Thursday, 24 March 2011 17:56

Noise Measurement and Exposure Evaluation

Rate this item
(3 votes)

For the prevention of adverse effects of noise on workers, attention should be paid to the choice of appropriate instrumentation, measuring methods and procedures for evaluating workers’ exposures. It is important to evaluate correctly the different types of noise exposures, such as continuous, intermittent and impulse noise, to distinguish noise environments with differing frequency spectra, as well as to consider the variety of working situations, such as drop-forge hammering shops, rooms housing air compressors, ultrasonic welding processes, and so forth. The main purposes of noise measurement in occupational settings are to (1) identify overexposed workers and quantify their exposures and (2) assess the need both for engineering noise control and the other types of control that are indicated. Other uses of noise measurement are to evaluate the effectiveness of particular noise controls and to determine the background levels in audiometric rooms.

Measuring Instruments

Instruments for noise measurement include sound level meters, noise dosimeters and auxiliary equipment. The basic instrument is the sound level meter, an electronic instrument consisting of a microphone, an amplifier, various filters, a squaring device, an exponential averager and a read-out calibrated in decibels (dB). Sound level meters are categorized by their precision, ranging from the most precise (type 0) to the least (type 3). Type 0 is usually used in the laboratory, type 1 is used for other precision sound level measurements, type 2 is the general purpose meter, and type 3, the survey meter, is not recommended for industrial use. Figure 1 and figure 2, illustrate a sound level meter.

Figure 1. Sound level meter—calibration check. Courtesy of Larson Davis


Figure 2. Sound level meter with wind screen. Courtesy of Larson Davis


Sound level meters also have built-in frequency weighting devices, which are filters that allow most frequencies to pass while discriminating against others. The most commonly used filter is the A-weighting network, which was developed to simulate the response curve of the human ear at moderate listening levels. Sound level meters also offer a choice of meter responses: the “slow” response, with a 1-sec time constant, the “fast” response with a 0.125-sec time constant, and the “impulse” response which has a 35 ms response for the increasing portion of the signal and a 1500 ms time constant for the signal’s decay.

Specifications for sound level meters may be found in national and international standards, such as the International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC) and the American National Standards Institute (ANSI). The IEC publications IEC 651 (1979) and IEC 804 (1985) pertain to sound level meters of types 0, 1, and 2, with frequency weightings A, B, and C, and “slow,” “fast”                                                                                                                         and “impulse” time constants. ANSI S1.4-1983, as amended by                                                                                                                       ANSI S1.4A-1985, also provides specifications for sound level                                                                                                                         meters.

To facilitate more detailed acoustical analysis, full octave-band and 1/3 octave-band filter sets may be attached to or included in modern sound level meters. Nowadays, sound level meters are becoming increasingly small and easy to use, while at the same time their measurement possibilities are expanding.

For measuring non-steady noise exposures, such as those that occur in intermittent or impulse noise environments, an integrating sound level meter is most convenient to use. These meters can simultaneously measure the equivalent, peak and maximum sound levels, and calculate, log and store several values automatically. The noise dose meter or “dosimeter” is a form of integrating sound level meter that can be worn in the shirt pocket or attached to the worker’s clothing. Data from the noise dosimeter may be computerized and printed out.

It is important to make sure that noise measuring instruments are always properly calibrated. This means checking the instrument’s calibration acoustically before and after each day’s use, as well as making electronic assessments at appropriate intervals.

Measurement Methods

The noise measurement methods to be used depend on the measurement objectives, namely, to assess the following:

    • the risk of hearing impairment
    • the need for and appropriate types of engineering controls
    • the “noise load” for compatibility with the type of job to be performed
    • the background level necessary for communication and safety.


          International standard ISO 2204 gives three types of method for noise measurement: (1) the survey method, (2) the engineering method and (3) the precision method.

          The survey method

          This method requires the least amount of time and equipment. Noise levels of a working zone are measured with a sound level meter using a limited number of measuring points. Although there is no detailed analysis of the acoustic environment, time factors should be noted, such as whether the noise is constant or intermittent and how long the workers are exposed. The A-weighting network is usually used in the survey method, but when there is a predominant low-frequency component, the C-weighting network or the linear response may be appropriate.

