Mu 1844 78 guidelines. Methodological guidelines for measuring and hygienic assessment of noise in the workplace. Correction in dB

MINISTRY OF HEALTH OF THE USSR

INSTRUCTIONS
for measurements
and hygienic assessment of noise
in the workplace

№ 1844-78

Moscow 1978

Methodical instructions the Orders of the Red Banner of Labor were developed by the Research Institute of Occupational Hygiene and Occupational Diseases of the Academy of Medical Sciences of the USSR and the SES of Moscow to unify the measurement of noise at workplaces for the purpose of their hygienic assessment and comparison of the results with GOST 12.1.003 -76 "Occupational Health and Safety Standards. Noise. General Safety Requirements ".

The instructions contain the basic definitions and units of measurement of acoustic quantities, information about noise measuring equipment, as well as methods and conditions for noise measurement, processing, design and hygienic evaluation of the results.

The guidelines are intended to serve as a guide for the Sanitary Epidemiological Service.

INSTRUCTIONS
MEASUREMENT
AND HYGIENIC ASSESSMENT OF NOISES
IN THE WORKPLACE

1. Purpose and scope

1.1. These guidelines are guidelines for measuring noise at workplaces for their hygienic assessment in accordance with current hygienic standards and are developed in the development of GOST 12.1.003-76 "Occupational safety standards. Noise. General safety requirements "and GOST 20445-75" Buildings in the structures of industrial enterprises. Method for measuring noise in workplaces ”.

1.2. The instructions apply to the following types of measurements:

Assessment of noise at workplaces in premises and on the territory of enterprises,

Noise assessment of machinery and equipment at their workplaces at typical operating levels,

Determination of the effectiveness of measures to reduce noise in the workplace, as well as identify sources of noise.

1.3. These guidelines do not apply to the measurement of the noise characteristics of machinery and equipment; these measurements must be carried out in accordance with GOST 8.055-73 "GSI. Machines. Measurement procedure for determining noise characteristics" or standards for specific types of machines and equipment.

1.4. The provisions given in the instructions must be observed by all institutions of the Sanitary and Epidemiological Service when exercising noise control at workplaces in various sectors of the national economy.

2. Definitions and units of measurement of basic acoustic quantities

2.5. Sound vibrations in the air cause alternating increases and decreases in pressure relative to atmospheric pressure; the difference between them is called sound pressure. Since sound pressures change over time, they are estimated by the rms value with averaging depending on the time characteristic of the sound level meter.

Sound pressure is measured in newtons per square meter. This unit in the international system of units is called pascal (I Pa = I N / m 2).

2.6. The organ of hearing distinguishes not the difference, but the frequency of changes in sound pressure, therefore, the intensity of sound is usually assessed not by the absolute value of sound pressure, but by its level, i.e. the ratio of the generated pressure to the pressure taken as a unit of comparison.

2.7. In the range from the hearing threshold to the pain threshold, the ratio of sound pressures changes by a factor of millions, therefore, to reduce the measurement scale, sound pressures are expressed through their levels in logarithmic units - decibels (dB) and determined by the formula:

L - sound pressure level, dB,

r- measured root-mean-square value of sound pressure, Pa.

r 0 =2× 10 -5 Pa - the threshold value of the root-mean-square sound pressure (approximately corresponding to the threshold of audibility of a tone of frequency 1000 Hz).

Zero decibel corresponds to sound pressure 2 × 10 -5 Pa.

2.8. A change in the objective perception of noise differs from a change in its sound pressure level: a change in the sound pressure level by 5, 10, 15 and 20 dB corresponds to a change in its loudness by 1.4; 2; 3 and 4 times.

№ № p / p	Sound level meter	Octave Filters	Manufacturer
	ISHV - 1	(built-in)	Zd "Vibropribor" (Taganrog)
	PSI-202	OF-101
	2203, 2204, 2209, 2218	1613	firm "Brüel & Kjr" (Denmark)

Note: to measure the sound level in dBA in accordance with the noise meter Shum-1 can be used.

3.2. The use of auxiliary devices is allowed: level recorders, tape recorders, statistical distribution analyzers or equivalent level meters.

3.3. A level recorder is used to record measured sound pressure levels in octave bands or the level of a noise gram - the change in sound level over time. The dynamic range of the registered levels is 25, 50 or 75 dB, depending on the used potentiometers supplied with the device.

3.4. A tape recorder is used to record noise for subsequent frequency analysis in the laboratory or to determine the equivalent level. It is allowed to use any tape recorder that has a frequency response of the "record-playback" end-to-end electrical path in the range of 50-10000 Hz with an unevenness of not more than 3 dB and a dynamic range of not less than 40 dB.

3.6. To measure the equivalent noise level, the following can be used: a noise level analyzer type 4426, an integrating sound level meter 2218 from Brüel & Kjерr (Denmark).

Technical characteristics of sound level meters

Characteristic	Device type
Characteristic	ISHV-1	PSI-202	2209
1. Range of measured levels, dB	30-130	30-140	15-140
2. Frequency response, Hz	20-11200	20-12500	2-40000
3. Correction of the frequency response	A, B, C, Lin "slowly"	A, B, C, Lin "slowly"	A, B, C, Lin "slowly"
4. Time constants	"quickly"	"quickly", "pulse"	"quickly", "pulse"
Power supply of the device	elements 373 ´ 8 pcs., Network 220 V 50 Hz	elements 373 ´ 4 pcs., Network 220 V 50 Hz	elements 373 ´ 3 pcs.
6. Weight, kg
7. Type of octave filters and their frequency range, Hz
8. Manufacturing company	plant "Vibropribor"	RFT, GDR (set No. 12)	Brüel & Kjr, Denmark (set No. 3507)

3.7. Noise measuring paths (sound level meter, octave filter and auxiliary devices) must (according to GOST 8.002-71) annually undergo state verification in the organizations of the USSR State Standard or other organizations that have the right to perform such verification. Devices of the noise measuring path are presented for verification in good condition, complete set, with new batteries.

Average geometric and cutoff frequencies of octave bands

Average geometric frequencies, Hz	Cutoff frequencies, Hz
Average geometric frequencies, Hz	Lower	Upper
31,5	22,4




1000		1400
2000	1400	2800
4000	2800	5600
8000	5600	11200

3.8. Maintenance of noise measuring instruments must be carried out by appropriately trained personnel. Before starting work, the descriptions and instructions for the operation of devices, safety rules are studied, the procedure for working with the devices is mastered, as well as measurement methods in the rules for processing results.

