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The ALARP (As Low As Reasonably Practicable) principle has been defined by the United Kingdom Health and Safety Executive (UK HSE) [1] to depict the concept that efforts to reduce risk should be continued until the incremental sacrifice in doing so is grossly disproportionate to the value of the incremental risk reduction achieved (see figure). Incremental sacrifice is defined in terms of time, effort, cost or other expenditure of resources [2]. Usually, each incremental reduction in risk will require a greater expenditure of resources. 

Three general levels of risk are shown in the figure. Negligible risks are so low as not to be of concern. This is sometimes called de minimis risk. Tolerable risks are considered acceptable if the benefit is seen to outweigh the impact. Unacceptable risks cannot be justified, except under extraordinary circumstances. The triangle represents the decreasing risk and the diminishing proportional benefit as risk is reduced.

The ALARP principle can be used to define two sets of risk tolerance criteria: a minimum requirement and a target value. Between the two sets of criteria, the range of risks is tolerable. The residual risk should fall either in the broadly acceptable region, or near the bottom of the tolerable region. This approach allows higher levels of safety to be provided where it is feasible. Risk tolerance criteria suggested by the UK HSE are shown in the figure at the two dividing lines between the three risk regions. The top line is known as the de manifestus risk level and the bottom line is known as the de minimis risk level.

The ALARP principle originated within a legal and regulatory framework. Increasingly, it is used by regulators and companies around the world as it provides a sensible basis for managing risks. The ALARP principle is now called So Far As Is Reasonably Practicable (SFAIRP) in the UK with some legal distinctions from ALARP [3]. 

References

1. Reducing Risks, Protecting People, HSE’s Decision-Making Process, HSE Books, 2001.

2. HSE Principles for Cost Benefit Analysis (CBA) in Support of ALARP Decisions, http://www.hse.gov.uk/risk/theory/alarpcba.htm.

3. Health and Safety at Work etc. Act 1974.

Further Reading

P. Baybutt, The ALARP Principle in Process Safety, Process Safety Progress, Volume 33, Issue 1, pages 36 – 40, March 2014.


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