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The Hazardous Facility Screening Procedure training manual.

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Table 5.2 An example of a semi-quantitative risk analysis used for the ranking and short listing of risks

(extracted from GCNZ Consultants and H M Tweeddale Consulting Service, 1989, published in Ministry for the Environment 1999: Assessment guide for hazardous facilities – resource for local authorities and hazardous facility operators)

1. Scale for frequency of initiation of incidents (expressed as frequency per million per year)
Frequency Score
Very frequent (e.g. once in two years) 500,000
Probable in the lifetime of the activity (e.g. once in 10 years) 100,000
Possible in the lifetime of the activity (e.g. once in 100 years) 10,000
Unlikely (e.g. once in 1000 years) 1,000
Very unlikely (e.g. once in 10,000 years) 100
Barely credible (e.g. once in 100,000 years) 10
2.Scale of severity on people
Effect Score
Several dead Number of dead
One dead 1
Significant chance of fatality 0.8
Small chance of fatality or severe nuisance/injury to many people 0.3
Severe nuisance to few people, or nuisance to many 0.1
Nuisance to few people 0.01
Minor nuisance to few people 0.001
3. Scale of severity of effect on the environment
Effect Score
Intense local and long term effect (>12 months) or high potential for widespread effect 2-10
Intense local but short-term effect (<12 months) or moderate potential for widespread effect 1
Moderate local and long-term effect (>12 months) or low potential for widespread effect. 0.3
Moderate local but short-term effect (<12 months) 0.1
Minor local short term effect (<12 months) 0.01
Minor local and very short-term effect (<3 months) 0.001-0.003
4. Scale of effect on property
Effect Score
Several houses destroyed Number of houses
Whole of neighbouring factory destroyed 3-10
One house destroyed 1
Originating factory destroyed, or part of neighbouring factory destroyed 0.3
Part of originating factory destroyed, or minor damage to neighbouring factory 0.03-0.1
Minor damage to originating factory 0.001-0.01
5. Scale for probability of failure of protective or emergency response
Description Probability of failure
Negligible chance of effective response 1 (or 100%)
Low chance of effective response 0.7 (or 70%)
Fair chance of effective response 0.3 (or 30%)
Good chance of effective response 0.1 (or 10%)
Very good chance of effective response 0.03 (or 3%)
Exceptional chance of an effective response 0.01 (or 1%)

 

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