Independent ISD PHA. This type of a review — also a team activity — focuses on specific hazards associated with the process and applies ISD strategies (substitute, minimize, moderate, simplify) to identify ways of eliminating or minimizing them. It uses one of the standard PHA tools (e.g., What If, Hazop) to pinpoint hazards but team discussion centers on ISD considerations. If, for example, the team finds a runaway exothermic reaction caused by water contamination in a batch reactor to be a hazard, it would look for opportunities to eliminate or reduce this risk. Some considerations might include:
• Substitute — using a non-reactive coolant in reactor coils instead of water;
• Minimize — removing all direct water connections to the inside of the reactor (for example, those to add water for reactor cleaning during shutdowns);
• Moderate — evaluating chemistry or solvent alternatives that might reduce sensitivity of the reaction mixture to water contamination; and
• Simplify — eliminating complex piping in the raw-material supply headers that increases potential for accidentally connecting water to the reactor.
CCPS has published another useful tool for consideration of ISD . This book provides a series of tables of potential failure mechanisms for a wide range of process equipment and identifies potential design solutions, including inherent, passive, active and procedural approaches to managing risk.