The HAZOP analysis technique uses a systematic process to (1) identify possible deviations from normal operations and (2) ensure that appropriate safeguards are in place to help prevent accidents. The HAZOP technique uses special adjectives (such as "more," "less," "no," etc.) combined with process conditions (such as speed, flow, pressure, etc.) to systematically consider all credible deviations from normal conditions. The adjectives, called guide words, are a unique feature of HAZOP analysis.
Most common uses
Requires a well-defined system or activity. The HAZOP process is a rigorous analysis tool that systematically analyzes each part of a system or activity. To apply the HAZOP guide words effectively and to address the potential accidents that can result from the guide word deviations, the analysis team must have access to detailed design and operational information. The process systematically identifies specific engineered safeguards (e.g., instrumentation, alarms, and interlocks) that are defined on detailed engineering drawings.
Time consuming. The HAZOP process systematically reviews credible deviations, identifies potential accidents that can result from the deviations, investigates engineering and administrative controls to protect against the deviations, and generates recommendations for system improvements. This detailed analysis process requires a substantial commitment of time from both the analysis facilitator and other subject matter experts, such as crew members, engineering personnel, equipment vendors, etc.
Focuses on one-event causes of deviations. The HAZOP process focuses on identifying single failures that can result in accidents of interest. If the objective of the analysis is to identify all combinations of events that can lead to accidents of interest, more detailed techniques should be used such as Fault Tree Analysis (FTA).
The procedure for performing a HAZOP analysis consists of the following five steps:
1. Define the system or activity
Intended functions. Because all HAZOP analyses are concerned with ways in which a system can deviate from normal operations, clearly defining the intended functions for a system or activity is an important first step. It is important to clearly document this step for the HAZOP analysis.
Boundaries. Few systems or marine activities operate in isolation. Most are connected to or interact with others. By clearly defining the boundaries of a system or activity, analysts can avoid (1) overlooking key elements at interfaces and (2) penalizing a system or activity by associating other equipment or operations with the subject of the study. This is especially true of boundaries with support systems, such as electric power and compressed air, or boundaries with other vessel activities, such as cargo loading and unloading. It is also important to clearly define the extent to which support systems will be analyzed.
The figures on the next two pages define the boundaries for a HAZOP analysis of fuel barge filling operations at small marine terminals. The procedure that follows describes the intended transfer operation.
2. Define the problems of interest for the analysis
Safety problems. The analysis team may be asked to look for ways in which improper performance of a marine activity or failures in a hardware system may result in personnel injury. These injuries may be caused by many mechanisms, including the following:
Environmental issues. The analysis team may be asked to look for ways in which the conduct of a particular marine activity or the failure of a system may adversely affect the environment. These environmental issues may be caused by many mechanisms, including the following:
Economic impacts. The analysis team may be asked to look for ways in which the improper conduct of a particular marine activity or the failure of a system may have adverse economic impacts. These economic risks may be categorized in many ways, including the following:
A particular analysis may focus only on events above a certain threshold of concern in one or more of these categories.
Example for the barge filling HAZOP
The project team defined the problems of interest for this analysis as:
For this brief demonstration workshop, the team chose not to address other possible consequences of interest, such as the following:
3. Subdivide the system or activity and develop deviations
Before the HAZOP team meets, the leader and scribe should conduct several activities to help make the team meeting time more efficient. These pre-meeting activities include the following:
3.1 Define sections. Sections are simply discrete parts of a process such as a section of piping a tank, etc. The leader and scribe must divide the system equipment into sections in order to properly apply the HAZOP technique. The leader must balance two competing factors: (1) the HAZOP team may overlook important deviations if the sections are too large and (2) the HAZOP team will waste time examining the same issues repeatedly if the sections are too small.
3.2 Develop credible deviations. Deviations are upset conditions compared to normal operations. The structured approach of the HAZOP analysis is accomplished by using special guide words. Deviations are derived in the following manner:
Guide Word + System Parameter = Deviation
The type of system section, such as piping or tank, will determine the applicable system parameters to be analyzed for that section. By combining guide words with the applicable process parameter, the leader develops a list of credible deviations to analyze during the study.
3.3 Develop HAZOP worksheets.The scribe is responsible for documenting a significant amount of information during the study. Preparing specialized worksheets before the meeting for each type of section and for the credible deviations will help the scribe more efficiently organize the HAZOP information collected during the meetings.
The following subsections describe these terms and steps in more detail.
