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www.hsl.gov.ukAn Agency of the Health and Safety Executive
www.hsl.gov.ukAn Agency of the Health and Safety Executive
Estimating societal risk: modelling and outputs
Dr Mike WardmanHSL
An Agency of the Health and Safety Executive
Modelling• Workbench tool Excel workbook/C code• Inputs required
– Scenarios– Weather– Population
• Dispersion calculations– Generate footprints
• Calculate fn pairs– Overlay footprints - fatalities– Calculate frequency
An Agency of the Health and Safety Executive
Scenarios• Set of scenarios used:
– Reduced set for ranking– Land use planning scenarios
• Specify– Substance– Event frequency– Instantaneous/continuous release– Size/Rate and duration– Release coordinates
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Weather• 12 sector wind rose• Data available for range
of stations closest to site used
• Weather conditions– e.g. F2, D5, B2, D2
• Probability – Sector– Weather conditions
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Population• National Population Database (NPD) used• 100m grid resolution• Extent determined by hazard range• Produces grid
0 5.42 0 0 0 0 2.57 0 21.84 5.46 2.73 20.22 26.10 0 5.38 0 10.28 5.14 0 4.42 11.05 2.73 71.96 89.49 15.720 2.69 2.69 272.1 2.35 5.14 8.84 2.21 32.17 21.62 33.12 5.46 10.48
2.69 2.69 72.26 1061.4 14.1 4.7 11.05 14.8 74.25 631.68 50.01 397.69 13.990 2.62 8.07 123.11 0 2.35 4.56 11.84 5.74 30.58 5.29 140.97 53.98
115.28 7.86 2.69 109.43 11.75 2.96 2.35 0 2.78 2.51 5.02 73.23 80.967.86 0 0 0 0 2.35 0 0 0 2.51 60.96 1158.82 2.48
858.4 10.48 2.62 0 2.35 0 0 0 0 0 844.76 4002.68 2256.72486.27 5.52 5.52 27.6 2.76 25.1 65.74 692.46 393.44 7.53 0 1244.61 391.1
0 5.52 0 0 0 2.51 102.04 344.58 108.68 0 2.46 0 8.74
An Agency of the Health and Safety Executive
NPD Database• GIS based analysis tool, hosted at HSL• Data for England Scotland and Wales• Different Populations available:
– Residential (day/night time term/non term time)– Sensitive populations (Schools, Hospitals, Care
Homes, Prisons)– Workplace (based on Census Output Area, COA)– Retail (town centre, out of town developments)– Transport (Motorway, dual/single carriageway A
roads)– Leisure (stadium, theme parks, camping grounds)
• Gives vulnerability, location, time differentiation
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National Population Database• Residential Layer - Night time population ~
504
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Dispersion• Parameterised dispersion used
– Generated from integral models– Defines footprints dimensions
Max Distance
Min Distance
Max Width
Distance to MaxWidth
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n values (fatalities)• Footprints generated for:
– Indoor/outdoor– 1%, 10%, 50% fatality doses– Each weather condition
• D5, F2, …– Different population sets (day/night)
• Overlay population data to calculate n values– Combine indoor/outdoor and doses– Fraction of the population covered
at each dose• Cover all sectors of windrose
– 1 degree steps used
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f values (frequencies)• Frequencies calculated
taking account of:– Weather condition probability
e.g. 80% D5, 20% F2– Bias factor for each wind
direction from wind rose– Different populations
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Outputs
• Numerical– Expectation Value– Risk Integral (scale aversion)
• Graphical – Cumulative FN Curve
• Geographical– Risk combined from each footprint (area plot)– Risk from each grid location (hot spots)
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Numerical• Expectation Value, EV
– Σ f.n• Risk Integral, RI
– RI is based on EV with factor a to reflect scale aversion
– Σ f.na
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Graphical• FN curve
– cumulative frequency of N or more fatalities
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Geographical Output• Based on numerical
representation– EV– F.N
• Value at grid location shown
• Types– Hot Spots plot– Area plot
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Hot Spots• Risk at each grid location
An Agency of the Health and Safety Executive
Area plot• Cumulative risk of overlaid footprints