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THE UNIVERSITY OF HONG KONGLIBRARIES<strong>Hong</strong> Kong Collectiongift from<strong>Hong</strong> Kong (China). Labour Dept.

<strong>Control</strong> <strong>of</strong> <strong>Asbestos</strong> <strong>at</strong> <strong>work</strong>Code <strong>of</strong> PracticeLabour Department<strong>Hong</strong> KongDecember 1986

Printed by the Government Printer, <strong>Hong</strong> Kong.

<strong>Control</strong> <strong>of</strong> <strong>Asbestos</strong> <strong>at</strong> <strong>work</strong>—Code <strong>of</strong> PracticeIntroduction<strong>Asbestos</strong> deserves its sinister reput<strong>at</strong>ion as a health hazard. Its use in the<strong>work</strong>place requires strict control to prevent serious occup<strong>at</strong>ional disease.Description'<strong>Asbestos</strong>' is a generic term for the fibrous forms <strong>of</strong> several mineralsilic<strong>at</strong>es, namely chrysotile, crocidolite, amosite, anthophylite, tremolite andactinolite. <strong>The</strong>se occur n<strong>at</strong>urally in seams in many rocks and belong to twolarge groups <strong>of</strong> rock-forming minerals, the serpentines and amphiboles.Chrysotile is one <strong>of</strong> the serpentine group while the others are amphiboles.Chrysotile is known as white, crocidolite as blue and amosite as brownasbestos.<strong>The</strong> annual world production <strong>of</strong> asbestos is over 6 million tons <strong>of</strong> which 97per cent is chrysotile and the remainder crocidolite and amosite. Commercialproduction <strong>of</strong> the other three amphiboles has been on a very small scale inthe past but they are found as contaminants <strong>of</strong> other minerals and soil andmay give rise to <strong>at</strong>mospheric pollution.Chrysotile is widely distributed with the largest production in Russia,Canada and Africa. Crocidolite is now mined almost exclusively in SouthAfrica and amosite is only exploited in the Transvaal although deposits havebeen confirmed in India.<strong>The</strong> properties which give asbestos its commercial value are incombustability,strength and effectiveness as a reinforcing or binding agent whencombined with other m<strong>at</strong>erials such as cement and plastic. <strong>The</strong> fibres whenbroken down can be woven.Uses <strong>of</strong> <strong>Asbestos</strong><strong>Asbestos</strong> has thousands <strong>of</strong> uses and is widespread throughout industry.Employed in insul<strong>at</strong>ion and he<strong>at</strong> resistant lagging in buildings and ships itis <strong>of</strong>ten combined with cement and plastics to produce ro<strong>of</strong>-sheeting, pipesand assorted other products. It is also used in brake and clutch linings,bearing packings and filters. As cloth it is manufactured into fire-pro<strong>of</strong>clothing, curtains and m<strong>at</strong>tresses. <strong>Hong</strong> Kong is not a producer or amanufacturer <strong>of</strong> asbestos products on a major scale but some raw asbestosis used and a large amount <strong>of</strong> asbestos products are consumed. <strong>Asbestos</strong> maybe found in many local industrial situ<strong>at</strong>ions such as ship building andrepairing, many construction and insul<strong>at</strong>ing processes, some plasticsmanufacturing and ship breaking and building demolition.

