale” correspond to infrasound expressiveness (dB”Lin” – dB”A” difference) is 5 to 42 dB.
Infrasound oscillations are generated in case of oscillations of large surfaces and powerful aerodynamic processes in the elastic media. Particularly, machines named above have maximal sound pressure levels of 100-135 dB (Table 1).
Table 1 -Workplace classification for transport means and technological equipment according to noise characteristics of the infrasound band (from Izmerov N.F. et al, 1998)
|Spectrum character||Octaval bands with maximal levels of the sound pressure||Machines and equipment|
|Infrasound||2, 4, 8, 16 Hz;82-133 dB||Automobiles, blast and oxygen converting furnaces, river and sea vessels, trains, compressors|
|Low frequency infrasound –||2-125 Hz;84-112 dB||Martin furnaces, some kinds of transport vehicles, self-propelled and semi- stationary machines|
|Low frequency||31.5, 63, 125 Hz;84-116 dB||Electric arc furnaces, drive trucks, caterpillar tractors, port cranes, turbine installations, loading trucks, dredges|
Biological effects of infrasound and low frequency oscillations
Systematic studies devoted to low frequency acoustic effects were started in 19701 -1980. Basic causes of this interest were the absence of regulating documents and new publications indicated to the high biological effectiveness of the infrasound.
The majority of these studies were represented (1973) and published (1974) in the Paris International Colloquium on infrasound health effects; L. Pimonow has published the monograph (1976) entitled “Infrasound”, which monograph, together with Russian researchers (Andreeva-Galanina E.Tc. Karpova N.I., Suvorov G.A., Malyshev E.N. and others), was the basis and start point of Russian research. At present time, N.F. Izmerov et al (1998) have published the monograph reflecting the viewpoint of Russian researchers.
These studies have indicated to the fact that 110 dB to 174 dB infrasound is able to induce unpleasant subjective reactions: nausea, chest vibration, stomach pains, headaches, giddiness, unexplained fear, swallowing and breath complications, spatial disorientation, tympanic oscillation and tyro.panic massage sensation (Andreeva-Galanina E.Tc., 1970; Karpova N.I. et al, 1973; Reutov 0.V., 1978; Evdokimova LB., Shypack E.Yu., 1979; Gavreau V., 1966; Pimonow L., 1976; von Gierke H.E., Parker D.E., 1976; Tempest W., 1976).
Russian and foreign researchers have advanced the infrasound health effects issue. The expressed unfavorable health effects of infrasound were established, essentially in psycho emotional area; they affect the workability, cardiovascular and endocrine systems, cochlear vestibular apparatus. It should be noted that attitudes regarding infrasound health effects are ambiguous. Some researchers indicate that infrasound is very health harmful factor even able to induce the fatal outcome in some conditions. Other authors are more constrained.
The accumulated data on the infrasound health effects have given the opportunity to make the conditional subdivision of its effects from fatal ones to very mild effects with unclear response. The first attempt of such subdivision into four groups was tried at 1973 Paris Colloquium (Pimonow L, 1974; Johnson D.L, 1974).
These groups of infrasound health effects, L. Pimonow (1973, 1976), are specified as follows:
I- infrasound of > 185 dB, which is of fatal danger (the variable pressure of such levels can induce pulmonary alveolar rupture);
II- infrasound of 140 dB to 172 dB, which 2 minute exposure is tolerable for healthy human;
III- infrasound of 120 dB to 140 dB, which is able to induce mild physical disturbances and fatigue in case of many hour exposures;
IV- infrasound of < 120 dB, which is not health harmful if its exposure time is less than several minutes; reactions of the long-time exposure are the subject for future studies.
Similar grouping are provided by A. Stan (1974) as follows: 180-200 dB is the fatal danger range; 150-180 dB is the range of clear dangerous effects; 140-150 dB at 0.1 Hz and 105-150 dB at 63 Hz is the range of dangerous effects; < 105 dB at 63 Hz and < 143 dB at 0.1 Hz are the ranges of the significant effect absence.
