SMMS Workshop (Targeted
Strategy Application)
Trevor Kletz's four ISD strategies — Substitute (replace the hazardous material), Minimise (reduce inventory), Moderate (operate at less severe conditions), Simplify (eliminate complexity) — originated at ICI in the 1970s following the Flixborough disaster (1974, 28 fatalities) and were codified into CCPS Inherently Safer Chemical Processes (1996, 2nd Ed. 2009) and the EPSC ISD Guidance. The discipline remains the most cost-effective hazard-reduction approach in chemical industry: a hazard eliminated at concept or FEED stage costs typically 1–10% of the equivalent control-layer retrofit, and avoids the cumulative reliability burden of safeguards. SMMS workshops are most consequential at three points: conceptual design (substitute / process route selection), FEED stage (minimise / moderate / simplify), and post-incident redesign (where the most aggressive ISD options surface). Modern practice also integrates the Heikkilä Inherent Safety Index (ISI) for quantitative scoring and uses ISD-by-design to reduce subsequent SIL allocation burden — a SIL-2 SIF on a hazard with 100 kg inventory becomes a SIL-1 (or eliminated) requirement when inventory drops to 10 kg, which is often achievable through continuous-flow conversion or feedstock substitution.