Health Hazards <strong>of</strong> <strong>Asbestos</strong>Air contamin<strong>at</strong>ion <strong>of</strong> the <strong>work</strong>place and neighbourhood may occur inhandling asbestos raw m<strong>at</strong>erial, its mixing and the disintegr<strong>at</strong>ion <strong>of</strong> productscontaining asbestos in machining, sawing or scrapping.Inhal<strong>at</strong>ion <strong>of</strong> asbestos fibres causes asbestosis which is a disease <strong>of</strong> progressivefibrosis <strong>of</strong> the lungs with increasing respir<strong>at</strong>ory disability. This is <strong>of</strong>tencomplic<strong>at</strong>ed by lung cancer. Mesothelioma affecting the lung and abdominallining membrane is another cancer caused by asbestos and is particularlyassoci<strong>at</strong>ed with crocidolite (blue asbestos) fibres. <strong>The</strong>re is some evidence <strong>of</strong>increase <strong>of</strong> gastro-intestinal cancers from ingestion <strong>of</strong> asbestos but inhal<strong>at</strong>ionto the lungs is by far the most important route <strong>of</strong> entry.Prevention <strong>of</strong> Health HazardHealth protection depends on preventing the inhal<strong>at</strong>ion <strong>of</strong> asbestos fibres andsafe practice is based on the following principles:—(a) Substitution—Replacement <strong>of</strong> asbestos by a safer substitute such asman-made fibres for insul<strong>at</strong>ion. This is the perfect solution.(b) Segreg<strong>at</strong>ion—<strong>Asbestos</strong> <strong>work</strong> and storage should be isol<strong>at</strong>ed frompersons engaged in other <strong>work</strong> to reduce exposure.(c) Dust control—Depends on enclosing a dust source or providingadequ<strong>at</strong>e exhaust ventil<strong>at</strong>ion to prevent fibres reaching the bre<strong>at</strong>hingzone <strong>of</strong> personnel. Dust reducing <strong>work</strong> methods such as wetting canalso help control as can the use <strong>of</strong> impervious m<strong>at</strong>erial such as polythenesheeting to confine dust spread and c<strong>at</strong>ch debris.(d) Good housekeeping—Regular cleaning <strong>of</strong> the <strong>work</strong>place by vacuum orwet methods is required. <strong>The</strong> vacuum cleaners used must have high(e)efficiency filter systems capable <strong>of</strong> trapping asbestos fibres.Respir<strong>at</strong>ory protection—Unless dust can be kept to minimum levelsrespir<strong>at</strong>ory protection for personnel is essential. Depending on the dustconcentr<strong>at</strong>ion this should be by respir<strong>at</strong>or (mask) fitted with theappropri<strong>at</strong>e dust filter, or more elabor<strong>at</strong>e equipment including air-linebre<strong>at</strong>hing appar<strong>at</strong>us.(/) Protective clothing—This is required to minimise skin and hair contact,prevent contamin<strong>at</strong>ion <strong>of</strong> personal clothing and stop the dissemin<strong>at</strong>ion<strong>of</strong> dust outside the <strong>work</strong>ing area. Nylon overalls and dust caps aresuitable. Cleaning <strong>of</strong> protective clothing should be planned to minimisedust dissemin<strong>at</strong>ion.(g)(h)Ablution and changing facilities for personnel should be provided andarranged to allow the separ<strong>at</strong>ion <strong>of</strong> personal from protective clothing.Waste disposal—Waste collection and disposal require <strong>at</strong>tention toavoid increasing the <strong>at</strong>mospheric concentr<strong>at</strong>ion <strong>of</strong> asbestos fibres. <strong>The</strong>usual method is sacking in impervious sack and disposing in anapproved manner e.g. burying in a controlled tipping site.

(f)Educ<strong>at</strong>ion—All personnel exposed to asbestos dust must be instructedon the health hazard involved and the necessary protective measures.Code <strong>of</strong> Practice<strong>The</strong> aim <strong>of</strong> the code is to protect the health <strong>of</strong> people <strong>at</strong> <strong>work</strong> by controllingtheir exposure to asbestos. It applies to all <strong>work</strong>s which expose people to therisk <strong>of</strong> inhaling asbestos dust and contains the fundamental requirementsneeded to prevent disease.<strong>The</strong> key to control is the requirement for the employer to assess the n<strong>at</strong>ureand extent <strong>of</strong> exposure to asbestos so th<strong>at</strong> on the basis <strong>of</strong> th<strong>at</strong> assessment hemay determine and implement the measures which will be adequ<strong>at</strong>e toprevent disease.<strong>The</strong> basic measure to protect employees in the prevention <strong>of</strong> the escape <strong>of</strong>asbestos dust into the <strong>work</strong>place and ensuring th<strong>at</strong> the amount <strong>of</strong> asbestos inair in the bre<strong>at</strong>hing zone <strong>of</strong> any person is below the accepted level. Because<strong>of</strong> particular carcinogens properties crocidolite (blue) or amosite (brown)asbestos should not be used.<strong>The</strong> spraying <strong>of</strong> asbestos on walls and pipes gener<strong>at</strong>es very high dust levelsduring the oper<strong>at</strong>ion itself and such co<strong>at</strong>ings have poor durability and areeasily damaged in such a way as to allow the release <strong>of</strong> respirable fibres.Because <strong>of</strong> the particular health risks asbestos or any products containingasbestos should not be applied by a spraying process.If circumstances arise when asbestos cannot be maintained below theacceptable levels adequ<strong>at</strong>e personal protection equipment should beprovided and worn and complemented by adequ<strong>at</strong>e changing, cleaningand laundry facilities as necessary. Good housekeeping methods require<strong>at</strong>tention.Employees should use the equipment and facilities provided and co-oper<strong>at</strong>ewith the employers in restricting the spread <strong>of</strong> asbestos contamin<strong>at</strong>ion.<strong>The</strong> spread <strong>of</strong> pollution from the <strong>work</strong>place is rel<strong>at</strong>ed to both process controlmeasure and the standards <strong>of</strong> general cleanliness. Adequ<strong>at</strong>e steps should betaken to avoid spread <strong>of</strong> contamin<strong>at</strong>ion to protect those in adjacent<strong>work</strong>places and also people in the neighbourhood.Assistance from Labour Department<strong>The</strong> Factory Inspector<strong>at</strong>e and the Occup<strong>at</strong>ional Health Division <strong>of</strong> theLabour Department would be pleased to give advice to any employer whoencounters problems in the use and control <strong>of</strong> asbestos. <strong>The</strong> Occup<strong>at</strong>ionalHealth Division can give assistance in determin<strong>at</strong>ion <strong>of</strong> asbestos in the airand advice on medical supervision <strong>of</strong> persons who are exposed to asbestos.

