Hazard and Operability (HAZOP).pdf. ppt.
- 1. Hazard and Operability Study (HAZOP) Dr. M. Azam Saeed
- 2. Hazard - any operation that could possibly cause a catastrophic release of toxic, flammable or explosive chemicals or any action that could result in injury to personnel. Operability - any operation inside the design envelope that would cause a shutdown that could possibly lead to a violation of environmental, health or safety regulations or negatively impact profitability. 2 DEFINITION OF HAZARD & OPERABILITY
- 3. Systematic technique to IDENTIFY potential HAZard and OPerating problems Involves a multi-disciplinary team methodically “brainstorming” the plant design A qualitative technique based on “guide-words” to help provoke thoughts about the way deviations from the intended operating conditions can lead to hazardous situations or operability problems 3 WHAT IS A HAZOP STUDY?
- 4. A HAZOP study is an examination procedure. Its purpose is to identify all possible deviation from the way in which a design is expected to work and to identify all the hazards associated with these deviations. When deviation arise that results in hazards, action are generated that require design engineers to review and suggest solutions to remove the hazard or to reduce its risk to an acceptable level. 4 WHAT IS A HAZOP STUDY?
- 5. HAZOP was initially 'invented' by Institute of Chemical Industry (ICI) in the United Kingdom, but the technique only started to be more widely used within the chemical process industry after the Flixborough disaster in 1974. This chemical plant explosion killed twenty eight people and injured scores of others. 5 ORIGIN OF HAZOP STUDY
- 6. 6 I suppose that I should have done that HAZOP Study!
- 7. 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. 7 A SCENARIO…
- 8. What was the cause of the accident? What was the consequence of the event? What can we do to prevent all those things to happen in the first place? What other possible accidents might happen on the road trip? Can we be prepared before the accident occurs? 8 POINTS TO PONDER
- 9. 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 9
- 10. Safety Issues: To identify scenarios that would lead to the release of hazardous or flammable material into the atmosphere, thus exposing workers to injury To check the safety of the design To improve the safety of an existing and or modified facility Operability Issues: To decide whether and where to build To check operating and safety procedures To verify that safety instrumentation is working optimally To facilitate smooth, safe prompt start-up To minimize extensive last minute modifications To ensure trouble-free long-term operation 10 OBJECTIVES OF A HAZOP STUDY “Prevention is better than control”
- 11. HAZOPs concentrate on identifying both hazards as well as operability problems. While the HAZOP study is designed to identify hazards through a systematic approach, more than 80% of study recommendations are operability problems and are not, of themselves, hazards. Although hazard identification is the main focus, operability problems should be identified to the extent that they have the potential to lead to process hazards, result in an environmental violation or have a negative impact on profitability. 11 PHILOSOPHY – HAZARD VS OPERABILITY
- 12. The circumstances when HAZOPs are likely to produce benefits are: during the design or installation of any new plant or process, or major modification to an existing one; when there are unique hazards such as environmental hazards and quality or cost issues associated with the operation; following a major incident involving fire, explosion, toxic release etc; and to justify why a particular code of practice, guidance note or industry code is not to be followed. 12 BENEFITS
- 13. Diammonium Phosphate (DAP) Production Phosphoric acid and ammonia are mixed, and a non- hazardous product, diammonium phosphate (DAP), results if the reaction of ammonia is complete. If too little phosphoric acid is added, the reaction is incomplete, and ammonia is produced. Too little ammonia available to the reactor results in a safe but undesirable product. Both chemicals will be used in large quantities and in concentrated form. Due to the highly corrosive nature of both chemicals, the project team was assigned to investigate the hazards posed to staff from the reaction resulting from study line 1 (phosphoric acid delivery line). 13 SIMPLE EXAMPLE OF A HAZOP STUDY
- 14. 14 PRODUCTION OF DAP (CONTINUOUS PROCESS) Ammonia Valve B Reactor Diammonium Phosphate (DAP) Valve C Valve A Phosphoric Acid Study line 1 Phosphoric acid delivery line
- 15. 15 HAZOP STUDY REPORT ON LINE 1 OF DAP
- 16. Refer to reactor system shown. The reaction is exothermic. A cooling system is provided to remove the excess energy of reaction. In the event of cooling function is lost, the temperature of reactor would increase. This would lead to an increase in reaction rate leading to additional energy release. The result could be a runaway reaction with pressures exceeding the bursting pressure of the reactor. The temperature within the reactor is measured and is used to control the cooling water flow rate by a valve. Perform HAZOP Study 16 PRELIMINARY HAZOP EXAMPLE TC Cooling Coils Monomer Feed Cooling Water to Sewer Cooling Water In Thermocouple
- 17. PRELIMINARY HAZOP ON REACTOR - EXAMPLE Guide Word Deviation Causes Consequences Action NO No cooling Temperature increase in reactor REVERSE Reverse cooling flow Failure of water source resulting in backward flow MORE More cooling flow Instruct operators on procedures AS WELL AS Reactor product in coils Check maintenance procedures and schedules OTHER THAN Another material besides cooling water Water source contaminated 17
- 18. 18 PRELIMINARY HAZOP ON REACTOR – ANSWER Guide Word Deviation Causes Consequences Action NO No cooling Cooling water valve malfunction Temperature increase in reactor Install high temperature alarm (TAH) REVERSE Reverse cooling flow Failure of water source resulting in backward flow Less cooling, possible runaway reaction Install check valve MORE More cooling flow Control valve failure, operator fails to take action on alarm Too much cooling, reactor cool Instruct operators on procedures AS WELL AS Reactor product in coils More pressure in reactor Off-spec product Check maintenance procedures and schedules OTHER THAN Another material besides cooling water Water source contaminated May be cooling inefffective and effect on the reaction If less cooling, TAH will detect. If detected, isolate water source. Back up water source?
