NT TR 515_Determination of Work Place Noise Exposure - Consideration of Measurements, Calculations and Uncertainty_Nordtest Technical Report

8/2/2019 NT TR 515_Determination of Work Place Noise Exposure - Consideration of Measurements, Calculations and Uncert

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TR 515Approved 2002-10

Published by Nordtest Phone: + 358 9 455 4600 Fax: + 358 9 455 4272Tekniikantie 12 E-mail: [email protected] Internet: www.nordtest.orgFIN02150 EspooFinland

Tnnes Ognedal

Iiris Turunen-Rise

Determination of work place noise

exposure - Consideration of

measurements, calculations and

uncertainty


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NT TECHN REPORT 515

Approved 2002-10

Authors:Tnnes Ognedal1Iiris Turunen-Rise

2

NORDTEST project number: 1566-01

Institution:1)

Sinus AS,2)Norwegian Council for Building Standardization

Title (English): -

Title (Original): Determination of work place noise exposure Consideration ofmeasurements, calculations and uncertainty

Abstract:

The aim of the present work is to prepare a Nordtest-method in two parts, namely a simplemethod for use to safety deputies, persons in industrial or occupational hygiene or inoccupational health care etc., and a more advanced method requiring a great deal ofcompetence in acoustics in order to achieve better accuracy in measurement results, if needed.The methods have to describe sources for errors and uncertainty, show how large these maybe, and give guidance on how to handle the errors in order to get a most correct description ofthe noise situation at the work place.

Second aim of this project has been to develop method(s) of calculation and measurement ofwork place noise exposure that are based on extensive platform from the Nordic countries. Thesources for errors and uncertainty are described. It is shown how to calculate how large thesemay be. Guidance is given on how to handle the errors or calculate uncertainty. There is a greathope to achieve an agreement on improved Nordtest method(s) that may be applied in allNordic countries.

Measurements inside hearing protectors at some ear canal position by using of miniature

microphones are described in EN-ISO 11904-1 for measurements at real ears [4], and in EN-ISO 11904-2 for manikin measurements [5]. These measurements are therefore not describedin the scope of the present project, but they are considered to be adequate for suchmeasurements. The calculation of daily 8-hour exposure may be made by using the presentmethods.

The project work does not include consideration of health risk for the workers or guidance fornoise reduction measures, but the resulting methods may be used to determine the noisesituation more precisely and improve the accuracy of the method(s).

Technical Group: Expert Group Sound and Vibration

ISSN: 0283-7234 Language: English Pages: 22

Class (UDC): 534.6:613.16 Key words: acoustics, occupational noise, workers, workplaces, test methods

Publication code:Distributed by:

NORDTEST

Tekniikantie 12

FIN-02150 ESPOO

Finland

Report Internet address:http://www.nordtest.org/register/techn/tlibrary/tec515.pdf


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Foreword

This method has been developed as an interactive work supported by Nordtest and The NorwegianOil Industry Association (OLF).

Project 1566-01Title: Determination of work place noise exposure by calculations and measurements.

Report titleNordtest Technical Report on Project No 1566-01: Determination of work place noise exposure Consideration of measurements, calculations and uncertainty

Method proposalsMeasurement of occupational noise exposure of workers Part I: Survey methodMeasurement of occupational noise exposure of workers Part II: Engineering method

Nordic project group

Tnnes Ognedal, Sinus AS, project leaderHeli Laitinen, Finnish Institute of Occupational HealthPer Mberg Nielsen, AkustikNet A/SPer ke Nilsson, Ingemansson TechnologyIiris Turunen-Rise, Norwegian Council for Building Standardization

ContentsNordtest Technical Report on Project No 1566-01 Determination of work place noise exposure Consideration of measurements, calculations and uncertaintyAppendixes:Method 1: Measurement and evaluation of occupational noise exposure of workers Survey methodMethod 2: Measurement and evaluation of occupational noise exposure of workers Engineeringmethod

AccountsExcel calculation sheet

Acknowledgements

Thanks to Norwegian Oil Industry Association and Nordtest for the financial support that enabled thisproject work to be performed. Also thanks to the companies and institutes that provided the membersto this Nordtest work and allowed to spend working hours for this project. We also thank Jan GybelJensen, Arbeijdstilsynet in Denmark, Jukka Starck in Finnish Occupational Health Institute and theNorwegian Committee for standardization of work place noise measurements for their contributions tothis work.

Oslo/Stavanger 2003-04-08

Tnnes Ognedal Iiris Turunen-Rise


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Summary

Reduction of work place noise has had low priority in the Nordic countries in many ways, but thisseems to be in change for the time being. The standards and measurement methods are old, noiselimits in regulations have been unchanged for a long time and the great uncertainty of themeasurement methods has resulted in uncertainty of the limit values and of the risk for noise-induced

hearing impairment at work. The EU work with an amended proposal for a Directive on requirementsregarding the exposure of workers to the risks arising from noise, introduces some new limits.However, there are no common measurement methods.

For the reasons mentioned, the need for improved methods of noise measurement and evaluationwas therefore found urgent. New Nordtest methods have been prepared with the aims to presentmethods with more reliable work place noise measurements and to quantify the uncertainty inmeasurements. The draft methods for survey and engineering measurements are presented. They arebased on short-term measurements and a new way of handling work place noise conditions. Theworking day may be split up in work operations with similar noise levels. The partial contributions fromthese with the related uncertainties, are calculated and used in the calculation of total noise exposurein a nominal day and related uncertainty for the working day.


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Contents

Summary..................................................................................................................................................2 0 Introduction......................................................................................................................................3 1 Scope of the project work ............................................... ..................................................... ............ 52 Time schedule and project organization .............................................. ............................................ 53 Background situation in Nordic countries - Regulations and measuring methods..........................6

3.1 Legal regulations .....................................................................................................................63.2 Denmark ..................................................................................................................................73.3 Finland .................................................. ....................................................... ............................ 73.4 Norway ....................................................................................................................................83.5 Sweden.....................................................................................................................................9 3.6 Europe......................................................................................................................................9

4 Problem description.......................................................................................................................104.1 Target groups of the measurement methods ........................................... ............................... 104.2 Factors influencing the measurements............................................ ....................................... 11

5 Methodology..................................................................................................................................11 5.1 Basic premises for the measurement methods.......................................................................115.2 Categorizing work place noise situations ............................................ .................................. 125.3 Determination of a nominal day (or week) and work operations ..........................................135.4 Splitting up of the working day to work operations having similar noise conditions ...........135.5 Selection of optimal measurement method............................................................................135.6 Sources for errors or natural variation? ................................................................................. 145.7 Measurement acceptance criteria - principles......... ............................................................. .. 16

6 Experimental data .............................................. ....................................................... ..................... 167 Differences between simplified and advanced measurements Survey and engineering method 17

8 Measurement uncertainty...............................................................................................................178.1 Introduction............................................................................................................................17 8.2 Calculation of uncertainty involving detailed information.................. .................................. 17

9 Conclusions on the project work ...................................................................................................20Annex A Bibliography...........................................................................................................................21

0 Introduction

Noise-induced hearing impairment is with great probability among the most common occupationalhazards in many countries. The reporting and statistics of work place hazards to authorities variesfrom country to country. In Norway, the reported number of cases is assumed to be just a top of thecases. These are estimated to be only 4 % of real number of cases. There are also reports that showthat the noiseinduced hearing damage is the largest group of occupational hazards in offshore. On

land a great number of employees are counted on to have hearing damage or tinnitus without beingaware of it to be an occupational hazard. In Finland the number of reported noise damages hasdecreased with 13 -14 % during the last 5 years. In Sweden noise damage was at the 4th place of thetotal number of work place hazards in 1999. In Denmark hearing damages were 11 % of the totalnumber of work place hazards in 2001. Noise-induced hearing damage occurs more often for menthan for women, for instance in Finland 95% of the cases were men and in Sweden about 75%. This isexplained by that men are more often working in noisy environments than women.

