Different methodologies are available for conducting the structured reviews known as process hazards analyses (PHAs) for new processes. PHAs are often conducted or moderated by specialists, with participation by the design team, representatives of the facility owner, and experienced process operators.
Each different PHA method is better-suited to a specific purpose and should be applied at different stages of the project development. The table below includes brief descriptions of some of the most widely used PHA methods in the chemical process industries (CPI).
When to use different methods
Different types of PHA studies have varying impact, depending on the design phase in which they are applied. For example, if a consequence analysis is not performed in a conceptual or pre-FEED (front-end engineering and design) phase, important plot-plan considerations can be missed, such as the need to own more land to avoid effects on public spaces; or the fact that the location might have a different elevation with respect to sea level than surrounding public places impacted by a flare plume.
Some other studies, like HAZOP, cannot be developed without a control philosophy or piping and instrumentation diagrams (P&IDs), and are performed at the end of the FEED stage or at the end of the detailed engineering phase (or for improved results, at the end of both) to define and validate the location of pressure safety valves (PSVs) as well as to validate other process controls and instrument safety requirements.
QRA or LOPA evaluations (or both) are undertaken after the HAZOP study to validate siting and define safety integrity levels (SIL), to finally meet the level required by the plant.
Editor’s note: The definitions in the table, and associated comments, were adapted from the following article: Giardinella, S., Baumeister, A. and Marchetti, M. Engineering for Plant Safety. Chem. Eng., August 2015, pp. 50–58. An additional reference is the following article: Wong, A., Guillard, P. and Hyatt, N. Getting the Most Out of HAZOP Analysis, Chem. Eng., August 1, 2004, pp. 55–58.