Hygienic characteristics of noise. The main physical and hygienic characteristics of noise. Spectral analysis of noise. The effect of noise on the human body

Noise is a combination of sounds of varying intensity and frequency. Any noise is characterized by sound pressure, sound intensity level, sound pressure level, noise frequency composition.

Sound. pressure-additional pressure arising in the medium during the passage of sound waves (Pa). The intensity of the sound is the number of sound. energy in a unit of time passing through a unit of area perpendicular to the propagation of a sound wave, (W \ m sq.) Sound intensity associated with sound. pressure ratio
, where
--RMS sound. pressure in this t-ke sound. fields, ρ - the density of the air, Kt / m3, s - the speed of sound in the air, m / s. Intensity level Sound, dB
, where - sound intensity , resp. threshold of hearing
W\m sq. at a frequency of 1000 Hz. Sound level value. pressure, dB, Р=2*
Pa is the threshold value of audibility at a frequency of 1000 Hz.

The frequency composition of the noise. Range- dependence of sound levels. pressure from geometric mean frequencies 63, 125, 250, 500, 1000, 2000, 4000, 8000 Hz., in eight octave bands of these frequencies. Octave-frequency band, in which the upper limit frequency is twice the lower limit. frequencies. Noise, depending on the nature of the spectrum, can be: low (for 300 Hz), medium (300-800 Hz), high-frequency (over 800 Hz).

34. The effect of noise on the human body

From a physiological point of view, noise is any sound that is unpleasant for perception, interferes with conversational speech and adversely affects human health. The human hearing organ responds to changes in the frequency, intensity and direction of sound. A person is able to distinguish sounds in the frequency range from 16 to 20,000 Hz. The boundaries of the perception of sound frequencies are not the same for different people; they depend on age and individual characteristics. Oscillations with a frequency below 20 Hz (infrasound) and with a frequency over 20,000 Hz (ultrasound), although they do not cause auditory sensations, they objectively exist and produce a specific physiological effect on the human body. It has been established that prolonged exposure to noise causes various adverse health changes in the body.

Objectively, the effect of noise is manifested in the form of increased blood pressure, rapid heart rate and breathing, decreased hearing acuity, weakening of attention, some disturbance in movement coordination and reduced efficiency. Subjectively, the effect of noise can be expressed in the form of headache, dizziness, insomnia, and general weakness. The complex of changes that occur in the body under the influence of noise has recently been considered by physicians as "noise disease".

When entering a job with an increased noise level, workers must undergo a medical examination. Periodic inspections of workers in noisy workshops should be carried out within the following periods: if the noise level in any octave band is exceeded by 10 dB - once every three years; from 11 to 20 dB - 1 time and two years; over 20 dB - 1 time per year.

The basis of noise regulation is to limit the sound energy that affects a person during a work shift to values that are safe for his health and performance. Rationing takes into account the difference in the biological hazard of noise depending on the spectral composition and temporal characteristics and is carried out in accordance with GOST 12.1.003-83. According to the nature of the spectrum, the noise is divided into: broadband with the emission of sound energy with a continuous spectrum with a width of more than one octave; tonal with the emission of sound energy in separate tones.

Rationing is carried out by two methods: 1) by the limiting noise spectrum; 2) according to the sound level (dBA), measured when the corrective frequency characteristic "A" of the sound level meter is turned on. According to the limiting spectrum, sound pressure levels are normalized mainly for constant noise in standard octave frequency bands with geometric mean frequencies of 63; 125; 250; 500; 1000; 2000; 4000; 8000 Hz.

Sound pressure levels at workplaces in the normalized frequency range should not exceed the values specified in GOST 12.1.003-83.

Total sound pressure level def. according to the formula: L= L 1 +ΔL,

where L 1 - max noise level from the source, ΔL - additive, depending on the difference between the two added levels and accept. according to the table.

If familiar sounds suddenly disappear from the environment, then a person will experience significant inconvenience, excitement and even a feeling of causeless fear: after all, people are born and live in the world of sounds. It should not be forgotten that civilization has reached a high level of development thanks to the ability to communicate in the form of speech - one of the types of communication using sounds. Nevertheless, noise is one of the main adverse production factors. Due to noise, workers experience faster fatigue, which leads to a decrease in productivity by 10 ... 15%, an increase in the number of errors in the performance of work process operations and, consequently, an increased risk of injury. With prolonged exposure to noise, the sensitivity of the hearing aid decreases, pathological changes occur in the nervous and cardiovascular systems.