          The engineering method

          With this method, A-weighted sound level measurements or those using other weighting networks are supplemented with measurements using full octave or 1/3 octave-band filters. The number of measuring points and the frequency ranges are selected according to the measurement objectives. Temporal factors should again be recorded. This method is useful for assessing interference with speech communication by calculating speech interference levels (SILs), as well as for engineering noise abatement programmes and for estimating the auditory and non-auditory effects of noise.

          The precision method

          This method is required for complex situations, where the most thorough description of the noise problem is needed. Overall measurements of sound level are supplemented with full octave or 1/3 octave-band measurements and time histories are recorded for appropriate time intervals according to the duration and fluctuations of the noise. For example, it may be necessary to measure peak sound levels of impulses using an instrument’s “peak hold” setting, or to measure levels of infrasound or ultrasound, requiring special frequency measuring capabilities, microphone directivity, and so forth.

          Those who use the precision method should make sure that the instrument’s dynamic range is sufficiently great to prevent “overshoot” when measuring impulses and that the frequency response should be broad enough if infrasound or ultrasound is to be measured. The instrument should be capable of making measurements of frequencies as low as 2 Hz for infrasound and up to at least 16 kHz for ultrasound, with microphones that are sufficiently small.

          The following “common sense” steps may be useful for the novice noise measurer:

            1. Listen for the main characteristics of the noise to be measured (temporal qualities, such as steady-state, intermittent or impulse qualities; frequency characteristics, such as those of wide-band noise, predominant tones, infrasound, ultrasound, etc.). Note the most prominent characteristics.
            2. Choose the most suitable instrumentation (type of sound level meter, noise dosimeter, filters, tape recorder, etc.).
            3. Check the instrument’s calibration and performance (batteries, calibration data, microphone corrections, etc.).
            4. Make notes or a sketch (if using a system) of the instrumentation, including model and serial numbers.
            5. Make a sketch of the noise environment to be measured, including major noise sources and the size and important characteristics of the room or outdoor setting.
            6. Measure the noise and note down the level measured for each weighting network or for each frequency band. Also note the meter response (such as “slow,” “fast,” “impulse,” etc.), and note the extent to which the meter fluctuates (e.g., plus or minus 2 dB).


                      If measurements are made outdoors, pertinent meteorological data, such as wind, temperature and humidity should be noted if they are considered important. A windscreen should always be used for outdoor measurements, and even for some indoor measurements. The manufacturer’s instructions should always be followed to avoid the influence of factors such as wind, moisture, dust and electrical and magnetic fields, which may affect the readings.

                      Measuring procedures

                      There are two basic approaches to measuring noise in the workplace:

                        • The exposure of each worker, worker type or worker representative may be measured. The noise dosimeter is the preferable instrument for this purpose.
                        • Noise levels may be measured in various areas, creating a noise map for the determination of risk areas. In this case, a sound level meter would be used to take readings at regular points in a coordinate network.


                          Worker Exposure Evaluation

                          To assess the risk of hearing loss from specific noise exposures, the reader should consult the international standard, ISO 1999 (1990). The standard contains an example of this risk assessment in its Annex D.

                          Noise exposures should be measured in the vicinity of the worker’s ear and, in assessing the relative hazard of workers’ exposures, subtractions should not be made for the attenuation provided by hearing protection devices. The reason for this caveat is that there is considerable evidence that the attenuation provided by hearing protectors as they are worn on the job is often less than half the attenuation estimated by the manufacturer. The reason for this is that the manufacturer’s data are obtained under laboratory conditions and these devices are not usually fitted and worn so effectively in the field. At the moment, there is no international standard for estimating the attenuation of hearing protectors as they are worn in the field, but a good rule of thumb would be to divide the laboratory values in half.

                          In some circumstances, especially those involving difficult tasks or jobs requiring concentration, it may be important to minimize the stress or fatigue related to noise exposure by adopting noise control measures. This may be true even for moderate noise levels (below 85 dBA), when there is little risk of hearing impairment, but the noise is annoying or fatiguing. In such cases it may be useful to perform loudness assessments using ISO 532 (1975), Method for Calculating Loudness Level.

                          Interference with speech communication may be estimated according to ISO 2204 (1979) using the “articulation index”, or more simply by measuring the sound levels in the octave bands centred at 500, 1,000 and 2,000 Hz, resulting in the “speech interference level”.

