HAZOP Guide words are one of the unique things about the Hazard and Operability technique. There are a set of commonly used words that can be used to generate multiple abnormal scenarios, which we call as "deviations" in the technique. Every such word coupled with a particular parameter, then represents a unique deviation. For example to study a deviation of a flow lesser than normal, we use the guideword less or lesser than, coupled with a parameter flow. These two combined give us the deviated scenario of less than normal flow.
This less than normal flow is then analyzed thoroghly by the HAZOP team members to brainstorm if it will lead to nay dangerous consequences. If such is indeed the case, then the team's scribe (also known as HAZOP Scribe) writes down this as a dangerous consequence in the worksheet. Generally if the plant's design is sufficiently robust, then such deviated conditions are taken care of by the basic process design such as for example, having a flow switch that trips the pumping if the flow is low (just an example). If not, then the team suggests this, which goes into the worksheet as a recommendation. There may be of course other ways in which these parameters can be recognized and safeguards built, to correct for the effects of such abnormal conditions happening.
But then we are deviating from the topic- we are here to learn about guide words, right? You may be wondering how can somebody think of all the guidewords that are needed? Well, you can simply write down all of them at the beginning itself, or enter them into your HAZOP Worksheet before you begin the study. If you are using a documenting HAZOP Software, then the guidewords are already in the database and will be used to generate the different scenario conditions.
What are some common examples of such guide words? Here is a snippet of such a list below:
LESS
MORE
OTHER THAN
REVERSE
NO
EARLY
LATE
Now if you couple them with a parameter such as FLOW, you get the deviations as below:
LESS FLOW
MORE FLOW
OTHER THAN FLOW (checks if the fluid has been substituted by another one)
REVERSE FLOW (direction of flow has changed)
NO FLOW (empty)
The below ones can be used for batch processes, where sequencing is of importance.
EARLY FLOW (fluid starts flowing earlier than what is designed)
LATE FLOW (starts flowing later than designed).
If you need a more comprehensive training in this technique, then simply go to the HAZOP training course here. You can get access to an excellent e-learning course and what's more, also earn a certificate and an electronic badge, if you pass the associated exam.