ContentsApplic<strong>at</strong>ion <strong>of</strong> CodeDuties <strong>of</strong> employerAssessment <strong>of</strong> <strong>work</strong> which exposes persons to asbestos dustHygiene standards for asbestosSamplingMeasurement <strong>of</strong> airborne dustInform<strong>at</strong>ion, instruction and trainingNotific<strong>at</strong>ionUse <strong>of</strong> blue and brown asbestosSpraying <strong>of</strong> asbestos<strong>Control</strong> measures for m<strong>at</strong>erial, plant and processesPersonal protective equipmentCleanliness <strong>of</strong> premises and plantStorageDisposal <strong>of</strong> wasteProtection <strong>of</strong> young personsMedical supervision <strong>of</strong> asbestos <strong>work</strong>ersAppendix I —Hygiene Standards for <strong>Asbestos</strong> DustAppendix II —SamplingAppendix III—<strong>The</strong> Measurement <strong>of</strong> Airborne <strong>Asbestos</strong> DustAppendix IV—Notific<strong>at</strong>ion <strong>of</strong> Processes involving <strong>Asbestos</strong>Paragraph1234591011-1819-242526272829

Code <strong>of</strong> Practice for<strong>Control</strong> <strong>of</strong> <strong>Asbestos</strong> <strong>at</strong> <strong>work</strong>Applic<strong>at</strong>ion <strong>of</strong> Code1. This code applies to <strong>work</strong> which exposes persons, both employeesand others to the inhal<strong>at</strong>ion <strong>of</strong> asbestos dust. In practice this meansany <strong>work</strong> in which raw asbestos fibres are used (e.g. lagging, manufacture<strong>of</strong> asbestos cement pipes, etc.) or any <strong>work</strong> on asbestos containingm<strong>at</strong>erial which gener<strong>at</strong>es dust (e.g. delagging, sawing asbestos board,etc.).Duties <strong>of</strong> Employer2. <strong>The</strong> employer has a duty to ensure th<strong>at</strong> he protects not only his ownemployees but also other persons who are engaged in any <strong>work</strong> <strong>at</strong> thepremises where the employer's <strong>work</strong> with asbestos is carried out and whichexposes them to asbestos dust. <strong>The</strong>se persons "would include for examplemaintenance contractors engaged in maintenance <strong>of</strong> plant or other personssuch as contract cleaners not directly engaged on asbestos <strong>work</strong> but who areexposed to dust. Any employer <strong>of</strong> these persons will also have duties as theiremployer to s<strong>at</strong>isfy himself in his own right th<strong>at</strong> adequ<strong>at</strong>e precautions aretaken to protect their health.Assessment <strong>of</strong> <strong>work</strong> which exposes persons to asbestos dust3. Where any <strong>work</strong> may expose persons to the inhal<strong>at</strong>ion <strong>of</strong> asbestosdust the employer should determine the n<strong>at</strong>ure and degree <strong>of</strong> the exposure.<strong>The</strong> assessment should be revised if there is any reason to suspect th<strong>at</strong>it is incorrect or where there is m<strong>at</strong>erial change in the process. <strong>The</strong>object <strong>of</strong> assessment is to ensure th<strong>at</strong> appropri<strong>at</strong>e preventive measures aretaken.Hygiene standards for asbestos4. In determining exposure the Hygiene Standards for <strong>Asbestos</strong> Dust asdetailed in Appendix I should be applied.Sampling5. Sampling should follow the guidelines as detailed in. Appendix II.Measurement <strong>of</strong> airborne dust6. In determining airborne asbestos fibres the method approved by the<strong>Asbestos</strong>is Research Council and detailed in Appendix III should befollowed.7

Inform<strong>at</strong>ion, instruction and training7. Every employer should ensure th<strong>at</strong> adequ<strong>at</strong>e inform<strong>at</strong>ion, instructionand training is given to his employees or others who are liable to be exposedto asbestos dust so th<strong>at</strong> they are aware <strong>of</strong> the health hazards and theprecautions necessary to prevent.Notific<strong>at</strong>ion8. Before a process involving asbestos, including the removal <strong>of</strong> asbestoscontaining lagging is undertaken, the employer should give <strong>at</strong> least 28 daysnotice to the Commissioner for Labour. <strong>The</strong> notific<strong>at</strong>ion form shown inAppendix IV should be used.Use <strong>of</strong> blue and brown asbestos9. Raw crocidolite (blue) or amosite (brown) asbestos should not be usedfor any purpose or in any circumstances.Spraying <strong>of</strong> asbestos10. <strong>Asbestos</strong> or any product containing it should not be applied by sprayprocess.<strong>Control</strong> measures for m<strong>at</strong>erial, plant and processes11. <strong>Asbestos</strong> should only be used when there is no suitable and safersubstitute.12. When used the process should be planned to prevent environmentalcontamin<strong>at</strong>ion and complete enclosure when possible should be the method<strong>of</strong> choice.13. When total enclosure is not reasonably practical the processes should asfar as possible be isol<strong>at</strong>ed from other <strong>work</strong>ing areas.14. Areas in <strong>work</strong>place where dust concentr<strong>at</strong>ion is likely to exceed thecontrol limit should be suitably marked and a scheme <strong>of</strong> restricting access tothese areas should be instituted.15. Wet <strong>work</strong>ing methods to reduce dust production should be considered.16. When dust is not otherwise prevented an effective exhaust systemdesigned to keep asbestos fibres out <strong>of</strong> the exposed persons' bre<strong>at</strong>hing zoneshould be installed and regularly inspected and serviced to ensure maximumefficiency.17. <strong>The</strong> amount <strong>of</strong> asbestos in air in the <strong>work</strong>ing area should be regularlymonitored and records maintained.18. <strong>Control</strong> measures for m<strong>at</strong>erials, plant and processes should be acceptedas adequ<strong>at</strong>e only when they can prevent exposure to asbestos dust whichexceeds the Hygiene Standards as specified in Appendix I.

