ALARP "at a glance"

These pages set out the approach that Health and Safety Executive (HSE) inspectors use to evaluate risks. It is not something we would expect the average dutyholder to look at.

Our guidance on Managing risks and risk assessment at work will help businesses control risks and protect their workers.

We are publishing the pages in the interests of openness and because we know it is useful to some health and safety professionals and academics.

ALARP explained

This guide has been produced to explain the concept of "reasonably practicable" in a simple way for HSE staff and incorporates guidance currently held on HSE's website. It's aimed mainly at staff new to HSE and those new to decision making.


"ALARP" is short for "as low as reasonably practicable". "SFAIRP" is short for "so far as is reasonably practicable". The two terms mean essentially the same thing and at their core is the concept of "reasonably practicable"; this involves weighing a risk against the trouble, time and money needed to control it. Thus, ALARP describes the level to which we expect to see workplace risks controlled.

How we use ALARP

Using "reasonably practicable" allows us to set goals for duty-holders, rather than being prescriptive. This flexibility is a great advantage but it has its drawbacks, too. Deciding whether a risk is ALARP can be challenging because it requires duty-holders and us to exercise judgement. In the great majority of cases, we can decide by referring to existing 'good practice' that has been established by a process of discussion with stakeholders to achieve a consensus about what is ALARP. For high hazards, complex or novel situations, we build on good practice, using more formal decision making techniques, including cost-benefit analysis, to inform our judgement.

Why do I need to know about ALARP?

The concept of "reasonably practicable" lies at the heart of the British health and safety system. It is a key part of the general duties of the Health and Safety at Work etc. Act 1974 and many sets of health and safety regulations that we and Local Authorities enforce. HSC's policy is that any proposed regulatory action (Regulations, ACOPs, guidance, campaigns, etc.) should be based on what is reasonably practicable. In some cases, however, this may not be possible because the Regulations implement a European directive or other international measure that adopt a risk control standard different from "reasonably practicable" (ie different from what is ALARP).

Because ALARP is fundamental to the work of the whole organisation, it is important that everyone, whatever their role, knows about it. Here are some specific reasons for you to know about ALARP and its relationship with good practice, but this is not an exhaustive list.

  • Policy makers and those engaged in Programme delivery need to know about ALARP because when you make proposals for HSC/E action to control health or safety risks, you need to make sure that, as far as possible, those controls will reduce the risks to employees (or other people, as the case may be) ALARP.
  • Enforcers need to know about ALARP because you will have to decide whether duty-holders have reduced their risks ALARP and so have complied with the law.
  • Technical specialists in HSE need to know about ALARP because you advise colleagues in HSE about whether control measures reduce risks ALARP and you help identify standards of risk control that are ALARP.

What is meant by reasonably practicable?

You may come across it as SFAIRP ("so far as is reasonably practicable") or ALARP ("as low as reasonably practicable"). SFAIRP is the term most often used in the Health and Safety at Work etc Act and in Regulations. ALARP is the term used by risk specialists, and duty-holders are more likely to know it. We use ALARP in this guidance. In HSE's view, the two terms are interchangeable except if you are drafting formal legal documents when you must use the correct legal phrase.

The definition set out by the Court of Appeal (in its judgment in Edwards v. National Coal Board, [1949] 1 All ER 743) is:

"'Reasonably practicable' is a narrower term than 'physically possible' … a computation must be made by the owner in which the quantum of risk is placed on one scale and the sacrifice involved in the measures necessary for averting the risk (whether in money, time or trouble) is placed in the other, and that, if it be shown that there is a gross disproportion between them – the risk being insignificant in relation to the sacrifice – the defendants discharge the onus on them."

In essence, making sure a risk has been reduced ALARP is about weighing the risk against the sacrifice needed to further reduce it. The decision is weighted in favour of health and safety because the presumption is that the duty-holder should implement the risk reduction measure. To avoid having to make this sacrifice, the duty-holder must be able to show that it would be grossly disproportionate to the benefits of risk reduction that would be achieved. Thus, the process is not one of balancing the costs and benefits of measures but, rather, of adopting measures except where they are ruled out because they involve grossly disproportionate sacrifices. Extreme examples might be:

  • To spend £1m to prevent five staff suffering bruised knees is obviously grossly disproportionate; but
  • To spend £1m to prevent a major explosion capable of killing 150 people is obviously proportionate.

Of course, in reality many decisions about risk and the controls that achieve ALARP are not so obvious. Factors come into play such as ongoing costs set against remote chances of one-off events, or daily expense and supervision time required to ensure that, for example, employees wear ear defenders set against a chance of developing hearing loss at some time in the future. It requires judgment. There is no simple formula for computing what is ALARP.

