parameters. Process deviations are determined by combining guide words with the
important process parameters. The established set of guide words is shown in Table 4.14.
Table 4.14 Guide Words for HAZOP Studies
Negation of Intention
No forward flow when there should be.
Sequential process step omitted.
More of any relevant physical parameter than
there should be, such as more flow (rate,
quantity), more pressure, higher temperature, or
Batch step allowed to proceed for too long.
Opposite of "MORE OF"
System composition different from what it
should be (in multi-component stream).
As well as
More things present than should be (extra
Transfer from more than one source or to more
than one destination.
Sequential process steps performed in reverse
What may happen other than normal continuous
operation (start-up, normal shutdown,
emergency shutdown, maintenance, testing,
Transfer from wrong source or to wrong
The process parameters and example deviations typically used in a HAZOP study are
shown in Table 4.15. Additional process parameters can be added if warranted. One
purpose of the guide words is to assure that all relevant deviations of process parameters
The following are examples of deviations created using guide words and process