There are many uncertainty factors related to work place noise exposure measurements. Uncertaintiesmay be caused either by natural variation in the work pattern or by potential errors in themeasurements. If the work situation is complex, repeated measurements at similar work situations can


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lead to large variation in the result. It is therefore essential to know whether the variation is natural orfalse. The present Nordic and International methods do not consider this in a proper manner.

The measurement methods in Nordic countries are out of date or give only limited guidance ondetermination of the noise dose by measurements. ISO 9612 describes mainly uncertainty ofmeasurement instrumentation not that of sources for errors in the test method. It is necessary toobtain better understanding of conditions that influence the measurements. This is necessary both for

calculations based on point measurements of sound level and duration of direct measurements withnoise dosimeters used for determination of noisy areas. The risk for hearing damage is calculatedaccording to ISO 1999, where the data from noise measurements are basic. If the basic data frommeasurements or calculations are uncertain or insufficient, the calculations of risk for noise-inducedhearing impairment are not better than the input parameters.

Noise reduction measures are also widely discussed in the other Nordic countries. Directorate ofLabour Inspection has prepared a strategy for noise policy in work places.

In Finland the Finnish measurement standard SFS 4578 [1] is short and simple. Additionally, ISO 9612is used. There is also an ongoing Noise scan program for hearing damage prognosis. Prognosis ismade at intervals of 10 years until the age of retirement. The program is applied for occupationalhealth care, and includes a database where all useful information may be gathered and the hearing ofindividuals monitored, and which also may be applied to educational purposes.

In Norway, work with a national Norwegian standard was started the year before the Nordic work, butit has been stopped in expectation of the results from the Nordtest-study. Sinus AS has worked with aproject on improvement of the calculation and measurement methods, which were basic for thepresent Nordtest-project. Noise exposures are calculated for a great deal at work places at theNorwegian sector of North Sea. It has been shown by experience that there often are great differencesbetween prediction of the exposure and measurement results. Measurements are made by usingnoise dosimeters. The results often show a large standard deviation and spread. Some exampleshave shown as much as 10 dB to 20 dB difference between measured and predicted noise exposure.Noise dosimeters may show up to 10 dB to 15 dB differences in results for the same category ofemployees, which is not acceptable. Norsk Hydro has the last years been funding research in order tofind reasons for the discrepancy between prediction and measurement methods. These studies havebeen basic for the project work [2].

In Sweden, the regulation AFS 1992:10 Bulleris in force. The Swedish Work environment authorities

have made studies on noise exposure values in industry [3]. Many noise exposure measurementshave been carried out.

The European member states are preparing revised EU directive on the minimum health and safetyrequirements regarding the exposure of the workers to the risks arising from the physical agents(noise) that introduces additional requirements that are not in force in Nordic countries today. Theseshould also be reflected in the measurement methods for work place noise. Common methods thatinclude all actual required measurements are therefore preferable.

As a result of this Nordtest work, improved methods for measuring noise exposure have beensuggested, including use of both hand held sound level meters and personnel sound level meters, so-called dosimeters. Both a simplified (survey) and an advanced (engineering) method are suggested.Determination of a typical working day and splitting-up into shorter activity periods in relation to noiseexposure and the complexity of the working situation are specified. In each activity period the noise

exposure level and the uncertainty are evaluated before calculating the total noise exposure and totaluncertainty in a nominal working day.

The benefit of this project is better certainty of the determination of noise exposure and understandingof which factors will influence the final result. By improving the measurement methods and accuracy inthe results, proper noise reduction measures may be applied. This again reduces the risk for hearingdamage at noisy work places.


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1 Scope of the project work

The aim of the present work is to prepare a Nordtest-method in two parts, namely a simple method foruse to safety deputies, persons in industrial or occupational hygiene or in occupational health careetc., and a more advanced method requiring a great deal of competence in acoustics in order toachieve better accuracy in measurement results, if needed. The methods have to describe sources forerrors and uncertainty, show how large these may be, and give guidance on how to handle the errors

in order to get a most correct description of the noise situation at the work place.

Second aim of this project has been to develop method(s) of calculation and measurement of workplace noise exposure that are based on extensive platform from the Nordic countries. The sources forerrors and uncertainty are described. It is shown how to calculate how large these may be. Guidanceis given on how to handle the errors or calculate uncertainty. There is a great hope to achieve anagreement on improved Nordtest method(s) that may be applied in all Nordic countries.

Measurements inside hearing protectors at some ear canal position by using of miniature microphonesare described in EN-ISO 11904-1 for measurements at real ears [4], and in EN-ISO 11904-2 formanikin measurements [5]. These measurements are therefore not described in the scope of thepresent project, but they are considered to be adequate for such measurements. The calculation ofdaily 8-hour exposure may be made by using the present methods.

The project work does not include consideration of health risk for the workers or guidance for noisereduction measures, but the resulting methods may be used to determine the noise situation moreprecisely and improve the accuracy of the method(s).

2 Time schedule and project organization

A three-year project was planned for accomplishment of the project, as following:

Year 2002: Preparation and development of a basis for the common Nordic method(s).Year 2003: Round robin in the Nordic countries. Analysis and summary of the results.Year 2004: Modification of the method(s) on the basis of Round robin-test. Preparation of a finalmethod and final report.

The work planned in the years 2003 and 2004 may be performed during one year depending on theresults of the round robin test.

Responsible of the project work is the Norwegian company Sinus AS by Mr. Tnnes Ognedal asProject leader. The project group consists of members from Denmark, Finland, Norway and Sweden,as following:

Tnnes Ognedal, Sinus AS, project leaderHeli Laitinen, Finnish Institute of Occupational HealthPer Mberg Nielsen, AkustikNet A/SPer ke Nilsson, Ingemansson TechnologyIiris Turunen-Rise, Norwegian Council for Building Standardization

The project proposal was prepared by the project leader Tnnes Ognedal, Sinus AS, in co-operationwith Norwegian Council for Building Standardization (NBR), represented by Iiris Turunen-Rise (projectsecretary, coordinator).

As reference groups or experts there have been used the Norwegian national Committee onstandardization of work place noise measurements. NBR is working in parallel with the revision ofcomparable Norwegian standard for determination of work place noise exposure with a nationalcommittee who is prepared to function as a reference group for the work. In addition, representativesin Denmark, Jan Gybel-Jensen, Arbejdstilsynet, and in Finland, Jukka Starck, Finnish Institute ofOccupational Health, have been functioning reference experts.


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3 Background situation in Nordic countries - Regulations andmeasuring methods

3.1 Legal regulations

Comparison of the work place noise abatement and measurement conditions in the Nordic countrieshas been discussed. There are in addition several related regulations and common European

Directives considering machinery noise reduction, room acoustics for work place facilities, etc. Therevised European Directive on health and safety requirements regarding the exposure of workers tothe risks arising from noise [6, 7], is handled in 3.5. The EU Directives give minimum limitrequirements, i.e. more stringent regulations may be given at the national level. The adoption of theDirective will influence the present situation in Nordic countries, e.g. due to that additional limits haveto be included in the regulations of the Member states. The present requirements for work place noiseinclude C-weighted peak sound pressure levels to be measured. The new draft directive requiresconsideration of noise exposure close-to-ear within hearing protectors. The new EU limits yield also forseagoing vessels.

In the following, the limits for 8-hour (or in some cases 12 h) work place noise exposure of employeesare given for Nordic countries, see Table 1. Several other regulations concerning machinery noiselevels, room requirements for work place facilities etc., are not considered here.