Noise is a collection of sounds of varying strength and frequency (pitch) that change randomly over time. By their nature, sounds are mechanical vibrations of solids, gases and liquids in the audible frequency range (16...20,000 Hz). In air, a sound wave propagates from a source of mechanical vibrations in the form of zones of condensation and rarefaction. Mechanical vibrations are characterized by amplitude and frequency.

The oscillation amplitude determines the pressure and strength of the sound: the larger it is, the greater the sound pressure and the louder the sound. The essence of auditory perception consists in catching with the ear the deviation of air pressure created by a sound wave from atmospheric pressure. The value of the lower absolute sensitivity threshold of the auditory analyzer is 2-10~5 Pa at a frequency of 1000 Hz, and the upper threshold is 200 Pa at the same sound frequency.

The oscillation frequency affects auditory perception and determines! sound height. Oscillations with a frequency below 16 Hz constitute the region of infrasounds, and above 20,000 Hz - ultrasounds. With age (from about 20 years old), the upper limit of frequencies perceived by a person decreases: in middle-aged people up to 13 ... 15 kHz, in the elderly - up to 10 kHz or less. The sensitivity of the hearing aid increases with an increase in frequency from 16 to 1000 Hz, at frequencies of 1000 ... 4000 Hz it is maximum, and at a frequency of more than 4000 Hz it drops.

A physiological feature of the perception of the frequency composition of sounds is that the human ear reacts not to an absolute, but to a relative increase in frequencies: a doubling of the oscillation frequency is perceived as an increase in the pitch by a certain amount, called an octave. Therefore, it is customary to call an octave a frequency range in which the upper limit is twice as large as the lower one. The audible frequency range is divided into octaves with geometric mean frequencies of 31.5; 63; 125; 250; 500; 1000; 2000; 4000; 8000 and 16000Hz. Average geometric frequencies occupy, as it were, an intermediate position in the octave. They are determined from the expression

where fn and fv are the lower and upper values of the frequency in an octave, respectively.

In the hygienic assessment of noise, its intensity (strength) is measured and the spectral composition is determined by the frequency of the sounds included in it. Sound intensity is the amount of sound energy carried by a sound wave per unit of time and related to a unit of surface area perpendicular to the direction of wave propagation. Sound intensity values vary over a very wide range - from 10-12 to 10 W/m2. In connection with the strong stretching of the range of intensity changes and the peculiarities of the perception of sounds (see the Weber-Fechner law), logarithmic quantities are introduced - the intensity level and the sound pressure level, expressed in decibels (dB). When using a logarithmic scale, the sound intensity level is:

Li = 101g(I/I0),

sound pressure level:

where I and I0 are, respectively, the actual and threshold values of the sound intensity, W/m2: I0= 10-12 W/m2 at the reference frequency fe= 1000 Hz; p and P 0 - respectively, the actual and threshold sound pressure, Pa: p0 \u003d 2 * 10-5 Pa at fe \u003d 1000 Hz.

Rice. 19.1. Curves of equal loudness of sounds

It is convenient to use a logarithmic scale of sound pressure levels, since sounds that differ in strength by a factor of billions fall within the range of 130 ... 140 dB. For example, the sound pressure level created during normal human breathing is within 10 ... 15 dB, whisper - 20 ... 25, normal conversation - 50 ... 60, created by a motorcycle - 95 ... 100, engines jet aircraft on takeoff - 110 ... 120 dB. However, when comparing different noises, it must be remembered that a 70 dB noise level is twice as loud as a 60 dB noise level and four times as loud as a 50 dB noise level, which follows from the logarithmic scale. In addition, sounds of the same intensity but different frequencies are perceived differently by ear, especially at an intensity level of less than 70 dB. The reason for this phenomenon is the greater sensitivity of the ear to high frequencies.

