What is the difference between a LOPA and a HAZOP, and how do I know which one I need for my facility?

A HAZOP is a qualitative method of defining what hazards are present in a process, the causes, how likely they are to occur, and how severe they could be (i.e. the overall risk). Protections against these scenarios are usually identified. LOPA is a semi-quantitative, closer look at those protections which will reveal shortcomings (see the section on “What is LOPA, and how does it relate to SIL?”). Normally both should be used for a complete evaluation of the process.