Individual vs Societal Risk So what? Caron Maloney HM Specialist - - PowerPoint PPT Presentation

Health and Safety Executive Health and Safety Executive

Individual vs Societal Risk So what?

Caron Maloney HM Specialist Inspector Risk Assessment

• 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

Presentation

• 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

Content

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

Detailed Risk Assessment - Legal bit:

• 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

Level of detail required

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

• f 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

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 – what is the risk to me?

Individual risk estimate - 1a

• Sum of all the frequency-

consequence pairings that affect the individual

• For example 1a

➢Event frequency x 12 ➢Probability of fatality 1

All Hazards

Representative Individual

“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 – total harm to the population

Societal risk estimate - 1a

• How many people are

affected by the event to specified level of harm

• For example 1a

➢Probability of fatality 1 ➢Approximately 100

houses 2.5 per household gives 250

Major Hazard

Total number of people at risk

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

subjective

• Events can lead to a range
• f outcomes
• R2P2 - a single point
• Intolerable if chance of

causing 50 or more deaths is greater than 1 in 5000

FN Plot for Hays Chemicals, Sandbach_15min_3X50te tanks

1.0E-02 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1 10 100 1000 10000 N Frequency of N or more (CPM)

RI (1.4) = 183432. RI (LUP) = 6345349. EV = 19660.02 NMax = 4228 FNMax = 2.54E-02

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 1a Example 1b

• 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

Level of detail

• 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

So what (2)

• 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

Legal bit:

“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?

SFAIRP – ALARP - AMN

Broadly Acceptable Intolerable Types of ALARP Demonstration Risk reduction almost regardless of cost Relevant Good Practice Gross disproportion Risk reduction Measures Relevant Good Practice Tolerable if ALARP Increasing risk

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

Briefly

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

Summary