In this regard, the concept of sound loudness is introduced, the units of which are backgrounds and sons. The loudness of sounds is determined by comparing them with a reference sound with a frequency of 1000 Hz. For a reference sound, units of its intensity in decibels are equated to backgrounds (Fig. 19.1). So, the loudness of a sound with a frequency of 1000 Hz and an intensity of 30 dB is equal to 30 backgrounds, the same value is equal to the loudness of a sound of 50 dB with a frequency of 100 Hz.

The measurement of loudness in sons shows more clearly how many times one sound is louder than another. The loudness level of 40 von is taken as 1 son, at 50 fon - for 2 sons, at 60 von - for 4 sons, etc. Therefore, with an increase in loudness by 10 phons, its value in sons doubles.

To ensure the safety of production activities, it is necessary to take into account the ability of sound waves to be reflected from surfaces or absorbed by them. The degree of reflection depends on the shape of the reflective surface and the properties of the material from which it is made. With a large internal resistance of materials (such as felt, rubber, etc.), the main part of the sound wave (energy) incident on them is not reflected, but absorbed. Features of the design and shape of the premises can lead to multiple reflections of sound from the surfaces of the floor, walls and ceiling, thereby lengthening the sound time. This phenomenon is called reverberation. The possibility of reverberation is taken into account at the design stage of buildings and premises in which noisy machines and equipment are supposed to be installed.

If familiar sounds suddenly disappear from the environment, then a person will experience significant inconvenience, excitement and even a feeling of causeless fear: after all, people are born and live in the world of sounds. It should not be forgotten that civilization has reached a high level of development due to the ability to communicate in the form of speech - one of the types of communication using sounds. Nevertheless, noise is one of the main adverse production factors. Due to noise, workers experience faster fatigue, which leads to a decrease in productivity by 10 ... 15%, an increase in the number of errors in the performance of work process operations and, consequently, an increased risk of injury. With prolonged exposure to noise, the sensitivity of the hearing aid decreases, pathological changes occur in the nervous and cardiovascular systems.

Noise is a collection of sounds of various strengths and frequencies (heights), randomly changing over time. By their nature, sounds are mechanical vibrations of solids, gases and liquids in the audible frequency range (16...20,000 Hz). In air, a sound wave propagates from a source of mechanical vibrations in the form of zones of condensation and rarefaction. Mechanical vibrations are characterized by amplitude and frequency.

Oscillation amplitude determines the pressure and strength of the sound: the larger it is, the greater the sound pressure and the louder the sound. The essence of auditory perception consists in catching with the ear the deviation of air pressure created by a sound wave from atmospheric pressure. The value of the lower absolute sensitivity threshold of the auditory analyzer is 2-10~5 Pa at a frequency of 1000 Hz, and the upper threshold is 200 Pa at the same sound frequency.

Oscillation frequency affects auditory perception and determines! sound height. Oscillations with a frequency below 16 Hz constitute the region of infrasounds, and above 20,000 Hz - ultrasounds. With age (from about 20 years old), the upper limit of frequencies perceived by a person decreases: in middle-aged people up to 13 ... 15 kHz, in the elderly - up to 10 kHz or less. The sensitivity of the hearing aid increases with an increase in frequency from 16 to 1000 Hz, at frequencies of 1000 ... 4000 Hz it is maximum, and at a frequency of more than 4000 Hz it drops.

f c =√ f n f c

where f n and f in - respectively, the lower and upper values of the frequency in the octave.

In the hygienic assessment of noise, its intensity (strength) is measured and the spectral composition is determined by the frequency of the sounds included in it. Sound intensity is the amount of sound energy carried by a sound wave per unit of time and related to a unit of surface area perpendicular to the direction of wave propagation. Sound intensity values vary over a very wide range - from 10 -12 to 10 W/m 2 . Due to the strong stretching of the range of intensity changes and the peculiarities of the perception of sounds (see the Weber-Fechner law), logarithmic quantities are introduced - the intensity level and the sound pressure level, expressed in decibels (dB). When using a logarithmic scale sound intensity level:

L i = 101 g(I/ I 0 ),

sound pressure level:

L = 20 lg(p/ p 0 )

where I and I 0 are, respectively, the actual and threshold values of the sound intensity, W / m 2: I 0 \u003d 10 -12 W / m 2 at the reference frequency f e = 1000Hz; R and P0- respectively, the actual and threshold sound pressure, Pa: p 0 \u003d 2 * 10 -5 Pa at f e = 1000 Hz.

