Introduction to HAZOP Study Dr. AA Process Control and Safety Group
A scenario You and your family are on a road trip by using a car in the middle of the night. You were replying a text message while driving at 100 km/h and it was raining heavily. The car hits a deep hole and one of your tire blows. You hit the brake, but due to slippery road and your car tire thread was thin, the car skidded and was thrown off the road. 2
Points to ponder What is the cause of the accident? What is the consequence of the event? What can we do to prevent all those things to happen? What other possible accidents might happen on the road trip? Can we be prepared before the accident occurs? 3
Can we make it more systematic? Parameter Guideword Possible Causes Consequences Action Safeguard Car speed Too fast Too slow Rushing Skidded when emergency brake - Slow down - Speed up -ABS brake system -Safety belt - Air bag Tire No thread Less thread Tire too old, often speeding and emergency break Car skidded - Check frequently - Have spare tire Window visibility Low Very low Rain Cannot see the road Car light Dim No light -Stop car -Go to nearest garage -Use emergency signal Road With holes Rocky Breaks the car tire - Put a signboard -Street lights Travel time Night Foggy No street light -Travel during daylight 4
Flash Drum Example Consider the following Flash drum system. The purpose is to separate multiple mixture of mostly A and B plus some other heavy components to produce main product leaving the top at 0 mol % of A. Steam at 5 bar is used to bring the temperature at the desired saturation temperature of 130 o C. Nominal operating conditions are as follows: T 1 = 70 o C T 2 = 120 o C T 3 = 100 o C T 4 = 110 o C P = 3 bar
Flash Drum Example 1 Process Fluid 2 2 2 3 6 E-30 Steam 7 V-40 X AD = 0 mol % X AF = 50 mol % 1 E-20 4 5 6
Problem 1 Safety through automation Consider the Flash Drum Plant. Propose the required component of safety through automation to provide safety and operability.
Flash Drum Example PIC 1 Process Fluid 2 2 2 3 6 E-30 Steam 5 V-40 X AD = 0 mol % X AF = 50 mol % E-20 C 1 3 7 4 7 LIC Is this good enough?
Problem 2 - HAZOP PIC 1 Process Fluid 2 2 2 3 6 E-30 Steam 5 V-40 X AD = 0 mol % X AF = 50 mol % E-20 C 1 3 7 4 7 LIC Study node Consider the Flash Drum as the HAZOP Study Node, conduct HAZOP
HAZOP Terminology 1 Node A node is the specific location in the process in which (the deviations of) the process intention are evaluated. Examples might be: separators, heat exchangers, scrubbers, pumps, compressors, and interconnecting pipes with equipment Flash Drum Example Separator as a node Other nodes: process to process heat exchanger, utility heat exchanger Alternatively, each process line can be taken as a node. 10
Terminology 2 Design Intent Description of how the process is expected to behave at the Study Node. This is qualitatively described as an activity (e.g., feed, reaction, sedimentation) and/or quantitatively in the process parameters, like temperature, flow rate, pressure, composition, etc. Flash Drum Example: To separate light components from the heavies (or to collect light component at the top product stream) 11
Terminology 3 - HAZOP Log Sheet Based on the selected NODE and the design intent of the node, HAZOP study is conducted. The output is summarised in HAZOP Log Sheet Example: Simplified HAZOP Log Sheet Deviation Causes Consequences Protection Action Guideword + Parameter Guideword: No, Less, More, reverse etc Parameter: Flow, temperature, level etc Possible causes of the deviation Effect of deviation of plant safety and operability Safety provision already considered. - Prevent causes - prevent/ reduce consequence - monitor/ detect Is the protection sufficient? If not, propose suitable action or recommendation 12
Terminology 4 Deviation Deviation is a way in which the process conditions may depart from their INTENON / DESIGN INTENT Expressed by combining parameters such as FLOW with Guideword such as MORE to indicate MORE FLOW meaning the flow is more than the design intent. Expresses as other unwanted condition such as Contamination or corrosion. Parameters: any process parameters such as Flow, temperature, pressure, ph etc Guideword: NO, MORE, LESS, AS WELL AS, PART OF, OTHER THAN, REVERSE, etc. 13
The suggested guide words No: negation of design intention; no part of design intention is achieved but nothing else happens More: Quantitative increase Less: Quantitative decrease As well as: Qualitative increase where all design intention is achieved plus additional activity Part of: Qualitative decrease where only part of the design intention is achieved Reverse: logical opposite of the intention Other than: complete substitution, where no part of the original intention is achieved but something quite different happens