                          Exposure criteria

                          The selection of noise exposure criteria depends on the goal to be attained, such as the prevention of hearing loss or the prevention of stress and fatigue. Maximum permissible exposures in terms of daily average noise levels vary among nations from 80, to 85, to 90 dBA, with trading parameters (exchange rates) of 3, 4, or 5 dBA. In some countries, such as Russia, permissible noise levels are set anywhere from 50 to 80 dBA, according to the type of job performed and taking into account the mental and physical work load. For example, the allowable levels for computer work or the performance of demanding clerical work are 50 to 60 dBA. (For more information on exposure criteria, see the article “Standards and regulations” in this chapter.)



                          Read 14719 times Last modified on Tuesday, 26 July 2022 21:33

                          " DISCLAIMER: The ILO does not take responsibility for content presented on this web portal that is presented in any language other than English, which is the language used for the initial production and peer-review of original content. Certain statistics have not been updated since the production of the 4th edition of the Encyclopaedia (1998)."


                          Noise References

                          American National Standards Institute (ANSI). 1985. ANSI SI.4-1983, As Amended By ANSI SI.4-1985. New York: ANSI.

                          —. 1991. ANSI SI2.13. Evaluation of Hearing Conservation Programmes. New York: ANSI.

                          —. 1992. ANSI S12.16. Guidelines for the Specification of Noise of New Machinery. New York: ANSI.

                          Arenas, JP. 1995. Institute of Acoustics, Universidad Austral de Chile. Paper presented at the 129th meeting of the Acoustical Society of America, Valdivia, Chile.

                          Boettcher FA, D Henderson, MA Gratton, RW Danielson and CD Byrne. 1987. Synergistic interactions of noise and other ototraumatic agents. Ear Hear. 8(4):192-212.

                          Council of the European Communities (CEC). 1986. Directive of 12 May 1986 on the protection of workers from the risks related to exposure to noise at work (86/188/EEC).

                          —. 1989a. Directive 89/106/EEC of 21 December 1988 on the approximation of laws, regulations and administrative provisions of the Member States relating to construction products, OJ No. L40, 11 February.

                          —. 1989b. Directive 89/392/EEC of 14 June 1989 on the approximation of the laws of the Member States relating to machinery, OJ No. L183, 29.6.1989.

                          —. 1989c. Directive 89/686/EEC of 21 December 1989 on the approximation of laws of the Member States relating to personal protective equipment, OJ No. L399, 30.12.1989.

                          —. 1991. Directive 91/368/EEC of 20 June 1991 amending Directive 89/392/EEC on approximation of the laws of the Member States relating to machinery, OJ No. L198, 22.7.91.

                          —. 1993a. Directive 93/44/EEC of 14 June 1993 amending Directive 89/392/EEC on approximation of the laws of the Member States relating to machinery, OJ No. L175, 19.7.92.

                          —. 1993b. Directive 93/95/EEC of 29 October 1993 amending 89/686/EEC on the approximation of laws of the Member States relating to personal protective equipment (PPE), OJ No. L276, 9.11.93.

                          Dunn, DE, RR Davis, CJ Merry, and JR Franks. 1991. Hearing loss in the chinchilla from impact and continuous noise exposure. J Acoust Soc Am 90:1975-1985.

                          Embleton, TFW. 1994. Technical assessment of upper limits on noise in the workplace. Noise/News Intl. Poughkeepsie, NY: I-INCE.

                          Fechter, LD. 1989. A mechanistic basis for interactions between noise and chemical exposure. ACES 1:23-28.

                          Gunn, P. N.d. Department of Occupational Health Safety and Welfare, Perth, Western Australia. Personal Comm.

                          Hamernik, RP, WA Ahroon, and KD Hsueh. 1991. The energy spectrum of an impulse: Its relation to hearing loss. J Acoust Soc Am 90:197-204.

                          International Electrotechnical Commission (IEC). 1979. IEC document No. 651.

                          —. 1985. IEC document No. 804.

                          International Labour Organization (ILO). 1994. Noise Regulations and Standards (Summaries). Geneva: ILO.

                          International Organization for Standardization. (ISO). 1975. Method for Calculating Loudness Level. ISO Document No. 532. Geneva: ISO.

                          —. 1990. Acoustics: Determination of Occupational Noise Exposure and Estimate of Noise-Induced Hearing Impairment. ISO Document No. 1999. Geneva: ISO.