Personal protective equipment19. When asbestos in air is above the accepted standards respir<strong>at</strong>oryprotection should be provided and used. <strong>The</strong> type <strong>of</strong> protection isdetermined by the dust level and may be either the cartridge type respir<strong>at</strong>orwith control designed to filter <strong>of</strong>f asbestos fibres or more elabor<strong>at</strong>eequipment including air-line fresh air supply if dust concentr<strong>at</strong>ions are high.20. Protective clothing should be provided and worn to preventcontamin<strong>at</strong>ion <strong>of</strong> skin, hair and personal clothing. Nylon is a suitablem<strong>at</strong>erial for protective clothing. Use <strong>of</strong> suitable disposable clothing isrecommended.21. Adequ<strong>at</strong>e washing and changing facilities should be provided andshould be sited so as to preventing asbestos from contamin<strong>at</strong>ing areas outsidethe <strong>work</strong>place. This should be achieved by separ<strong>at</strong>ion <strong>of</strong> changing andstorage accommod<strong>at</strong>ion for protective clothing from personal clothing bymeans <strong>of</strong> separ<strong>at</strong>e rooms or one large room divided into clean (personalclothing) and dirty (protective clothing) areas. <strong>The</strong> washing and showeringfacilities should be loc<strong>at</strong>ed between the areas to enable the person to removeasbestos contamin<strong>at</strong>ed clothing in the dusty area, then pass to the washingarea and finally enter the clean area to put on personal clothing.22. Protective clothes should be cleansed by vacuum cleaner after the<strong>work</strong>ing shift. <strong>The</strong>y should be stored separ<strong>at</strong>ely and sent for laundry insealed sacks labelled '<strong>Asbestos</strong> Contamin<strong>at</strong>ed'. Laundry personnel shouldbe acquainted with the dust hazards and the need to avoid shaking. Sacksshould not be opened until they can be tipping into the washing machinesso th<strong>at</strong> the contents are immedi<strong>at</strong>ely wetted. <strong>Asbestos</strong> contamin<strong>at</strong>ed laundryshould be kept separ<strong>at</strong>e from other items and the machines thoroughlyflushed after use.23. E<strong>at</strong>ing, drinking or smoking should not take place in the presence <strong>of</strong>asbestos dust.24. Because <strong>of</strong> the synergestic effect between tobacco and asbestos in theproduction <strong>of</strong> cancer all persons whose <strong>work</strong> is liable to expose themregularly to asbestos dust should be advised not to smoke.Cleanliness <strong>of</strong> premises and plant25. Special <strong>at</strong>tention should be paid to good housekeeping using vacuumor wet methods to ensure th<strong>at</strong> asbestos dust is not allowed to accumul<strong>at</strong>e inthe <strong>work</strong>place. Only vacuum cleaners fitted with high efficiency filtersystems capable <strong>of</strong> trapping asbestos fibres should be used.Storage26. All loose asbestos in use should be kept in suitable closed receptacleswhich prevent escape <strong>of</strong> dust and all asbestos waste should be suitablycontained for disposal.

Disposal <strong>of</strong> waste27. <strong>Asbestos</strong> waste disposal methods should ensure th<strong>at</strong> the dust doesnot contamin<strong>at</strong>e the environment. Sealing in polythene sacks or otherimpervious container and burying <strong>at</strong> the tipping site are recommendedmethods <strong>of</strong> disposal.Protection <strong>of</strong> young persons28. Young persons under 18 years <strong>of</strong> age should not be employed in anyprocess which entails exposure to asbestos dust.Medical supervision <strong>of</strong> asbestos <strong>work</strong>ers29. Persons regularly exposed to asbestos dust should be under medicalsupervision with examin<strong>at</strong>ion annually.10