When timing matters Add the following guide words: Early: something happens earlier in time than intended Late: something happens later in time than intended Before: something happens earlier in a sequence than intended After: something happens later in a sequence than intended
Terminology 5 Causes The reason(s) why the DEVIAON could occur More CAUSES can be identified for one DEVIAON. PIC Flash Drum Example Steam Causes for LESS LEVEL in V-40 stuck open E-30 V-40 LESS inlet Flow MORE Flow in line etc 7 C 7 LIC P 16
Terminology 6 Consequences The results of the DEVIAON, in case it occurs. CONSEQUENCES may both comprise process hazards and operability problems, like plant shutdown. More CONSEQUENCES can follow from one cause and, in turn, one CONSEQUENCE can have several CAUSES Consequence for LESS LEVEL in V40 V-40 empty, leading to pump P running dry Steam PIC No separation E-30 V-40 7 C 7 LIC P 17
Terminology 7 Protection Sometimes termed as Safeguard, or Existing Provision These are facilities that help to reduce the occurrence frequency of the DEVIAON or to mitigate its CONSEQUENCES. There are, in principle, five types of SAFEGUARDS: Facilities that identify the DEVIAON. eg. alarm instrumentation and human operator detection. Facilities that compensate the DEVIAON, e.g., an automatic control system Facilities that prevent the DEVIAON to occur. e.g. an inert blanket gas in storages of flammable substances. Facilities that prevent a further escalation of the DEVIAON, e.g., by (total) trip of the activity (SIS facility) Facilities that relieve the process from the hazardous DEVIAON. These comprise for instance: pressure safety valves (PSV) and vent systems. 1
Terminology 7- Protection Flash Drum Example Protection against LESS LEVEL in V40 LIC controlling the liquid level Steam PIC Is it enough??? E-30 V-40 C 7 LIC 7 P 1
Terminology Action/Recommendation Where a credible cause results in a negative consequence, it must be decided whether some action should be taken. It is at this stage that consequences and associated safeguards are considered. If it is deemed that the protective measures are adequate, then no action need be taken, and words to that effect are recorded in the Action column. Actions fall into two groups: Actions that remove the cause. Actions that mitigate or eliminate the consequences. 20
Terminology Action Existing Protection for LESS LEVEL is considered not adequate. Actions Proposed Add Low level Alarm (LAL and LALL) Steam PIC Add SIS to stop pump P when LALL triggered. E-30 V-40 C 7 LIC 7 P 21
Terminology Comments Various additional columns can be added to the HAZOP Log Sheet. Comments Any remarks to be given to the ACONS/RECOMMENDAONS or which, in another way, showed up during the HAZOP sessions. Action Party is also typically identified and noted in the HAZOP Sheet. 22
Flash Drum: Less Level Deviation Causes Consequences Protection Action Less Level (Low Level) Valve stuck open Less feed LIC malfunction Level drop leading to dry separator, hence no separation Risk of pump running dry (damage) LIC Install LAL Install LALL with SIS to stop pump P Note: Sometimes, more than one consequences may arise and for each consequence, different actions are required Sometimes different causes require different actions 23
Flash Drum Example PIC 1 Process Fluid 2 2 2 3 6 E-30 Steam 7 V-40 X AD = 0 mol % X AF = 50 mol % E-20 C 1 3 7 4 5 LIC Now, consider MORE PRESSURE as deviation 24
Flash Drum: MORE PRESSURE Deviation Causes Consequences Protection Action More Pressure (High Pressure) Valve stuck Close PIC Malfunction More temperature in Feed increase in pressure leading to risk of explosion PIC C7 Install PAH Install Pressure relieve valve 25
HAZOP STUDY TEAM
HAZOP Team HAZOP Leader CORE Team Project Process Engineer Independent Process Engineer Project Instrument Engineer Operation Representative (covering maintenance) HAZOP Secretary Specialists (as required) Maintenance Engineer Corrosion Engineer Pipeline Engineer Others 27
Responsibility of HAZOP Team Members HAZOP leader - The leader should be independent (i.e. has no responsibility for the process and/or the performance of operations) Plan sessions and timetable Agree on the nodes, study approach etc Be thorough Manage the HAZOP Team Control and limit discussion when necessary Encourage team to actively participate, be creative, draw conclusion Keep team in focus. If conflict arises, handle with care. Do not let anybody (including the leader himself to dominate). Judge importance issues Stop the team trying to redesign the process. Leader must be strong, yet diplomatic. 2
