Definition:
Tolerable Risk is a level of risk accepted in a specific context considering economic, social, legal and technical factors as “livable: – not ideal. It is defined by external standards, regulations, or societal expectations. It is a threshold.
Acceptable risk is sometimes used interchangeably with tolerable risk, but “tolerable risk” is the preferred term under IEC functional safety standards. Acceptable risk is used in UK space.
Also can be called: upper limit of risk, ALARP limit. regulatory risk limit
Key Points:
- IEC standards prefer the term Tolerable Risk.
- Tolerable risk can never be zero.
- This can often be a hard concept for people to swallow. In the occupational safety world, zero accidents is the goal. But in the process safety industry, risk has to be accepted.
- Different industries and jurisdictions may define different thresholds for what is considered tolerable based on risk appetite and regulations.
Example:
HSE UK or CCPS may state a fatality probability of 1E-4 is acceptable.
See also: Acceptable Risk, stated risk tolerance
Cited Source:
- IEC 61508-5:2010, Annex C.
- IEC 61511-2:2016, Annex F