When is risk low enough : Risk Acceptance and ALARP

I would like to thank you all for continued interest in the blog posts. Keep reading and do like, share and comment. In this blog, we will be discussing what is the risk acceptance criteria and what is ALARP to define When is the risk low enough.

No activity is entirely free of risk in an industrial plant and hence it is imperative that safety risks are reduced to acceptable levels. The key question that remains is what level of risk is considered to be acceptable? 

As per framework, risk criteria is usually divided into three bands, Unacceptable, ALARP and Acceptable regions.

• Unacceptable Region: Band in risk criteria, where risks are intolerable except in extraordinary circumstances, and risk reduction measures are essential to be implemented. Sometimes, this zone is also denoted as the Red Zone.
• ALARP Region: Band where risk reduction measures are desirable, but might not be implemented if the cost of implementation is disproportionate to the benefit achieved i.e. cost of implementation is higher than the benefit achieved. Sometimes, this zone is also denoted as the Yellow Zone.
• Acceptable Region: Band where no further risk reduction measures are needed. Sometimes, this zone is also denoted as the Green Zone.

Risk criteria are usually defined by standards and are used to help decide whether the risk associated with an industrial plant or an activity is low enough to proceed further or not. In other words, we can say that these risk criteria are used to interpret numerical risk estimates as produced by a Quantitative Risk Assessment (QRA) study into a decision in the decision-making process, e.g. 10-8 per year falls in ‘negligible risk’.

Risks to people are usually expressed in two major forms, i.e. Individual Risk and Societal Risk. Individual Risk is the risk experienced by an individual person while Societal Risk (or Group Risk) is the risk experienced by the whole group of people including workers and the public.

INDIVIDUAL RISK

Individual Risk is most commonly expressed in form of Location Specific Individual Risk/ LSIR (assuming a hypothetic individual placed at any particular location for 24 hours a day and 365 days a year) and in form of Individual Risk Per Annum/ IRPA (considering LSIR and fraction of time spent by an individual at different locations). The maximum tolerable IRPA criteria utilized is 10-3 per year for site workers and 10-4 per year for members of the public are generally accepted internationally. However, most facilities and companies often set more stringent criteria as much as 10-4 and 10-5 per year for site worker and the public.

Note: Individual Risk is independent of the number of persons at a particular location.

SOCIETAL (OR GROUP) RISK

For the same facility with 10 people and 100 people within the same plant area, the individual risk will be the same (if other conditions are maintained same), however, societal or group risk will be different for both scenarios and will be higher for 100 people scenario. 

Any accident resulting in a fatality is unfortunate, but society generally tends to be more concerned about multiple fatalities in a single event. While such low-frequency high-consequence events might represent a very small risk to an individual, they may be seen as unacceptable when a large number of people are exposed. Such incidents can significantly impact shareholders value and, in many cases, the company never recovers

Societal Risk is most commonly expressed in form of FN Curve, where maximum and minimum risk criteria lines divide the space into three regions, i.e. unacceptable, ALARP and acceptable.

Reference: Risk Criteria - When is low enough good enough by Risktec

Unlike, individual risk criteria, there are no single risk criteria which are being used by operators and regulators in the major hazard industries worldwide. The criteria for Netherland is very stringent and restrictive as compared to the UK or Hong Kong.

Reference: Risk Criteria - When is low enough good enough by Risktec

For a company operating in regions where there are no regulatory criteria to meet, the choice of criteria to help decision-making therefore largely comes down to the company values in terms of safety, commitment and reputation.

In the absence of regulatory FN-criteria, some operators have set their own FN-criteria but other operators believe there are simply too many issues associated with defining the upper and lower criterion lines.

Now the next question arises that if the risk is in the ALARP region is it good enough? 

This is a major misconception among industries. Even when a level of risk for the base case has been estimated originally to be in ALARP region it is still necessary to consider introducing further risk reduction measures to drive the residual risk downwards towards acceptable. 

The ALARP level is reached when the time, trouble and cost of further reduction measures become unreasonably disproportionate to the additional risk reduction obtained. This process is called as Cost Benefit Analysis.

Risk can be reduced by avoidance, adopting an alternative approach, or increasing the number and effectiveness of controls. After the selection of possible risk reduction measures, QRA shall be carried out for each of the options to identify the associated reduction in risk. Combining this improvement with the total cost of each option enables the options to be ranked in order of cost-effectiveness. The Implied Cost of Averting a Fatality (ICAF) is expressed in terms of amount per statistical fatality averted: 

ICAF = Net cost of Measure Implementation 

                Potential saving of life

UK HSE Guidelines have set the value of a life at £1,336,800 in 2003. This value should be indexed before going for the ALARP Demonstration.

Hope this helps in understanding the risk acceptance criteria and ALARP Demonstration. If you have any questions, drop me an email on himanshuchichra@gmail.com. Also, write to me if you would like clarification on any particular topic via these blog posts.

Thank you all for reading.