Misją Instytutu jest dzialalność naukowo-badawcza prowadząca do nowych rozwiązań technicznych i organizacyjnych użytecznych w kształtowaniu warunków pracy zgodnych z zasadami bezpieczeństwa pracy i ergonomii oraz ustalanie podstaw naukowych do właściwego ukierunkowywania polityki społeczno-ekonomicznej państwa w tym zakresie.
PRINCIPLES OF ASSESSMENT OF EXPOSURE TO ULTRASONIC NOISE
BASIC TERMS RELATED TO ULTRASONIC NOISE IN THE WORK ENVIRONMENT
The basic concepts and concepts related to ultrasonic noise, such as sound, frequency and sound pressure, are the same as for noise in the audible range. The main differences between noise and ultrasonic noise concern the frequency range of vibrations of the elastic medium (acoustic waves) that create a given type of noise and the quantities used to characterize a given type of noise in the working environment. This description only covers the topics and concepts that are mainly related to ultrasonic noise. The basic concepts relating to both types of noise are discussed in the noise section.
Ultrasonic noise
Ultrasonic noise is defined as noise, sounds with high audible and low ultrasonic frequencies
(or in other words: in the spectrum of which there are sounds with such frequencies) - from 10 kHz
to 40 kHz. The frequencies given in the definition refer to the frequencies of the middle third octave bands (see further), which means that ultrasonic noise includes sounds with frequencies from
8.91 kHz to 44.88 kHz. The range of ultrasonic noise on the sound frequency scale is shown in Fig. 1.
(or in other words: in the spectrum of which there are sounds with such frequencies) - from 10 kHz
to 40 kHz. The frequencies given in the definition refer to the frequencies of the middle third octave bands (see further), which means that ultrasonic noise includes sounds with frequencies from
8.91 kHz to 44.88 kHz. The range of ultrasonic noise on the sound frequency scale is shown in Fig. 1.
Fig. 1. Ultrasonic noise on the frequency axis.
Third (one third octave band)
Due to its specificity, ultrasonic noise is analyzed and assessed in frequency bands (i.e. in certain frequency ranges) known as thirds. Third is the frequency band between the lower fd and upper
fg frequencies, which satisfy the following relationship:
fg frequencies, which satisfy the following relationship:
The third octave bands used in acoustics and noise measurements are characterized by the center frequency of the third octave band f0. The center frequency of the third octave band and its lower and upper frequencies meet the following relationship:
The center frequencies of the standard third octave bands used in measuring ultrasonic noise are sequentially: 10, 12,5, 16, 20, 25, 31,5 i 40 kHz.
Equivalent sound pressure level
The employee's exposure to ultrasonic noise can vary over the course of an 8-hour working day.
In such a case, in order to determine the risk of ultrasonic noise for the worker during the shift,
the equivalent level of sound pressure should be used. Equivalent sound pressure level is the sound pressure level of a noise which, while operating for the same duration as noise with varying
sound pressure levels, carries the same acoustic energy and the same risk of hearing impairment.
Fig. 2 shows an example of changes in the sound pressure levels of ultrasonic noise during an 8-hour working day. The employee worked for the first two hours in a noise with a sound pressure level of 60 dB, the next two hours in a noise with a sound pressure level of 90 dB, then two hours in a noise with a sound pressure of 75 dB and two hours in a noise with a sound pressure level of 75 dB.
From an occupational exposure point of view, this corresponds to a situation where a worker would work eight hours in a noise with a sound pressure level of 84.5 dB.
In such a case, in order to determine the risk of ultrasonic noise for the worker during the shift,
the equivalent level of sound pressure should be used. Equivalent sound pressure level is the sound pressure level of a noise which, while operating for the same duration as noise with varying
sound pressure levels, carries the same acoustic energy and the same risk of hearing impairment.
Fig. 2 shows an example of changes in the sound pressure levels of ultrasonic noise during an 8-hour working day. The employee worked for the first two hours in a noise with a sound pressure level of 60 dB, the next two hours in a noise with a sound pressure level of 90 dB, then two hours in a noise with a sound pressure of 75 dB and two hours in a noise with a sound pressure level of 75 dB.
From an occupational exposure point of view, this corresponds to a situation where a worker would work eight hours in a noise with a sound pressure level of 84.5 dB.
Fig. 2. Changes in the sound pressure level as a function of time and the corresponding equivalent sound pressure level.
