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.