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

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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

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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

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Area plot• Cumulative risk of overlaid footprints