The HAZOP (Hazard and Operability) method is a widely used technique for identifying the hazards on process facilities. Even those who are not familiar with the hazards analysis process will often have heard of the term HAZOP, even if they are not really sure what it means.
A HAZOP is organized by dividing the unit to be analyzed into nodes. A node represents a section of the process where a significant process change takes place. For example, a node might cover the transfer of material from one vessel to another through a pump. In this case the process change is the increase in pressure and flow that occurs across the node. Another node might include an overhead air-cooler on a distillation column. Here temperature and phase are the process variables that change.
Although the strength of the HAZOP method lies in its clear organization, it is important not to allow the analysis to become too rigid. If the team finds that it is talking about "Reverse Flow" even though the current guideword is "High Flow", the leader should probably let the discussion continue. If he or she were to postpone the discussion until the "right" guideword, the current thinking and creativity may be lost. On the other hand, the leader must also keep the discussion focused on the issue at hand, and should prevent too many digressions.
Steps in a HAZOP
- Select a node, define its purpose and determine the process safe limits.
- Select a process guideword.
- Identify the hazards and their causes using the deviation guidewords.
- Determine how the hazard is "announced", i.e., how the operator knows a safe limit has been exceeded.
- Estimate the consequences (safety, environmental, economic) of each identified hazard.
- Identify the safeguards.
- Estimate the frequency of occurrence of the hazard.
- Risk rank the hazard, with and without safeguards.
- Develop findings and potential recommendations.
- Move on to the next process guide word, or to the next node if the guideword discussion is complete.