The measurement methods in all Nordic countries are not up-to-date, are insufficient for determiningthe work place noise exposure with acceptable accuracy and lack expression of measurementuncertainty. Ways of performing the practical measurements also differ in the Nordic countries. Forinstance, foot following of the worker during the working day or the whole measurement duration iscommon in Danish measurements. In Sweden, point measurements of equivalent levels or maximumlevels by using Fast or Impulse response are very usual. Measurements with noise dosimeters onemployees are rarely used in Sweden. The difference between predicted work place noise levels andmeasured levels are often large.

The present situation is described in the following sections.

Table 1 - Comparison of the main regulations for avoiding risk for hearing impairment andsafety in the Nordic countries

Type of limit Denmark Finland Norway Sweden

0Aeq,TpL (dB)

85 (- 5)1) 85 85/70/552)833)754)

< 905)

85

LpAFmax (dB) - - (110)6)

(120)7)115

LpApeak (dB) 1158) - - -

LpCpeak (dB) 1158) 1409) 130 140

1) Measured as LpAeq. 5 dB is added if the noise is repetitive impulsive and the peak value exceeds 115 dB (C) or 115dB(A) more than once in a minute, i.e. the limit is then more stringent.

2) Three levels of limits depending on type of the work.

3) On offshore 83 dB for 12h working day.

4) On board vessels. At the boatmans place, telecommunication shall be available at levels above 75 dB.5) On board vessels. Obliged use of hearing protectors and signs on rooms from 90 dB.

6) Previous limit before revision of the work place noise regulations in 1993. Still used in evaluation of the noise-inducedhearing damage.

7) On board vessels, sign with Caution. Excessive high noise levels. Use of ear protectors mandatory. For shortinspections only. is given.

8) EitherLpApeak orLpCpeak may be selected.

9) Decision of the Council of the State provides the value to be unweighted. However, in practise C-weighted value isused.


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3.2 Denmark

3.2.1 RegulationsIn Denmark, there are regulations [8] and guidance for fulfilment of the regulations in the form ofofficial notice (bekentgrelse), information (meddelelse) and guidance (vejledning) that concern workplace noise abatement [9, 10, 11,12]. The limits are given in Table 1. In addition, consideration ofinfrasound (frequencies below about 20 Hz) [13] and ultrasound (frequencies above 18 kHz) [14] arerequired to be as low as possible and in accordance with the technical level of knowledge. Hearing

protectors are offered to be worn at work places where0

Aeq,TpL exceeds 80 dB [8] and have to be

used when the level exceeds 85 dB.

Directorate of Labour Inspection (Arbejdstilsynet) in Denmark has prepared a strategy for noise policyin work places with focus on the noisiest trades. Noise reduction measures are also widely discussed.Danish authorities, represented by Jan Gybel Jensen, participate at the work with EU draft Directiveon work place noise abatement [6, 7].

3.2.2 Measurement methodsGuidelines (AT-vejledning [12] )from Directorate of Labour Inspection (Arbejdstilsynet)contain advice

for methods for measurement and handling of noise problems. There are no direct obligations on howto measure. Most of the measurements are made by occupational health service at the place of work.Measurements by using dosimeters and calculations are usually combined. Only few people make 8-hour measurements.

3.3 Finland

3.3.1 Regulations

In Finland, the decision no. 1404/93 of the Council of State about protection of the employee fromdanger and damage caused by noise, states the principles used at work. The limits for noise are givenin Table 1.

The employer shall ensure that the noise at work is evaluated and if necessary, measured, and thatthe measurement is planned and performed with competence.

The employer shall ensure that the risk for danger and hearing damage, caused by noise, are as smallas possible. If the limits are exceeded in spite of the cautions, a noise control program shall beprepared. If the noise cannot be lowered by technical means, hearing protectors are provided, and theemployee is to be trained to use them. Also the areas of the noise are to be marked with warningsigns. The decision provides additional suggestive guidelines for noise measurements and hearing ofthe employee.

Finnish authorities represented by Ilkka Kyttl, Ministry of Social Affairs and Health, participate at thework with EU draft Directive on work place noise abatement.

3.3.2 Measurement methods

Finnish standard SFS 4578 [1] and ISO 9612 [16] are applied for work place noise measurements.However, SFS 4578 is out-of-date, and can be used as guidance only. The Institute of OccupationalHealth makes most of the work place measurements in Finland, but problems are solved andresearched elsewhere as well. A mapping method and follow-up methods are used.


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3.4 Norway

3.4.1 RegulationsIn Norway, several authorities specify regulations for work places depending on the type of workconditions. On land, the Directorate of Labour (Arbeidstilsynet) and The Ministry of Labour andGovernment Administration have the main regulations for noise levels at work places [17] both in orderto reduce the risk for noise-induced hearing damage and to improve the environment at work placesrequiring communication, concentration etc.

On offshore, Ministry of Petroleum and Energy and the Norwegian Petroleum Directorate have theirown regulations with limit values for work place noise exposure [18], see table 1. On board seagoingvessels, the Ministry of Trade and Industry and Norwegian Maritime Directorate specify the noiseregulations [19]. Implementation of the new European Directive on work place noise, intended for landuse, offshore and on board seagoing vessels, may reduce the number of legislative regulations inNorway, if/when implemented.

As mentioned initially, in addition to the common noise limit of 85 dB, there are two other level limitsfor work place noise in Norway, depending on the type of the work. If the workers are exposed toconditions normalised equivalent continuous A-weighted sound pressure level above the limits inTable 2, the employer is obliged to take measures to reduce the noise exposure. At work place projectplanning stage and when buying production equipment, the recommended limit for workers noiseexposure is set to 10 dB lower than the required limit.

Table 2 - Regulations for land use in the Norway

Category Work conditions Normalised equi-valent continuous A-

weighted SPLdB

I Great requirements for continuous concentrated workor need for non-stressing communication

55

II Important to keep communication or continuous greatneed for precision, fast responses or awareness

70

III Noisy machinery and equipment under conditions thatdo not belong to category I or II

85

Allcategories

Rest rooms 55

The Norwegian building authorities also give minimum room acoustics criteria of work place facilitiesand requirements for the construction works of buildings intended as working environments.Requirements for noise from building services at the working rooms and sound absorption of thematerials at work places have to fulfil the minimum limit values given in Norwegian Standard NS 8175[20].

Hearing ability of the workers shall be regularly examined.

3.4.2 Measurement methods

For workers in categories I and II, the regulations require that the equivalent level shall be measuredfor more than 1 hour. The limits in categories I to II and also III apply to the noisiest hour during aworking day. The present measurement methods that are used on land in Norway are NS 4814:1977Measurement of noise with sound level meter [21] and NS 4815:1982 Determination of occupationalnoise exposure [22]. For offshore installations, Norsok standard NORSOK S-002N:1997 Workingenvironment [23] specifies guidance and procedures on noise and vibration control and noisereduction measures. In addition, guidance on setting noise limits at the various environments on


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offshore, are provided. Noise from permanent building services at work places is controlled bymeasurements in accordance with prNS 8172:1999 [24]. On board on vessels, a detailedmeasurement method is included in the national regulations [18].

The present main Norwegian standards NS 4814 [25] describing simplified measurements andNS 4815 [26] describing more advanced methods, are under revision at the moment. These standardsare not up-to-date concerning present legal and technical requirements for work place noise measure-

ments. The revision is therefore urgent. However, the present Nordtest work has caused that the workhas more or less stopped because the national committee is awaiting results from the Nordtest study.

3.5 Sweden

3.5.1 RegulationsThe national regulations on noise at work environment are given in AFS 1992:10 Buller (Noise) [3].Noise exposure limits are stated, but active improvement of the work place environment throughplanning and protective measures is also required.

The common rules require that the work shall be planned in order to get lowest possible noiseexposure on the employees. If the exposure exceeds the given values, measures shall be initiated.The program for noise reduction measures shall be documented and shown to the authorityinspectors. Workers with hearing damage are to be offered more quiet surroundings, if possible.Communication during the work shall be possible.