3.9. Measuring and auxiliary devices during operation and transportation must not be subjected to shock and vibration, excessive cooling or heating, etc. During operation, the devices must be protected from dust, splashing water, oils, corrosive liquids, vapors and gases, etc.

3.10. Noise measuring devices should be stored in dry, heated rooms, taking into account the special conditions specified in the factory instructions.

4. Measurement points

If the noise level is only 4 dB or less below the machine noise level, or the noise level fluctuates greatly over time, then measurements are not allowed.

4.5. For approximate identification of noise sources in individual machines, a sequential measurement of sound levels in dBA is performed for individual machine nodes at a distance of 10 cm from them. After identifying the most noisy nodes of the machine, the noise spectra are measured for them.

4.6. Measurement of noise to check the effectiveness of measures to reduce it is carried out in accordance with the instructions of cl. -.

5. Carrying out measurements

5.1. Sound level meters and auxiliary devices before and after measurements must be calibrated in accordance with the manufacturer's instructions for the devices.

5.2. When making noise measurements, the measures specified in the manufacturer's instructions for the devices should be taken to eliminate the influence external factors distorting instrument readings (vibration, magnetic and electric fields, etc.).

5.3. The microphone should be positioned 1.5 m above the floor (platform) or at head level when seated or in other positions. The microphone should be directed towards the source of the noise and at least 0.5 m away from the operator taking measurements.

5.4. When measuring noise in air currents with a speed of more than 1 m / s, in order to avoid distortion of readings, the microphone should be protected with a windscreen that improves its flow. When measuring aerodynamic noise, the microphone should be positioned at an angle of 45 ° to the jet axis.

5.5. The required number of measuring points and their location are determined according to the instructions. When measured in accordance with p. -. at least 2/3 of the installed equipment should work in a characteristic mode, while ventilation and other commonly used devices that are sources of noise should be turned on.

5.6. For a hygienic assessment of noise, the characteristics must be measured in accordance with. In this case, intermittent noises are assessed by equivalent sound levels in dBA, and when they exceed the permissible values (when evaluating new machines and equipment or research work, it is recommended to determine the equivalent levels of lock pressure in octave frequency bands.

5.7. At the beginning of the measurement, the sound level meter should be turned on for correction "A" and the characteristic "slow". When the instrument needle oscillates up to 5 dBA, the noise should be considered constant and the reading should be taken according to its average position. When the arrow oscillates more than 5 dBA, the noise should be considered unstable, while it can be fluctuating in time, intermittent or impulsive (see). For impulse noises (perceived by ear as single blows against a noise background), an additional measurement should be made according to the "impulse" characteristic with the reading of the maximum arrow reading. With the difference in the sound level readings in dBA in the "impulse" and "slow" more than 10 dBA noise should be considered impulsive.

An example of indication of the counting results: sound level 84 dBA "slow" (or 84 dBAS), sound level 92 dBA "impulse" (or 92 dBAI).

5.8. Measurement of sound pressure levels in octave bands (octave sound pressure levels) should be carried out by a sound level meter with octave band-pass filters connected to it, with the switch for the type of sound level meter should be in the "filters" (or "external filters") position. For all types of noises, the reading is made according to the average position of the arrow oscillations on the "slow" characteristic of the sound level meter.

An example of indication of the reading results: octave sound pressure level of 78 dB in an octave of 2000 Hz.

Note:

In the absence of octave filters for a rough estimate of the nature of the spectrum, measurements are made according to the corrections "A" and "C" (or "Lin") of the sound level meter. If the difference in readings in dBC and dBA is more than 5 dB, the noise should be considered low-frequency, and if the difference or equality of readings is less, it should be considered high-frequency.

5.9. The tone of the noise is determined by ear: the tonal nature of the noise in disputable cases should be established by measuring in one-third-octave frequency bands by the excess of the level in one band over the adjacent ones by at least 10 dB.

5.10. For constant impulse noise - measurements should be made at least three times at each point with averaging over.

5.11. For intermittent noises (intermittent and fluctuating), readings of sound levels in dBA (or octave sound pressure levels in cases of exceeding the norm, when evaluating new equipment or research works) with an interval of 5-6 seconds, followed by the calculation of the equivalent level according to the method of GOST 20445-75 or according to.

It is allowed to determine the operating time of the machine or the time of action of different noise levels according to the timing or technical documentation with the subsequent determination of the equivalent level according to.

5.12. For a visual graphical representation of the distribution of noise levels in rooms (or areas), it is recommended to draw up noise maps. To do this, a grid is applied to the floor plan (or territory) with a distance between its lines of 6 or 12 m for rooms and no more than 50 m for territories. Noise measurement points are selected at the nodes of this grid. The results of measurements of sound levels at these points are plotted on the plan of the room or territory and points with equal levels are connected by smooth lines, while lines of equal sound levels are drawn at intervals of 5 and 10 dBA.

6 Expression of results

6.1. The measured octave sound pressure levels, due to errors introduced by the measuring paths and the influence of noise interference, need to be corrected, which is carried out during the processing of the measurement results. Amendments are made to:

Unevenness of the frequency response of the noise measuring path,

The presence of noise interference (when evaluating the noise of a single machine).

6.1.1. Corrections for the unevenness of the frequency response of the noise measuring path are determined based on the results of its verification in the organizations of the USSR State Standard: they are an integral part of the documentation for this noise measuring path and must be algebraically (taking into account the sign) summed up with the results of measurements of octave sound pressure levels.

, dB ()

DB ()

where are the measured levels, dB,

n- number of measurements.

6.3. For intermittent noises, taking into account the timing data, equivalent levels are calculated according to.

After the calculation of the equivalent level, no correction is made for the duration of the noise exposure, as long as the calculated equivalent level already takes into account the duration of the noise per work shift.

Annex 1

Determination of the average value of the levels

To determine the average value of the levels according to p . 6.2. the measured levels must be summed using. and subtract from this sum 10lgn, determined by; in this case, item 6.2 takes the form:

(A.1.1)

The summation of the measured levels is performed in pairs sequentially as follows. By the difference between the two levels L 1 and L 2, the additive is determined D L, which is added to the higher level L 1, resulting in the level L 1 2 =. The L 1 2 level is added in the same way to the L 3 level to obtain the L 1 2 3 level, and so on. The final result L c mm is rounded to the nearest whole decibel.

The difference between the terms of the levels L 1 - L 3, dB (L 1 ³ L 3)
Additive DL added to the larger of the L levels 1, dB 3	4	5	6	8	10	20	30	50	100
DB

Example. The average value for the measured sound levels of 84, 90 and 92 dBA is to be determined.

