Project-Level Inherent Safer
Design Review
Inherent Safer Design is the most economically effective risk-reduction strategy available — but only if it is applied before the design freezes. Once P&IDs are issued for construction, the cost of eliminating a hazard through Substitute or Minimise is 10–100× higher than at conceptual design. The CCPS Guidelines for Inherently Safer Chemical Processes (3rd Ed., 2009, updated CCPS alignment 2024) and the IChemE ISD Guide codify the SMMS hierarchy: Substitute (replace hazardous material or reaction), Minimise (reduce inventory to the minimum required), Moderate (use less hazardous conditions — lower temperature, pressure, or concentration), and Simplify (eliminate complexity and failure modes). ISD is also the only risk-reduction measure with no reliability requirement — a substituted chemical cannot fail to be safer. Modern ISD practice integrates quantitative Inherent Safety Index assessment (ISI / ISHI) to compare design alternatives, process intensification techniques (microreactors, flow chemistry, distributed production), and explicit LOPA integration to demonstrate SIL-target reduction where hazards have been eliminated at source.
