Process Hazard Process Hazard analysis ..
- 1. Overview of Process Hazard Analysis (PHA) 1 DR. AA, Process Control and Safety Group
- 3. Causes of Accidents and Incidents Incidents and Accidents are caused by either unsafe behaviours (substandard practice) and/or unsafe conditions (substandard designs). Unsafe behaviours are handled by Occupational Safety Program, Unsafe conditions are managed through Process Safety Programs. 3
- 6. LOSS CAUSATION MODEL LACK OF CONTROL INADEQUATE PROGRAM BASIC CAUSES PERSONAL FACTORS & JOB FACTORS IMMEDIATE CAUSES SUB STANDARD ACTS & CONDITIONS INCIDENT CONTACT WITH ENERGY OR SUBSTANCE LOSS PEOPLE PROPERTY PROCESS PLANET LOSS CAUSATION PROBLEM SOLVING Workers exposed to hazards THRESHOLD OSH-MS Safe Operating Procedures, Training, Supervision, Maintenance, PPE Activity: PREVENTION Activity: MITIGATION 6
- 7. ACCIDENT RATIO STUDY SERIOUS OR DISABLING Including disabling and serious injuries MINOR INJURIES Any reported injury less than serious PROPERTY DAMAGE ACCIDENTS All types INCIDENTS WITH NO VISIBLE INJURY OR DAMAGE Near-miss accident 10 30 600 1 7
- 8. Process Hazards HAZARDOUS MATERIALS + PROCESS CONDITIONS Flammable materials Combustible materials Unstable materials Reactive materials Corrosive materials Asphyxiates Shock-sensitive materials Highly reactive materials Toxic materials Inert gases Combustible dusts High temperatures Extremely low temperatures High pressures Vacuum Pressure cycling Temperature cycling Vibration/liquid hammering Rotating equipment Ionizing radiation High voltage/current Erosion/Corrosion
- 9. Human Factors or Errors HUMAN FAILURE ERRORS VIOLATIONS • Deliberate actions • Different from those prescribed • Carries known associated risks • Ignores operational procedures • Violation errors occur because of a perception of lack of relevance, time pressure or laziness. • Competency exists • Intentions are correct • Slips occur while carrying out habitual, routine, skill based activity. • Incorrect intention • Inadequate knowledge • Incorrect information processing • Inadequate training • Mistakes occur because of incorrect assumptions or incorrect “tunnel vision” application of rules. SLIPS MISTAKES
- 10. Process Hazard Analysis (PHA) Methodologies 10 DR. AA, Process Control and Safety Group
- 12. Process Hazards Analysis PROCESS HAZARDS ANALYSIS What can go wrong? How likely is it? What are the consequences? PROCESS HAZARDS ANALYSIS STRUCTURE FOUNDATION FOR PROCESS HAZARDS ANALYSIS Historical Experience PHA Methodology Knowledge and Intuition
- 13. Qualitative Risk Analysis Process Hazards Analysis is the predictive identification of hazards, their cause & consequence and the qualitative estimation of likelihood and severity.