Thus, the averaged border of the infrasound health effect threshold is in the area of 112 dB at 31.5 Hz up to 140-143 dB at 0.1 Hz. A. Stan (1974) has proposed the interpretation of infrasound effect ranges: 180-200 dB (fatal danger), 150-180 dB (dangerous health effects), 140-150 dB at 0.1 Hz and 105-150 dB at 63 Hz (harmful effect range) and -3 dB at 0.1 Hz (absent effect range). Thus, the averaged threshold of the infrasound health effects is 112 dB (31.5 Hz) to 140-143 dB (0.1 Hz).
Before the analyzing literature data regarding infrasound health effects, it is necessary to consider experimental equipment applied to generate infrasound oscillations.
The majority of published studies were elaborated applying dynamic pressure chambers (DPC). These are different hermetic chambers with rigid walls. Infrasound sources are either electric loud speakers or rigid membranes moved by different driving mechanisms. These membranes of loud speaker membranes make reciprocating shifts with rate of less than 20 Hz, which results to sinusoid change of the air pressure inside the chamber. It should be noted that DPC do not have the sound wave propagation but only pressure oscillations, which imitate infrasound exposure (Pimonow L., 1974). DPC application is considered to be applicable to reveal infrasound physiological effects; it is economically positive and easy to be designed (Malyshev E.N., 1979).
To directly expose examinee ears, some researchers (Evans M., 1972; Leventhall H.G., 1974 and others) have designed specialized infrasound headphones (so-called aural way of infrasound exposure). These headphones were tightly attached to examinee ears. Because of the elastic layer, only infrasound air oscillations have affected ears without vibration interference. However, such way results to the exposure of ears only, which is not adequate to environmental infrasound exposure.
The application of DPC, headphones and other appliances is related to significant technical difficulties of formed acoustic field generation. These difficulties consist in the fact that formed acoustic field is present at distance of the wavelength. For infrasound this distance is tens or even hundreds of meters. Taking into account the low source efficiency and spherical character of acoustic oscillation propagation, the energy portion is very low in the formed field. Therefore, it is necessary to apply very powerful sources to get significant infrasound levels, which is difficult to realize in practice.
To get real infrasound waves, V. Gavreau has designed and constructed the infrasound emitter of the enlarged police whistle type, which size was – 1.5 m. The air supply was provided by the compressor. At present time, the units specific to larger infrasound SPL are available. These are emitters of directed effect. One of such source described in literature consists of a number of powerful infrasound loud speakers placed at half wavelength distances. To get the sound “beam” the even dynamics are provided one phase signal and the odd ones are provided the alternative phase signal. Because of summation of sound waves, the resulting sound wave has almost plane front.
Early published health effects of the infrasound are generalized by Table 2.
The literature data on industrial infrasound effects in human and organism are sparse. These studies have indicated to the fact that 110 dB to 174 dB infrasound is able to induce unpleasant subjective reactions: nausea, chest vibration, stomach pains, headaches, giddiness, unexplained fear, swallowing and breath complications, spatial disorientation, tympanic oscillation and tympanic massage sensation (Andreeva-Galanina E. Tc., 1970; Karpova N.I. et al, 1973; Reutov O.V., 1978; Evdokimova I.B., Shypack E.Yu., 1979; Gavreau V., 1966; Pimonow L., 1976; von Gierke H.E., Parker D.E., 1976; Tempest W., 1976).