Add the first two levels 84 and 90 dB; their difference of 6 dB corresponds to an addition equal to 1 dB, i.e. their sum is 90 + 1 = 91 dB. Then add the resulting 91 dB level with the remaining 92 dB level; their difference of 1 dB corresponds to an addition of 2.5 dB, i.e. the total level is 92 + 2.5 = 94.5 dB, or we get 95 dB rounded.

This calculation is made for sound levels or sound pressure levels in each octave band.

Example 1. Noise levels per 8 hour work shift were 80, 86 and 94 dB for 5, 2 and 1 hour, respectively. These times correspond to corrections according to the table equal to -2, -6, -9 dB. Adding them to the noise levels, we get 78, 80, 85 dB. Now using. Appendix 1, we add these levels in pairs: the sum of the first and second gives 82 dB, and their sum with the third is 86.7 dB. Rounding off, the final equivalent noise level is 87 dB. Thus, exposure to this noise is equivalent to exposure to a constant 87 dB for 8 hours.

Example 2. Intermittent noise of 119 dBA acted during a 6 hour shift for a total of 45 minutes. (i.e. 11% shift), the background noise level in pauses (i.e. 89% shift) was 73 dBA.

By . the corrections are -9 and -0.6 dB: adding them with the corresponding noise levels, we get 110 and 72.4 dB and since the second level is much less than the first (see Appendix 1), it can be neglected. Finally, we get an equivalent noise level per shift of 110 dBA, which exceeds the permissible level of 85 dBA by 25 dB.

MINISTRY OF HEALTH OF THE USSR

INSTRUCTIONS
for measurements
and hygienic assessment of noise
in the workplace

№ 1844-78

Moscow 1978

Methodological guidelines were developed by the Order of the Red Banner of Labor by the Scientific Research Institute of Occupational Hygiene and Occupational Diseases of the USSR Academy of Medical Sciences and the SES of Moscow to unify the measurement of noise in workplaces for the purpose of their hygienic assessment and comparison of the results with GOST 12.1.003-76 "Occupational Safety Standards System. Noise. General Safety Requirements" ...

The instructions provide basic definitions and units for measuring acoustic quantities, information on noise measuring equipment, as well as methods and conditions for noise measurement, processing, and hygienic evaluation of the results.

The guidelines are intended to serve as a guide for the Sanepid service.

INSTRUCTIONS
MEASUREMENT
AND HYGIENIC ASSESSMENT OF NOISES
IN THE WORKPLACE

1. Purpose and scope

1.1 These instructions are guidelines for the measurement of noise in the workplace for their hygienic assessment in accordance with the current hygienic standards and have been developed as a follow-up.GOST 12.1.003-76 "SSBT. Noise. General safety requirements "and GOST 20445-75" Buildings in the structures of industrial enterprises. Method for measuring noise in the workplace. "

1.2. The instructions apply to the following types of measurements:

Assessment of the noise in workplaces in premises and on the territory of enterprises,

Noise assessment of machines and equipment at their workplaces at typical operating levels,

Determination of the effectiveness of measures to reduce noise in the workplace, as well as the identification of sources of noise.

1.3. These guidelines do not apply to the measurement of machine noise characteristics; these measurements must be carried out in accordance with GOST 8.055-73 "GSI. Machines. Measurement procedure for determining noise characteristics" or standards for machines and equipment of specific types.

1.4. The provisions specified in the instructions must be observed by all sanitary and epidemiological service institutions when exercising noise control at workplaces in various sectors of the national economy.

2. Definitions and units of measurement of basic acoustic quantities

Sound pressure is measured in newtons per square meter. This unit in the international system of units is called pascal (I Pa = I N / m 2).

2.6. The organ of hearing is distinguished not by the difference, but by the multiplicity of changes in sound pressure, therefore, the intensity of sound is usually assessed not by the absolute value of sound pressure, but by its level, that is, by the ratio of the generated pressure to the pressure taken as a unit of comparison.

2.7. In the range from the hearing threshold to the pain threshold, the ratio of sound pressures changes millions of times, therefore, to reduce the measurement scale, sound pressures are expressed through their levels in logarithmic units - decibels (dB) and determined by the formula:

L - sound pressure level, dB,

r- measured root-mean-square value of sound d pressure, Pa.

r 0 =2× 10 -5 Pa - the threshold value of the root-mean-square sound pressure (approximately corresponding to the threshold of audibility of a tone of frequency 1000 Hz).

Zero decibels corresponds to sound pressure 2 × 10 -5 Pa.

№ № p / p	Sound level meter	Octave Filters	Manufacturer
	ISHV - 1	(built-in)	plant "Vibropribor" (Taganrog)
	PSI -202	OF -101
	2203, 2204, 2209, 2218	1613	firm "Brüel & Kjr" (Denmark)

Note:to measure the sound level in dBA in accordance with the noise meter Shum-1 can be used.

3.2. It is allowed to use auxiliary devices: level recorders, tape recorders, statistical distribution analyzers or equivalent level meters.

3.3. A level recorder is used to record measured sound pressure levels in the frequency bands or the level of a noise gram - the change in sound level in time. The dynamic range of the registered levels is 25, 50 or 75 dB, depending on the potentiometers used supplied with the device.

3.4 A tape recorder is used to record noise for subsequent frequency analysis under laboratory conditions or to determine an equivalent level. It is allowed to use any tape recorder that has a frequency response of the "record-playback" loop-through electrical path in the range of 50-10000Hz with an unevenness of not more than 3 dB and a dynamic range of not less than 40 dB.

3.6. To measure the equivalent noise level, the following can be used: a noise level analyzer type 4426, an integrating sound level meter 2218 from Brüel & Kjr (Denmark).

Technical characteristics of sound level meters

Characteristic	Device type
Characteristic	ISHV-1	PSI-202	2209
1. Range of measured levels, dB	30-130	30-140	15-140
2. Frequency response, Hz	20-11200	20-12500	2-40000
3. Correction of the frequency response	A, B, C, Lin "slowly"	A, B, C, Lin "slowly"	A, B, C, Lin "slowly"
4. Time constants	"quickly"	"quickly", "pulse"	"quickly", "pulse"
Power supply of the device	elements 373 ´ 8 pcs., Network 220 V 50 Hz	elements 373 ´ 4 pcs., Network 220 V 50 Hz	elements 373 ´ 3 pcs.
6. Weight, kg
7. Type of octave filters and their frequency range, Hz
8. Manufacturing company	plant "Vibropribor"	RFT, GDR (set No. 12)	Brüel & Kjr, Denmark (set No. 3507)

3.7. Noise measuring paths (sound level meter, octave filter and auxiliary devices) must (according to GOST 8.002-71) undergo state verification annually Kuv organizations of the State Standard of the USSR or other organizations that have the right to carry out such verification. Devices of the noise measuring path are presented for verification in good condition, complete set, with new batteries.

