ALARP ("as low as reasonably practicable"), or ALARA ("as low as reasonably achievable"), is a principle in the regulation and management of safety-critical and safety-involved systems. The principle is that the residual risk shall be reduced as far as reasonably practicable. In UK and NZ Health and Safety law, it is equivalent to SFAIRP ("so far as is reasonably practicable"). In the US, ALARA is used in the regulation of radiation risks.
For a risk to be ALARP, it must be possible to demonstrate that the cost involved in reducing the risk further would be grossly disproportionate to the benefit gained. Not to be confused with the ALARP program offered in many high schools, the ALARP principle arises from the fact that infinite time, effort and money could be spent in the attempt of reducing a risk to zero; not the fact that reducing the risk in half would require a finite time, effort and money. It should not be understood as simply a quantitative measure of benefit against detriment. It is more a best common practice of judgement of the balance of risk and societal benefit.
Factors
In this context, risk is the combination of the frequency (likelihood) and the consequence of a specified hazardous event.
Several factors are likely to be considered when deciding whether or not a risk has been reduced as far as reasonably practicable: Health and safety guidelines and codes of practice Manufacturer's specifications and recommendations Industry practice International standards and laws Suggestions from advisory bodies Comparison with similar hazardous events in other industries Cost of further measures would be disproportionate to the risk reduction they would achieve
Another factor is often the cost of assessing the improvement gained in an attempted risk reduction. In extremely complex systems, this can be very high, and could be the limiting factor in practicability of risk reduction, although according to UK HSE guidance, cost alone should never be a justification for taking extra safety risks.
Determining that a risk has been reduced to ALARP involves an assessment of the risk to be avoided, of the sacrifice (in money, time and trouble) involved in taking measures to avoid that risk, and a comparison of the two. This is a cost–benefit analysis (CBA). A difficulty arising in CBAs is assigning a meaningful and agreed financial value to human life. A CBA exercise, in the context of ALARP, must have a means of assigning financial values to impacts to the environment, physical assets, production stoppage, company reputation, etc., which also presents significant challenges to the analyst.
Origin in UK law
The term ALARP arises from UK legislation, particularly the Health and Safety at Work etc. Act 1974, which requires "Provision and maintenance of plant and systems of work that are, so far as is reasonably practicable, safe and without risks to health". The phrase So Far As is Reasonably Practicable (SFARP) in this and similar clauses is interpreted as leading to a requirement that risks must be reduced to a level that is As Low As is Reasonably Practicable (ALARP).
The key question in determining whether a risk is ALARP is the definition of reasonably practicable. This term has been enshrined in the UK case law since the case of Edwards v. National Coal Board in 1949. The ruling was that the risk must be significant in relation to the sacrifice (in terms of money, time or trouble) required to avert it: risks must be averted unless there is a gross disproportion between the costs and benefits of doing so.
Including gross disproportion means that an ALARP judgement in the UK is not a simple cost benefit analysis, but is weighted to favour carrying out the safety improvement. However, there is no broad consensus on the precise factor that would be appropriate: the HSE recommends that the bias towards safety "has to be argued in the light of all the circumstances applying to the case and the precautionary approach that these circumstances warrant".
Use outside the UK
The ALARP or ALARA principle is mandated by particular legislation in some countries outside the UK, including Australia, the Netherlands and Norway. Where the ALARP principle is used, it may not have the same implications as in the UK, as "reasonably practicable" may be interpreted according to the local culture, without introducing the concept of gross disproportionality.
The term ALARA, or "as low as reasonably achievable" is used interchangeably in the United States of America. It is used in the field of radiation protection. Its application in the regulation of radiation risk in some areas has been challenged.