Rice. 19.1. Curves of equal loudness of sounds

It is convenient to use a logarithmic scale of sound pressure levels, since sounds that differ in strength by a factor of billions fall within the range of 130 ... 140 dB. For example, the sound pressure level created during normal human breathing is within 10 ... 15 dB, whisper - 20 ... 25, normal conversation - 50 ... 60, created by a motorcycle-95 ... 100, engines jet aircraft on takeoff - 110 ... 120 dB. However, when comparing different noises, it must be remembered that a 70 dB noise level is twice as loud as a 60 dB noise level and four times as loud as a 50 dB noise level, which follows from the logarithmic scale. In addition, sounds of the same intensity but different frequencies are perceived differently by ear, especially at an intensity level of less than 70 dB. The reason for this phenomenon is the greater sensitivity of the ear to high frequencies.

For this reason, the concept sound volume, whose units of measurement are backgrounds and sons. The loudness of sounds is determined by comparing them with a reference sound with a frequency of 1000 Hz. For a reference sound, units of its intensity in decibels are equated to backgrounds (Fig. 19.1). So, the loudness of a sound with a frequency of 1000 Hz and an intensity of 30 dB is equal to 30 backgrounds, the same value is equal to the loudness of a sound of 50 dB with a frequency of 100 Hz.

The measurement of loudness in sons shows more clearly how many times one sound is louder than another. Volume level at 40 phon

taken as 1 son, at 50 fon - for 2 sons, at 60 fon - for 4 sons, etc. Consequently, with an increase in volume by 10 vons, its value in sons doubles.

Features of the design and shape of the premises can lead to multiple reflections of sound from the surfaces of the floor, walls and ceiling, thereby lengthening the sound time. Such a phenomenon is called reverb. The possibility of reverberation is taken into account at the design stage of buildings and premises in which noisy machines and equipment are supposed to be installed.

NOISE CLASSIFICATION

According to the source of formation, noise is divided into:

mechanical - created by vibrations of a solid or liquid surface;

aero- and hydrodynamic - arises as a result of turbulence, respectively, of a gas or liquid medium;

electrodynamic - due to the action of electro- or magnetodynamic forces, an electric arc or a corona discharge.

By frequency distinguish low-frequency noise (up to 300 Hz), mid-frequency (from 300 to 800 Hz) and high-frequency (more than 800 Hz).

By the nature of the spectrum noise happens:

broadband - has a continuous spectrum with a width of more than one octave;

tonal - is characterized by an uneven distribution of sound energy with a predominance of most of it in the region of one or two octaves.

By time of action There are the following types of noise:

constant - changes during the work shift by no more than 5 dBA in one direction or another from the average level;

unstable - the level of its sound pressure during a shift can change by 5 dBA or more in any direction from the average level.

Intermittent noise, in turn, can be divided into:

oscillating - with a smooth change in sound level over time;

intermittent - characterized by a stepwise change in the sound pressure level by more than 5 dBA with a duration of intervals with a constant sound pressure level of at least 1 s;

impulse - consists of one or more sound signals, the duration of each of which is less than 1 s.

Noise classification is important to consider when developing measures to reduce its harmful effects on workers. For example, determining the source of noise and developing appropriate optimal countermeasures aimed at reducing the level of sound pressure generated by its generator contribute to increasing the efficiency of people and reducing their incidence.

The impact of noise on the body can manifest itself both in the form of a specific lesion of the hearing organ, and disturbances in many organs and systems. To date, quite convincing data have been accumulated that make it possible to judge the nature and features of the influence of the noise factor on the auditory function. The course of functional changes can have different stages. A short-term decrease in hearing acuity under the influence of noise with a rapid recovery of function after the cessation of the factor is considered as a manifestation of an adaptive protective response of the auditory organ. Adaptation to noise is considered to be cases of a temporary decrease in hearing by no more than 10 ... 15 dB with its restoration within 3 minutes after the cessation of the noise. Prolonged exposure to intense noise can lead to re-irritation of the cells of the sound analyzer and its fatigue, and then to a permanent decrease in hearing acuity.