HYGIENE STANDARDS FOR ASBESTOS DUSTAPPENDIX 11. Exposure to all forms <strong>of</strong> asbestos dust should be reduced to theminimum th<strong>at</strong> is reasonably practicable.2. In any case, occup<strong>at</strong>ional exposure to asbestos dust should not exceed:For crocidolite:0.2 fibres/ml.For amosite:0.2 fibres/ml.For other forms <strong>of</strong> asbestos: 0.5 fibres/ml.Note:Fibres means particles <strong>of</strong> length gre<strong>at</strong>er than 5 micrometres, adiameter <strong>of</strong> less than 3 micrometres and having a length to breadthr<strong>at</strong>io <strong>of</strong> <strong>at</strong> least 3:1, observed by transmitted light under phasecontrast conditions <strong>at</strong> a magnific<strong>at</strong>ion <strong>of</strong> approxim<strong>at</strong>ely 500x.11

APPENDIXIISAMPLINGBulk sampling1. <strong>The</strong> object <strong>of</strong> bulk sampling is to determine the presence <strong>of</strong> asbestos andits type and so the precautions which need to be taken. Old insul<strong>at</strong>ion willfrequently contain asbestos, including crocidolite, in varying proportionswith other m<strong>at</strong>erials and care should be taken to ensure th<strong>at</strong> the samples arerepresent<strong>at</strong>ive.Evalu<strong>at</strong>ion <strong>of</strong> bulk samples2. <strong>The</strong> type <strong>of</strong> asbestos used cannot be readily identified by its appearanceor colour, particularly if it is mixed with other m<strong>at</strong>erials. Crocidolite (blueasbestos) may be significantly changed in appearance by the action <strong>of</strong> he<strong>at</strong>.<strong>The</strong> techniques employed should be capable <strong>of</strong> positively identifying all <strong>of</strong>the types <strong>of</strong> asbestos th<strong>at</strong> are present in the sample. Optical microscopy, X--ray diffraction or electron microscopy coupled with X-ray probe or electrondiffraction are suitable techniques. In many cases, the use <strong>of</strong> polarized lightoptical microscopy with immersion refractometry is sufficient to identify theindividual forms <strong>of</strong> asbestos and provide an indic<strong>at</strong>ion <strong>of</strong> the amount present.X-ray diffraction techniques supplement optical microscopy though thepresence <strong>of</strong> silic<strong>at</strong>e m<strong>at</strong>erials other than asbestos can make the results difficultto interpret. Electron microscopic techniques coupled with X-ray probeanalysis enables single fibres to be identified but the results may not berepresent<strong>at</strong>ive <strong>of</strong> the whole sample.Environmental sampling3. <strong>The</strong> purpose <strong>of</strong> environmental sampling is to measure the concentr<strong>at</strong>ionand to identify the type <strong>of</strong> airborne asbestos dust in the bre<strong>at</strong>hing zone <strong>of</strong> the<strong>work</strong>er.4. Sampling is normally carried out over a ten-minute or four-hour periodin order to determine ceiling concentr<strong>at</strong>ions and time weighted averageconcentr<strong>at</strong>ions respectively.5. <strong>The</strong> membrane filter method is normally used for measurement <strong>of</strong>airborne asbestos dust. Autom<strong>at</strong>ic particle counters, calibr<strong>at</strong>ed against themembrance filter method, provide more rapid results than the membranefilter method but they are <strong>of</strong> little use in mixed dust <strong>at</strong>mospheres because <strong>of</strong>their inability to distinguish asbestos fibres when mixed with other dusts.6. <strong>The</strong> method involves drawing a known volume <strong>of</strong> dust laden airthrough a membrance filter using either a b<strong>at</strong>tery, or hand-oper<strong>at</strong>ed pump.<strong>The</strong> collected fibres are subsequently counted and examined under a lightmicroscope.12

