ASSIGNED PROTECTION FACTORS AND ISO PROTECTION LEVELS

1. ASSIGNED PROTECTION FACTORS AND ISO PROTECTION LEVELS Robin Howie Robin Howie Associates ISRP, York, April 2013

2. There are known knowns.These are things we know we know.There are known unknowns.That is to say, these are things we know we don’t know.But there are also unknown unknowns.These are things we don’t know we don’t know. Donald Rumsfeldt

3. THE ISO DTS 16973 CLASSIFICATION REGIMEN Determine max Lab TIL; Compare max TIL with Table 2 and assign to relevant TIL Level; Apply the “Safety Factor” relevant to the TIL Level; Determine the Protection Level (PL) Class.

4. TABLE 18: Protection level classes

5. OBSERVATION From personal experience most “high” performance devices give much lower Lab TIL than the maxima specified in the EN. So, Lab PF may be higher than the relevant EN NPF for such devices.

6. OBSERVATION PL5 is effectively equivalent to current TM3 and full-face –ve pressure P3. A more stringent assessment of the data would set the APF for these devices at somewhere around 20.

7. OBSERVATION PL5 effectively sets the “NPF” for these devices at 2000 whereas BS4275 set the APF at 40.

8. OBSERVATION The draft ISO classification takes no account of the nature of the device and therefore fails to address factors that could affect performance in the workplace, e.g. sweating during heavy work and/or in hot conditions is likely to be more deleterious with ½-mask -ve performance than with ff-ve or PAPR.

9. OBSERVATION Consider the case where YOU may be exposed to, say, 50 fibres/ml of amosite, and you are offered 3 devices fitted with P3 filters, all meeting ISO PL5: a ½-mask -ve pressure device; a full-mask -ve pressure device; and, a full-mask TM3.

10. QUESTION How many would choose the ½-mask -ve pressure device?

11. QUESTION How many would choose the full-mask -ve pressure device?

12. QUESTION How many would choose the full-mask TM3?

13. OBSERVATION Consider a full-mask PAPR that gave a max TIL of 0.003%: i.e. a Lab PF of 33,000; The device would be assigned to an ISO TIL class of 0.01%, i.e. a PF of 10,000; The ISO Safety Factor would be 5, so giving an ISO “NPF” of 2,000.

14. OBSERVATION But a known known is that WPF measured for such devices using suitable in-mask sampling probes give 95%iles in the region of 20-100.

15. OBSERVATION The current ISO draft would therefore take us back 20 years to effectively selecting RPE on the basis of NPF.

16. WPF DATA There is a fundamental error in how data are presented for WPF studies that involve continuous in-mask sampling. For the inhale part of the sample duration in-mask contaminant is collected. For the exhale part only the non-body deposited contaminant is collected. If all of the contaminant deposits in the body the true WPF is half of the reported WPF. For continuous flow powered or air-fed devices any exhaled contaminant will be diluted by the incoming air; and the true WPF will be about half of the reported WPF.

17. WPF DATA It would be prudent to half all WPF results from studies with continuous in-mask sampling; including the data from Howie et al (1996).

18. WPF DATA I proposed such correction when drafting of BS4275 but, as such correction would have “rolled down” into setting very low APF for FFR and ½-mask devices, the proposal was rejected.

19. WPF DATA The then available WPF data were evaluated when setting the APF for BS4275: copies of these data should be available in the BSI archives. If not available from BSI the relevant references were cited in BS4275. Further WPF data are now available.

20. WPF DATA A major problem, addressed in BS4275, is that most WPF studies carried out in the USA use/used in-mask probes that are likely to have significantly under-measured in-mask concentrations and therefore caused WPF to be significantly over-estimated.

21. POSSIBLE PROBE EFFECTS

22. WPF DATA WPF derived from US studies must therefore be assessed with care.

23. A KNOWN KNOWN “The quantitative fit factors that were obtained did not predict which workers would have the highest or lowest WPF. Although the data were limited, it appears there was no correlation between WPF and quantitative fit factor.” Colton et al (1989). 8.8.1 “Fitting tests only identify gross misfits and do not guarantee adequacy of fit.” BS4275: 1997

24. A KNOWN KNOWN The Zhuang et al (2003) and Han (2002) studies reported correlation between WPF and QnFF. Zhuang et al studied the correlation over a short period and did not address long-term effects. Han’s r^2 values for FF <100, the normal “pass” criterion for such devices, was 0.31 and for FF >100 was 0.02.

25. A KNOWN KNOWN The Zhuang et al (2003) and Han (2002) studies reported correlation between WPF and QnFF. Zhuang et al’s data exhibit declining correlation as FF increases above 100. Han’s r^2 values for FF <100, the normal “pass” criterion for such devices, is 0.31 and for FF >100 is 0.02.

26. ASSUMPTION Where QnFF are available but Lab PF data are not, it will be assumed that QnFF can used as an indicator of likely Lab PF.

27. CALCULATION BASIS “Required Safety Factors” below will be based on ISO TIL class/95th%ile WPF

28. AVAILABLE WPF DATA Howie et al (1996) 4 x TM3 devices Large diameter deep probe No Fit Testing for workmen. All investigators achieved QnFF >10,000

29. Howie et al (1996)

30. AVAILABLE WPF DATA Riala & Riipinen (1998) 6 x PAPR, P3, assumed TM3 Small diameter probe, depth not defined. No Fit testing ----------------------------------------------------- Colton et al (1989), PAPR Liu probe effectively flush with inner surface of inner cup All QnFF >1000

31. Riala & Riipinen, Colton et al (1990)

32. AVAILABLE WPF DATA Tannahill (1990, 1991) 3 x Full-mask –ve AP with P3 filters Sampling in visor area No Fit Testing -------------------------------------------- Colton et al (1989) Full-face –ve Liu probe effectively flush with inner surface of inner cup All QnFF >500

33. Tannahill, Colton et al (1989)

34. AVAILABLE WPF DATA Myers et al (1984) 2 x loose-fitting AP PHR Probe on inside surface of vizor opposite mouth Minimum QnFF >1000

35. Myers et al (1984)

36. AVAILABLE WPF DATA Zhuang et al (2003) 2 x ½masks -ve with P100 filters Probably shallow Liu probe ZZ very kindly supplied raw data Study deliberately included wearers with QnFF <100 Only data for wearers with QnFF >100 analysed herein

37. Zhuang et al (2003)

38. AVAILABLE WPF DATA Myers & Zhuang (1998) 3 x ½ mask DFM, 2 x FFR DM, 8-11 subjects per mask type Probe probably on inside surface of mask All QnFF >100.

39. Myers & Zhuang (1998)

40. AVAILABLE WPF DATA Hery et al (1993) 2 x FFP2, 3 x ½-mask P2, 1 x ½-mask P3 Flush probe No Fit Testing

41. Hery et al (1993)

42. AVAILABLE WPF DATA Liu et al (2006) 2 x ½ mask OV Probe on inner surface of mask QnFF with pass level of 100, FF for 3M device ranged 155-15000 FF for Survivair device ranged 219-76000

43. Liu et al (2006)

44. AVAILABLE WPF DATA Han (2002) 3 x N95 FFR Probe probably on inner surface of mask QnFF 10-200

45. Han (2002)

46. Summary The known knowns.

47. TM3, FF-ve AP

48. PHR, ½-mask, FFR

49. FFR, ½-mask -ve AP

50. Known unknowns What are the effects of higher then moderate work rates on TIL? (See TNO data on Gas Masks and consider the sweating of wearers working hard; particularly when wearing impervious clothing.)