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COV4 2006 Long term exposure to respirable volcanic ash on Montserrat: a time series simulation T. Hincks, R.S.J. Sparks University of Bristol W.P. Aspinall.

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Presentation on theme: "COV4 2006 Long term exposure to respirable volcanic ash on Montserrat: a time series simulation T. Hincks, R.S.J. Sparks University of Bristol W.P. Aspinall."— Presentation transcript:

1 COV Long term exposure to respirable volcanic ash on Montserrat: a time series simulation T. Hincks, R.S.J. Sparks University of Bristol W.P. Aspinall Aspinall and Associates and University of Bristol P.J. Baxter Dept of Public Health and Primary Care, Univ. Cambridge A. Searl Institute of Occupational Medicine, Edinburgh G. Woo Risk Management Solutions

2 COV Aim: Estimate risk of silicosis from cumulative exposure to cristobalite Volcanic activity Ash composition Deposition and erosion Weather conditions Human activity / occupation

3 COV Risk assessment for Montserrat Active since high cumulative exposures? DfID and DoH research on health risks associated with volcanic ash silicosis, lung cancer, pulmonary tuberculosis, autoimmune diseases Health risks? Exposure to date Continuing volcanic activity weight % crystalline silica in <10 m (inhalable) fraction of ground deposits Baxter et al. (1999) preferentially fractionated in PM4 (<4 m) Horwell et al. (2003)

4 COV Aleatory uncertainty eruptive history ash isopach data air quality monitoring weather data Difficult to assess risk in populations Information highly uncertain and poorly constrained probabilistic risk assessment Observations Numerical models ash dispersal weather simulation Expert elicitation formal and unbiased process for obtaining information from experts limited data full extent of system behavior? Observables represented by probability density functions Uncertainty and expert judgment

5 COV Time series simulation Code generates daily exposures for PM 10 (<10 m) and cristobalite crystalline silica 6 occupation groups 4 sites Multiple runs (10,000 runs/simulation) Sample from PDF for each parameter Correlated sampling

6 COV Model structure

7 COV Model structure

8 COV Dome growth Periodic dome growth function controls replacement of material frequency of collapses increased probability of vulcanian explosions at high growth rates Growth rate m 3 s -1

9 COV Rainfall Rainfall time series simulated as two part process: Incidence of rain (true/false) Quantity of rain (24h) Mean Standard deviation Rain depth: Lognormal distribution with time dependent parameters

10 COV Volcanic activity 6 event categories are considered: significant ash deposits x 10 6 m 3 dome collapse x 10 6 m 3 dome collapse x 10 6 m 3 dome collapse x 10 6 m 3 dome collapse >75 x 10 6 m 3 dome collapse Series of 0.4 x 10 6 m 3 vulcanian explosions Assume event magnitudes and frequencies ~similar to past 10 years activity daily P(event) Probability of Vulcanian explosions increases after major dome collapses and during periods of high extrusion rate

11 COV Ash deposition Ash deposits generated with HAZMAP 2-D advection diffusion model for ash transport (Bonadonna et al. 2002) 3 years of daily wind data Dome collapse pyroclastic flows down 5 valleys Single source Vulcanian explosions correlated lognormal deposits distributions for 4 locations

12 COV Ash removal (wind and rain) levelDepth (cm) Lifetime (lower, expected & upper bounds) Negligible<= 0.1 cmremains on ground Minor cm 1 day / 14 days / 3 mo Moderate cm1 mo / 6 mo / 12 mo Major>3.0 cm 1 year / 2 y / 3 y Approximate with 4 deposit levels Use beta distribution to represent variation in deposit lifetime Expert elicitation for mean, upper and lower bounds

13 COV Individual exposure PDF: VARIATION IN EXPOSURE Beta distribution function of deposit depth cristobalite content of ash occupation Modified to account for rainfall High exposure Gardeners Public works department Low exposure indoor occupations elderly dust trak data

14 COV Individual exposure Sum daily exposure values over 5, 10 and 20 years estimate cumulative exposure risk of silicosis