7. It is important th<strong>at</strong> the fibres to be counted under the microscope are notso numerous th<strong>at</strong> they overlap. However, it is not possible to indic<strong>at</strong>e thevolume <strong>of</strong> air to be drawn through the sampling head or the number <strong>of</strong>times which the filter should be changed during the sampling period as thesewill depend on the dust concentr<strong>at</strong>ion in the environment being measured.<strong>The</strong> presence <strong>of</strong> dusts other than asbestos dust should also be taken intoconsider<strong>at</strong>ion as these tend to obscure the presence <strong>of</strong> fibres on the filter.8. Personal samplers, th<strong>at</strong> is sampling devices, fixed to the upper lapel orshoulder <strong>of</strong> the <strong>work</strong>er's clothing w r ithin 300 mm <strong>of</strong> his nose are able to givea more accur<strong>at</strong>e indic<strong>at</strong>ion <strong>of</strong> personal exposures although in continuousprocesses background samplers fixed <strong>at</strong> head height may provide a goodindic<strong>at</strong>ion <strong>of</strong> exposure levels.9. Before sampling is undertaken air sampling pumps must be calibr<strong>at</strong>edagainst an external flow meter with the sampling head and filter connected.A clean filter should, <strong>of</strong> course, be fitted and the flow r<strong>at</strong>e readjusted beforesampling takes place. Flow r<strong>at</strong>es should be checked <strong>at</strong> least every hour duringthe sampling period and readjusted when necessary.Ten-minute sampling10. Ten minutes is the minimum continuous sampling period needed toassess the concentr<strong>at</strong>ion <strong>of</strong> asbestos dust in the <strong>work</strong>er's bre<strong>at</strong>hing zone.Ideally the sample should be taken during a period <strong>of</strong> maximum dustemission so as to determine peak exposure level. Experience has shown th<strong>at</strong>for ten-minute sampling periods the optimum r<strong>at</strong>e for drawing air throughthe filter is 2 litres/minute for most asbestos oper<strong>at</strong>ions.Four-hour sampling11. A four-hour continuous sample will give a reasonable indic<strong>at</strong>ion <strong>of</strong>the average exposure to asbestos dust. An air flow r<strong>at</strong>e through the filter <strong>of</strong>200-500 ml/minute has been found to be most suitable for this period <strong>of</strong>sampling although <strong>at</strong> processes giving rise to high levels <strong>of</strong> dust it wouldprobably be necessary to replace the filter during the sampling period so asto avoid counting difficulties arising from overlapping fibres on the filter.Evalu<strong>at</strong>ion <strong>of</strong> airborne samples12. <strong>The</strong> method used for counting asbestos fibres is th<strong>at</strong> given in TechnicalNote No. 1 <strong>The</strong> Measurement <strong>of</strong> Airborne Dust by the Membrance FilterMethod' published by the U.K. <strong>Asbestos</strong>is Research Council Counting isundertaken by means <strong>of</strong> an optical microscope fitted with a 4 mm/40xobjective <strong>at</strong> a magnific<strong>at</strong>ion <strong>of</strong> 450-500 using transmitted light and phasecontrast techniques. <strong>The</strong> diameter <strong>of</strong> asbestos fibres found in airborne dustsamples obtained from asbestos processes varies considerably, some beingsmaller than the limit <strong>of</strong> resolution <strong>of</strong> the optical microscope. Meaningfulresults can only be obtained if the size range <strong>of</strong> fibres to be counted is defined13

and only fibres having length gre<strong>at</strong>er than 5 micrometres, breadth less than 3micrometres and length to breadth r<strong>at</strong>io <strong>of</strong> <strong>at</strong> least 3:1 should be countered.<strong>The</strong> Technical Note is reproduced <strong>at</strong> Appendix III.14

APPENDIXTHE MEASUREMENT OF AIRBORNE ASBESTOS DUST1. Introduction<strong>The</strong> methods adopted by the <strong>Asbestos</strong>is Research Council for thedefinition <strong>of</strong> airborne asbestos fibre concentr<strong>at</strong>ions have now beengenerally accepted. This test method describes in detail the membranefilter method <strong>of</strong> sampling air and the procedure to be followed foranalysing the dust deposit obtained from the sample. It is generally onlysuitable for measuring concentr<strong>at</strong>ions encountered occup<strong>at</strong>ionally infactories, <strong>work</strong>shops and on constructional sites.2. Definitions2.1 FibresFibres are defined as being <strong>of</strong> a length gre<strong>at</strong>er than 5 //m andhaving a length/breadth r<strong>at</strong>io <strong>of</strong> <strong>at</strong> least 3:1. <strong>The</strong>re is no upper limitfor the length <strong>of</strong> the fibres, but a maximum diameter <strong>of</strong> 3 jum isdefined. Airborne asbestos dust concentr<strong>at</strong>ions are expressed infibres per millilitre <strong>of</strong> air (f/ml).2.2 Continuous SampleA continuous sample is defined as a sample which is collected overa period and therefore represents the average dust concentr<strong>at</strong>ionduring th<strong>at</strong> period. This type <strong>of</strong> sample is suitable where theconcentr<strong>at</strong>ion does not vary widely over the period <strong>of</strong> sampling.2.3 Snap SampleA snap sample is defined as a sample taken over a very short period,generally <strong>of</strong> a few seconds and not exceeding 30 seconds. This type<strong>of</strong> sample is suitable for situ<strong>at</strong>ions where dust emission isintermittent. A series <strong>of</strong> such samples can be used to indic<strong>at</strong>e thedegree <strong>of</strong> vari<strong>at</strong>ion in environments where the dust concentr<strong>at</strong>ionis fluctu<strong>at</strong>ing.2.4 Personal SampleA personal sample is defined as a sample collected on a membranefilter which is <strong>at</strong>tached to the oper<strong>at</strong>or. <strong>The</strong> filter holder must bepositioned in the oper<strong>at</strong>or's bre<strong>at</strong>hing zone.3. Equipment3.1 Membrane FilterWhite gridded membrane filters <strong>of</strong> 25 mm diameter, with a poresize <strong>of</strong> up to 5 ^um (0.8 ^m is recommended).3.2 Sampling HeadA leakpro<strong>of</strong> open filter holder to take a 25 mm membrane.15III

