Guide words can be used to identify how activities can fail in a systematic way. Although the methodology (HAZOP) was originally designed for industrial processes, it can also be used to identify possible failure modes of other types of activity.
|NO OR NOT||Complete negation of the design intent|
|AS WELL AS||Qualitative modification/increase|
|PART OF||Qualitative modification/decrease|
|REVERSE||Logical opposite of the design intent|
|OTHER THAN||Complete substitution|
|EARLY||Relative to the clock time|
|LATE||Relative to the clock time|
|BEFORE||Relating to order or sequence|
|AFTER||Relating to order or sequence|
As an example, let's consider how a building's Heating, Ventilation and Air Conditioning (HVAC) system might fail:
Parameters (for this example): air temperature, power supply voltage.
Using this method of combining guide words with parameters / attributes forces us to consider the many ways any process or activity can fail.
More information on the HAZOP methodology and the use of guide words can be found on Wikipedia.