ALARP

One concept of risk tolerability requires that measures be taken to reduce the likelihood of hazards and to limit their consequences until further reduction of risks cannot be justified. Putting it another way, the risks to individuals and to society should be as low as reasonably practicable (ALARP). When this approach was first developed in the area of pollution control in the UK in the 1860s, process operators had to use the best practicable means (BPM) to eliminate or control pollution. This concept was later adopted by the European Union as the principle of BATNEEC, or best available techniques not entailing excessive cost.

The principle of ALARP is illustrated in Figure 11, which indicates two regions of unacceptable and acceptable risk separated by a region where the risk is acceptable only in exceptional circumstances. The terms used (1 in 1000, etc.) are explained later in the course.

Figure 11 The ALARP concept

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The ALARP concept as a scale from significant risk to negligible risk through four bands

Top band – Unacceptable region – risk cannot be justified except in extraordinary circumstances – 1 in 1000 per person per year (workers)

Middle two bands - ALARP or tolerability region (risk is undertaken only if a benefit is desired) – split into two sections:

• 1 in 10 000 per person per year (public) – Tolerable only if risk reduction is impracticable or if cost of risk reduction is grossly disproportionate to improvement gained
• Tolerable if cost of risk reduction would exceed improvement gained – 1 in 1 million per person per year

Bottom band – Broadly acceptable region (no need for detailed working to demonstrate ALARP) – necessary to maintain assurance that risk remains at this level – 1 in 10 million per person per year.

Figure 11 The ALARP concept

The core of ALARP is ‘reasonably practicable’; this involves weighing a risk against the trouble, time and money needed to control it. In some cases ‘good practice’ can be referred to, but in other situations deciding whether a risk is ALARP can be challenging, as it requires a degree of judgement as well as an economic evaluation.