3.3 Pumping Systems<strong>The</strong> pumping technique recommended is to draw the dustladenair through the filter by means <strong>of</strong> a suitable sealed pump. <strong>The</strong>flow-r<strong>at</strong>e can be controlled by a needle valve. <strong>The</strong> Draeger handpump is suitable for short period and snap samples. For personalsampling the Casella portable b<strong>at</strong>tery driven pump has been founds<strong>at</strong>isfactory.3.4 FlowmeterFor continuous samples the flow r<strong>at</strong>e can be monitored by means<strong>of</strong> a suitable flowmeter (see Figure 1). If this is not practicable (e.g.personal sampler) the flow r<strong>at</strong>e can be checked using a tripodflowmeter as provided by Casella.needlevaivefilter head-aipumpflowmeterFigure 1 — An assembly for collection <strong>of</strong> st<strong>at</strong>ic membrane filter samples4. Sampling4.1 <strong>The</strong> filters must be placed into the filter holders with the gridsfacing the open end. <strong>The</strong> holder should be washed in warm w<strong>at</strong>erbefore use, especially after sampling in dusty environments.4.2 Continuous Samples<strong>The</strong> sampling orifice will usually be positioned <strong>at</strong> head height.<strong>The</strong> filter surface should not be facing upwards to ensure th<strong>at</strong> thelarge particles and airborne aggreg<strong>at</strong>es are not collected. Samplingperiods and r<strong>at</strong>es should be adjusted to suit the anticip<strong>at</strong>ed dustlevels. <strong>The</strong> sampling flow r<strong>at</strong>e should not exceed 2 litres perminute. <strong>The</strong> sample volumes given below are suggested asconvenient:—16

Anticip<strong>at</strong>ed <strong>Asbestos</strong> Dust Concentr<strong>at</strong>ion Sample Volume(f/ml)(ml)less than 2 10,000-20,0002-4 5,000-10,0004-12 2,000- 5,000gre<strong>at</strong>er than 12pro r<strong>at</strong>a4.3 Short Period or Snap Samples<strong>The</strong> Draeger pump, with the sampling head fitted, is held <strong>at</strong> therequired position. With each stroke the pump draws in a volume<strong>of</strong> 100 + 5 ml air through the membrane. <strong>The</strong> number <strong>of</strong> strokesrequired, and consequently the total volume <strong>of</strong> the sample, willvary according to the anticip<strong>at</strong>ed dust concentr<strong>at</strong>ion. N<strong>at</strong>urally thelower the concentr<strong>at</strong>ion, the larger should be the volume <strong>of</strong>sample.4.4 Personal SamplesPersonal samples may be collected with the membrane filterholder <strong>at</strong>tached to the person. <strong>The</strong> air is drawn through the filter<strong>at</strong> a r<strong>at</strong>e <strong>of</strong> 2 litres per minute by means <strong>of</strong> the Casella portablepump.4.5 Whichever method is used, immedi<strong>at</strong>ely after the sample has beentaken the sampling orifice should be covered by a plastic cap orother convenient means, and the filter holder should then beplaced in a suitable box with the filter surface facing upwards. <strong>The</strong>sample should be fixed before transit.5. Fixing the Sample5.1 <strong>The</strong> dust deposit is fixed on the membrane surface whilst the filteris in the sampling head. <strong>The</strong> following method is preferred:—(a)Several drops <strong>of</strong> polymethyl methacryl<strong>at</strong>e (perspex) solution(0.025% in chlor<strong>of</strong>orm) are applied to the membrane, whileclean air is being drawn through it by means <strong>of</strong> a low velocitypump (e.g. w<strong>at</strong>er pump).(6) An altern<strong>at</strong>ive method <strong>of</strong> fixing for use in the field is to spraythe filter surface with a cytological fix<strong>at</strong>ive from an aerosoldispenser. <strong>The</strong> filter holder is held with the filter surfacefacing upwards and the aerosol dispenser held some 18" awayso th<strong>at</strong> the spray falls in an arc gently on to the membranesurface for <strong>at</strong> least 5 seconds. Care should be taken not to directthe aerosol spray onto the filter causing the dust deposit to bedisturbed.If this method <strong>of</strong> fixing is used the filter holders requirewashing more <strong>of</strong>ten than usual.17

6. Mounting the Sample6.1 Filtered triacetin (Glycerol Triacet<strong>at</strong>e) is placed on a clean 76 mmx 25 mm (0.8 to 1.0 rnm thick) microscope slide. Sufficienttriacetin should be used to enable it to be spread out into a circle <strong>of</strong>the same diameter as the filter (25 mm). <strong>The</strong> triacetin may bedispensed through a solvent resistant membrane filter held in asyringe filter holder. Filtr<strong>at</strong>ion <strong>of</strong> the cleaning agent is particularlyimportant if asbestos contamin<strong>at</strong>ion is possible and if rel<strong>at</strong>ively lowdust levels (i.e.

