Hazard and operability study (HAZOP)
HAZOP is a structured collective process of detailing and identification of hazards and problems in system performance, completed by a group of experts. The HAZOP study is designed to identify potential deviations from the project objectives, assess their possible causes and assess their consequences. This article describes an approach to the use of risk factors for the study by HAZOP in the oil and gas industry for the presence of hazards associated with the integrity of pressurized equipment.
A qualitative approach is similar to quantitative analysis, except that a qualitative approach requires less detail and does not require significant time. Although the results of this method are not as accurate as the results of quantitative analysis, it provides a basis for determining priorities for a risk-based inspection program.
Fig. 1. HAZOP stages
- Definition (scope and objectives, composition of the expert group, responsibility)
The HAZOP procedure is carried out on the basis of analysis of the main technical documents, which include a description of the design process, General schemes of pipe and instrument systems (P & ID-Piping & Instrument Diagram), topological plans (drawings) of equipment units location on the site, description of the main operation processes, operating instructions, block diagrams of subsystems, requirements for engineering systems, specifications or passports for the main technological equipment, information on protection systems, start-up, shutdown, etc.
HAZOP analysis is the result of a structured, collaborative study in which each member has a role to play. The number of specialists should be minimal. Usually a group consists of seven or ten people.
Depending on the type and the task, the team should include specialists in various fields of technology. In addition to the safety and design engineer (HAZOP or FSA specialist), the process engineer, specialists of narrow profiles who understand the P&ID system and its elements should be invited.
Therefore, the HAZOP study should be supported by a team that (at a minimum) will consist of the following specialists:
- Chairman of HAZOP, which is approved by the Customer;
- HAZOP Secretary (Registrar);
- Specialist in HAZOP procedure;
- Security specialist;
- Environmental protection specialist;
- Operation and maintenance specialist;
- Design engineers;
- Technology engineers.
The working group may invite other experts to participate. For example, if the evaluation process includes the complex of rotating equipment, a mechanical engineer will be involved in group. The responsibilities of HAZOP group members are determined by the Project manager and agreed with the Chairman (Leader) of HAZOP before starting the work.
Chairman of HAZOP. This person is responsible for the entire hazard analysis process, including the planning and coordination of the HAZOP session. The Chairman should collect all necessary information that should be provided to the group members before the work starts. He is responsible for conducting HAZOP study, preparing a comprehensive report on the results and guiding the group in making decisions based on his own experience. However, the participation of Chairman does not release the members of the group from their responsibility for the safe design and operation of the facility. The Chairman can provide additional HAZOP training if necessary.
Security engineer. He is responsible for all administrative preparations for the HAZOP study, including but not limited to the following:
- development of a schedule of inspections;
- availability of all necessary documents;
- timely distribution of relevant documents among the members of group;
- coordinating the response to HAZOP;
- correction of the HAZOP report in order to conduct final review;
- registration of modifications to the main P&ID related to HAZOP.
Technologtext in boldy engineer. He is responsible for the following operations:
- participation in meetings of security checks;
- resolution of issues related to technology that require its direct participation.
HAZOP Secretary (Registrar). The group should include a Secretary (Registrar) who should have sufficient technical skills to understand the problem under analysis. This person is responsible for maintaining of protocol and related records. Usually this person is a member of the group, the most experienced in the application of the selected method. His responsibilities include the following:
- description of the approach to be used;
- conducting a meeting on the development of hazards using the method used;
- ensuring the participation of all persons present in the discussion;
- registering a discussion.
- Preparation. Creation of plan for HAZOP carrying out
While planning process of HAZOP schedule, an initial review of existing documents, drawings and diagrams of designed facility, a review of previous HAZOP reports, process descriptions, existing safety reports, etc. is required. The Chairman should agree on the methodology and scope of work for the HAZOP session and prepare a work plan, bring them to the team of specialists. Prior to the session, the units are prepared on the flow charts and agreed with specialists who will participate in HAZOP. Information to be contained in flow-charts prior to the HAZOP study:
- Item number
- System number
- Design solutions
- Drawings and diagrams
- Technical instructions
- Power supply system
- Control system
- Security systems, etc.
Fig. 2. Example of the selected technological scheme for the HAZOP study
According to IEC 61882: 2001, the Chairman must conduct the meeting in accordance with the research plan. HAZOP analysis should be consistent with the technological route or sequence determined by the topic from inputs to outputs. Now, there are two possible sequences of examination: “element first” and “guide word first”, as shown in Figures 3 and 4, respectively.
The sequence of “element first”:
- The Chairman chooses the part of project description that should be the starting point of study. Then explains the purpose of project. Parts, elements and any characteristics associated with these elements must be identified.
- The Chairman chooses one of the elements and agrees with the group whether the guide word should apply directly to the element or to the individual characteristic of that element, and which guide word should be applied first.
