Improved Methods for Clearance Testing and Visual ...

1 Broad Lane, Sheffield, S3 7 HQTelephone:+44 (0)114 289 2000 Facsimile:+44 (0)114 289 2500 HEALTH AND SAFETY LABORATORYAn agency of the Health and Safety Executive Crown copyright 2001 Improved Methods for Clearance Testing andVisual Assessment of Asbestos Measurement GroupMr Peter R Stacey MRSC CChem and Dr G BurdettDr G BurdettProject Leader:SummaryObjectives1. To further develop and define a standardised method for Visual Clearance and for disturbance (oraggressive) sampling inside the enclosure and after the site has been To research and test a surface sampling method (by PCM and TEM) to collect surface dust as ameasure of site cleanliness after a removal To investigate the current standard of Visual Clearance being carried out after asbestos removaland to document findings to inform and provide future guidance and To assess any residual levels of asbestos remaining after the contractor has left by carrying outdisturbance sampling before reoccupation and/or surface To prepare a draft MDHS on Clearance sampling and Testing and publish investigations to determine the detection limit of simple Visual wipe tests.

2 Atorch test and quantitative assessment of surface fibre sampling Methods wereundertaken before evaluating them in a field survey. A laboratory investigation of theability of different dust raising Methods was also carried out along with measurements ofthe settlement rates and decline of asbestos concentrations with total of 20 site visits were made. Fifteen sites had enclosures still intact and clearanceassessments were carried out. At two large sites, an additional visit was made to asecond enclosure, making a total of 17 Clearance assessments. Due to the difficulty inarriving at the start of the Clearance , it was only possible to observe the site analystsclearance procedure at 11 of the 15 sites.

3 A total of 12 clearances involving 11different analysts from 6 different laboratories were observed. The removal sites variedin size from a small boiler room to a large multi-story car park. A range of materials hadbeen removed: 4 sites involved the removal of ceiling tiles, 3 sites involved the removalof lagging, 4 sites involved the removal of AIB board and 5 sites involved the removalof sprayed observations on surface tests based on the density of the deposit and colouration of the wipe media bythe surface dust were found to be a simple way to estimate whether surface dust levelsare likely to present a problem and whether the site has been adequately AND SAFETY LABORATORYAn agency of the Health and Safety likely lower level of detection for aluminium oxide and amosite was measured inlaboratory trials on different wipe media.

4 The Whatman 540 filters and Mediwipeswere found to give a visible contamination line after a 10 cm wipe at aluminium oxideparticle concentrations of about 200 p/mm2 and at amosite concentrations of 60 f/mm2. wipe test appeared too sensitive for the current levels of cleaning in UKenclosures as 94 % of enclosures failed the wipe test. However, a similar percentagefailed HSL s Clearance air it was not envisaged that the project examine Methods of cleaning,observations of working practices employed in enclosures suggest that the mostcommon Methods employed; vacuuming and wet mopping are not very effective or arenot applied effectively.

5 HSL operator found the HSL low angle of incidence torch test very useful todetect surface dust but could only be used on smooth surfaces. However, differentoperators are not consistent with their approach or tape was found to be a simple method to sample surface dust and phasecontrast microscopy could be used to quantify the amount of asbestos fibres on thesurfaces. Adhesive tapes can also be treated to allow further analysis by SEM or PLMto identify the fibres present. It does not, however, work well on rough or Forensic tape produces a clearer mount than adhesive tape for PCM , it is limited, if further identification of fibres is tape was found to be the most versatile and efficient sampling medium over arange of surface types.

6 In the simplified form used, was found to be less efficient than tapesampling but gave a more integrated sample, as larger areas or multiple areas could concentration of fibres on a surface of 100 f/mm2, determined using forensic tape,produced a concentration in air of about fibres/ml, when an area of about 50 m2was brushed with a hand brush for 5 minutes. This means that the Visual wipe test whichcan detect down to 60 f/mm2 of amosite will have the potential sensitivity to detectsurface dust levels which may fail the Clearance air surface tests can only provide an indicator of the likely outcome as chrysotileasbestos will not discolour a white wipe media while other dust particles will.

7 It shouldalso be noted that the efficiency of surface sampling is dependent on the type ofsurface and the sampling media used. Also, the small areas sampled may not berepresentative of other AND SAFETY LABORATORYAn agency of the Health and Safety ExecutiveExperimental observations on disturbance / resuspension of surfacedusts and asbestos survey identified that the most common method of disturbing dust in the enclosureswas to shake a plastic bag in the air or to fill a plastic bag with air and hit it against thewalls. These practices were shown in laboratory tests, to be very ineffective Methods ofdust disturbance (less than one tenth compared to brushing).

8 Blower s were found in experimental comparisons to be the most efficienttechnique for resuspending and mixing settled dust, and were some 4-5 times moreefficient than brushing. effectiveness of a leaf blower will dependent on the outlet velocity and the distancebetween the outlet nozzle and the surface. Leaf blowers also generally require anelectrical supply inside the enclosure. efficiency of the leaf blower may mean that surface dust levels which may not bedetected by a simple Visual wipe test, may fail the Clearance air monitoring. Also atsome of the enclosures sampled in the survey, the airborne levels produced if a leafblower had been used, would have been likely to exceed the control limit and will putclearance assessors at increased risk, as the respirators they use have low Brushing is also an effective method of resuspending the dust from the surface but itdoes not mix and disperse the particles as efficiently as a leaf blower.

9 With ground amosite asbestos and resuspension of the fibres with a leafblower indicate that 40 % of asbestos fibres settle out in the first 60 minutes. With handbrushing, there was a sharper decline in the airborne concentration of amosite fibres,which had halved after about 10 minutes and over 90% of the airborne fibres hadsettled out within 30 minutes after disturbance. additional mixing action of the leaf blower had an important influence on the airmeasurements as the fibres lofted by the leaf blower took longer to settle out. Thisobservation alone accounted for most of the difference between the relative efficienciesof brushing and leaf also suggests that for brushing, the sampling period should be short (30 minutes orless), or the surfaces should be subject to more frequent disturbance ( every 15minutes instead of every hour).

10 Alternatively, fans could be used to further mix anddistribute the dust in the AND SAFETY LABORATORYAn agency of the Health and Safety ExecutiveField observations on Visual assessment by site most cases the analyst was involved in a remedial cleaning process rather than aseparate Visual Clearance assessment. role of the analyst in the Clearance process is ambiguous and they need arecognised independent role without any financial relationship with the removalcontractor. At some sites visited the analytical firm did have a supervisory where the analyst had a recognised supervisory role, generally allowed a period oftime for the enclosure to dry, before starting the Clearance assessment.