An important element of any system for the prevention of major accidents is conducting a hazard and operability study (HAZOP) at the detail design stage, of the plant in general and the operating and safety control system in particular. HAZOPs seek to minimise the effect of a typical situation in the operation / process by ensuring that control and other safety systems such as functional safety (e.g. emergency safe shutdown) are in place and work with a high level of reliability to achieve a safe outcome from a situation that could have resulted in a major accident. The HAZOP process is used to identify potential hazards and operational problems in terms of plant design and human error. The technique is applied during final design of the process and plant items before commencement of construction.