In the case of ultrasonic noise, equivalent sound pressure levels are determined for individual third octave bands in the frequency range from 10 to 40 kHz. The equivalent sound pressure level in the
i-th third octave band is denoted by the symbol:
i-th third octave band is denoted by the symbol:
where Te symbolizes exposure time.
If exposure to ultrasonic noise during the working day can be divided into n clearly distinguishable time periods Tej, with different conditions of exposure to ultrasonic noise, then the equivalent sound pressure level in the i-th frequency band for the total exposure time Te can be determined from the dependence:
where:
- equivalent sound pressure level in the i frequency band for the j-th time interval Tej, in dB,
- total exposure time during the working day.Equivalent sound pressure level in the i-th third octave band related to the 8-hour daily
working time
working time
The detrimental effect of ultrasonic noise on the worker depends on the amount of acoustic energy reaching the worker, and therefore on the level of sound pressure acting on the worker by the ultrasonic noise and the duration of its impact. As the sound pressure level of the noise affecting the worker may vary and the duration of exposure to this noise may vary from 8 hours (the worker may, for example, work in ultrasonic noise for a part of his shift), a value was introduced - the equivalent sound pressure level in a third octave band related to the 8-hour daily working time - to assess the impact of ultrasonic noise on the worker. It is one of the two basic quantities characterizing the ultrasonic noise in the work environment. This value is determined for individual third octave bands belonging to the ultrasonic noise range in accordance with the relationship:
where Te is the exposure time during the working day and To is the reference time of
8 h = 480 min = 28800 s.
8 h = 480 min = 28800 s.
Equivalent sound pressure level in the i-th third octave band related to the average weekly working time
If an employee's exposure to noise is uneven on individual days of the working week, the noise exposure assessment is based on equivalent sound pressure levels defined in frequency bands, related to the average weekly (defined in the Labour Code) working time. This value is determined by the relationship:
where:
k - next business day in the week under consideration,
n - number of working days in the week under consideration (may be less than 5).
Maximum sound pressure level in a third octave band.
The maximum sound pressure levels in one-third octave bands with center frequencies ranging from 10 to 40 kHz are the second of the basic values for the assessment of ultrasonic noise. This value means the highest level of sound pressure recorded during the entire duration of work (at any time) in a given frequency band. This size is marked with the symbol Lfi,max
ULTRASONIC NOISE LIMIT VALUES
The values characterizing the ultrasonic noise in the working environment and the values of the maximum allowable intensity (PEL) for these values (hereinafter referred to as the limit values) are specified in the annex to the Regulation of the Minister of Labour and Social Policy of June 12, 2018 on the maximum allowable concentrations and intensities of harmful factors for health in the work environment (Journal of Laws Dz.U. 2018, item 1286). According to this regulation, ultrasonic noise in the working environment is characterized by:
The values characterizing the ultrasonic noise in the working environment and the values of the maximum allowable intensity (PEL) for these values (hereinafter referred to as the limit values) are specified in the annex to the Regulation of the Minister of Labour and Social Policy of June 12, 2018 on the maximum allowable concentrations and intensities of harmful factors for health in the work environment (Journal of Laws Dz.U. 2018, item 1286). According to this regulation, ultrasonic noise in the working environment is characterized by:
- equivalent levels of sound pressure in third octave bands with central frequencies from 10 to 40 kHz related to the 8-hour daily or the average weekly working time specified in the Labour Code (exceptionally in the case of the impact of ultrasonic noise on the human body in an uneven manner on individual days) in the week),
- maximum sound pressure levels in third octave bands with center frequencies
from 10 to 40 kHz.
The limit values specified for these values apply simultaneously and for all employees may not exceed the values given in Table 1.
Table 1. Ultrasonic noise limit values for all workers
|
The center frequency of one third octave band [kHz] |
Permissible equivalent sound pressure level related to the 8-hour daily (Lfeq,8h,dop) or to the average weekly (Lfeq,w,dop), defined in the Labour Code, working time [dB] |
Permissible maximum sound pressure level Lfmax [dB] |
|
10; 12,5; 16 |
80 |
100 |
|
20 |
90 |
110 |
|
25 |
105 |
125 |
|
31,5; 40; |
110 |
130 |
The ultrasonic noise limit values given above apply unless lower values are specified in other specific regulations.
In the regulation of the Council of Ministers of August 24, 2004 on the list of works forbidden to young people and the conditions of employing them for some of these works (Journal of Laws Dz.U. of 2004, No. 200, item 2047, consolidated text of Journal of Laws Dz.U. of 2016, item 1509) are given ultrasonic noise limit values for young workers. Pursuant to this regulation, it is forbidden to employ adolescents in workplaces where the ultrasonic noise values exceed the permissible values specified in Table 2.