The producer, importer etc. is responsible for machinery to produce as little noise as possible, andthey have to give descriptions of noise reducing measures, if needed. The lowest possible noise levelsare to be achieved. The machinery has to be placed in such a way that the noise exposure is limited tosmallest possible area, e.g. by shielding or placement in other rooms. A warning plate on risk forhearing damage shall be placed on machinery or plant areas where noise exposure limits areexceeded. Also, signs for use of hearing protectors has to be used. Measurements are to beperformed to such an extent that all noise exposure is considered.

Hearing ability of the workers shall be examined, more often in places where the noise levels ashigher, i.e. with the increasing risk.

3.5.2 Measurement methodsMeasurement procedures are sparsely described in AFS 1992:10. The Swedish Technical Committee(SIS TK 110) has prepared a preliminary draft of guidelines for the measurement of occupational noiseexposure [27] based on ISO 9612.

3.6 Europe

3.6.1 Regulations

Draft Amended proposal for a directive of the European parliament and of the council on the minimum

health and safety requirements regarding the exposure of workers to the risks arising from physicalagents (noise) (nth individual directive within the meaning of Article 16(1) of Directive 89/391/EEC) [6,7] is at final stage for acceptance. The time-weighted average, defined in accordance with ISO1999:1990 [28], is recommended to be measured on daily basis as a daily noise exposure level.

For the purposes of this Directive the exposure limit values and exposure action values in respect ofthe daily noise exposure levels and peak sound pressure are fixed as following:

a) Exposure limit values: LAEX,8h = 87 dB andppeak = 200 Pa

b) Upper exposure action values: LAEX,8h = 85 dB andppeak = 200 Pa


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c) Lower exposure action values: LAEX,8h = 80 dB andppeak = 112 Pa

In duly justified circumstances, for activities where daily noise exposure varies markedly from oneworking day to the next, Member States may, for the purposes of applying the exposure limit valuesand the exposure action values, use the weekly noise exposure level in place of the daily noiseexposure level to assess the levels of noise to which workers are exposed.

The weekly noise exposure level as shown by adequate monitoring, is not allowed to exceed theexposure limit value 87 dB, and appropriate measures have to be taken in order to reduce the riskassociated with these activities to a minimum.

3.6.2 European and International measurement methods

As the draft Directive refers only to International standard ISO 1999:1990Acoustics Determination ofoccupational noise exposure and estimation of noise-induced hearing impairment[28], there is not anyguidance on measurements. This enables the Member states to use or prepare their own methods.ISO 1999 contains only a calculation method for probability of noise-induced hearing impairment afterknowing the workers noise exposure at ear position (10 cm from the ear) during exposed workingyears, corrected for the age, etc. It is used by health services and does not include any further

guidance on measurements.

The International standards for determination of sound pressure levels close to the ear, ISO 11904-1and 2 [4, 5], are actual to be used in cases when determining the noise exposure for sources close tothe ear. These methods do not contain any calculation of 8-hour daily or weekly noise exposure of theworker.

The International standard ISO 9612 [16], which might have been the most actual to be used at thepresent situation, has not been accepted by the majority of European countries (CEN) to be publishedas European standard. The revised EU directive on the exposure of the workers to the risks arisingfrom noise introduces also additional requirements, which should be reflected in the measurementmethods for work place noise. The contents of ISO 9612 do not sufficiently describe the followingmatters:

Choice of measurement procedure related to work situation Specific requirements for measurements using personnel noise level meters (dosimeters) Specific requirements for measurements using hand held sound level metres How to avoid typical sources for errors and how to evaluate results with respect to these. How to observe and handle natural variations How to calculate uncertainty caused by natural variations and/or by sources of errors Calculation and presentation of final result and total uncertainty

In case of vibrations, a measurement method for 8-hour-exposure is in preparation and is described inprEN 14253 [29]. The contents of this standard have also been considered in the present Nordtest-project.

4 Problem description

4.1 Target groups of the measurement methods

The target groups for making work place measurements are often very variable. The measurementoperators may have very different occupational and educational background, e.g. these problems maybe handled by persons in industrial or occupational hygiene, environmental health sanitary service,safety deputies, personnel in companies and industry, consultants, etc. This caused a great challengefor the project work and preparation of the method for determination of noise exposure at work. Themeasurement and calculation method(s) have therefore to be dependent on the competence of the


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measurement operator. They have to be practical in order to be used and in the same time givequalified measurement results.

In conclusion, both survey (simplified) and engineering (advanced) methods are needed. A surveymethod has to be descriptive enough to give desired results without detailed consideration ofuncertainty or extensive description of possible sources for errors, variables etc. This is done on thecost of accuracy of the method. The draft methods are in addition related to the complexity of the

types of work activities and noise situation. The engineering method is especially needed for situationswhere the noise exposure is very complex and when the uncertainty of measurement result is greatafter measuring by using the survey method. Measuring problems and handling of the results areexpected to arise although a data calculation sheet is made available.

4.2 Factors influencing the measurements

There are many factors related to work place noise exposure measurements. These matters may bedealt with in two main groups that influence the measurement results, firstly definition of the workingday, i.e. the nominal day, and secondly the measurement technique and the method selected. Thefollowing matters have been thoroughly considered during the project work.

a) Determination of the measurement time intervals and the duration of work operations;Determination of the duration of a work operation is connected the related necessarymeasurement time to achieve the desired accuracy and repeatability.

b) Work operation conditions for a normal situation, determination of the nominal day;Proper description and defining of a complex working situation is decisive for the quality of thefinal results. Determination and specification of a typical working day, the nominal day, has agreat influence on the further measurements. If it is erroneous, the following measurements areconsequently influenced by this definitions. Use and preparation of a detailed log for themeasurement operator, or a log for the worker in the survey method, gives necessary informationand may be valuable when searching possible sources for errors or uncertainty in the results.

c) Selection of workers locations and related measurement positions;Changes in the workers positions and locations, movements from a working place to anotherincrease the spread in measurements and possibility for selecting erroneous measurementpositions. Sources close to the ear add the possibility for varying measurement results..

d) Selection of measurement technique and optimal measurement method;The factors purely related to the used measurement technique may increase the uncertainty ofthe measurements. The presented measurement methods have to allow use of both sound levelmeter and a noise dosimeter. The measurements may also, preferably, be made by combiningboth sound level meter and noise dosimeter measurements during the same working day. Theresulting noise levels should be possible to calculate on the basis of shorter measurementperiods than 8 hours combined with observations.

e) Determination of normal work activity pattern during a nominal day;Due to the influence of numerous matters, measurements at similar work situations may lead tolarge variation in the result or give a great difference if measurements are repeated inconsecutive days. It is therefore essential to determine whether there is variation in the work,which is natural for the actual working situation, or if there are false responses due to that theinitial parameters used in defining the nominal working day are not correct or if the measurement

technique is not suitable.Sources for errors due to own working activity are handled in different ways in the Nordiccountries. The methods have to cover the possibility to measure these contributions, and to givea possibility to exclude them in the final calculations.

5 Methodology

5.1 Basic premises for the measurement methods


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As mentioned initially, there were several matters, legal and others, that set the premises for thepresent Nordtest project work. The following general conditions were considered to be basic for themethodology to be used for the work place noise measurement methods:

1. Measurements have to be made at the exposed ear in relation to a reference time (8 h or 12 h), inagreement with EU Directive, and consideration of ISO 1999.

2. The method shall be general and basic in such a way that as many of the work conditions are

covered as possible. Both daily and weekly noise exposure calculations may be performed inaccordance with the draft EU Directive.3. A normal working day, the nominal day, shall be determined both in survey and engineering

methods.4. The method shall contain all the basic quantities used in the Nordic countries and the draft EU

Directive: LpAeq,T, LpApeak, LpCpeak and LpAmax.5. A frequency analysis is allowed to be made in order to take measures or for other purposes, but it

is not required as a normal procedure.6. Various methods are included in order to get methods being applicable at the various work

situations, and by the various measurement operators.7. The possible sources for errors in measurements have to be described and guidance is needed in

order to distinguish these from the natural variation in the measurement results due to the actualwork pattern.

