Risk must be reduced as low as reasonably practicable, weighing residual risk against the cost of further reduction.
The gross-disproportion test comes from the reasonably practicable doctrine set out in Edwards v National Coal Board in 1949; the duties were codified in the Health and Safety at Work Act 1974, and the HSE uses the ALARP and SFAIRP terminology. In practice a duty-holder must show the cost of further risk reduction is grossly disproportionate to the benefit, not merely inconvenient.
In practice
- A rail operator installs platform-edge doors at £40m because the residual risk is real; it declines a £900m tunnel rebuild that would remove a risk one-tenth the size.
- A hospital adds a second check on high-risk drugs and declines a third, because the third would delay treatment more than it prevents error.
- Possible explanations
- The explanation is diminishing returns: each further reduction in risk costs more than the last, so a rule that demanded zero risk would stop the activity altogether. The gross-disproportion test puts the burden on the duty-holder to show where that point lies.
- In its favour
- It is workable law, tested repeatedly in British courts, and it forces a duty-holder to justify stopping rather than to justify acting.
- Against it
- What counts as grossly disproportionate is decided case by case and usually after an accident, so duty-holders cannot know in advance whether their judgement will stand, and the test puts a monetary value on harm that many object to in principle.
- Standing
- Often misattributed to the Haldane principle.
- Subject
- Risk & Reliability
- Essay
- How much caution, and the jokes about its limits