Three general considerations should guide the leader when dividing a system into sections:
Define sections appropriate for the HAZOP objectives. A HAZOP analysis investigating the potential for reportable material releases into the waterway may require consideration of many more system sections than a HAZOP analysis investigating material releases large enough to create long-term chronic health risks.
Define sections small enough to include all important deviations. It is far better to discover that a section has deviations that are the same as another section than to miss an important deviation. Experienced leaders will quickly recognize the unnecessary section and move the team on. Inexperienced leaders will learn to recognize unnecessary sections, but by defining small sections, they will be less likely to miss an important deviation, while gaining experience as a leader.
Define sections at a consistent level of detail. The HAZOP leader should not define every sample connection and instrument line as sections for one part of a process, while defining a shoreside tank farm as a single section elsewhere in the process. If the HAZOP objectives require sectioning the unit to a certain level of detail, then that same level should be applied throughout the analysis.
Dividing a system or activity into sections and selecting appropriate deviations are interrelated activities. The suggested deviations for sections presume these guidelines for sectioning have been followed. Specific circumstances will dictate exceptions to these sectioning guidelines and to the guidelines for selecting deviations. In most situations, following these guidelines will produce process sections that can be thoroughly reviewed by the HAZOP team with a minimum risk of overlooking important deviations. The guidelines are as follows:
Beginning guidelines (for leaders with less experience)
Experienced leaders will recognize that the beginning guidelines often produce some "unnecessary" process sections. The following are supplemental guidelines that will help experienced leaders reduce duplication:
Example sections for the barge filling HAZOP
To facilitate the HAZOP analysis, the team divided the system into the following three distinct sections:
Develop credible deviations
Deviations are developed in the HAZOP technique by applying guide words to system conditions.
Example sections for the barge filling HAZOP
For each section, the team developed a list of possible deviations (off-normal conditions) that could develop and cause consequences of interest. Consistent with the HAZOP analysis approach, the team developed this list of deviations by combining "guide words" (essentially a standard list of adjectives) with normal process parameters for sections of the system. The following table lists the deviations that the team considered for each section and illustrates how the team developed the list.
Develop HAZOP worksheets
During the meeting, the scribe will document the HAZOP information on worksheets. The following information will be documented for the HAZOP:
Section. Name of the section. This is usually documented by the leader and scribe before the meeting.
Intent. The team will describe the design intent for the particular HAZOP section being analyzed. Declaring this intent is important, because the remainder of the discussion will focus on ways that the process can deviate from this intent. An example of a design intent for a vessel unloading line may be: "Transfers crude oil from vessel cargo tanks to the shoreside storage tank using flow control."
Deviation. Specific deviation that will be analyzed by the team
Causes. Credible causes for the deviation as postulated by the HAZOP team
Accidents. Ultimate accidents of the deviation as postulated by the HAZOP team. These should correspond to the problems of interest that were defined as an objective for the study.
Safeguards. Engineering and administrative controls that protect against the deviations. These safeguards can either help prevent the cause from occurring or help mitigate the severity of the accidents should the cause occur.
Recommendations. Suggestions made by the team to help reduce the risk associated with specific issues if the team is not comfortable with the level of safeguards that currently exist
The table on the following page includes an example HAZOP worksheet. Completed HAZOP worksheets are presented later in this section.
The systematic analysis process of the HAZOP technique is conducted in the following manner:
Step 1. Introduce the team members.
Step 2. Describe the HAZOP approach.
Step 3. Identify Section 1.
Step 4. Ask the team to define the design intent of Section 1.
Step 5. Apply the first deviation to Section 1, and ask the team "What are the consequences of this deviation?"
Allow time for the team to consider the system upset. Some prompting may be necessary to get the discussion going.
If no accidents of interest are identified, go back to the beginning of Step 5 and apply the next deviation. If there are no credible accidents, there is no need for the team to investigate causes or safeguards.
Step 6. After the team has exhausted its analysis of accidents, prompt the team to identify all of the causes of the deviation.
Step 7. Identify the engineering and administrative controls that protect against the system upset. Remember, these controls can be either preventive (i.e., they help prevent the upset from occurring) or mitigative (i.e., they help reduce the severity of the accidents associated with the upset if it occurs).
Step 8. If the team is concerned that the level of protection is not adequate for the particular system upset, then the team should develop recommendations to investigate alternatives. Level of protection includes the number, type, and pedigree of the safeguards.
Step 9. Summarize the information collected for this deviation.
Step 10. Repeat Steps 5 through 9 for the remaining deviations associated with this section.
Step 11. Repeat Steps 3 through 10 for the remaining sections.
Source: USCG Risk-based Decision-making (RBDM) Guidelines.
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