deviations. These guide words are applied at specific points or sections in a process and are
combined with specific process parameters to identify potential deviations from intended
4.4.1 Description of the Method
A HAZOP study requires considerable knowledge of the process, its instrumentation, and its
operation. This information is usually provided by expert team members. The team should
include individuals with a variety of experience, including design, engineering, operations, and
The primary advantages of a HAZOP study are creativity and new ideas. Creativity is the result of
interactions among team members with diverse backgrounds. Such interactions often generate
new ideas. The success of a HAZOP study depends on the freedom of members to freely express
their views. Combining this approach with a systematic protocol for examining hazards promotes
thoroughness and accuracy.
4.4.2 Analysis Procedure
A HAZOP study has three steps: (1) defining the process, (2) performing the study, and
(3) documenting the results. Defining the process and documenting the results can be performed
by a single person. The study itself must be performed by a team.
DEFINING THE PROCESS TO BE STUDIED.
This step identifies the specific vessels, equipment, and
instrumentation to be included in the HAZOP study and the conditions under which they are
analyzed. Defining the problem involves defining the boundaries of the analysis and establishing
an appropriate level of resolution for the study. For most HAZOP studies, the causes of deviations
are identified at the component level (i.e., control valve CV101 fails open).
PERFORMING THE STUDY.
A HAZOP study focuses on specific points of a process called "study
nodes," process sections, or operating steps. Depending on the experience of the study leader, the
portion of a process included in a single study node can vary. In the most conservative studies,
every line and vessel are considered separately. If the HAZOP study leader is experienced, he or
she may elect to combine two or more lines into a single study node. For example, the cooling
water chlorination system (Example Process 2) could be separated into three study nodes (chlorine
supply to venturi, recirculation loop, and tower water basin), two study nodes (recirculation loop
and tower water basin combined as a single study node), or one study node (the entire process).
If too much of a process is included in a single study node, deviations may be missed. If too little of
a process is included, the study can become tedious. In addition, root causes of deviations and their
potential consequences can become separated. Too many study nodes is common for novice HAZOP
study leaders. On the positive side, a study with too many nodes is less likely to miss scenarios than
one with too few nodes.
The HAZOP team examines each study node for potentially hazardous process deviations.
First, the design intent is defined to delineate the purpose of the equipment and the process
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