- 19. The HAZOP process is based on the principle that a team approach to hazard analysis will identify more problems than when individuals working separately combine results. The HAZOP team is made up of individuals with varying backgrounds and expertise. The expertise is brought together during HAZOP sessions and through a collective brainstorming effort that stimulates creativity and new ideas, a thorough review of the process under consideration is made. 19 HAZOP – THE CRITICAL SUCCESS FACTOR
- 20. HAZOP TERMINOLOGY - 1 Term Definition Cause The reason(s) why the DEVIATION could occur. More CAUSES can be identified for one DEVIATION. Comments Any remarks to be given to the RECOMMENDATIONS or which, in another way, showed up during the HAZOP sessions. Consequence The results of the DEVIATION, 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. 20
- 21. HAZOP TERMINOLOGY - 2 Term Definition Deviation A way in which the process conditions may depart from their INTENTION. Intention / Design intent Description of how the process is expected to behave at the Study Line. 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. Keyword/ Guideword A short word to create the imagination of a DEVIATION of the INTENTION. The mostly used set of Guidewords is: NO, MORE, LESS, AS WELL AS, PART OF, OTHER THAN and REVERSE. The GUIDEWORDS are applied, in turn, to all the PARAMETERS, in order to identify unexpected and yet credible DEVIATIONS from the INTENTION. 21
- 22. HAZOP TERMINOLOGY - 3 Term Definition Parameter The relevant parameter for the condition(s) of the process, e.g., pressure, temperature, composition, etc. Study Line/ Node A 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 Recommendation Activities identified during a HAZOP study for follow-up. These may comprise technical improvements in the design, modifications in the status of drawings and process descriptions, procedural measures to be developed or further in-depth studies to be carried out. 22
- 23. Term Definition Safeguard Facilities that help to reduce the occurrence frequency of the DEVIATION or to mitigate its CONSEQUENCES. There are, in principle, five types of SAFEGUARDS: Facilities that identify the DEVIATION. These comprise, among others, alarm instrumentation and human operator detection. Facilities that compensate the DEVIATION, e.g., an automatic control system that reduces the feed to a vessel in case of overfilling it (increase of level). These usually are an integrated part of the process control. Facilities that prevent the DEVIATION to occur. An example is an inert blanket gas in storages of flammable substances. Facilities that prevent a further escalation of the DEVIATION, e.g., by (total) trip of the activity. These facilities are often interlocked with several units in the process, often controlled by logical computers. Facilities that relieve the process from the hazardous DEVIATION. These comprise for instance: pressure safety valves (PSV) and vent systems. 23 HAZOP TERMINOLOGY - 4
- 24. Term Definition Action – 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 to 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. – Whereas the former is to be preferred, it is not always possible, especially when dealing with equipment malfunction. However, always investigate removing the cause first, and only where necessary mitigate the consequences. 24 HAZOP TERMINOLOGY - 4
- 25. HAZOP Study Planning and Preparations HAZOP Study Team - Role and Responsibilities Meeting Arrangements Reporting and Follow-up HAZOP Guidewords; Possible Causes & Consequences Plant; Safeguards & Action Required Working Session 2: Chemical Plant 25 HAZOP METHODOLOGY - CONTENT
- 26. 26 HAZOP PLANNING AND EXECUTION PLAN Select Team Examine System Keywords CLOSE OUT Record/File Completed Actions TRACK ACTIONS HAZOP Review Meeting TEAM System Assessment Team Activity REPORT Action List HAZOP Report
- 27. Independent leader (e.g., not from plant studied) Preferred but complete independence not essential Project engineer Provide engineering input Operations representative Plant operation Discipline engineers Process Instrument/ electrical Mechanical/ maintenance HAZOP minute recorder One of the above 27 HAZOP STUDY TEAM
- 28. 28 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 •Control discussion •Limit discussion •Encourage team to draw conclusion •Ensure secretary has time for taking note •Keep team in focus •Encourage imagination of team members •Motivate members •Discourage recriminations •Judge important issues
- 29. Always prepare study program in advance. Agree on the format or form to be used. Prepare follow up procedures. Brief members about HAZOP during first meeting. Stop the team trying to redesign the process. HAZOP is a team exercise. Do not let anybody (including the leader himself) to dominate. 29 CHECKLIST FOR HAZOP LEADER