7.5 If desired, the fibres are divided into the length ranges 5-10 /mi,10-20 /mi, 20-50 /xm and gre<strong>at</strong>er than 100 /mi. <strong>The</strong> sizing is carriedout by reference to a suitable gr<strong>at</strong>icule in one <strong>of</strong> the eyepieces. Acontinuous size distribution may be obtained using the methodrecommended in BS3406. <strong>The</strong> gr<strong>at</strong>icule is calibr<strong>at</strong>ed against a stagemicrometer.7 6 5 4 3 2 1ft **•*••Figure 2 — Illustr<strong>at</strong>ion <strong>of</strong> field <strong>of</strong> view and BS 3625 Gr<strong>at</strong>icule8. Evalu<strong>at</strong>ion <strong>of</strong> Results8.1 Dust concentr<strong>at</strong>ion is determined from the total fibre count above5 jam in length.8.2 If the diameter <strong>of</strong> the dust deposit=D and the diameter <strong>of</strong> eachfield <strong>of</strong> view =d, then the dust concentr<strong>at</strong>ion=19

x — x — (fibres per ml)d 2 n Vwhere V = volume <strong>of</strong> sample (ml),N = number <strong>of</strong> fibres counted,n = number <strong>of</strong> fields examined.If the gr<strong>at</strong>icule grid is used to deline<strong>at</strong>e the counting areas, then thedust concentr<strong>at</strong>ion =TiD 2 N 1x — x— (fibres per ml) where A = grid area4A n V V 5* '8.3 Where there is a possibility <strong>of</strong> rel<strong>at</strong>ively high background fibrecounts on the membrane filters, due to instrument or labor<strong>at</strong>orycontamin<strong>at</strong>ion, unexposed control samples are counted to evalu<strong>at</strong>ethe significance <strong>of</strong> this possible source <strong>of</strong> error.20

Annex iSPECIFICATION FOR PHASE MICROSCOPE SUITABLEFOR COUNTING ASBESTOS DUST PARTICLESLight SourceA built in substage illumin<strong>at</strong>or is preferred, but an external lamp with acondenser and a plane mirror is also s<strong>at</strong>isfactory. A variable intensity controlis necessary for both. A green light filter is also recommended.Substage AssemblyAn achrom<strong>at</strong>ic condenser incorpor<strong>at</strong>ed into a substage unit containing theannular diaphragms is recommended. <strong>The</strong>re should also be means <strong>of</strong>centering the diaphragms with respect to the corresponding phase pl<strong>at</strong>es inthe objectives.StageA built in mechanical object stage, fitted with verniers and side clamps, isrequired.ObjectivesA rot<strong>at</strong>ing nose-piece fitted with lOx and 40x parfocal phase achrom<strong>at</strong>icobjectives is suitable. It is recommended th<strong>at</strong> the dry 4 mm, 40x objective beused for routine counting and it is an advantage if this is <strong>of</strong> the fl<strong>at</strong>-field typeincorpor<strong>at</strong>ing a phase ring <strong>of</strong> higher than normal absorption (e.g. 95%).EyepiecesBinocular eyepieces <strong>of</strong> the compens<strong>at</strong>ing type are recommended, theirmagnific<strong>at</strong>ion to be such as to give a total magnific<strong>at</strong>ion <strong>of</strong> around 500x.Gr<strong>at</strong>icule<strong>The</strong> following gr<strong>at</strong>icules have been found s<strong>at</strong>isfactory:(a) P<strong>at</strong>terson Globe and Circle.(b) Gr<strong>at</strong>icule to BS 3625.(c) Microscope eyepiece micrometer.<strong>The</strong> gr<strong>at</strong>icule is calibr<strong>at</strong>ed against a stage micrometer (100 jam divided into2 iim parts). A different micrometer (1 mm divided into 10 /mi parts) may beused to measure the diameter <strong>of</strong> the field <strong>of</strong> view.Auxiliary Viewing TelescopeThis is essential for correct phasing. Modern microscopes are normallyprovided with suitable equipment (e.g. focusable Bertrand lens).21

11APPENDIXIVNOTIFICATION OF PROCESSES INVOLVING ASBESTOS(Thisform is to be completed in duplic<strong>at</strong>e)To: <strong>The</strong> Commissioner for Labour,<strong>Hong</strong> KongName <strong>of</strong> industrialundertakingAddress <strong>of</strong> industrialundertakingCorrespondence/registered<strong>of</strong>ficeName <strong>of</strong> Proprietor/ManagerApproxim<strong>at</strong>e total number <strong>of</strong>employees in the industrialundertakingApproxim<strong>at</strong>e number <strong>of</strong>asbestos <strong>work</strong>ersForms <strong>of</strong> asbestosused/involvedMaleMaleTel. No.Tel. No.FemaleFemaleProcess using/involvingasbestosSign<strong>at</strong>urePosition...D<strong>at</strong>e.......22

X1S3123DTHKP 363.1791 C76 L<strong>Control</strong> <strong>of</strong> asbestos <strong>at</strong> <strong>work</strong>code <strong>of</strong> practice<strong>Hong</strong> Kong : Labour Dept.,[1986]D<strong>at</strong>e Due

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