Responsibility of Team Members HAZOP Secretary Take adequate notes and record documentations Inform leader if more time required in taking notes Produce draft report of study Team Members Provide inputs based on the discipline that they represent e.g., instrumentation, process, operation etc. 2
Open questions Questioning Techniques Help person being asked to think use words how, what and why. Closed questions To focus on an issue or problem. Start with words who, when, where. Required answer yes or no only. Question mix Mix between open and closed questions. 30
Questioning Techniques Things to avoid Ambiguous or vague questions. Double barelled/multiple questions. Long complicated questions. Interrogation type of questions. A loaded questions implied judgement. 31
Required information P & IDs Process flow diagrams Heat and Material Balances Layouts Logic Diagrams Equipment Data Sheets Material Hazard Data Sheets Hazardous area Layouts 32
Modes of operation to consider The following modes of plant operation should be considered for each node: Normal operation Reduced throughput operation Routine start-up Routine shut-down Emergency shutdown Commissioning Special operating modes 33
Proposed agenda: HAZOP meeting Introduction & presentation of participation Overall presentation of the system/operation to be analyzed Description of the HAZOP approach Presentation of the first node or logical part of the operation Analyze the first node/ part using the guide-words and parameters Continue presentation and analysis (steps 4 & 5) Coarse summary of findings Focus should be on potential hazards as well as potential operational problems. 34
Sequence for conducting a HAZOP Study Flow diagram for the HAZOP analysis The parameter-first approach PHASE 1: DIVIDE SECON Divide section into Study node PHASE 2: SELECT A LINE PHASE 3: ANALYSIS Specify the section or stage to be examined Describe & discuss the step/ operation; determine the design envelope. Develop & record the design intention From the description and the design intention select a parameter Combine this parameter with a guideword to develop a meaningful deviation Seek a possible cause of the deviation and identify the consequences Evaluate the safeguards and decide if they are adequate of if a change or further study is needed. PHASE 4: RECORDING PHASE 5: REEVALUATE Record Have all causes of this deviation been considered? YES NO Does any other guideword combine with this parameter to give a meaningful deviation? YES NO Are there further parameters to consider? YES NO Examination of the steps/ stage is complete 35
How to be a good HAZOP participant Be active! Everyone contribution is important Be to the point. Avoid endless discussion of details Be critical in a positive way not negative, but constructive Be responsible. He who knows should let the other know 36
HAZOP recording The findings are recorded during the meeting(s) using a HAZOP work-sheet, either by filling in paper copies, or by using a computer connected to a projector (recommended). The HAZOP worksheet may be different depending on the scope of the study generally the following entries (columns) are included Ref. no. Guidewords Deviations Possible causes Consequences Safeguards Actions required (or, recommendations) Actions allocated to (follow up responsibility) 37
Process HAZOP worksheet Hazards and Operability Review Project Name: Date: Page of Process : Section: Item Study node Process Parameter Ref. Drawing: Deviations (guide words) Possible causes Possible consequences Action Required 3
HAZOP Worksheet Plant Drawings referred to Secretary: Team Names: Equipment Properties: Flow Pressure Temperature Equipment Tag Numbers Guide Words: No More Less Opposite Also Other (Early Late) Special conditions for Hazop: none, start-up, abnormal operation, maintenance, other (details): Line no. Deviation Cause Consequences Safeguard Action 3
Flash Drum Example PIC 1 Process Fluid 2 2 2 3 6 E-30 Steam 5 V-40 X AD = 0 mol % X AF = 50 mol % E-20 C 1 3 7 4 7 LIC Now, complete the HAZOP Study 40
Some References Frank P. Lees (10). Loss Prevention in the Process Industries. Hazard Identification, Assessment and Control. Volume 1. Butterworth & Co (Publishers) Ltd. Frank P. Lees (10). Loss Prevention in the Process Industries. Hazard Identification, Assessment and Control. Volume 2. Butterworth & Co (Publishers) Ltd. Frank Crawley, Malcolm Preston & Brian Tyler (2000). HAZOP: Guide to best practice. Guidelines to best practice for the process and chemical industries. Institution of Chemical Engineers, UK. Risk Management Group (12). Hazard & Operability Studies. Basic 2-day Training Course Notes. ICI Australia Engineering Pty Ltd. Marvin Rausand (2004). HAZOP. Hazard and Operability Study. Department of Production and Quality Engineering, Norwegian University of Science and Technology. 41