Where HAZOP Sits Among Hazard Studies

A hazard and operability study (HAZOP) is one of several structured methods for finding what can go wrong in a process. A senior engineer must be able to say why HAZOP is the right method for a given design, and also when it is not. Choosing the wrong method wastes weeks of expert time or, worse, leaves real hazards unexamined.

Each method has a different "engine" that generates questions. In HAZOP, the engine is the combination of a parameter and a guideword applied to a defined section of the design. This makes HAZOP very thorough for fluid systems with a clear design intent. It also makes it slow and expensive, and it depends on detailed drawings being available.

The other methods trade depth for speed, or look at a different kind of system. A good study plan for a project usually uses more than one of them, each at the stage where it gives the most value.

Worked example: a gas compression project

A project adds a new gas compressor to an existing plant. At concept stage, the team runs a HAZID on the layout. It finds that the proposed position is close to the control room and under a crane lifting path. The layout is changed before any detailed design is done. At detailed design, a full HAZOP is run on the compressor suction, discharge, recycle and seal gas systems. The compressor vendor also supplies an FMEA of the machine's own lubrication and seal systems, which the HAZOP team reviews rather than repeats.

Worked example: a small change

Six years later, operations want to add a sample point on the discharge line. The change is one valve, one sample cooler and one connection. A full HAZOP would need the whole team for a day. The site instead uses a What-If review with a process engineer, an operator and an instrument technician, supported by the existing HAZOP worksheet for that node. The choice is recorded, with the reason, in the change record.