Average geometric and cutoff frequencies of octave bands

Average geometric frequencies, Hz	Cutoff frequencies, Hz
Average geometric frequencies, Hz	Lower	Upper
31,5	22,4




1000		1400
2000	1400	2800
4000	2800	5600
8000	5600	11200

3.8. Maintenance of noise-measuring devices should be carried out by appropriately trained personnel. Before starting work, the descriptions and operating instructions for the devices, safety rules are studied, the procedure for working with the devices is mastered, as well as measurement methods in the rules for processing the results.

3.9. Measuring and auxiliary devices during operation and transportation should not be subject to shock and vibration, excessive cooling or heating, etc. During operation, the devices should be protected from dust, splashing water, oils, corrosive liquids, vapors and gases, etc.

3.10. Noise measuring devices should be stored in dry heated rooms, taking into account the special conditions specified by the factory instructions.

4. Measurement points

If the noise level is only 4 dB or less below the machine noise level, or the noise level fluctuates strongly over time, then measurements are not allowed.

4.5. For approximate identification of noise sources in individual machines, a sequential measurement of sound levels in dBA is performed for individual machine units at a distance of 10 cm from them. After identifying the most noisy nodes of the machine, the noise spectra are measured for them.

4.6. Measurement of noise to check the effectiveness of measures to reduce it is carried out in accordance with the instructions of p. -.

5. Carrying out measurements

5.1. Sound level meters and auxiliary devices before and after measurements must be calibrated in accordance with the manufacturer's instructions for the devices.

5.2. When making noise measurements, the measures specified in the factory instructions for the devices must be taken to eliminate the influence of external factors that distort the readings of the devices (vibration, magnetic and electric fields, etc.).

5.3. The microphone should be positioned 1.5 m from the floor (platform) or head level when seated or in other positions. The microphone should be directed towards the source of the noise and at least 0.5 m away from the measuring device.

5.5 The required number of measuring points and their location are determined in accordance with the instructions. When measured in accordance with p. -. at least 2/3 of the installed equipment must operate in a characteristic mode, while ventilation and other commonly used devices that are sources of noise must be turned on.

5.7. At the beginning of the measurement, the sound level meter should be turned on for correction "A" and the characteristic "slow". When the instrument needle oscillates up to 5 dBA, the noise should be considered constant and the reading should be taken according to its average position. When the arrow vibrates more than 5 dBA, the noise should be considered unstable, while it can be fluctuating in time, intermittent or impulsive (see). For impulse noises (perceived by ear as single blows against a noise background), an additional measurement should be made according to the "impulse" characteristic with the reading of the maximum indication of the arrow. When the difference in sound level readings in dBA in the "impulse" and "Slowly" more than 10 dBA noise should be considered impulsive.

An example of indication of counting results: sound level 84 dBA "slow" (or 84 dBA), sound level 92 dBA "impulse" (or 92 dBAI).

5.8. Measurement of sound pressure levels in octave bands (octave sound pressure levels) should be performed by a sound level meter with octave band-pass filters connected to it, while the sound level meter switch should be in the "filters" (or "external filters") position. For all types of noises, the reading is made by the average position of the arrow oscillations on the "slow" characteristic of the sound level meter.

An example of the indication of the counting results: octave sound pressure level 78 dB at 2000 Hz.

Note:

5.9. The tone of the noise is determined by ear: the tonal nature of the noise in disputable cases should be established by measuring the third-octave frequency bands by the excess of the level in one band over the adjacent one by less than 10 dB.

5.10. For constant impulse noise, measurements should be made at least three times at each point with averaging over.

5.11. For intermittent noises (intermittent and fluctuating), readings of sound levels in dBA (or octave sound pressure levels in cases of exceeding the norm, when evaluating new machinery or research works) should be made with an interval of 5-6 seconds, followed by calculation of the equivalent level according to the method of GOST 20445-75 or according to ...

It is allowed to determine the operating time of the machine or the duration of different noise levels according to the timing or technical documentation, followed by the determination of the equivalent level according to.

5.12. For a visual graphical representation of the distribution of noise levels in rooms (or areas), it is recommended to draw up noise maps. To do this, a grid with a distance between its lines of 6 or 12 m for premises and no more 50 m for territories. Noise measurement points are selected at the nodes of this grid. The results of measurements of sound levels at these points are plotted on the plan of the room or territory and points with equal levels are connected by smooth lines, while lines of equal sound levels are drawn at intervals of 5 and 10 dBA.

6 Expression of results

6.1. The measured octave sound pressure levels, due to errors introduced by the measuring paths and the influence of noise interference, need to be corrected, which is made during the processing of the measurement results. Amendments are made to:

Unevenness of the frequency response of the noise measuring path,

The presence of noise interference (when assessing the noise of a single machine).

6.1.1. Corrections for the unevenness of the frequency response of the noise measuring path are determined based on the results of its calibration in the organizations of the USSR State Standard: they are an integral part of the documentation for this noise measuring path and should be algebraically (taking into account the sign) summed up with the results of measurements of the octave sound pressure levels.

, dB ()

dB ()

where are the measured levels, dB,

n- number of measurements.

6.3. For intermittent noises, taking into account the timing data, equivalent levels are calculated according to.

After the calculation of the equivalent level, no correction is made for the duration of the noise exposure, since the calculated equivalent level already takes into account the duration of the noise per work shift.

Annex 1

Determination of the average value of the levels

To determine the average value of the levels according to p . 6.2. the measured levels must be summed using. and subtract from this sum 10lgn, determined by, in this case, item 6.2 takes the form:

(A.1.1)

Summation of measured levels produced in pairs in succession in the following manner. By the difference of two levels L 1 and L 2 by define additiveD L which is added to the higher level L 1 , as a result of which the level L 1 2 =. Level L 1 2 summed up in the same way with the level L 3 and get a level L 1 2 3 etc. Final Result L c mind round to whole decibels.

Difference of terms of levels L 1 - L 3 , dB ( L 1 ³ L 3 )
AdditiveD Ladded to the larger of the levels L 1 , dB

At equal terms of levels, i.e., at L 1 = L 2 = ¼ = L n = L in the formula (A.1.2.) Can be determined by the formula:

Example. The average value for the measured sound levels of 84, 90 and 92dBA should be determined.