Table 2. Ultrasonic noise limit values for young workers
|
The center frequency of one third octave band [kHz] |
Permissible equivalent sound pressure level related to the 8-hour daily (Lfeq,8h,dop) or to the average weekly (Lfeq,w,dop), defined in the Labour Code, working time [dB] |
Permissible maximum sound pressure level Lfmax [dB] |
|
10; 12,5; 16 |
75 |
100 |
|
20 |
85 |
110 |
|
25 |
100 |
125 |
|
31,5; 40; |
105 |
130 |
In the regulation of the Council of Ministers of April 3, 2017 on the list of burdensome, dangerous or harmful work for pregnant women and breast-feeding women (Journal of Laws Dz.U. 2017, item 796), the limit values for ultrasonic noise for pregnant women were specified. According to this regulation, it is forbidden to employ pregnant women in conditions of exposure to ultrasonic noise, the values of which exceed the limit values given in Table 3.
Table 3. Ultrasonic noise limits for pregnant women
|
The center frequency of one third octave band [kHz] |
Permissible equivalent sound pressure level related to the 8-hour daily (Lfeq,8h,dop) or to the average weekly (Lfeq,w,dop), defined in the Labour Code, working time [dB] |
Permissible maximum sound pressure level Lfmax [dB] |
|
10; 12,5; 16 |
75 |
95 |
|
20 |
85 |
105 |
|
25 |
100 |
120 |
|
31,5; 40; |
105 |
125 |
RISK ASSESSMENT
The assessment of the occupational risk related to exposure to ultrasonic noise consists primarily in the comparison of the measured or determined values (Lzm) of the quantities characterizing the ultrasonic noise at the workplace (equivalent sound pressure levels related to an 8-hour working day or working week and the maximum sound pressure levels - in frequency bands), to their permissible values (Ldop), valid at the same time. It should be taken into account whether the employee for whom the assessment is carried out belongs to the special risk group (adolescent or pregnant woman). When assessing occupational risk, one can adopt the principle described in the PN-N-18002 standard "Occupational health and safety management systems. General guidelines for occupational risk assessment", taking into account the multiplicity (k) of the limit value, which is the quotient of the measured value and the limit value (i.e. k = [ measured value] / [limit value]). According to the recommendations of the standard, based on the multiplication of the limit value, the occupational risk is assessed as:
The assessment of the occupational risk related to exposure to ultrasonic noise consists primarily in the comparison of the measured or determined values (Lzm) of the quantities characterizing the ultrasonic noise at the workplace (equivalent sound pressure levels related to an 8-hour working day or working week and the maximum sound pressure levels - in frequency bands), to their permissible values (Ldop), valid at the same time. It should be taken into account whether the employee for whom the assessment is carried out belongs to the special risk group (adolescent or pregnant woman). When assessing occupational risk, one can adopt the principle described in the PN-N-18002 standard "Occupational health and safety management systems. General guidelines for occupational risk assessment", taking into account the multiplicity (k) of the limit value, which is the quotient of the measured value and the limit value (i.e. k = [ measured value] / [limit value]). According to the recommendations of the standard, based on the multiplication of the limit value, the occupational risk is assessed as:
|
k ≤ 0,5 |
low risk |
|
0,5 < k ≤ 1 |
medium risk |
|
k > 1,0 |
high risk |
Since in the case of ultrasonic noise the limit values are expressed in decibels (i.e. in a relative logarithmic measure), the multiplicity of the limit values cannot be determined by dividing the values given in dB.
The multiplicity of the limit value for equivalent sound pressure levels related to an 8-hour working day or working week in the frequency bands from 10 to 40 kHz is determined using the relationship:
where:
Lfi,eq,8h,zm - measured (or determined) equivalent sound pressure level in the i-th third frequency band related to an 8-hour working day.
Lfi,eq,8h,dop - permissible equivalent sound pressure level in the i-th third frequency band, related to an 8-hour working day.
The multiplicity of the limit value for the maximum sound pressure levels in the frequency bands in the range from 10 to 40 kHz is determined using the relationship:
where:
Lfi,max,zm - the measured maximum sound pressure level in the i-th third frequency band,
Lfi,max,dop - the maximum permissible sound pressure level in the i-th third frequency band.
The result of the occupational risk assessment is determined by the greatest of the designated multiplicity (for both quantities characterizing ultrasonic noise and all frequency bands).
Computer tools available on the Website may be helpful in determining the multiplicity.
