ALARP Demonstration
Studies
ALARP — derived from UK Edwards v National Coal Board (1949) and codified in HSE's R2P2 (Reducing Risks, Protecting People) — is the dominant Western risk-acceptance test. The principle is asymmetric: as risk approaches the intolerable region (typically 10⁻³ worker / 10⁻⁴ public per year), the disproportion factor required to reject further mitigation increases sharply (HSE's gross-disproportion factor of 3–10 for high-hazard cases). ALARP is not a single calculation but a documented argument that combines codes-and-standards adherence, good practice benchmarking, cost-benefit analysis (CBA) for genuinely novel decisions, and ALARP-by-design at FEED. The post-Buncefield, post-Macondo, and post-Texas-City regulatory environment has tightened scrutiny: ALARP arguments must now defensibly address Bow-Tie barrier escalation, low-frequency / high-consequence cases, and the so-called 'cliff edge' where modest investment crosses from intolerable to tolerable. ALARP also increasingly applies in Indian PSM contexts (PESO Schedule 7, MoEFCC EIA) and across Australian / Canadian / Brazilian safety case regimes.