It can get very complicated. More detailed ALARP suite of guidance and your Directorate/Divisional ALARP guidance (where available) explains how to deal with some of these complications.

Hazard or risk?

Definition of a hazard

A hazard is something (eg an object, a property of a substance, a phenomenon or an activity) that can cause adverse effects. For example:

  • Water on a staircase is a hazard, because you could slip on it, fall and hurt yourself.
  • Loud noise is a hazard because it can cause hearing loss.
  • Breathing in asbestos dust is a hazard because it can cause cancer.

Definition of a risk

A risk is the likelihood that a hazard will actually cause its adverse effects, together with a measure of the effect. It is a two-part concept and you have to have both parts to make sense of it. Likelihoods can be expressed as probabilities (eg "one in a thousand"), frequencies (eg "1000 cases per year") or in a qualitative way (eg "negligible", "significant", etc.). The effect can be described in many different ways. For example:

  • The annual risk of a worker in Great Britain experiencing a fatal accident [effect] at work [hazard] is less than one in 100,000 [likelihood];
  • About 1500 workers each year [likelihood] in Great Britain suffer a non-fatal major injury [effect] from contact with moving machinery [hazard]; or

The lifetime risk of an employee developing asthma [effect] from exposure to substance X [hazard] is significant [likelihood].

How to tell if a risk is ALARP

Using "reasonably practicable" allows us to set goals for duty-holders, rather than being prescriptive. This flexibility is a great advantage. It allows duty-holders to choose the method that is best for them and so it supports innovation, but it has its drawbacks, too. Deciding whether a risk is ALARP can be challenging because it requires duty-holders and us to exercise judgment.

Deciding by good practice

In most situations, deciding whether the risks are ALARP involves a comparison between the control measures a duty-holder has in place or is proposing and the measures we would normally expect to see in such circumstances ie relevant good practice. "Good practice" is defined in the general ALARP guidance as "those standards for controlling risk that HSE has judged and recognised as satisfying the law, when applied to a particular relevant case, in an appropriate manner." We decide by consensus what is good practice through a process of discussion with stakeholders, such as employers, trade associations, other Government departments, trade unions, health and safety professionals and suppliers.

Once what is good practice has been determined, much of the discussion with duty-holders about whether a risk is or will be ALARP is likely to be concerned with the relevance of the good practice, and how appropriately it has been (or will be) implemented.. Where there is relevant, recognised good practice, we expect duty-holders to follow it. If they want to do something different, they must be able to demonstrate to our satisfaction that the measures they propose to use are at least as effective in controlling the risk.

Deciding on 'first principles'

Where the situation is complex, it may be difficult to reach a decision on the basis of good practice alone. There may also be some cases (for example, a new technology) where there is no relevant good practice. In such cases, good practice should be followed as far as it can be, and then consideration given to whether there is any more that can be done to reduce the risk. If there is more, the presumption is that duty-holders will implement these further measures but this needs to be confirmed by going back to first principles to compare the risk with the sacrifice involved in further reducing it.

Often such "first principles" comparisons can be done qualitatively, ie by applying common sense and/or exercising professional judgment. or experience. For example if the costs are clearly very high and the reduction in risk is only marginal, then it is likely that the situation is already ALARP and further improvements are not required. In other circumstances the improvements may be relatively simple or cheap to implement and the risk reduction significant: here the existing situation is unlikely to be ALARP and the improvement is required. In many of these cases a decision can be reached without further analysis.

But there are some instances (often in high hazard industries or where there is a new technology with potentially serious consequences) where the situation is less clear-cut. In such cases, a more detailed comparison has to be undertaken. The trouble is that risk and sacrifice are not usually measured in the same units, so it's a bit like comparing apples and pears. In these instances, a more formal Cost Benefit Analysis (CBA) may provide additional insight to help come to a judgment.

In a CBA, we convert both risk and sacrifice to a common set of units – money – so that we can compare them. We represent:

  • Sacrifice as a cost; and
  • Risk , in so far as it is being reduced, as a benefit.

There's more detail (such as which costs to take into account and which risks to consider) in the 'CBA checklist' and Directorates' own guidance.

We then compare the sacrifice (cost) and the risk reduction (benefits). In a standard CBA, the usual rule applied is that the measure should be adopted only if benefits outweigh costs. However, in ALARP judgments, the rule is that the measure must be adopted unless the sacrifice is grossly disproportionate to the risk. So, the costs can outweigh benefits and the measure could still be reasonably practicable to introduce. How much costs can outweigh benefits before being judged grossly disproportionate depends on factors such as how big the risk is to begin with (the larger the risk, the greater can be the disproportion between the cost and risk).