Add the first two levels 84 and 90 dB; their difference of 6 dB corresponds to an addition equal to 1 dB, i.e. their sum is 90 + 1 = 91 dB. Then add the resulting 91 dB level with the remaining 92 dB level; their difference of 1 dB corresponds to an addition of 2.5 dB, that is, the total level is 92 + 2.5 = 94.5 dB, or we get 95 dB rounded.

This calculation is made for sound levels or sound pressure levels in each octave band.

Example 1. Noise levels for an 8-hour work shift were 80, 86 and 94 dB for 5, 2 and 1 hours, respectively. Corrections according to the table correspond to these times, equal to ny -2, -6, -9 dB. Adding them with the noise levels, we get 78, 80, 85 dB. Now using. 1, we add these levels in pairs: the sum of the first and second gives 82 dB, and their sum with the third is 86.7 dB. Rounding off, we get the final value of the equivalent noise level of 87 dB. Thus, the effect of this noise is equivalent to the effect of noise with a constant level of 87 dB within 8 hours.

Example 2.Intermittent noise of 119 dBA acted during a 6 hour shift for a total of 45 minutes. (i.e. 11% shift), the background noise level in pauses (i.e. 89% shift) was 73 dBA.

By . the corrections are -9 and -0.6 dB: adding them with the corresponding noise levels, we get 110 and 72.4 dB, and since the second level is much less than the first (see Appendix 1), it can be neglected. Finally, we get an equivalent noise level per shift of 110 dBA, which exceeds the permissible level of 85 dBA by 25 dB.

ABOUT THE GENERAL PLANNING PROJECT OF NALCHIK

In accordance with the decree of the Council of People's Commissars of the USSR dated February 4, 1936, No. 174 p. 1 "On the construction and improvement of the city of Nalchik, the Kabardino-Balkarian Autonomous Region of the North Caucasian Territory", the Council of People's Commissars of the RSFSR decides:

To approve the following main provisions of the general planning project for the city of Nalchik.

1. Establish, a) the estimated population of the city is 100 thousand people; b) the design capacity of the resort is 7250 people.

2. The total composition of land in Nalchik should be set at 4536 hectares, within the boundaries: from the east - the Nalchik River with the inclusion of Mount Kizilovka, from the south - a tributary of the Nalchik River (Floridin Clay Region), from the west along a line parallel to the Kizilovka River. Sukhaya Shalushka at a distance of 500 meters to the west from it, from the north - the design right-of-way railroad including the territory of the hippodrome.

Outside the indicated boundaries of the urban lands, to provide in the northern direction beyond the Sukhaya Shalushka River a territorial reserve for the placement of an airfield in the amount of 130 hectares.

From general composition land of the city of Nalchik to assign 2692 hectares to the resort, establishing an internal border between the city and the resort on the southern side of the PKK. and O., Central Square, on the southern side of the projected residential quarters (the area of the hospital and the House of Soviets) with access to Baksanskaya Street and further along Baksanskaya Street to the Sukhaya Shalushka River.

ConsultantPlus: note.

Paragraph numbering is given in accordance with the official text of the document.

4. Location area new industry to be installed in a northern direction from residential areas of the city on adjacent areas with existing industrial enterprises(Meat processing plant, mill, etc.).

5. Housing construction the city and the related construction of cultural and welfare institutions, as well as the placement of new special educational institutions to carry out on the territory within the boundaries: the Nalchik river - Baksanskaya street (with the adjacent blocks on the southern side); the existing railway line to the ash-pumice mine - the inner border of the industrial region; the project railway right-of-way.

6. The location of the new city hospital should be foreseen to the west of the residential area within 1 kilometer.

7. The territory of P.K. and O. to establish in the amount of about 90 hectares to the south-west of the residential area within the boundaries: the Nalchik River - the central square - the continuation of Stepnaya Street.

8. The average population density should be 250 - 300 people per 1 hectare of a residential area, with the main type of residential construction - 3 floors. On the main city highways and squares, allow building of a higher number of storeys (4 - 6 floors) with the permission of the NKKH of the RSFSR.

9. The main thoroughfares of the city of Nalchik are: Stepnaya, Kabardinskaya, Karataevskaya, Baksanskaya, Pervomayskaya streets with their continuation in new territories, of which Stepnaya street is the main city thoroughfare.

10. Establish the following distribution of resort areas:

a) the area of rest houses - within the boundaries: the existing highway to Dolinskoye - an extension of Stepnaya Street - Park K. and O .;

b) the area of sanatoriums and resort hotels on the 2nd and 3rd above-floodplain terraces in the southern direction from the area of rest houses along the highway to the bath building on the White River;

c) Pioneer camp area - at the head of the Sukhaya Shalushka river;

d) resort dachas in the existing forest park (adjacent to the sanatorium area) and on the left bank of the Sukhaya Shalushka River - (adjacent to the Pioneer camp);

e) district tourist bases- adjacent to the area of rest houses, to the west of the continuation of Stepnaya Street;

f) the resort park as part of the "Grushovnik" territory, part of the "Gardens" and the above-floodplain terrace, along the Nalchik River, adjacent to the areas of the recreation centers and a sanatorium.

11. The spa center, including the spa hall, should be located on the eastern border of the spa park, Hrushovnik (between the areas of the recreation centers and the sanatorium).

12. Consider the main resort highways: the continuation of Stepnaya Street and the existing highway to the bathrooms on the White River.

13. To consider it expedient to move the railway and the railway station in the future 2 kilometers to the north-east from their existing location, with the construction of two overpasses on the Baksanskoye and Prokhladnenskoye highways.

MINISTRY OF HEALTH OF THE USSR

INSTRUCTIONS
for measurements
and hygienic assessment of noise
in the workplace

№ 1844-78

Moscow 1978

Methodological guidelines were developed by the Order of the Red Banner of Labor by the Research Institute of Occupational Hygiene and Occupational Diseases of the USSR Academy of Medical Sciences and the SES of Moscow to unify the measurement of noise at workplaces for the purpose of their hygienic assessment and comparison of the results with GOST 12.1.003 -76 "Occupational Health and Safety Standards. Noise. General safety requirements".

The guidelines are intended to serve as a guide for the Sanitary Epidemiological Service.