8. Handling of the measurement uncertainties have to be described in order to get more reliableresults. [30]

Definitions were taken, as far as possible, from relevant standards.

5.2 Categorizing work place noise situations

The most of the work place noise conditions may be described by grouping of the working situation inrelation to noise conditions and working activity. The following four categories were found to covermost of the cases:

1. SPL in the room is constant (one level number for the whole room) and the working place isstationary, i.e. constant noise exposure. Simple single point measurements are possible.

2. SPL is constant but the working place is movable.

3. SPL varies and the working place is stationary.4. SPL varies and the working place is movable. This gives a complex noise situation andmeasurements done by observing workers are strongly desirable.

In Table 1 this is shown schematically. Noise exposure at a fixed working place with a constant noiselevel is simpler to survey than the noise exposure of a moving employee in areas with changing typeand level of the noise. The splitting up of noise and working conditions then improves themeasurement accuracy in a complex work place noise situation. The table is therefore included in thedraft methods.

Table 1 Categories of working day based on the complexity of the working situation

Category Work place Noise level Complexity

Stationary Movable Constant Varying

1 X X Low

2 X X

3 X X

4 X X High


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5.3 Determination of a nominal day (or week) and work operations

Determination of a typical working day, hereafter called a nominal day, is one of the main, basicsources for uncertainty in measurements. It is not in itself connected to measurement technique andmethodology, but the definition of the nominal day has a great influence on the selection of themeasurement method, selected measurement time interval, selected duration of the working operationfor the calculations and the resulting measured SPL.

The typical working day is usually defined by the actual employer/company in cooperation with theemployee. The correct and accurate information of the working day or work pattern and routines arevery important for the later measurements. Errors in these background data influence the measured orcalculated duration used in the determination of total noise exposure. In order to improve the accuracyof the measurements, it is important to define the working day as well as possible. It is essential forselecting measurement time intervals and when calculating the daily noise exposure.

The following matters are to be clarified for determination of the nominal working day:

A. Describe/identify the test person (worker).B. Describe/identify the various work operations the person does.C. Describe typical working operations during the day according to the table 1.D. Describe if the work consists of work patterns that belong to one or several categories.

E. Categorise the various parts of the work.

5.4 Splitting up of the working day to work operations having similar noiseconditions

After determining the category of the typical work situation, the nominal working day may be split intosimilar work operations or shorter segments that have similar and repeatable noise patterns, and thathave as equal noise conditions as possible, for which the most suitable measuring method can beapplied. In each work operation or segment the noise exposure level and the uncertainty due to themeasurements and changing working conditions during a typical working day, have to be evaluated.After determining the noise exposure for the actual working operations, the overall (total) noiseexposure and overall uncertainty may then be calculated from the exposure data at these workoperations or partial segments.

Sometimes the nominal day may not be split up and then the whole day is considered as one period.By splitting up the working day, the measurement accuracy is expected to get better. On the otherhand, the apparent statistical uncertainty may become greater under some conditions and there isboth a practical and statistical limit for reasonable splitting, see section 8.3.3. Therefore, it is essentialto make the splitting in a reasonable manner in order to avoid excessive erroneous results.

There are several possibilities to handle these activity periods in the final calculations. The periods oflow sound levels that do not contribute significantly to the final result of noise level, may be consideredas one group when calculating the final result. These will then not change the final result. Analternative way is to combine all groups with the same kind of noise exposure level during a nominalday in order to simplify the calculations. Noise exposure from each type of noise period and estimationof partial uncertainty for these periods is used in calculation of the final estimated total uncertainty forthe daily or weekly exposure, whichever relevant.

5.5 Selection of optimal measurement method

The selection of a good measuring procedure is strongly connected to both the defined work situationand the purpose of the measurements. There are various matters that should be evaluated beforestarting the measurements and during the investigation process. The guidance Table 1 forcategorizing of the working day on the basis of the complexity of the working situation may be helpfulin this.


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As mentioned previously, the proposed measurement methods include the possibilities to use bothsound level meter and noise dosimeters. It was found that both types of instrumentation might be usedin most of the cases of noise exposure or working situations. In some cases, it is an advantage tocombine both sound level meter and noise dosimeter measurements during the same nominal day.Measurements with noise dosimeter placed close to the workers ear, have to be observed by themeasurement operator in order to get the engineering grade of accuracy. Short stay in areas with veryhigh sound levels has a great importance for the measured SPL. Using parallel methods may also

reveal errors. Own working activity and stay close to the noisy equipment may cause great variationsin the SPL and is a source for measurement errors. In such cases use of a noise dosimeter is anadvantage.

Limits for the noise exposure inside hearing protectors are given according to the draft EU Directiveand, in addition to the traditional measurement instrumentation, measurements below hearingprotectors or similar, i.e. at ear canal or concha, may be necessary. This Nordtest project has notconsidered measurements in such cases, since the Draft International Standards with methods forsuch cases exist [4, 5]. Then the use of miniature microphone in accordance with ISO 11904 isrecommended. Measurements according to ISO 11904 may also be performed when consideringclose-to-ear-levels, e.g. noise from nail guns. The calculations of 8-hour noise exposure anduncertainty, given in the present methods, may be used for the close-to-ear noise situations.

The following technical matters may be useful to keep in mind when selecting appropriatemeasurement technique. In a fixed point/steady state noise situation, the measurement position isrelevant, but there is no need to have a person following the worker and the use of noise dosimeter isnot required. In a variable noise situation, the measurement position is important. In a homogenousnoise field, the measurement position not especially important.

In some cases and when predicting the noise situation before measurements, other means of differingbetween various work activities, are in use. Then the noise conditions are often, e.g. in offshore, dealtwith as following: 1) Area noise levels; 2) Close-to-ear noise levels; and 3) Noise from hand held tools.These three cases may be handled differently in regulations, e.g. the limit may be related to the typicalnoise level of the installation. When predicting work place noise levels prior to planning or measuring,it is useful to distinguish between the three cases.

The noise contributions in these three cases are regarded somewhat different by nature due to thefollowing matters. The diff iculty of the measurements is increasing, and consequently the uncertainty,when measuring very local noise levels. In cases 2 and 3, it is normally more difficult to take noise

reduction measures than when determining area noise levels, and the measuring method is mostcertainly different from case 1. The contribution from area noise levels may be calculated fairly well,while contribution from close-to-ear levels more or less has to be estimated. If the purpose is tocompare measurements with calculations, this separation of the cases is relevant. Prediction is not apart of the draft Nordtest proposals and these matters are not described in specific.

5.6 Sources for errors or natural variation?

Obviously, measurement errors shall be avoided. This may be done by repeating measurements, orby ensuring that false contributions are not recorded or included in the measurements. However, itshould be distinguished between sources for errors and natural variation in the working pattern orconditions that influence the SPL and performance of the measurements.

Sometimes false contributions are difficult to avoid and such sources for errors normally lead to ahigher measured value. This may be unavoidable and acceptable in survey measurements, when themain purpose is to evaluate if the noise exposure is within the limits. However too high values may beregarded as increased safety for reduced risk for damage.