- 30. If conflict arises, handle with care. Avoid long discussions by recording areas which need to be resolved outside meeting. Leader must be strong, yet diplomatic. Speak clearly. Make your point. Better have experience working as team member previously. Do not skip anything….some time small things may cause big accident. 30 CHECKLIST FOR HAZOP LEADER
- 31. P & IDs Process flow diagrams Heat and Material Balances Layouts Logic Diagrams Equipment Data Sheets Material Hazard Data Sheets Hazardous area Layouts 31 REQUIRED INFORMATION
- 32. GUIDEWORDS/ KEYWORDS The basic HAZOP guide-words are: Guide-word Meaning Example No (not, none) None of the design intent is achieved No flow when production is expected More (more of, higher) Quantitative increase in a parameter Higher temperature than desired Less (less of, lower) Quantitative decrease in a parameter Lower pressure than normal As well as (more than) An additional activity occurs Other valves closed at the same time (logic fault or human error) Part of Only some of the design intention is achieved Only part of the system is shut down Reverse Logical opposite of the design intention occurs Back-flow when the system shuts down Other than (Other) Complete substitution – another activity takes place Liquids in the gas piping 32
- 33. ADDITIONAL GUIDEWORDS Guide-word Meaning Early/ late The timing is different from the intention Before/ after The step (or part of it) is effected out of sequence Faster/ slower The step is done/not done with the right timing Where else Applicable for flows, transfer, sources and destinations 33
- 34. Some examples of combinations of guide-words and parameters: NO FLOW Wrong flow path – blockage – incorrect slip plate – incorrectly fitted return valve – burst pipe – large leak – equipment failure – incorrect pressure differential – isolation in error MORE FLOW Increase pumping capacity – increased suction pressure – reduced delivery head – greater fluid density – exchanger tube leaks – cross connection of systems – control faults MORE TEMPERATURE Ambient conditions – failed exchanger tubes – fire situation – cooling water failure – defective control – internal fires 34 GUIDEWORDS + PARAMETER
- 35. Human error - which are acts of omission or commission by an operator, designer, constructor or other person creating a hazard that could possibly result in a release of hazardous or flammable material. Equipment failure - in which a mechanical, structural or operating failure results in the release of hazardous or flammable material. External Events - in which items outside the unit being reviewed affect the operation of the unit to the extent that the release of hazardous or flammable material is possible. External events include upsets on adjacent units affecting the safe operation of the unit (or node) being studied, loss of utilities, and exposure from weather and seismic activity. 35 CAUSES OF DEVIATIONS – 3 TYPES
- 37. Using relevant guide works, perform HAZOP study on shell & tube heat exchanger 37 CASE STUDY – SHELL & TUBE HEAT EXCHANGER Process fluid Cooling water
- 38. 38 HAZOP ON HEAT EXCHANGER – ANSWER 1 Guide Word Deviation Causes Consequences Action Less Less flow of cooling water Pipe blockage Temperature of process fluid remains constant High Temperature Alarm More More cooling flow Failure of cooling water valve Temperature of process fluid decrease Low Temperature Alarm More of More pressure on tube side Failure of process fluid valve Bursting of tube Install high pressure alarm Contamination Contaminatio n of process fluid line Leakage of tube and cooling water goes in Contamination of process fluid Proper maintainance and operator alert Corrosion Corrosion of tube Hardness of cooling water Less cooling and crack of tube Proper maintainence
- 39. 39 HAZOP ON HEAT EXCHANGER – ANSWER 2 Guide Word Deviation Causes Consequences Action NONE No cooling water flow Failure of inlet cooling water valve to open Process fluid temperature is not lowered accordingly Install Temperature indicator before and after the process fluid line Install TAH MORE More cooling water flow Failure of inlet cooling water valve to close Output of Process fluid temperature too low Install Temperature indicator before and after process fluid line Install TAL LESS Less cooling water Pipe leakage Process fluid temperature too low Installation of flow meter REVERSE Reverse process fluid flow Failure of process fluid inlet valve Product off set Install check valve (whether it is crucial have to check?) CONTAMINATION Process fluid contamination Contamination in cooling water Outlet temperature too low Proper maintenance and operator alert