INSTRUCTIONS
MEASUREMENT
AND HYGIENIC ASSESSMENT OF NOISES
IN THE WORKPLACE

1. Purpose and scope

1.2. The instructions apply to the following types of measurements:

Assessment of noise at workplaces in premises and on the territory of enterprises,

Noise assessment of machinery and equipment at their workplaces at typical operating levels,

Determination of the effectiveness of measures to reduce noise in the workplace, as well as identify sources of noise.

2. Definitions and units of measurement of basic acoustic quantities

2.1. Noise refers to any unwanted sound or a collection of such sounds. In the hygienic assessment of noises in the workplace, one should bear in mind their possible interfering, harmful or traumatic effect on the human body.

2.2. Sound is the vibration of air particles perceived by the hearing organ.

2.3. The sound current is estimated by the number of vibrations per second, that is, by its frequency. Oscillation frequency is measured in hertz (Hz), one hertz is one oscillation per second. The human ear perceives sounds with frequencies ranging from 20 to 20,000 Hz.

2.4. For the hygienic assessment of noise, of practical interest is the audio frequency range from 45 to 11000 Hz, including eight octave bands with geometric mean frequencies of 63, 125, 250, 500, 1000, 2000, 4000 and 8000 Hz (Table 3).

Sound pressure is measured in newtons per square meter. This unit in the international system of units is called pascal (I Pa = I N / m 2).

L - sound pressure level, dB,

r is the measured root-mean-square value of the sound pressure, Pa.

r 0 = 2 × 10 -5 Pa - the threshold value of the root-mean-square sound pressure (approximately corresponding to the threshold of audibility of a tone of frequency 1000 Hz).

Zero decibels corresponds to a sound pressure of 2 × 10 -5 Pa.

2.9. For hygienic assessment of noise, use:

Noise spectrum (sound pressure levels in dB in octave bands) for comparison with hygiene standards and the development of noise reduction measures,

For an approximate assessment of the noise situation, it is allowed to use the sound level in dB A, measured according to the characteristic "A" of the sound level meter (approximately corresponding to the frequency characteristic of human hearing).

2.10. Noises contain sounds of different frequencies and differ among themselves by the distribution of levels for individual frequencies and the nature of the change in the overall level over time.

2.11. For hygienic assessment, noise is classified as follows:

2.11.1. By the nature of the spectrum, noises are divided into:

Broadband;

Tonal.

2.11.2. In terms of time characteristics, noises are subdivided into:

Permanent;

Fickle.

Intermittent noises are subdivided into:

Fluctuating in time, the sound level of which is continuously changing over time;

Intermittent, the sound level of which drops sharply to the background noise level, and the duration of the intervals during which the level remains constant above the background noise level is more than one second;

Pulse, consisting of one or more sound signals with a duration of less than one second, while the sound levels in dBA, measured when the characteristics "slow" and "impulse" of the sound level meter are switched on, differ by at least 10 dBA.

Intermittent noise is characterized by an equivalent (in energy) level that has the same effect on a person as constant noise of the same level.

2.11.3. By frequency composition (conditionally) to:

Low-frequency with a predominance of the maximum sound pressure levels relative to the limiting spectrum (for example, PS-80) in octave bands up to 250 Hz inclusive,

Mid-frequency - in the octave band of 500 Hz,

High-frequency - in octave bands of 1000 Hz and above.

3. Apparatus for measuring noise

3.1. Noise measurement is carried out using sound level meters in accordance with GOST 17187-71 and octave band-pass filters in accordance with GOST 17168-71, as well as auxiliary devices (level recorders, tape recorders, etc.).

Note: to measure the sound level in dBA in accordance with clause 2.9, the noise meter Shum-1 can be used.

3.2. The use of auxiliary devices is allowed: level recorders, tape recorders, statistical distribution analyzers or equivalent level meters.

3.6. To measure the equivalent noise level, the following can be used: a noise level analyzer type 4426, an integrating sound level meter 2218 from Brüel & Kjерr (Denmark).

table 2

Technical characteristics of sound level meters

Characteristic	Device type
Characteristic	ISHV-1
1. Range of measured levels, dB
2. Frequency response, Hz
3. Correction of the frequency response	A, B, C, Lin "slowly"	A, B, C, Lin "slowly"	A, B, C, Lin "slowly"
4. Time constants		"quickly", "pulse"	"quickly", "pulse"
Power supply of the device	elements 373 × 8 pcs., network 220 V 50 Hz	elements 373x4 pcs., network 220 V 50 Hz	elements 373´3 pcs.
6. Weight, kg
7. Type of octave filters and their frequency range, Hz
8. Manufacturing company	plant "Vibropribor"	RFT, GDR (set No. 12)	Brüel & Kjr, Denmark (set No. 3507)

Table 3

Average geometric and cutoff frequencies of octave bands

Average geometric frequencies, Hz	Cutoff frequencies, Hz
Average geometric frequencies, Hz	Lower	Upper

3.10. Noise measuring devices should be stored in dry, heated rooms, taking into account the special conditions specified in the factory instructions.

4. Measurement points

4.1. Noise measurements are carried out at permanent workplaces in premises, on territories manufacturing enterprises, on production facilities and in machines (at control panels, in cabins, etc.); in case of non-permanent workplaces, measurements are made in at least three evenly distributed points of the working area in order to cover the largest possible part of it.

Measurement points at workplaces (working areas) are selected at a distance of no more than 20 m from each other at a distance of 2 m from the walls of the building; if the difference in sound levels in two adjacent points is more than 5 dBA, an intermediate point is selected.

4.2. To assess the noise regime in rooms, the number and location of measurement points should be taken:

a) for rooms with the same type of equipment - at least at 3 permanent workplaces (work areas);

6) for rooms with group placement of the same type of equipment - at the workplace (work area) in the center of each group of equipment;

c) for premises with mixed placement of different types of equipment - at least at three workplaces (work areas).

4.3. Measurement of noise in observation cabins and remote control, as well as in rooms that did not have noisy equipment, is performed at least at three points closest to sources of external noise, and for small cabins - in the middle of the cabin with closed windows and doors and ventilation and other sources of noise inside the premises.

4.4. To assess the noise from a single machine, measurements are made at the workplace (work area) with other equipment stopped and ventilation of this room, after which the noise is measured with the loaded machine under investigation. The noise level must be at least 10 dB lower than the noise level of the machine under study against the background noise in all octave bands, otherwise the measured noise levels of the machines are corrected in accordance with clause 6.1.2.

If the noise level is only 4 dB or less below the machine noise level, or the noise level fluctuates greatly over time, then measurements are not allowed.

