The Three Regions
The tolerability triangle and the obligations attached to each band.
11 min
Risk decisions are usually framed with a triangle divided into three regions, narrow at the top where risk is highest.
| Region | Meaning | Obligation |
|---|---|---|
| Unacceptable | Risk cannot be justified except in extraordinary circumstances | The activity must not proceed in this form |
| Tolerable (the ALARP region) | Risk is accepted only if the benefit is wanted and risk is reduced as low as reasonably practicable | Demonstrate ALARP, review periodically |
| Broadly acceptable | Comparable with everyday background risk | Maintain existing controls; no further action normally required |
The asymmetry
The obligation to reduce risk strengthens as risk rises. Near the top of the triangle, very large sacrifices are expected for modest reductions; near the bottom, little more is required. This gradient is the whole content of the framework and it is why a single cost threshold cannot be applied across all risks.