Current issues in asbestos fibre counting: changes in rules and national and international comparability

Transcription

1 Current issues in asbestos fibre counting: changes in rules and national and international comparability AD Jones 1, MC Arroyo 2, P Brown 1, R Grosjean 3, BG Miller 1, B Tylee 4 1 Institute of Occupational Medicine (IOM); 2 Instituto Nacional de Seguridad e Higiene en el Trabajo; 3 Laboratory of FPS Employment, Labour and Social Dialogue, Belgium; 4 Health and Safety Laboratory, UK INSTITUTE OF OCCUPATIONAL MEDICINE EDINBURGH, EH14 4AP, UK

2 Background Airborne Asbestos fibre monitoring by Phase Contrast Optical Microscopy; Change to the WHO all-fibre method, following European Directive 2003/18/EC, scheduled for April 2006 International Comparability in asbestos fibre counting A special exchange of reference slides 1 ; and regular exchanges in the Asbestos Fibre Regular Informal Counting Arrangement (AFRICA); Data from training exercises for UK labs prior to changeover. 1 Jones AD, Arroyo MC, Grosjean R, Tylee B, Miller BG, Brown P. A comparison of fibre counting across three European national proficiency testing schemes. Annals of Occupational Hygiene, 2005.

3 The national PT schemes for fibre counting UK (RICE) procedures, and similar arrangements in Spain and Belgium Permanently mounted samples on glass slides; Reference values (R) assigned to each sample - Consensus (median) density from counts from all labs. Target range for reported densities Labs sent a batch of 8 samples every 3 months, Laboratory performance is assessed over 4 batches (32 samples) ratings performance on each single batch classified on 4 consecutive batches

4 Aims to assess consistency in international counting levels as evident from regular international exchanges AFRICA; to describe and discuss some preparations for the changeover to the WHO fibre counting method; to present some indications of the effect of the new rules: on fibre counts, and on inter-laboratory consistency; to discuss some of the implications.

5 Improvement in lab performance over first 50 rounds of the UK PT scheme RICE Rating 1 % of labs Round Rating 2 Rating 3 Limits tightened Low density samples & visual reference counts Reference adjustment

6 And the equivalent graph for AFRICA % of labs Round Rating 1 Rating 2 Rating 3 Low density samples & visual reference counts

7 International Comparability Asbestos Fibre Regular informal Counting Exchanges AFRICA: 36 participating laboratories across the world; Special exchange: samples from national PT fibre counting PT schemes in UK, Spain, and Belgium; 40 samples with reference values from the national PT scheme; samples circulated to 2 labs in the UK, 2 in Spain, and 2 in Belgium; data analysed for evidence of consistency in: national reference values (see publication); and to compare WHO and ERM counts.

8 AFRICA membership, by location of labs Europe 25 Elsewhere 11 Belgium 1 Brazil 2 Denmark 1 Canada 1 Finland 1 Colombia 1 France 1 Hong Kong 3 Germany 1 India 2 Hungary 2 South Africa 2 Italy 10 Luxembourg 2 Portugal 2 Spain 2 Switzerland 1 UK 1

9 Expected effect of WHO rules Two main differences with respect to current European Reference Method (ERM1); Discrimination of non-asbestos fibres, by a valid method, will be explicitly allowed. Probably not widely used? But may need proficiency testing? (Under discussion in UK) Fibres touching particles Fibres that touch particles larger than 3 µm diameter are excluded currently under ERM1; These fibres will be included under the WHO rules.

10 Survey of fibre counting methods currently used by labs in the AFRICA scheme Lab location Number of labs using each method Total ERM 1 WHO undeclared Europe Outside Europe Total

11 How much difference can the change in rule make to the count on clearance samples? 1 Iles et al (1989) (n=50) 2 RICE samples n=8 2 Belgian samples Geo mean Gsd n=8 1 separate counts, 2 WHO & ERM on same fields

12 And for Asbestos Cement samples? WHO density /ERM density 1 Iles et al (1989) AC manufacturing (n=50) 2 Spanish PICC-FA dust box AC cloud, n=8 1 separate counts, 2 WHO & ERM on same fields Geo mean Gsd

13 Difference observed on 40 samples from three national PT schemes Samples Belgian scheme (n=8) Spanish PICC-FA, (n=16) UK RICE (n=16) All samples (n=40) Geometric mean ratio Geometric standard deviation

14 And the spread in individual results Geometric means 8 Belgian samples 16 Spanish PICC-FA samples 16 UK RICE samples Ratio WHO to ERM Individual counts IOM HSL concurrent counts HSL separate counts Spanish lab 1 Spanish lab ERM mean density / fibres.mm

15 Training exercise in UK Purpose To help labs train analysts in the new counting rules; Participation a requirement for UK labs (to maintain accreditation to EN ISO/IEC 17025/2005); Design Special counts; fields, fibres countable under ERM, additional fibres countable under WHO method (on the same fields); Samples counted initially by expert labs; Samples sent to labs; Pilot round with 30 volunteer labs; Rounds for all 160 other RICE labs; Reports on results to labs for their training records. Steered by HSE committee

16 ERM counts from Training Exercise ERM-1 1 st Training round 2005 Pilot study 2003 RICE Round 68 for comparison number of % of counts by labs in each performance band counts -C -B A +B +C

17 WHO counts from training exercise WHO counts 1 st Training round 2005 Pilot study 2003 number of % of counts by labs in each performance band counts -C -B A +B +C

18 Geometric mean ratio WHO density to ERM density, participant compared to expert lab ratio from participant labs geometric mean equality ratio from "expert" lab

19 All the data for 15 slides (23 to 79 counts / slide) 2.4 ratio from participant labs equality ratio estimated by "expert" lab

20 Expected effect of changeover to WHO rules In principle, the new rule should be less subjective (and hence lead to slightly better inter-laboratory agreement eventually); Densities reported by labs on PT schemes should increase; Reference values will need to be adjusted accordingly; Reference values on the permanent samples in RICE will change; The training exercise in the UK; is raising awareness among analysts; but data have shown a higher proportion of poor counts in the training exercise, for some labs; Rules used by AFRICA labs will be monitored, and reports and reference values will take account of the change.

21 Thanks to The UK HSE for funding IOM s work in the studies; the many staff at the laboratories who generated the fibre counting data; and colleagues who helped with discussions.