The following factors were considered to contribute to the total measurementuncertainty and may alsolead to errors:

a) Operators;Typical errors caused by the measurement operator may be reflections from the body to


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microphone due to small distance, position of the noise dosimeter on the test subject and humanfactors like within operator and between operator variations.

b) Instrumentation;Factors that may become sources for errors due to the measuring equipment, may be calibrationand within and between instrument variation, e.g. component variation in equipment.

c) Ambient conditions;Ambient conditions may influence the functioning of the measurement equipment in the worksituation. Wind-induced noise, air movements indoors and temperature have therefore to beconsidered by the measurement operator. Changes in wind speed and air humidity conditions arevery predictable and the measurements should be made under conditions that do not causemeasurement errors. Weather conditions, work place activity and external noise sources may besometimes considered as natural variation in the work and sometimes they may be defined assources for errors. If the measurements have to be performed in wind or at high-speed airflows,comparable measurements may enable a better understanding of the noise contribution in thatperiod.If for instance the measurements are performed by using a personal sound level meter without awindscreen, comparable measurements may be performed by using a handheld sound level meter.This may be held outside the airflow and/or may be fitted with a suitable windscreen.The measurement period that is disturbed by the wind noise, has to be analysed separately.Provided the contribution from the windy period to the total noise exposure is less than 3 dB, thenthe calculated total noise exposure may be accepted as an estimate. Such matters have to bethoroughly described in the test report. When the contribution is higher than 3 dB, the result have tobe considered unreliable and the results have to be rejected.

d) Test method;The workers own working activity and stay close to the noisy equipment are easily sources formeasurement error. When the workers noise exposure occurs close to the noisy equipment, it canbe strongly dependent on the head position and use of a noise dosimeter is an advantage. Evensmall changes in the posture of the worker may cause great changes in the result and measuring ina wrong position. Unclear matters in the results due to the working situation may be clarified byinterviewing the worker, which is necessary to do both in the survey and engineering methods.

e) Working conditions;

Impacts on the microphone create false contributions. The risk for measurement errors increasewhen the worker takes his clothes on and/or of, when the work is performed in narrow spaces, andwhen the worker is creeping, crawling or similar. If the risk for errors or false contributions of thistype is high, it is recommended to increase the number of measurements.

f) Noise levels between different measurement occasions;If the measurements that are performed at different days give very variable SPLs, it is consideredto reflect uncertainty. Changes in the work place (indoors/ outdoors/ by a machine/in the far field ofmachines etc), the workers posture (standing/sitting/moving), the dominating noise sources in theworking area, e.g. stationary equipment, noisy machines and use of hand held tools and similar,influence the measurements from day to day. In such situations the effect of these errors may becalculated and discussed as described in the engineering method. This was considered to be toocomplicated to perform in a survey method.The highest and lowest noise conditions may be defined and calculated. The results may be given

as the minimum and maximum duration with the related noise exposure levels since both durationof work operation and SPL contribute to the total statistical uncertainty.

g) Stay duration for personnel between different measurement occasions;Stay duration for personnel between different measurement occasions is a cause for uncertainty.Changes in duration of each work operation, in the area sound levels or close-to-ear noise levelsfrom use of hand held tools or hearing protectors or similar may be considered as natural variableswhen they are a part of the typical working situation. If they are not, then it may be a matter ofredefining the typical working situation and a source of error in the basic assumptions behind themeasurements. If the measurement time has to be very long because of a complex work pattern,


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the risk for such errors always increases. The amount of work in several long-term measurementsalso increases with the measurement time.

h) Various types of non-relevant noise for instance mechanical affects of the microphone, shouting orhigh speech, high sound levels from radio, etc.;Non-relevant noise may be handled in various ways in different regulations and countries. PA-systems may sometimes be considered non-relevant and sometimes a part of the noise situation.

Therefore whether these contributions may be regarded as variables or as sources of errors, has tobe evaluated in each case. It is also a question of whether this background noise may be ofimportance or not.

5.7 Measurement acceptance criteria - principles

A principal matter in evaluating the measurement results is if extremely high peak values that oftenoccur in work place measurements (especially with noise dosimeter), shall be valid or not. Thequestion is if these may be considered as errors, e.g. non-relevant peak values, or not.

There are two possibilities for action: 1) to delete or correct such erroneous extremely high peakvalues as measurement errors after checking the work situation and by interviewing the worker, or 2)to repeat the measurements. In order to avoid such peak SPLs, instructions should be given to theworker on how to behave during the measurements with respect of wearing the clothes on

continuously etc.

Repeated measurements have been considered to reduce the risk for measurement errors. At leastthree measurements in each period are considered necessary for increasing the statistical accuracy,but increasing the number of measurements will reduce the uncertainty. Repeating the measurementsgives more also information on the variation. When splitting up the working day to periods with moreequal noise conditions, a shorter time for measurements may be allowed. Consequently, shortermeasurement durations increase possibility of making several measurements.

The acceptance criteria have been suggested for repeated measurements. In experience, a differenceof 2 dB between consecutive measurements was considered to be very stringent. A 3 dB differencewas then accepted in the engineering method. However, it is preferred to be tested during a futureround robin test of the method in order to confirm it or adjust it. It is not possible to describe theaccuracy of the presented new methods without testing them. Therefore the accuracy and need for

exclusion or other handling of erroneous measurement results have to be investigated in a futurework.

In order to be able to give more exact evaluation, systematic measurements by using the engineeringmethod is needed. Performing a Round robin study where this Nordtest-method is used, may do this.

6 Experimental data

Since the measurement methods are new and differ from the existing national methods and nofinancial support has been available for practical measurements, there are hardly any data based onthe presented methods. Norwegian data from practical measurements and predictions have beenused for calculations to test the considerations of measurement uncertainty. Some measurementsthat have been performed by Sinus AS, have been evaluated both by using foot-following andinterviewing of the workers.

In 3 4 larger noise exposure surveys performed for the offshore industry, the measurements and thecalculations have been performed on the same principles as given in this NORDTEST method. Even ifthe method was not fully developed when these projects were performed, the way to structure thework and the report was based on the same concept. Noise exposure evaluations were based on botharea noise level measurements and measurements with noise-dose metres. The reports gave a goodoverview of the partial contributions, for further evaluation of noise reduction.

In Annex C examples of practical calculations are shown with the use of the formulas. However forpractical use, spreadsheet calculations are recommended.


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7 Differences between simplified and advanced measurements Survey and engineering method

The survey draft method is based on the engineering method and items that were considered to benon-relevant or too complicated for survey measurements, are deleted. The following matters weredecided to be excluded from the survey method:

1 Calculation of uncertainty;2 Repeating of measurements. Only three measurements are required;3 Elimination of the sources of errors, just reporting of these.4 No foot following of the worker by the measurement operator.5 Presentation of the results without statistical expression of the uncertainty/variability.

The survey method is intended for evaluating if the noise exposure is within limit, above limit or iffurther studies should be performed. The calculation of statistical uncertainty is complicated andrequires advanced knowledge in acoustics and statistics. Since no specific calculation of statisticaluncertainty is performed, the need for repeating of measurements is less.

Handling of sources for measurement errors also requires a qualified operator. In the survey method,the operator has to only report possible sources for errors. These may be used in further examination

of the noise conditions, if needed. The measurements are additionally simplified by less observation ofthe worker. The worker should register his/hers movements in an activity log, as often is the casetoday. For better accuracy in complex work situations, advanced measurements by using theengineering grade of accuracy are usually necessary. Then the evaluation of uncertainty, as given inSection 7, is necessary.

8 Measurement uncertainty

8.1 Introduction

The main goal for the estimation of uncertainty is to enable repeatable measurement results, within areasonable, but sufficient number of measurements. To obtain repetitive measurements theuncertainty must be determined to be within a given margin M. If the uncertainty exceeds the required

margin M, several measurements are needed. The uncertainty can be calculated from a number ofcomplete measurements, where the measurement time is set equal to the length of the entire workingday, but at least three measurements should be made..

8.2 Calculation of uncertainty involving detailed information

8.2.1 GeneralThe number of total measurements required to obtaining an uncertainty within a margin, M, could bereduced by using detailed information as:

Noise levels and uncertainty;

Occupation time and corresponding uncertainty.