This looks straightforward, but it is worth noting that there are many assumptions and uncertainties involved in CBA – further discussion can be found in 'HSE principles for Cost Benefit Analysis (CBA) in support of ALARP decisions' - and indeed in many aspects of risk analysis. In any case, the outcome of a CBA is only one of several considerations that go towards the judgment that a risk has been reduced ALARP. For example, in policy work and in those parts of operational work dealing with high hazards you may also need to consider how the public feel about the risk. There is more detail about taking account of such "societal concerns" in "Reducing Risks, Protecting People".

Some fallacies about ALARP

Some myths or fallacies about what ALARP means have grown up over the years. Here we explain what some of these myths are and, why they are wrong.

Fallacy 1 - Ensuring that risks are reduced ALARP means that we have to raise standards continually

It is part of HSC/E's philosophy that we seek continual improvements in health and safety standards. That philosophy is widely shared in HSE and because of it, Britain has one of the best records for occupational health and safety in the world. HSE is rightly respected for this. However, we need to make sure that we encourage improvements in a responsible way.

Deciding whether something is safe enough (ie the risk is reduced ALARP) is a separate exercise from seeking a continual improvement in standards. Of course, as technology develops, new and better methods of risk control become available. Duty-holders should review what is available from time to time and consider whether they need to implement new controls. But that doesn't mean that the best risk controls available are necessarily reasonably practicable. It is only if the cost of implementing these new methods of control is not grossly disproportionate to the reduction in risk they achieve that their implementation is reasonably practicable. For that reason, we accept that it may not be reasonably practicable to upgrade older plant and equipment to modern standards. However, there may still be other measures that are required to reduce the risk ALARP: for example, partial upgrades or alternative measures.

Our decision about what is ALARP will also be affected by changes in knowledge about the size or nature of the risk presented by a hazard. If there is sound evidence to show that a hazard presents significantly greater risks than previously thought, then of course we should press for stronger controls to tackle the new situation. However, if the evidence shows the hazard presents significantly lesser risks than previously thought, then we should accept a relaxation in control provided the new arrangements ensure the risks are ALARP.

Fallacy 2 - If a few employers have adopted a high standard of risk control, that standard is ALARP

Some organisations implement standards of risk control that are more stringent than good practice. They may do this for a number of reasons, such as meeting corporate social responsibility goals, or because they strive to be the best at all they do, or because they have reached an agreement with their staff to provide additional controls. It does not follow that these risk control standards are reasonably practicable, just because a few organisations have adopted them. Until such practices are evaluated and recognised by HSE as representing good practice, you should not seek to enforce them (whether at a policy level or an operational one). It is also acceptable for a duty holder to choose to relax from a self-imposed higher standard to one which is accepted as ALARP (eg just meeting the requirements of a relevant ACOP).

Fallacy 3 - Ensuring that risks are reduced ALARP means that we can insist on all possible risk controls

ALARP does not mean that every measure that could possibly be taken (however theoretical) to reduce risk must be taken. Sometimes, there is more than one way of controlling a risk. These controls can be thought of as barriers that prevent the risk being realised and there is a temptation to require more and more of these protective barriers, to reduce the risk as low as possible. (The so-called "belt and braces" approach.) You must remember that ALARP means that a barrier can be required only if its introduction does not involve grossly disproportionate cost.

Fallacy 4 - Ensuring that risks are reduced ALARP means that there will be no accidents or ill-health

ALARP does not represent zero risk. We have to expect the risk arising from a hazard to be realised sometimes, and so for harm to occur, even though the risk is ALARP. This is an uncomfortable thought for many people, but it is inescapable. Of course we should strive to make sure that duty-holders reduce and maintain the risks ALARP, and we should never be complacent but, nevertheless, we have to accept that risk from an activity can never be entirely eliminated unless the activity is stopped. This relates to the issue of the "tolerability" of a risk, which is covered in detail in Reducing Risks, Protecting People (88 pages). It also goes some way to explaining why risk assessments feed into contingency planning.

Useful links and divisional contacts

Directorate/Divisional ALARP guidance

Some parts of HSE have also produced supplementary ALARP guidance that put the issues in context for different sectors:

Useful documentation

HSE has also published a document that sets out how we use risk ideas to take decisions about heath and safety regulation. While not written as guidance, it summarises some of the important concepts relating to ALARP:

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Updated 2023-04-25