cov4 2006 long term exposure to respirable volcanic ash on montserrat: a time series simulation t....
Post on 28-Mar-2015
213 Views
Preview:
TRANSCRIPT
COV4 2006
Long term exposure to respirable volcanic ash on Montserrat: a time series simulation
T. Hincks, R.S.J. Sparks University of BristolW.P. Aspinall Aspinall and Associates and University of BristolP.J. Baxter Dept of Public Health and Primary Care, Univ. CambridgeA. Searl Institute of Occupational Medicine, EdinburghG. Woo Risk Management Solutions
COV4 2006
Aim:Estimate risk of silicosis from cumulative exposure
to cristobalite
• Volcanic activity
• Ash composition
• Deposition and erosion
• Weather conditions
• Human activity / occupation
COV4 2006Risk assessment for
Montserrat
Active since 1995 - high cumulative exposures?
1996 - 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
3 - 24 weight % crystalline silica in <10m (inhalable) fraction of ground deposits
Baxter et al. (1999)
preferentially fractionated in PM4 (<4m)Horwell et al. (2003)
COV4 2006
Aleatory uncertainty
eruptive historyash isopach dataair quality monitoringweather data
• Difficult to assess risk in populations
• Information highly uncertain and poorly constrainedprobabilistic risk assessment
Observations
Numerical models ash dispersalweather 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
COV4 2006
Time series simulation
Code generates daily exposures for PM10 (<10m) and cristobalite crystalline silica
• 6 occupation groups• 4 sites
• Multiple runs (10,000 runs/simulation)
• Sample from PDF for each parameter• Correlated sampling
COV4 2006
Model structure
COV4 2006
Model structure
COV4 2006
Dome growth
Periodic dome growth function controls replacement of material
frequency of collapses increased probability of vulcanian explosions at high growth rates
Gro
wth
rat
e m
3 s-1
COV4 2006
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
COV4 2006
Volcanic activity
6 event categories are considered: significant ash deposits
• 3 - 10 x 106 m3 dome collapse• 10 - 30 x 106 m3 dome collapse• 30 - 50 x 106 m3 dome collapse• 50 - 75 x 106 m3 dome collapse• >75 x 106 m3 dome collapse• Series of 0.4 x 106 m3 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
COV4 2006
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
COV4 2006Ash removal (wind and
rain)
level Depth (cm)Lifetime
(lower, expected & upper bounds)
Negligible <= 0.1 cm remains on ground
Minor 0.1 - 1.0 cm 1 day / 14 days / 3 mo
Moderate 1.0 - 3.0 cm 1 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
COV4 2006
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
COV4 2006
Individual exposure
Sum daily exposure values over 5, 10 and 20 years estimate cumulative exposure risk of silicosis
COV4 2006
Simulated time series
COV4 2006
Simulated time series
COV4 2006
Simulated time series
US NIOSHrecommended 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
COV4 2006
Results: 20 year cumulative cristobalite exposure%
tria
ls e
xcee
ding
exp
osur
e
cumulative cristobalite exposure mg.m-3.year
cumulative cristobalite exposure mg.m-3.year
c
wf
s
COV4 2006
Estimating risk: exposure-response functions for silicosis
Upper limit of risk:
Buchanan et al. 2003Study of silicosis in Scottish coalminers
• High intensity exposure> 0.1 mg m-3
• Heavy ash fall areas only
COV4 2006
Estimating risk: exposure-response functions for silicosis
Upper limit of risk:
Buchanan et al. 2003Study of silicosis in Scottish coalminers
Most analogous:
Hughes et al. 1998occupational exposure for diatomaceous earth workers
exposure intensity affects risk
> 0.5 mg m-3
≤ 0.5 mg m-3
COV4 2006
20 year risk of silicosis
20 years continuous exposure
Hughes et al. (1998) risk function
TYPICAL ADULT
North 0.4 - 0.8 % MODERATE
Salem 1% MODERATE
Cork Hill: 1.1 - 2.5 % HIGH
CMO risk scale
Estimated exposures lie within bottom 20% of Hughes cohort (<100 cases)
RISK?
COV4 2006
20 year risk of silicosis
20 years continuous exposure
Hughes et al. (1998) risk function
TYPICAL ADULT
OUTDOOR WORKER
North 0.4 - 0.8 % MODERATE
Salem 1% MODERATE
Cork Hill: 1.1 - 2.5 % HIGH
CMO risk scale
North 1.3 - 2.4 % HIGH
Salem 2.0 - 3.2% HIGH
Cork Hill: 3 - 5 % HIGH
COV4 2006
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 PM10 measurement
+ weather data
• Personal exposure sampling
• Ash erosion rates - very poorly constrained• Duration of hazard• Implications for lahar and flood hazard assessment
COV4 2006
Validation & future work
Exposure control measures
• dust masks for outdoor
workers in ash affected areas
• minimize exposure during
cleanup operations
• minimize children’s exposure
(clear sports & play areas
after ash fall)
COV4 2006
Further applications
PopocatépetlPM10, ash leachates
Ash-leachates
• water contamination
• risk to livestock
• crop damage
Guadeloupe concerns about contamination of aquifer
COV4 2006
Acknowledgements
Thanks to my PhD supervisors: Steve Sparks, Willy Aspinall and Gordon Woo
Constanza Bonadonna for reconfiguring and running HAZMAP ash dispersal code
DATAAsh data from Clare Horwell, Univ. CambridgePersonal exposure DustTrak data from The Institute of Occupational Medicine Montserrat & Antigua rainfall data from the Montserrat Volcano Observatory and IOMGuadeloupe rainfall data from the Hong Kong Observatory www.hko.gov.hk
CODESCYTHE C++ Statistical Library GNU GPL 2001 A.D. Martin and K.M. QuinnMT19937 Mersenne Twister random number generator 2002 T. Nishimura and
M. Matsumoto
COV4 2006
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): 159-164
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): 477-481
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, 807-814 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: 10.1007/S00445-002-0266-6.
National Institute for Occupational Safety and Health (2002). NIOSH Hazard Review: Health effects of occupational exposure to respirable crystalline silica.
top related