                          Ising, H and B Kruppa. 1993. Larm und Krankheit [Noise and Disease]. Stuttgart: Gustav Fischer Verlag.

                          Kihlman, T. 1992. Sweden’s action plan against noise. Noise/News Intl 1(4):194-208.

                          Moll van Charante, AW and PGH Mulder. 1990. Perceptual acuity and the risk of industrial accidents. Am J Epidemiol 131:652-663.

                          Morata, TC. 1989. Study of the effects of simultaneous exposure to noise and carbon disulfide on workers’ hearing. Scand Audiol 18:53-58.

                          Morata, TC, DE Dunn, LW Kretchmer, GK Lemasters, and UP Santos. 1991. Effects of simultaneous exposure to noise and toluene on workers’ hearing and balance. In Proceedings of the Fourth International Conference On the Combined Environmental Factors, edited by LD Fechter. Baltimore: Johns Hopkins Univ.

                          Moreland, JB. 1979. Noise Control Techniques. In Handbook of Noise Control, edited by CM Harris. New York: McGraw-Hill

                          Peterson, EA, JS Augenstein, and DC Tanis. 1978. Continuing studies of noise and cardiovascular function. J Sound Vibrat 59:123.

                          Peterson, EA, JS Augenstein, D Tanis, and DG Augenstein. 1981. Noise raises blood pressure without impairing auditory sensitivity. Science 211:1450-1452.

                          Peterson, EA, JS Augenstein, DC Tanis, R Warner, and A Heal. 1983. Proceedings of the Fourth International Congress On Noise As a Public Health Problem, edited by G Rossi. Milan: Centro Richerche e Studi Amplifon.

                          Price, GR. 1983. Relative hazard of weapons impulses. J Acoust Soc Am 73:556-566.

                          Rehm, S. 1983. Research on extraaural effects of noise since 1978. In Proceedings of the Fourth International Congress On Noise As a Public Health Problem, edited by G Rossi. Milan: Centro Richerche e Studi Amplifon.

                          Royster, JD. 1985. Audiometric evaluations for industrial hearing conservation. J Sound Vibrat 19(5):24-29.

                          Royster, JD and LH Royster. 1986. Audiometric data base analysis. In Noise and Hearing Conservation Manual, edited by EH Berger, WD Ward, JC Morrill, and LH Royster. Akron, Ohio: American Industrial Hygiene Association (AIHA).

                          —. 1989. Hearing Conservation. NC-OSHA Industry Guide No. 15. Raleigh, NC: North Carolina Department of Labor.

                          —. 1990. Hearing Conservation Programs: Practical Guidelines for Success. Chelsea, Mich.: Lewis.

                          Royster, LH, EH Berger, and JD Royster. 1986. Noise surveys and data analysis. In Noise and Hearing Conservation Manual, edited by EH Berger, WH Ward, JC Morill, and LH Royster. Akron, Ohio: American Industrial Hygiene Association (AIHA).

                          Royster, LH and JD Royster. 1986. Education and motivation. In Noise & Hearing Conservation Manual, edited by EH Berger, WH Ward, JC Morill, and LH Royster. Akron, Ohio: American Industrial Hygiene Association (AIHA).

                          Suter, AH. 1992. Communication and Job Performance in Noise: A Review. American Speech-Language Hearing Association Monographs, No.28. Washington, DC: ASHA.

                          —. 1993. Noise and conservation of hearing. Chap. 2 in Hearing Conservation Manual Milwaukee, Wisc: Council for Accreditation in Occupational Hearing Conservation.

                          Thiery, L and C Meyer-Bisch. 1988. Hearing loss due to partly impulsive industrial noise exposure at levels between 87 and 90 dBA. J Acoust Soc Am 84:651-659.

                          van Dijk, FJH. 1990. Epidemiological research on non-auditory effects of occupational noise exposure since 1983. In Noise As a Public Health Problem, edited by B Berglund and T Lindvall. Stockholm: Swedish Council for Building Research.

                          von Gierke, HE. 1993. Noise regulations and standards: Progress, experiences, and challenges. In Noise As a Public Health Problem, edited by M Vallet. France: Institut National de Recherche sur les Transports et leur Sécurité.

                          Wilkins, PA and WI Acton. 1982. Noise and accidents: A review. Ann Occup Hyg 2:249-260.