The degree of occupational hearing loss depends on the work experience in noise conditions, the nature of the noise, the duration of its exposure during the working day, the intensity and spectrum. It has been established that the tiring and damaging effect of noise is proportional to its frequency. The most pronounced changes are observed at a frequency of 4000 Hz and a region close to it; subsequently, the increase in hearing thresholds extends to a wider spectrum.

It is shown that impulse noise (at equivalent power) acts more unfavorably than continuous noise. Features of its impact significantly depend on the excess of the impulse level over the root-mean-square level, which determines the noise background at the workplace.

In the development of occupational hearing loss, the total time of exposure to noise during the working day and the presence of pauses, as well as the total work experience, are important. The initial stages of professional hearing impairment are observed in workers with an experience of 5 years, expressed (hearing damage at all frequencies, impaired perception of whispered and colloquial speech) - over 10 years.

In addition to the effect of noise on the organ of hearing, its damaging effect on many organs and systems of the body, primarily on the central nervous system, in which functional changes occur before a violation of auditory sensitivity is diagnosed, has been established. With mental activity against the background of noise, there is a decrease in the pace of work, its quality and productivity. In persons exposed to noise, there are changes in the secretory and motor functions of the gastrointestinal tract, shifts in metabolic processes (disturbances in basic, vitamin, carbohydrate, protein, fat, salt metabolism).

Workers in noise occupations are characterized by a violation of the functional state of the cardiovascular system (hypertensive, less often hypotonic state, increased tone of peripheral vessels, changes in the ECG, etc.).

The presence of a symptom complex, which consists in the combination of occupational hearing loss (acoustic neuritis) with functional disorders of the central nervous, autonomic, cardiovascular and other systems in persons working in noise conditions, gives good reason to consider these health disorders as an occupational disease of the body in in general, and include this nosological form, noise disease, in the list of occupational diseases.

Occupational neuritis of the auditory nerve (noise disease) can occur more often in workers in various industries of mechanical engineering (including shipbuilding and aircraft construction), textile industry, mining, metallurgical industries, etc. Cases of the disease occur in people working on looms (weavers) , with chipping, riveting hammers (cutters, riveters), serving press and stamping equipment (blacksmiths), for test-minders and other professional groups exposed to intense noise for a long time. The probability of hearing damage depending on the length of service and exceeding the standard value for permanent jobs is shown in the graph (Fig. 6.2).

Sound level, dBA

Rice. 6.2. Probability of hearing damage: 1 – work experience 1 year;
2 – work experience of 5 years; 3 – work experience of 10 years; 4 - work experience
15 years; 5 – work experience 25 years

6.3. Hygienic regulation of noise

Noise regulation is carried out in accordance with GOST 12.1.003-83, which defines the main characteristics of industrial noise and the corresponding noise standards at workplaces. The standards comply with the recommendations of the Acoustics Technical Committee of the International Organization for Standardization and establish acceptable sound pressure levels in octave frequency bands, sound levels and equivalent sound levels in dBA at workplaces. The standards provide for a differentiated approach in accordance with the nature of production activities in noise conditions, i.e., the normalized sound pressure levels have different limiting spectra for different professional groups and premises where work of a different nature is carried out (mental work, neuro-emotional stress, mainly physical labor, etc.). The norms take into account the nature of the current noise (tonal, impulse, constant) and the time of exposure to the noise factor when calculating its equivalent levels for intermittent noise. In addition to the standard, sanitary norms also apply. In these documents, the characteristics of constant noise at workplaces are sound pressure levels in dB in octave bands with geometric mean frequencies: 31.5; 63; 125; 250; 500; 1000; 2000; 4000; 8000 Hz.

For an approximate assessment (for example, when checking by supervisory authorities, identifying the need to apply noise suppression measures, etc.), it is allowed to take the sound level in dBA measured on the “slow” time characteristic of the sound level meter, determined by the formula

where R A is the root-mean-square value of the sound pressure, taking into account the correction according to the sensitivity curve "A" of the sound level meter, Pa.