The total noise exposure level can then be defined by the following quantitiesx1,...,xN,t1,...,tNwithpartial uncertainties x1,...,xN, t1,...,tN, wherexidenotes the noise level associated with activity i,and ti the corresponding duration. The total noise exposure level LpAeq,twith corresponding uncertaintymay than be derived from a function f(x1,...,xn,t1,...,tn). Assuming that all parameters are independent,the uncertainty can be estimated by:


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22

1

1

22

1

1

++

+

++

= N

N

N

N

tt

f...t

t

fx

x

f...x

x

ff 1)

The problem can now be defined as: finding parametersx1,...,xN,t1,...,tN in a such way that we can find,within a minimum number of measurements, f M.

8.2.2 Partial noise levels

The partial noise levels and corresponding uncertainty can be derived from several measurements (atleast three for each activity. The noise levelxifrom an event icould be estimated from Nindividualmeasurements,xi,n. The noise levelxiassociated with activity ishould then be defined as:

==

N

n

x,

in,i

Nx

1

1010

1log10 2)

the corresponding uncertainty could be estimated by:

= ==

2

11

2 1

1

1 N

nn,i

N

nn,ii xNxNx 3)

8.2.3 Influence of the duration

The duration of a work operation or time spent in a certain area or work operation, may be derivedfrom:

Definition of a nominal day: (e.g. a working day duration is 8 hours, of which 45 min arebreaks)

Measurement: the time spent on various work operations may be measured several times.

The time spent on a particular event i, can than be defined as:

==

N

nn,ii t

Nt

1

14)

with corresponding uncertainty given by

=

==

2

11

2 1

1

1 N

nn,i

N

nn,ii t

Nt

Nt 5)

8.2.4 Calculation of total noise exposure level

The function f(x1,...,xN,t1,...,tN) for the total noise exposure of a worker is then as following:

( )

===

N

n

x,

nT,pNNnt

TLt,...t,x,...,x

1

10

Aeq11 101

log10f0

6)

From this expression the time and noise level dependent quantity defined in expression 1) can befound:


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=

=

N

n

x,

n

x,

i

n

i

t

t

x

f

1

10

10

i 10

107)

( )

=

=

N

n

x,

n

x,

in

i

tt

f

1

10

10

10

10

10ln

108)

It is assumed that a 95 % confidence interval for the total noise exposure level can be determined asfollowing:

LpAeq,t 2 x f i.e. P(LpAeq,t- 2 x f < LpAeq,t < LpAeq,t+ 2 x f) = 0,95

One may find it unnatural that the confidence interval is symmetric about the mean value. Uncertaintydue to duration is of course not symmetric. For instance, an increase in occupation time of 50 %means maybe an increased level of 1 dB while a reduced occupation time of 50 % means 2 dB lowernoise level. Consequently, one might suppose that the confidence interval should be unsymmetrical aswell. However, the uncertainty due to level is not symmetric, but it is lopsided the other way. Sincenormally it is dealt with only small values, it may be expected that the confidence interval is very close

to symmetric and that the first order approximation is good.

8.2.5 Practical application of the uncertainty calculations

To reduce the uncertainty of the sound levels from each work operation, it is desirable to define thework operations sharply, i.e. the number of different work operations should be divided into sub areasand sub operations in such a way that the sound level dispersion within each operation is limited. Ifthis is done correctly, the uncertainty should decrease with increasing resolution.

However by dividing the work in to sub-periods, the uncertainty due to uncertainty in the duration ofthe work operation will increase. At some point, the uncertainty due to the duration will exceed the

uncertainty due to noise level. At this point one should evaluate if it is reasonable to split the workingday and the work tasks into several sub-periods or not. From the formulae 1), 7) and 8) it may befound that the uncertainty due to the duration exceeds the uncertainty due to noise level when:

( )i

i

i xt

t

10

10ln9)

At this point, the uncertainty will increase if one increases the resolution. However, the resolution maybe increased if several determinations of the duration of the work operations are made and therebythe uncertainty due to the duration is reduced.

An Excel spreadsheet for these calculations is included in the method in order to enable automaticcalculation of the final results.

8.2.6 Estimation of the standard deviationThe main goal for the calculation of uncertainty is to obtain the mean noise exposure level within adesired accuracy. If the accuracy is too low, the number of measurements must be increased. Byincreasing the number of measurements the accuracy can become very good, but traces of the naturalspread in noise level from one day to another or variation between the workers, may be lost.


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It is therefore suggested to make an estimation of the total standard deviation. The calculation of thestandard deviation may be found from the function f(x1,...,xn,t1,...,tn). Assuming that all parameters areindependent, the standard deviation may be estimated from the formulae:

22

1

1

22

1

1

ffff

++

+

++

= N,t

N

,tN,L

N

,L

t

...

tx

...

x

10)

where

( )

=

==

2

11

2 1

1

1 N

nn,i

N

nn,ii,L x

Nx

N 11)

and

( )

=

==

2

11

2 1

1

1 N

n n,i

N

n n,ii,t tNtN

12)

If one wishes to estimate the standard deviation, it should at least be performed six separatemeasurements of each activity. Accuracy of these calculations has not been evaluated.

9 Conclusions on the project work

Qualified draft measurement methods are presented for both survey and engineering purposes. Thedraft Nordtest method proposals present a new way of thinking and performing measurements ofnoise exposure at work places. The aim of the methods was to improve the noise exposuredetermination, of a worker or at a work place, both under simple work conditions and in complex work

situations where the noise conditions are difficult to predict and measurements are complicated.The draft measurement methods are provided both for advanced engineers or other measurementoperators, and for surveying measurements with less requirements for the measurement operators.The methods also provide possibilities to determine all the basic quantities used in the Nordiccountries and required in the draft EU Directive.

The methods provide specifications and guidance for determination of the nominal working day andhandling of complex work situations for reliable measurements. The engineering method provides inaddition specifications and guidance for calculation of measurement uncertainty and handling ofsources for errors and natural variation in the work pattern.

In order to quantify and control the functionality of the described methods, it is strongly desirable totest these e.g. by performing round robin-tests on selected work places. Such testing will giveinformation of the statistical accuracy, the practical applicability of the methods and acceptance criteriafor the number of measurements needed in order to achieve a certain accuracy. An application for thefuture work on testing of the presented methods has therefore been sent to Nordtest.


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Annex A Bibliography

[1] SFS 4578 Melualtistuksen mittaaminen (Mtning av bullereksponering). Finsk standard, 1982-06-

30.[ 2 ] Norsk Hydro. Prediksjon og mling av styeksponering. En Fou-studie av forhold som pvirker

personlig stydoser og hvordan beregninger og mlinger kan forbedres. Tnnes Ognedal, SinusAS.

[3a] AFS 1992:10 Arbetarskyddstyrelsens forfatningssamling: Buller. Arbetarskyddstyrelsenskungrelse med freskrifter om buller samt allmnna rd om tillmpningen av frskrifterna.Swedish regulations. 1992.

[3b] Buller ananlys och lsningar. Bullerbekmpning. Demo CD-rom Arbetarskyddsnemden 2000.

[4] prEN-ISO/FDIS 11904-1 Acoustics - Determination of sound immissions from sound sourcesplaced close to the ears - Part 1: Real-ear technique (REAR)

[5] prEN-ISO/DIS 11904-2 Acoustics - Determination of sound immissions from sound sourcesplaced close to the ears - Part 2: Technique using a manikin (manikin-technique).

[6] Draft EU Directive: Amended proposal for a Directive of the European Parliament and of theCouncil on the minimum health and safety requirements regarding the exposure of workers to therisks arising from physical agents (noise) (nth individual Directive within the meaning of Article16(1) of Directive 89/391/EEC)

[7] Council common position for adopting a European Parliament and Council directive on theminimum health and safety requirements regarding the exposure of workers to the risk arisingfrom physical agents (noise). 2002/C45 E/02. 2002-02-19.

