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In the first example, the guide word "No" combined with the process parameter "Flow" results
in the deviation "No flow." Considering this deviation, the study team agrees on its possible
causes (e.g., operator error causes block in pump), the consequences of the deviation (e.g., line
rupture due to high pressure), and the safety levels which prevent the cause from leading to the
consequence (e.g., pressure relief valve on pump discharge line). The consequence specified
presupposes the failure of active protection systems (e.g., relief valves, process trip signals). If
the causes and consequences are significant, and the safety levels are inadequate, the team may
recommend a follow-up action. In some cases, the team may identify a deviation with a realistic
cause but unknown consequences (e.g., an unknown reaction product) and recommend follow-
up studies to determine the potential consequences.
The HAZOP study should be performed in a deliberate, systematic manner to reduce the
possibility of omissions. Within a study node, all deviations associated with a given process
parameter should be analyzed before the next process parameter is considered. All of the
deviations for a given study node should be analyzed before the team proceeds to the next node.
The documentation of a HAZOP study is a systematic and
consistent tabulation of the effects of process deviations. The study generates narratives about
the normal operating conditions and analysis boundary conditions for each equipment item. In
addition, it provides a list of potential actions that should be evaluated. Table 4.16 is an
example of a HAZOP study worksheet. A typical HAZOP study report should include a brief
system description, a list of drawings or equipment analyzed, the design intents, the HAZOP
study tables, and a list of actions items.
4.4.3 Staffing Needs and Time
Staff requirements for HAZOP studies vary with the size and complexity of the process. Time
and cost are proportional to the size of the process being analyzed and the experience of the
study leader and team members. Table 4.17 presents estimates of the time needed to perform a
PrHA using the HAZOP study method (CCPS, 1992). Study sessions should be limited to 3
consecutive days.
4.4.4 Limitations of the Hazard and Operability Study
The primary limitation of a HAZOP study is the length of time required to perform it. Because
the study is designed to provide a complete analysis, study sessions can be intensive and tiring.
HAZOP studies typically do not look at occupational hazards (e.g., electrical equipment,
rotating equipment, hot surfaces) or chronic hazards (e.g., chronic chemical exposure, noise,
heat stress).

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