15 COV Simulated time series

16 COV Simulated time series

17 COV Simulated time series US NIOSH recommended limit US NIOSH recommended limit: 0.05 mg m -3 time weighted average for up to 10 hour work day during 40 h working week UK HSE recommended maximum occupational exposure to crystalline silica: 0.3 mg m -3 Suggested limit: 0.1 mg m -3 8h time weighted average UK HSE (2003) suggested limit

18 COV Results: 20 year cumulative cristobalite exposure % trials exceeding exposure cumulative cristobalite exposure mg.m -3.year c w f s

19 COV Estimating risk: exposure-response functions for silicosis Upper limit of risk: Buchanan et al Study of silicosis in Scottish coalminers High intensity exposure > 0.1 mg m -3 Heavy ash fall areas only

20 COV Estimating risk: exposure-response functions for silicosis Upper limit of risk: Buchanan et al Study of silicosis in Scottish coalminers Most analogous: Hughes et al occupational exposure for diatomaceous earth workers exposure intensity affects risk > 0.5 mg m mg m -3

21 COV year risk of silicosis 20 years continuous exposure Hughes et al. (1998) risk function TYPICAL ADULT North %MODERATE Salem1%MODERATE Cork Hill: %HIGH CMO risk scale Estimated exposures lie within bottom 20% of Hughes cohort (<100 cases) RISK?

22 COV year risk of silicosis 20 years continuous exposure Hughes et al. (1998) risk function TYPICAL ADULT OUTDOOR WORKER North %MODERATE Salem1%MODERATE Cork Hill: %HIGH CMO risk scale North %HIGH Salem %HIGH Cork Hill:3 - 5 %HIGH

23 COV Validation & future work Medical studies 2000: x-ray survey of 421 high risk workers showed no evidence of chest abnormalities (< 5 years exposure) X-ray survey after 10 years exposure Risk to children highly uncertain limited data - better estimates of cumulative exposure? applicability of exposure response functions? Field data Continuous PM 10 measurement + weather data Personal exposure sampling Ash erosion rates - very poorly constrained Duration of hazard Implications for lahar and flood hazard assessment

24 COV Validation & future work Exposure control measures dust masks for outdoor workers in ash affected areas minimize exposure during cleanup operations minimize childrens exposure (clear sports & play areas after ash fall)

25 COV Further applications Popocatépetl PM 10, ash leachates Ash-leachates water contamination risk to livestock crop damage Guadeloupe concerns about contamination of aquifer

26 COV Acknowledgements Thanks to my PhD supervisors: Steve Sparks, Willy Aspinall and Gordon Woo Constanza Bonadonna for reconfiguring and running HAZMAP ash dispersal code DATA Ash data from Clare Horwell, Univ. Cambridge Personal exposure DustTrak data from The Institute of Occupational Medicine Montserrat & Antigua rainfall data from the Montserrat Volcano Observatory and IOM Guadeloupe rainfall data from the Hong Kong Observatory CODE SCYTHE C++ Statistical Library GNU GPL 2001 A.D. Martin and K.M. Quinn MT19937 Mersenne Twister random number generator 2002 T. Nishimura and M. Matsumoto

27 COV References Buchanan, D., B. G. Miller, et al. (2003). "Quantitative relations between exposure to respirable quartz and risk of silicosis." Occupational and Environmental Medicine 60(3): Burmaster, D. E. and P. D. Anderson (1994). "Principles of Good Practice for the Use of Monte Carlo Techniques in Human Health and Ecological Risk Assessments." Risk Analysis 14(4): Cooke, R. M. (1991) Experts in Uncertainty: Opinion and Subjective Probability in Science. Environmental Ethics and Science Policy Series. Oxford University Press, New York. Hughes et al. (1998) Radiographic Evidence of Silicosis Risk in the Diatomaceous Earth Industry. Am. J. Respir. Crit. Care Med., Volume 158, Number 3, Horwell, C.J., Sparks, R.S.J., Brewer, T.S., Llewellin, E.W., and Williamson, B.J. (2003). The characterisation of respirable volcanic ash from the Soufrière Hills Volcano, Montserrat, with implications for health hazard. Bull. Volcanol., DOI: /S National Institute for Occupational Safety and Health (2002). NIOSH Hazard Review: Health effects of occupational exposure to respirable crystalline silica.


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