[8] Stjgrnser p arbejdspladsen. Arbejdstilsynets bekendtgrelse nr. 801 af 4. oktober 1993.

[9] At-vejledning: Stj. Erstatter At-meddelelse nr. 4.06.1 af september 1995.

[10] Stj p arbejdspladsen. 4.06.1.Erstattet af At-vejledning D.6.1.

[11] At-anvisning. Akustik i arbejdsrum. Nr. 1.1.0.1. November 1995. Erstatter: December 1991.

[12a] At-vejledning. Et stjsvakt arbejdsmilj. En vejledning om mling av sty p arbejdspladsen.1992-413-43

[12b] Grundbog i stjbekmpelse. Jan Gybel Jensen, Per Mberg Nielsen. ArbejdsmiljrdetsService Center. 1999

[13] At-meddelelse. Infralyd. Nr. 4.06.4. Februar 1998. Erstatter: September 1987.[14] At-meddelelse. Brug af ultralyd. Nr. 4.06.3. September 1987.[15] At-vejledning. Hrevrn. D.5.2 Marts 2001. Erstatter At-meddelelse nr. 4.09.5 af oktober 1985.

[16] ISO 9612:1997 Acoustics -- Guidelines for the measurement and assessment of exposure tonoise in a working environment. ISO. International Organization for Standardization

[17] Forskrift om sty p arbeidsplassen. 1993-06-22 nr 0787. Arbeidstilsynet, Norway.

[18] Oljedirektoratets regelverk for reduksjon av sty: Forskrift om systematisk oppflging avarbeidsmiljet i petroleumsvirksomheten, (SAM). Utgitt av OD frste gang 1995. 40 Sty.

[19] 1973-12-05 nr 0003 Forskrift om vern mot sty om bord i skip. Nrings- oghandelsdepartementet.

[20] NS 8175:1997 Lydforhold i bygninger - Lydklasser for ulike bygningstyper

[21] NS 4814:1977 Mling av sty med lydnivmler

[22] NS 4815:1982 Bestemmelse av stybelastning i arbeidet.


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[23] NORSOK S-002N Sty i arbeidsmilj Rev. 3 Nov 1997.

[24] prNS 8172 Lydforhold i bygninger - Mling av lydniv fra tekniske installasjoner

[25] NS 4815-1 Akustikk Bestemmelse av stybelastning i arbeidet Del 1: Forenklet mlemetode.Revisjonsutkast, 2002. Arbeidsdokument.

[26] NS 4815-2 Akustikk Bestemmelse av stybelastning i arbeidet Del 2: Teknisk mlemetode.Revisjonsutkast, 2002. Arbeidsdokument.

[27] Draft Swedish standard. Riktlinjer fr mtning av bullerexponering i arbetsmiljn. SS XXXXX.Dated 2001-09-21. SIS, Sverige.

[28] ISO 1999:1990 Acoustics -- Determination of occupational noise exposure and estimation ofnoise-induced hearing impairment. ISO. International Organization for Standardization.

[29] prEN14253 Mechanical vibration Measurement and evaluation of occupational exposure towhole-body vibration with reference to health Practical guidelines. CEN. The EuropeanCommittee for Standardization.

[30] GUM. Guide to expression of uncertainty in the measurements. ISO, 1995.


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NORDTEST TECHNICAL REPORTS - ACOUSTICS AND NOISE

Notice: Only technical reports with a bold number on the left leaf of the page can be orderedfree of charge from the Nordtest secretariat. Others have to be ordered from the publishingorganisation or institute. Information for ordering those reports can be obtained from Nordtestsecretariat and Nordtest Web-site.

383 Strm, T., Road traffic noise - Prediction of uncertainty. Bors 1998. 1273-96. SwedishNational Testing and Research Institute, SP Report 1997:24. 11 p (in Swedish). NTProject No.1273-96.

384 Rindel, J.H., Measurements of acoustic attenuation in workrooms. Lyngby 1998.Technical University of Denmark, Department of acoustic Technology, Report no 72,1997. 88 p. NT Project No. 1274-96.

385 Simmons, C., Measurement of sound pressure levels at low frequencies in rooms.Bors 1998. Swedish National Testing and Research Institute, SP Report 1997:27. 107p. (in Swedish) NT Project No. 1347-97.

411 gren, M. & Jonasson, H., Measurement of the acoustic impedance of ground. Bors

1998. Swedish National Testing and Research Institute, SP Report 1998:28. 63 p. NTProject No. 1365-97.

425 Sipari, P., Gudmundsson, S., Olsen, H., Simmons, C. & Pedersen, D.B., Nordic Basis ofcalculation of sound insulation in buildings. Aarhus 1999. DELTA Acoustic & Vibration,DELTA Report PNT 870022. 133 p. NT Project No. 1346-97.

426 Olofsson, J. & Jonasson, H.G., Measurement of Impulse Noise - An Inter-NordicComparison. Bors 1999. Swedish National Testing and Research Institute, SP Report1998:47. 28 p. NT Project No. 1413-98.

470 Sipari, P., Method for measuring the reduction of impact sound pressure level of a floorcovering - Experiments for field application. Espoo 2001. Technical Research Centre ofFinland, Nordtest technical report 470. 57 p. NT Project No. 1515-00.

471 (Notice - consist of a report with a separate Nordtest method proposal) Parmanen, J.,System for rating of airborne sound insulation in buildings and of building elements(report, 42 p), Acoustics - System for rating of airborne sound insulation in buildings andof building elements (17 p, method proposal). Espoo 2001. Technical Research Centreof Finland, Nordtest Technical Report 471. NT Project No. 1453-99.

478 Sndergaard, B., Extended firing sheds and shooting blinds. Espoo 2001. Nordtest, NTTechn Report 478. 16 p. NT Project No. 1518-00.

487 Ollikainen, V.-J.,. Performance testing of Active Noise Control (ANC) systems -Guideline. Espoo 2001. Nordtest, NT Techn Report 487. 64 p. NT Project No. 1517-00.

488 Kartous, M. & Jonasson, H.G., A Simplified method to determine impact soundimprovement on light-weight floors. Espoo 2002. Nordtest, NT Techn Report 488. 64 p.NT Project No. 1544-01.

489 Olesen, H.S., Laboratory measurement of sound insulation in the frequency range 50Hz to 160 Hz A Nordic intercomparison. Espoo 2002. Nordtest, NT Techn Report 489.63 p. NT Project No. 1545-01.

515 Ognedal, T. & Turunen-Rise, I., Determination of work place noise exposure Consideration of measurements, calculations and uncertainty. Espoo 2003. Nordtest,NT Techn Report 515. 22 p. NT Project No. 1566-01.


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NORDTEST

TECHNICAL REPORT 515

Nordtest endeavours to

promote viable industrial development and industrial competitive-

ness, remove technical barriers to trade and promote the concept

Approved Once Accepted Everywhere in the conformity assess-

ment area

work for health, safety, environment in methods and standards

promote Nordic interests in an international context and Nordic par-

ticipation in European co-operation

finance joint research in conformity assessment and the develop-

ment and implementation of test methods

promote the use of the results of its work in the development of

techniques and products, for technology transfer, in setting up stand-

ards and rules and in the implementation of these

co-ordinate and promote Nordic co-operation in conformity assess-

ment

contribute to the Nordic knowledge market in the field of conform-

ity assessment and to further development of competence among

people working in the field

Nordtest, founded in 1973, is an institution under the Nordic Council of

Ministers and acts as a joint Nordic body in the field of conformityassessment. The emphasis is on the development of Nordic test methodsand on Nordic co-operation concerning conformity assessment. The maintask is to take part in the development of international pre-normativeactivity. Nordtest is yearly funding projects in its field of activity.

Documents

NT TR 515_Determination of Work Place Noise Exposure - Consideration of Measurements, Calculations and Uncertainty_Nordtest Technical Report