A characteristic of intermittent noise at workplaces is the equivalent (in terms of energy) sound level in dBA and, according to CH 2.2.4 / 2.1.8-562-96, the maximum sound levels L A max , dBA

Evaluation of non-permanent noise for compliance with permissible levels should be carried out simultaneously on the equivalent and maximum sound levels. Exceeding one of the indicators should be considered as non-compliance with sanitary standards.

The main normalized parameters for broadband noise are given in Table. 6.3 (extract from GOST 12.1.003-83).

In sanitary standards, the maximum permissible sound levels and equivalent sound levels at workplaces are given taking into account the intensity and severity of labor activity and are presented in Table. 6.4.

A quantitative assessment of the severity and intensity of the labor process is recommended to be carried out in accordance with the guide R 2.2.2006-05 “Occupational health. Guidelines for the hygienic assessment of factors of the working environment and the labor process. Criteria and classification of working conditions.

Noise is a random combination of sounds of different heights and loudness, causing an unpleasant subjective sensation and objective changes in organs and systems.

Noise consists of individual sounds and has a physical characteristic. The wave propagation of sound is characterized by frequency (expressed in hertz) and strength, or intensity, i.e., the amount of energy carried by a sound wave for 1 s through 1 cm2 of a surface perpendicular to the direction of sound propagation. The strength of sound is measured in energy units, most often in ergs per second per 1 cm2. Erg is equal to a force of 1 dyne, i.e., the force imparted to a mass, weighing 1 g, an acceleration of 1 cm2 / s.

The unit of sound pressure is the bar, which corresponds to a force of 1 dyne per 1 cm2 of surface and equal to 1/1,000,000 of atmospheric pressure. Speech at normal volume creates a pressure of 1 bar.

The smallest amount of sound that a person perceives is called the hearing threshold for that sound.

The hearing thresholds for sounds with different frequencies are not the same. The lowest thresholds have sounds with a frequency of 500 to 4000 Hz. Outside this range, hearing thresholds increase, indicating a decrease in sensitivity.

An increase in the physical strength of the sound is subjectively perceived as an increase in volume, but this occurs up to a certain limit, above which painful pressure is felt in the ears - the threshold of pain, or the threshold of touch. With a gradual increase in the energy of sound from the threshold of audibility to the threshold of pain, features of auditory perception are revealed: the sensation of sound volume increases not in proportion to the growth of its sound energy, but much more slowly.

To quantify sound energy, a special logarithmic scale of sound intensity levels in bels or decibels has been proposed. In this scale, zero, or the initial level, is conventionally taken as a force (10-9 erg/cm2 h h sec or 2 h 10-5 W/cm2/s), approximately equal to the threshold of audibility of sound with a frequency of 1000 Hz, which is accepted in acoustics for standard sound. Each step of such a scale, called bel, corresponds to a change in sound strength by 10 times.

If we express in white the range of sound intensity with a frequency of 1000 Hz from the threshold of hearing to the pain threshold, then the entire range on a logarithmic scale will be 14 Bel.

According to the spectral composition, all noise is divided into 3 classes.

Class 1. Low-frequency (noises of low-speed non-impact units, noise penetrating through soundproof barriers).

Class 2. Medium-frequency noise (noises of most machines, machine tools and units of non-impact action).

Class 3. High-frequency noises (ringing, hissing, whistling noises typical for impact units, air and gas flows, units operating at high speeds).

Hygienic characteristic noise. Noise a random combination of sounds of different pitches and loudness is called ...

Hygienic characteristic noise(continuation). Distinguish noises: 1) broadband with a continuous spectrum of more than 1 octave

Hygienic characteristic noise. Noise is called a chaotic combination of sounds of different heights and loudness, causing an unpleasant ... more ».

Hygienic characteristic noise(continuation). Distinguish noises: 1) broadband with a continuous spectrum of more than 1 octave; 2) tonal.

By temporary characteristics noises there are constant, intermittent, impulsive, oscillating. in
For practical purposes, it is convenient characteristic sound, measured in decibels.

Characteristic physical factors of the environment.
sudden changes in the level of air humidity - increased dust and gas contamination - increased level noise, infrasound ...