Health and Safety Health and Safety Executive Executive Individual vs Societal Risk So what? Caron Maloney HM Specialist Inspector Risk Assessment
Presentation • Introduction • Detailed Risk Assessments • Frequent questions ➢ Which type should be considered individual or societal risk? ➢ What is the right approach for each type? ➢ Should both be considered, and which dominates? • Intelligent Customers
Content • What the presentation will not cover ➢ Detailed methodology for risk assessment • What the presentation aims to cover ➢ What is required ➢ Proportionality (depth of detail) ➢ Risk - individual and societal
Detailed Risk Assessment - Legal bit: Management of Health and Safety Regs 1999 (Reg 3) (1) Every employer shall make a suitable and sufficient assessment (a) the risks to the health and safety of his employees … (b) the risks to the health and safety of persons not in his employment … Therefore level of detail in a risk assessment should be proportionate to the risk and nature of the undertakings
Level of detail required • Proportionality – key to establishing the level of detail required for demonstration • Principle – the greater the risk the greater the degree of rigour required • Factors to consider ➢ Hazard potential ➢ Complexity of operations ➢ Size and nature of populations that could be affected
Fantasy Tank storage site Fantasy tank storage site Illustrative purposes only
Example 1 At this point assume • 12 tanks in 3 bunds. • Assuming tanks same size • Assuming low volatility flammable substance • Low complexity of operations • population in the vicinity but limited impact
Example 2 In example 2 • 24 tanks in 6 bunds. • tanks are of different sizes • Different flammable substances with different volatility • Higher hazard potential • Still low complexity • Significant population affected in the vicinity
Individual Risk vs Societal Risk Reducing Risk Protecting People (R2P2) • both the level of individual risks and the societal concerns….. must be taken into account when deciding whether a risk is unacceptable, tolerable or broadly acceptable; • ... HSE starts from the position that, for every hazard, the law requires that: – a suitable and sufficient risk assessment must be undertaken to determine the measures needed to ensure that risks from the hazard are adequately controlled;
R2P2 • http://www.hse.gov.uk/risk /theory/r2p2.pdf
Returning to our tank farm - example 1 Risk assessment • Could consider all tanks individually or • given they are similar could calculate the hazard extent of 1 tank • Pool over topping bund gives hazard extent to specified level of harm
Example 1 Risk assessment • No offsite populations identified within the hazard extent (1800tdu dangerous dose) • On site populations? • So what?
Example 1a • More volatile - hazardous substance in some of the tanks • same level of detail results in larger hazard extent • Now there is significant offsite population affected • Look to refine assessment - adding an increased level of detail
Individual Risk – what is the risk to me? Definition • the likelihood an individual will be exposed to a specified level of harm - usually fatality (risk of fatality per year) Aproach • Identify individual (groups) that could be affected both on site and off site (any vulnerable groups) but consider a representative individual • For each identify which scenarios could have an impact on the individual to the specified level of harm • Summate the risk from all the events
Individual risk estimate - 1a • Sum of all the frequency- consequence pairings All Hazards that affect the individual • For example 1a ➢ Event frequency x 12 ➢ Probability of fatality 1 Representative Individual
Societal Risk – total harm to the population “The relationship between the frequency and the number of people suffering a specific level of harm” • How many people will be affected - both on and off site • This often focusses on numbers of fatalities • but should include estimates of number of people harmed
Societal risk estimate - 1a • How many people are Major Hazard affected by the event to specified level of harm • For example 1a ➢ Probability of fatality 1 Total number of people at risk ➢ Approximately 100 houses 2.5 per household gives 250
So What (1) • So what does it mean? • Is the risk level acceptable? • Tolerability of Risk Criteria • HSE ➢ Tolerablility of risk from nuclear power stations (1992) ➢ R2P2 (2001)
Risk Tolerability Criteria - Individual Risk
Risk Tolerability Criteria - Societal Risk • More problematic and N Max = 4228 F NMax = 2.54E-02 FN Plot for Hays Chemicals, Sandbach_15min_3X50te tanks EV = 19660.02 RI (1.4) = 183432. RI (LUP) = 6345349. subjective 1.0E+04 • Events can lead to a range 1.0E+03 Frequency of N or more (CPM) of outcomes 1.0E+02 • R2P2 - a single point 1.0E+01 • Intolerable if chance of 1.0E+00 causing 50 or more deaths 1.0E-01 is greater than 1 in 5000 1.0E-02 1 10 100 1000 10000 N
Example 1a • Simplistic approach based on largest tank • Takes largest tank with most hazardous substance as representative • Individual risk – depending on failure rate could be high • Societal risk – frequency greater than 30cpm maybe intolerable • So what?
Example 1b – refine level of detail • Consider at the individual bund level • Only tanks in bunds 2 and 3 have higher volatility flammable substance • Tank in bund 1 similar substance to that given in example 1 • Less population affected • Some affected to lower frequency
Comparison Example 1b Example 1a
Level of detail • Level of detail depends on the level of risk • Hazard potential • Populations affected • Do you have enough detail to be confident in the risk calculated and does it enable you to make a demonstration • Trade off - More refinement could lead to more work to quantify/qualify the assumptions • May require sensitivity analysis
So what (2) • suitable controls must be in place to address all significant hazards, and • HSE also starts with the expectation that: – those controls, at a minimum, must achieve the standards of relevant good practice precautions, irrespective of specific risk estimates; “The greater the risk, no doubt, the less will be the weight to be given to the factor of cost” – Lord Justice Tucker
Legal bit: • HSWA – reduce risk to as low as far as is reasonably practicable • COMAH Regulation 5 General Duties of operators ➢ (1) Every operator must take all measures necessary to prevent major accident and to limit their consequences for human health and the environment ➢ (2)Every operator must demonstrate to the competent authority that it has taken all measures necessary as specified by these Regulations
SFAIRP – ALARP - AMN “ So far as is reasonably practicable” = “As low as reasonably practicable” = “All measures necessary” Basically asking – So what (3) • What more can be done to reduce the risk? • Is it worth doing? • Why is it not being done?
Types of ALARP Demonstration Risk reduction almost regardless of cost Intolerable Gross disproportion Increasing risk Risk reduction Measures Tolerable if ALARP Relevant Good Practice Relevant Good Practice Broadly Acceptable
Briefly Societal consideration more than fatalities: Cost benefit analysis should consider more than just fatalities when considering the benefits gained – same level detail on either side balance COMAH Reg 13(3) require operator “to provide the local authority with the information necessary to enable it to prepare an external emergency plan - Including major accident scenarios and the consequences
Summary Level of detail - depends – governed by proportionality - such that it is suitable and sufficient Both Individual Risk and Societal Risk needs to be considered The approach depends on the proportionality of the site and the hazards presented If you can, keep it simple ! Ask the " so what " questions Hopefully with a good understanding of the proportionality you can be a more focused intelligent customer
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