Table 2 – Infrasound human health effects
|Author(s)||Sound pressure level, frequency, exposure time||Health effects|
|Slarve R.N., Johnson D., 1975||144 dB; 1-20 Hz;6 min||Audiometry has not revealed significant shifts for aural analyzer in males.|
|Borredon P., Nathi L., 1974||130 dB; 7,5 Hz;50 min||Some increase of diastolic pressure in males from 61.9 to 63.2 mm.|
|Karpova N.I. et al 1972||136 dB; 10 Hz;15 min||Pulse rate increase and minimal AD increase (for 7-11 mm) in males.|
|Reutov O.V., Erofeev N.P., 1976||135 dB; 5 H 10 Hz;15 min||Heart automatism disorder with peculiar change of cardiac constrictions|
|von Gierke H., 1974||154 dB; 1-100 Hz;||Unpleasant sensations in the ear have risen from 145 dB; 150-153 dB was the limit threshold of voluntary tolerance. At these levels, the scratching sensation and outside body presence sensation have occurred in the throat; caught attacks have started and some males had nausea feeling.|
|Nixon Ch., 1974||> 125 dB;1-20 Hz; 8 min||125 dB and more results to tympanic massage coinciding to the oscillation frequency. > 140 dB has induced pain sensation. At 10 Hz, the pain threshold was – 150 dB.The pain threshold is increased for the decreasing frequency.|
|Karpova N.I. et al 1972||136 dB; 10 Hz||Significant change of the peripheral blood circulation (20-22% blood flow increase if compared to initial data).|
|Evans M., Tempest W., 1972||140 dB; 7 Hz||7 Hz frequency is most “effective” for vestibular apparatus; this frequency is sensible for semicircle channels and otolith system detecting the gravity.|
|Prazak B., 1974||80-152 dB; 4 Hz||At 4 Hz the tolerance threshold is 87 dB and pain threshold is -152 dB.|
|Sherer, J., 1973||140-170 dB; 3, 15and 100 Hz;||The pain threshold was found to be as follows: 170 dB for static pressure; 165 dB at 3 Hz;140 dB at 15 Hz and 120 dB at 100 Hz.|
|Leventhall H., 1974||126 dB; 2 – 20 Hz||Subjective reaction studies in 6 volunteers have indicated to the average reaction time change from 0.414 s to 0.430 s in case of the infrasound exposure only. The “arrow surveillance” test was found to get 10% productivity loss in case of the noise or alcohol.|
|Mohr G. et al, 1965||119 – 144 dB; <22Hz;3 min||Subjective body vibration. At 144 dB, half of examinees had breath rate increase. All examinees had transient shift of the aural threshold (> 120 dB).|
|Alford B. et al, 1966||Up to 154 dB; 1 – 100 Hz||150 dB is tolerable for heart rhythm, aural threshold, vision power, spatial orientation changes.|
|Gavreau V., 1968||7 Hz||Low intensive 7 Hz infrasound induces nausea and fatigue at hour 2 of the exposure of intellectual operator.|
|Sharp M., 1971||Low frequencynoise during||Low frequency noise and vibration result to discomfort, irritation, nausea, abdominal and vertebral pains, obstructed breath and other unpleasant sensations, which pre-cause anxiety and fear.|
|Johnson D., 1974||< 144 dB;1 -30 Hz||Voice modulation and middle ear pressure sensation in case of > 132 dB.|
|Leventhall H., 1974||140 dB; 2 Hz||Mild nausea, rotation sensation, eyeball rotation, discomfort in all experiments.|
|Fecci R. et al, 1971||65-80 dB; 8 Hz;Industrial exposure within 4 months||Arterial pressure indices were very stable within 4 months. Only 18% had mild AP decrease and 22% had mild AP increase. Pulse rate was stable. ECG changes were not found.|
|Malyshev E.N., Skorodumov G.E., 1974||135 dB; 10 Hz;15 min||Cardiovascular status examination has revealed pulse rate increase (5-30 min-‘), minimal AP increase (20 mm) and maximal AP increase (15 mm) in males.|
|Pimonow L., 1976||–||10 year material generalization has suggested to the infrasound pressure limit of 140 dB for space fliers and 120 dB for space flight technical personnel.|
|Johnson D., 1974||144 dB and more; 1 – 30 Hz||160 dB is considered to be maximum permissible even for short-time exposure.|
Note: * SPL – sound pressure level, dB
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