4.5. For approximate identification of noise sources in individual machines, a sequential measurement of sound levels in dBA is performed for individual machine nodes at a distance of 10 cm from them. After identifying the noisiest components of the machine, the noise spectra are measured for them.

4.6. Measurement of noise to check the effectiveness of measures to reduce it is carried out in accordance with the instructions in cl. 4.1. - 4.4.

5. Carrying out measurements

5.1. Sound level meters and auxiliary devices before and after measurements must be calibrated in accordance with the manufacturer's instructions for the devices.

5.5. The required number of measuring points and their location is determined in accordance with the instructions in Section 4. When measuring in accordance with p. 4.1. - 4.3. at least 2/3 of the installed equipment must operate in a typical mode, while ventilation and other commonly used devices that are sources of noise must be turned on.

5.6. For a hygienic assessment of noise, the characteristics shall be measured in accordance with 2.9. In this case, intermittent noises are assessed by equivalent sound levels in dBA, and when they exceed the permissible values (when evaluating new machines and equipment or research work, it is recommended to determine the equivalent levels of lock pressure in octave frequency bands.

5.7. At the beginning of the measurement, the sound level meter should be turned on for correction "A" and the characteristic "slow". When the instrument needle oscillates up to 5 dBA, the noise should be considered constant and the reading should be taken according to its average position. When the pointer oscillates more than 5 dBA, the noise should be considered unstable, while it can be fluctuating in time, intermittent or impulsive (see clause 2.1.). For impulse noises (perceived by ear as single blows against a noise background), an additional measurement should be made according to the "impulse" characteristic with the reading of the maximum arrow reading. If the difference between the sound level readings in dBA in the "impulse" and "slow" positions is more than 10 dBA, the noise should be considered as impulsive.

An example of indication of the counting results: sound level 84 dBA "slow" (or 84 dBAS), sound level 92 dBA "impulse" (or 92 dBAI).

An example of indication of the reading results: octave sound pressure level of 78 dB in an octave of 2000 Hz.

Note:

5.10. For constant impulse noise - measurements should be made at least three times at each point with averaging according to clause 6.2.

5.11. For intermittent noises (intermittent and fluctuating), readings of sound levels in dBA (or octave sound pressure levels in cases of exceeding the norm, when evaluating new equipment machines or research works) should be made with an interval of 5-6 seconds, followed by calculating the equivalent level according to the method of GOST 20445 -75 or according to Appendix 2.

6 Expression of results

Unevenness of the frequency response of the noise measuring path,

The presence of noise interference (when evaluating the noise of a single machine).

6.1.2. Noise corrections are made when noise levels are less than 10 dB below the measured noise level in all octave frequency bands.

If the difference between the measured total octave level (generated by the machine against the background noise) and the octave noise level (measured when the machine is not in operation) is greater than or equal to 10 dB, then the influence of the noise on the measurement result is not taken into account.

If this difference is from 6 to 9 dBA, then 1 dB should be subtracted from the measured total octave level, and 2 dB should be subtracted if the difference is from 4 to 5 dB.

6.2. The average sound pressure level from the results of several measurements at one point or from the results of measurements at several points (working area) is determined as the arithmetic mean according to the formula (2), if the measured levels differ by no more than 7 dB, and according to the formula (3) if they differ by more than 7 dB (see Appendix 1):

DB (2)

DB (3)

where are the measured levels, dB,

n- number of measurements.

6.3. For unstable noises, taking into account the timing data, equivalent levels are calculated according to Appendix 2.

Annex 1

Determination of the average value of the levels

To determine the average value of the levels according to the formula (3) p . 6.2. the measured levels must be summed using table. A.1.1. and subtract from this sum 10lgn, determined from the table. A.1.2, while the formula (3) in Section 6.2 takes the form:

The summation of the measured levels is performed in pairs sequentially as follows. By the difference between the two levels L 1 and L 2 according to the table. A.1.1 determine the additive DL, which is added to the higher level L 1, resulting in the level L 1 2 =. The L 1 2 level is added in the same way to the L 3 level to obtain the L 1 2 3 level, and so on. The final result L c mm is rounded to the nearest whole decibel.

Table P.1.1

With equal terms of levels, that is, with L 1 = L 2 = ¼ = L n = L in the formula (A.1.2.) Can be determined by the formula:

Table A.1.2 shows the values of 10lgn depending on n.

Table P.1.2

Number of levels or sources n

Example. The average value for the measured sound levels of 84, 90 and 92 dBA is to be determined.

Add the first two levels 84 and 90 dB; their difference of 6 dB corresponds to the addition according to table. A.1.1, equal to 1 dB, i.e. their sum is 90 + 1 = 91 dB. Then add the resulting 91 dB level with the remaining 92 dB level; their difference of 1 dB corresponds to an addition of 2.5 dB, i.e. the total level is 92 + 2.5 = 94.5 dB, or we get 95 dB rounded.

According to the table. A.1.2 the value for three levels is 5 dB, so we get the final result for the average value equal to 95 - 5 = 90 dBA.

Appendix 2

Payment equivalent level

The energy equivalent level, which is an unambiguous characteristic of intermittent noise, is obtained by averaging the actual levels taking into account the duration of each action.

Levels in dB (or dBA) acting over time, respectively, T = t 1 + t 2 + ¼ + t n - total time noise action in seconds or hours.

The calculation is made in accordance with Appendix 2 to GOST 20445-75.

Practically more convenient is the method of calculation using corrections for the duration of each level, determined from the table.

Table A.2.1

Time

in hours

15 minutes

5 minutes

Correction in dB

The calculation is done as follows. To each measured level is added (taking into account the sign) a correction according to the table, corresponding to its operating time (in hours or% of the total operating time). Then the resulting levels are added in accordance with Appendix 1.

This calculation is made for sound levels or sound pressure levels in each octave band.

Example 1. Noise levels for an 8-hour work shift were 80, 86 and 94 dB for 5, 2 and 1 hours, respectively. These times correspond to corrections according to the table equal to -2, -6, -9 dB. Adding them to the noise levels, we get 78, 80, 85 dB. Now, using table A.1.1. Appendix 1, we add these levels in pairs: the sum of the first and second gives 82 dB, and their sum with the third is 86.7 dB. Rounding off, the final equivalent noise level is 87 dB. Thus, exposure to this noise is equivalent to exposure to a constant 87 dB for 8 hours.

Example 2. Intermittent noise of 119 dBA acted during a 6 hour shift for a total of 45 minutes. (i.e. 11% shift), the background noise level in pauses (i.e. 89% shift) was 73 dBA.

