Vibroacoustic safety

VIBROACOUSTIC SAFETY (EN: vibroacoustic safety; DE: vibroakustische Sicherheit; FR: securite vibroacoustique; ES: seguridad vibroacustica; RU: виброакустическая безопасность) is the prevention of the harmful impact of the vibration and noise of the machines and mechanisms onto the working persons.

The major sources of the vibration and noises at the mining enterprises are: perforators, jackhammers, drilling rigs, hand-held augers, combined mining machines, loading-delivering machines, ventilators for the general and local airing, compressor installations, locomotives, conveyors, excavators, crushers, screens, and so on. Under the underground conditions, the vibroacoustic impact onto the working persons is compounded by: the existence of the acoustically rigid reflecting surfaces within the mine workings, which are causing the significant (up to 6 decibels) increasing of the level of the noise; the emergence (during the work of the machines and mechanisms within the limited space) of the intense noise with the complicated spectral composition of the frequencies; the combined impact of the vibration, noise, increased temperatures, humidity, atmospheric pressure, and dust factor, which, in case of the normal microclimate, is equivalent to the increasing of the intensity of the noise by 10-15 decibels. There also generate the elevated levels of the noise the drilling rigs, pumps, ventilators, and other mechanisms of the petroleum-extracting installations, which are situated at the sea and on the dry land, and also the enterprises of the gas industry.

The vibroacoustic safety within the mining industry is ensured through the comprehensive solving of the technical, hygienic, and organizational issues: the decreasing of the noise and vibration of the machines within the source of their emergence, and along the way of the propagation to the working places; the development of the means for the individual protection against the noise and vibration; the establishment of the normative levels for the noise and vibration, which are safe for the person (the sanitary rationing of the noise and vibration), for the noise and vibratory characteristics of the machines (the technical rationing of the noise and vibration); the conducting of the therapeutic-prophylactic activities.

The decreasing of the vibration and noise of the machines is based on the dynamic balancing, balancing, and elimination of the harmful collisions, or on the decreasing of the shock stresses through the changing of the rigidity of the colliding contacts; on the usage of the elastic elements as the intermediate links of the kinematic chain, and so on. For the vibratory isolation of the surfaces of the contact of the worker with the machine, they mostly use the devices, within which there are used the inertial properties of the protected masses, which are separated using the elastic elements. For example, they isolate against the vibration the handles for the control and holding of the perforators with the help of the springs, and they isolate the working places of the drilling rigs and excavators with the help of the supports, which are made of the reinforced rubber shells. The expenditures, which are necessary for the decreasing of the noise and vibration during the designing of th e new mining machines, account for approximately 3% of the total cost of the machine; in case of the conducting of the analogous work for the finished machine, the expenditures increase to 10-15%.

As the means for the decreasing of the noise at the enterprises within the mining industry, they use the structural materials with the decreased sound emission, and with the high coefficient of the absorption of the sound energy. They mostly use the sound-absorbing materials within the facings for the enclosed production spaces and technical devices (the industrial workshops, ventilators for the general and local airing, silencers, and so on). They widely use the sound-absorbing and vibration-damping mastics and materials, coatings, facings, covers, sound-isolating gasket materials in the form of the rolls or plates. For the decreasing of the aerodynamic noise from the exhaust (suction) of the ventilators, pneumatic motors, jackhammers, perforators, and other machines, which are powered by the pneumatic energy, they use the silencers. Within the places with the high intensity of the noise, they install for the servicing personnel the remote control and the sound-isolated cabins fo r the supervision. They use the means for the individual protection (earmuffs, helmets, headbands, insertions) for the silencing of the noise within the range of the frequencies of 2000-6000 hertz; they have the silencing ability of up to 40 decibels. The choice of these means depends on the level of the noise at the working place, on the spectral characteristic of this noise, and on the conditions of the work.

They determine the regulatory levels of the noise and vibration, which are safe for the person, using the sanitary rationing. The sanitary rationing of the noise is performed according to the limiting acceptable levels of the sound pressure within the octave bands from 63.5 to 8000 hertz. Another principle of the sanitary rationing is the integral principle (the regulation of the noise with the help of the corrected level, in terms of the A-weighted decibels). The classification, characteristics, and norms of the noise (and vibration) at the working places, and also the requirements for the noise (and vibratory) characteristics of the machines within the USSR are regulated using the system of the standards of the safety of the work. The sanitary rationing of the vibrations, both general (which is transmitted through the supporting surfaces onto the body of the person, who is sitting or standing), and local (which is transmitted through the arms of the person), is performed according to the limiting acceptable average quadratic levels of the oscillatory speed (in terms of the metres per second), or according to the logarithmic levels of this speed (in therms of the decibels), within the octave bands from 1 to 63 hertz (for the general vibration), and from 8 to 1000 hertz (for the local vibration).

According to the requirements about the ensuring of the acceptable level of the noise and vibration at the working places, there is performed the technical rationing of these parameters, namely, the establishment of the noise and vibratory characteristics of the machines. They use the determined characteristics: for the evaluation of the noise (vibratory) properties of the machine during the monitoring of their quality; for the comparison of the mass-produced machines with the etalon samples; for the determining of the necessary effectiveness of the means, which are ensuring the vibroacoustic safety. The noise characteristics are established preferably in terms of the octave levels of the sound power, while the vibratory characteristics are established in terms of the octave levels of the vibratory speed.

The therapeutic and prophylactic work for the ensuring of the vibroacoustic safety within the USSR includes the periodic medical examinations of the working persons with the aim of the identification of the early symptoms of the vibration disease (see the "Vibration disease" article), and also the audiometric monitoring, which is conducted at least one time per year in case of the impact from the production noise with the level of more than 80 A-weighted decibels (the hearing ability is considered damaged, if the increasing of the threshold of the hearing within the limits of the three octave bands with the median frequencies of 500, 1000, and 2000 hertz amounts to 25 decibels on average).