- The interpretation of the guide word is studied in relation to the investigated element or characteristic to identify the probable deviation. If a probable deviation is identified, possible causes and consequences are investigated. In some cases, the categories of variation by severity or relative risk based on the use of the risk matrix are indicated.
- The group performs identification of protection mechanisms, detection and indication of deviations, which can be included in the selected part or to attain the objectives of the project in other parts.
- The Chairman summarizes the results, which are then documented by the Registrar. In case of additional work specialist necessity, it is necessary to register him as responsible for this work.
- The process is repeated first for all other interpretations of these guide words, then for the other guide words, then for each characteristic of the element (if the characterization level analysis was consistent for that element), then for each element of the investigated part.
Alternative method (“guide word first”) is to apply the first guide word to each elements of part. After that, the results of study with following guide word are applied to all elements. The process is repeated until all control words are applied to all elements of the part (Figure 4).
The sequence and actions should be chosen by the Chairman and the whole HAZOP group. This choice affects the way of HAZOP examination. Other factors influencing the choice are the nature of methods used, the need for flexibility in examination and the qualifications of group members.
Fig. 3. Flow chart of the HAZOP examination procedure – “Element first” sequence
Fig. 4. Flow chart of the HAZOP examination procedure – “Guide word first” sequence
Examples of deviations and corresponding guide words are shown in Fig. 5.
Fig. 5. Examples of deviations and their associated guide words
Guide word in different systems can be interpreted differently at different stages of system life cycle and when applied to different project views. The interpretation of all control words must be defined and documented. If this combination has more than one plausible interpretation for the project, then all interpretations must be reviewed and documented.
At the beginning of each day of the HAZOP study, the lead engineer or chief technologist should briefly describe to working group process functions and indicate the nature of the hazards associated with the materials and processes. In this regard, at the beginning of each day, the appropriate specialist should describe the specific system under consideration.
The Chairman should conduct the audit by assigning for each system a special appropriate guide word.
When a potential hazard is detected, it must be ranked. Risk ranking plays an important role in the HAZOP process. It is used to provide consequences on issues taken up for discussion, i.e. assessment can be made on the impact on human health and safety, on the impact on production and on the cost of repairs and on the impact on the environment.
Risk assessment can be used to demonstrate whether risks are acceptable or not and to support decisions for creation of recommendations that reduce risks. Risk ranking also puts priority in the recommendations. If a potential hazard has been detected, it may require repair or rework depending on the degree of probability that the event will occur and its possible consequences. If an immediate solution exists and it is acceptable to the working group, this should be reflected in the HAZOP Report accordingly. If a decision cannot be made without a technical assessment, the Chair should refer the matter to a special assessment. Discussion of problems during the meeting should be kept to a minimum.
The main advantage of the HAZOP study is that it is a systematic, orderly and documented approach. All discussions during the HAZOP analysis should be recorded using appropriate software or tables.
The next step is to fill in the “Report of the HAZOP study results “. If the result of consideration of the system was not proposed for performance of any action, then this should be recorded. For each technology, auxiliary and other systems, a separate report must be prepared. It should contain the following information:
- details of the identified hazards and health issues, together with detailed condition data for their detection and / or mitigation;
- recommendations for further research on aspects of the project using different methods (if necessary);
- actions required to identify sources of uncertainty found in the study;
- recommendations to reduce the impact of identified problems based on the group’s knowledge of the system (research areas);
- notes that draw attention to specific maintenance and operation points;
- list of group members present at each meeting;
- list of all parts considered in the analysis, together with an explanation of when each was deleted.
As part of the HAZOP, the following actions should also be carried out:
- Monitoring of decision implementation. After HAZOP study, the Contractor shall prepare sheets for all of the measures proposed according to the results. The statement of activities provides ways to implement them after the release of the initial report on HAZOP. The contractor shall be responsible for the acceleration of action through the issue of statement and the inclusion of an agreed solution in the Report.
- Changes in design. Upon completion of HAZOP inspection, the Contractor shall prepare a list of all technical improvements. This list should indicate the reason for change, effect of change, and whether change would require additional official HAZOP verification.
- Final safety check. The HAZOP study report forms the basis for the final safety inspection. The column under “actions taken” in the HAZOP study Report should be completed during the final safety inspection, unless it has been completed previously. All measures should have a clear implementation process. Normally, it is not necessary to reconvene the working group to fill in the “actions taken”. However, if the need arises, the group should be reconvened. The contractor is responsible for the satisfactory implementation of the observations.
The working group should also be reconvened to consider the relevant sections of the P&ID, if they have been substantially improved after the initial HAZOP study. If there are doubts about the significance of the changes for a partial or completely new HAZOP study on the P&ID, then a decision must be made to conduct additional analysis of the HAZOP