According to the table. A.2.1. the corrections are -9 and -0.6 dB: adding them with the corresponding noise levels, we get 110 and 72.4 dB, and since the second level is much less than the first (see Table P.1.1. Appendix 1), it can be neglected. Finally, we get an equivalent noise level per shift of 110 dBA, which exceeds the permissible level of 85 dBA by 25 dB.

MINISTRY OF HEALTH OF THE USSR

INSTRUCTIONS
for measurements
and hygienic assessment of noise
in the workplace

№ 1844-78

Moscow 1978

The guidelines are intended to serve as a guide for the Sanitary Epidemiological Service.

INSTRUCTIONS
MEASUREMENT
AND HYGIENIC ASSESSMENT OF NOISES
IN THE WORKPLACE

1. Purpose and scope

1.2. The instructions apply to the following types of measurements:

Assessment of noise at workplaces in premises and on the territory of enterprises,

Noise assessment of machinery and equipment at their workplaces at typical operating levels,

Determination of the effectiveness of measures to reduce noise in the workplace, as well as identify sources of noise.

2. Definitions and units of measurement of basic acoustic quantities

Sound pressure is measured in newtons per square meter. This unit in the international system of units is called pascal (I Pa = I N / m2).

2.6. The organ of hearing distinguishes not the difference, but the multiplicity of changes in sound pressure, therefore, the sound intensity is usually assessed not by the absolute value of the sound pressure, but by its level, that is, by the ratio of the generated pressure to the pressure taken as a unit of comparison.

L - sound pressure level, dB,

r is the measured root-mean-square value of the sound pressure, Pa.

r0 = 2 × 10-5 Pa - the threshold value of the root-mean-square sound pressure (approximately corresponding to the threshold of audibility of a tone of frequency 1000 Hz).

Zero decibels corresponds to a sound pressure of 2 × 10-5 Pa.

Note: to measure the sound level in dBA in accordance with the noise meter Shum-1 can be used.

3.2. The use of auxiliary devices is allowed: level recorders, tape recorders, statistical distribution analyzers or equivalent level meters.

3.6. To measure the equivalent noise level, the following can be used: a noise level analyzer type 4426, an integrating sound level meter 2218 from Brüel & Kjерr (Denmark).

Technical characteristics of sound level meters

Characteristic	Device type
Characteristic	ISHV-1	PSI-202
1. Range of measured levels, dB
2. Frequency response, Hz
3. Correction of the frequency response	A, B, C, Lin "slowly"	A, B, C, Lin "slowly"	A, B, C, Lin "slowly"
4. Time constants		"quickly", "pulse"	"quickly", "pulse"
Power supply of the device	elements 373 × 8 pcs., network 220 V 50 Hz	elements 373x4 pcs., network 220 V 50 Hz	elements 373´3 pcs.
6. Weight, kg
7. Type of octave filters and their frequency range, Hz
8. Manufacturing company	plant "Vibropribor"	RFT, GDR (set No. 12)	Brüel & Kjr, Denmark (set No. 3507)

Average geometric and cutoff frequencies of octave bands

Average geometric frequencies, Hz	Cutoff frequencies, Hz
Average geometric frequencies, Hz	Lower	Upper

3.10. Noise measuring devices should be stored in dry, heated rooms, taking into account the special conditions specified in the factory instructions.

4. Measurement points

If the noise level is only 4 dB or less below the machine noise level, or the noise level fluctuates greatly over time, then measurements are not allowed.

4.5. For approximate identification of noise sources in individual machines, a sequential measurement of sound levels in dBA is performed for individual machine nodes at a distance of 10 cm from them. After identifying the noisiest components of the machine, the noise spectra are measured for them.

4.6. Measurement of noise to check the effectiveness of measures to reduce it is carried out in accordance with the instructions of cl. -.

5. Carrying out measurements

5.1. Sound level meters and auxiliary devices before and after measurements must be calibrated in accordance with the manufacturer's instructions for the devices.

An example of indication of the counting results: sound level 84 dBA "slow" (or 84 dBAS), sound level 92 dBA "impulse" (or 92 dBAI).

An example of indication of the reading results: octave sound pressure level of 78 dB in an octave of 2000 Hz.

Note:

5.10. For constant impulse noise - measurements should be made at least three times at each point with averaging over.

5.11. For intermittent noises (intermittent and fluctuating), readings of sound levels in dBA (or octave sound pressure levels in cases of exceeding the norm, when evaluating new equipment machines or research works) should be made with an interval of 5-6 seconds, followed by calculating the equivalent level according to the method of GOST 20445 -75 or by.

6 Expression of results

Unevenness of the frequency response of the noise measuring path,

The presence of noise interference (when evaluating the noise of a single machine).

, dB ()

DB ()

where are the measured levels, dB,

n- number of measurements.

6.3. For intermittent noises, taking into account the timing data, equivalent levels are calculated according to.

Annex 1

Determination of the average value of the levels

To determine the average value of the levels according to p . 6.2. the measured levels must be summed using. and subtract from this sum 10lgn, determined by; in this case, item 6.2 takes the form:

(A.1.1)

The summation of the measured levels is performed in pairs sequentially as follows. By the difference between the two levels L1 and L2, the additive DL is determined, which is added to the higher level L1, as a result of which the level L1 2 = is obtained. L1 2 is added in the same way to L3 to get L1 2 3 and so on. The final result Lsum shall be rounded to the nearest whole decibels. tab. A.1.1, equal to 1 dB, i.e. their sum is 90 + 1 = 91 dB. Then add the resulting 91 dB level with the remaining 92 dB level; their difference of 1 dB corresponds to an addition of 2.5 dB, i.e. the total level is 92 + 2.5 = 94.5 dB, or we get 95 dB rounded.

This calculation is made for sound levels or sound pressure levels in each octave band.

Example 1. Noise levels for an 8-hour work shift were 80, 86 and 94 dB for 5, 2 and 1 hours, respectively. These times correspond to corrections according to the table equal to -2, -6, -9 dB. Adding them to the noise levels, we get 78, 80, 85 dB. Now using. Appendix 1, we add these levels in pairs: the sum of the first and second gives 82 dB, and their sum with the third is 86.7 dB. Rounding off, the final equivalent noise level is 87 dB. Thus, exposure to this noise is equivalent to exposure to a constant 87 dB for 8 hours.

Example 2. Intermittent noise of 119 dBA acted during a 6 hour shift for a total of 45 minutes. (i.e. 11% shift), the background noise level in pauses (i.e. 89% shift) was 73 dBA.