- 14. Qualitative vs. Quantitative PROCESS HAZARDS ANALYSIS RISK ANALYSIS IDENTIFIES HAZARDS, estimates likelihood and severity, suggests improvements. USE ON EVERY PROJECT QUALITATIVE - based on experience, knowledge and creative thinking. Most often done by MULTIDISCIPLINARY TEAM Several methodologies available What-if or Hazid What-if/Checklist HAZOP FMEA Preliminary Hazards Analysis ASSESSES HAZARDS SELECTIVE - use when other methods prove inadequate or excessive in cost. QUANTITATIVE - requires extensive data and special expertise. Done by ONE OR TWO SPECIALLY TRAINED PEOPLE Also called: • Hazan • Risk Assessment • Probabilistic Risk Assessment (PRA) • Quantitative Risk Assessment (QRA)
- 15. Process Hazard Analysis Simply, PHA allows the employer to: • Determine locations of potential safety problems • Identify corrective measures to improve safety • Preplan emergency actions to be taken if safety controls fail 15
- 16. PHA Must Address … • The hazards of the process • Identification of previous incidents with likely potential for catastrophic consequences • Engineering and administrative controls applicable to the hazards and their interrelationships • Consequences of failure of engineering and administrative controls, especially those affecting employees • Facility siting; human factors • The need to promptly resolve PHA findings and recommendations 16
- 17. PROJECT PHASE Conceptual Process development Project sanction Design, engineering, construction Hand over operation Stage 1 Concept Stage 2 Process design Stage 3 Detailed Engineering Stage 6 Post- commis sioning Stage 5 Pre- Commis sioning Stage 4 Construction Relationship of six-stage process study system to project life-cyc Safety issues must be embedded within all project life-cycle 17
- 18. PHA and project phase Method used Project life cycle stage 0 1 2 3 4 5 6 7 Checklist X X X X X X X X RR X X (X) (X) What-If X X X X FMEA (X) X X (X) LOPA X X X HAZOP (X) X X PHR X (X) 18
- 19. What If 19
- 20. What-If • Experienced personnel brainstorming a series of questions that begin, "What if…?” • Each question represents a potential failure in the facility or mis-operation of the facility • The response of the process and/or operators is evaluated to determine if a potential hazard can occur • If so, the adequacy of existing safeguards is weighed against the probability and severity of the scenario to determine whether modifications to the system should be recommended 20
- 21. What-If – Steps 1. Divide the system up into smaller, logical subsystems 2. Identify a list of questions for a subsystem 3. Select a question 4. Identify hazards, consequences, severity, likelihood, and recommendations 5. Repeat Step 2 through 4 until complete 21
- 22. What-If Question Areas • Equipment failures – What if … a valve leaks? • Human error – What if … operator fails to restart pump? • External events – What if … a very hard freeze persists? 22
- 23. What If What If…? Initiating Cause Consequence 1. There is higher pressure in the vessel 1.1 External fire in the process area 1.1 potential increase in temperature and pressure leading to possible leak or rupture. Potential release of flammable material to the atmosphere. Potential personnel injury due to exposure. 1.2 pressure regulator for inert gas fails open 1.2 potential for vessel pressure to increase up to the inert gas supply pressure. Potential vessel leak leading to release of flammable material to the atmosphere. Potential personnel injury due to exposure. 23
- 24. Checklist 24
- 25. Checklist • Review an installation against known hazards identified on previous studies of similar plant • Examine the checklist for relevance to plant being studied – Ask questions based on a pre-defined list • The checklist is a corporate memory of what could go wrong – Should be augmented by industrial-wide experience when available 25
- 26. Strength of checklist • Is quick and simple to perform and is easily understood • Makes use of existing experience and knowledge of previous systems • Helps check compliance with standard practice and design intention • Ensures that known hazards are fully explored 26
- 27. Weakness of checklist • Does not provide a list of initiating events (failure cases) for a QRA • May not be comprehensive and does not encourage analysts to consider new or unusual hazards • Highly dependent upon the quality of the prepared checklists 27
- 28. Checklist Question Categories • Causes of accidents – Process equipment – Human error – External events • Facility Functions – Alarms, construction materials, control systems, documentation and training, instrumentation, piping, pumps, vessels, etc. 28
- 29. Checklist Questions • Causes of accidents – Is process equipment properly supported? – Is equipment identified properly? – Are the procedures complete? – Is the system designed to withstand hurricane winds? • Facility Functions – Is is possible to distinguish between different alarms? – Is pressure relief provided? – Is the vessel free from external corrosion? – Are sources of ignition controlled? 29
- 31. Hazard Indices • Hazard indices give a quantitative indication of the relative potential for hazardous incidents associated with a given plant or process. They are used to most effect at the early design stage of a new plant. • The best known hazard indices are the Dow Index (1981) and the Mond Index (1979). 31
- 32. • Operates like an income tax form. • Penalties for unsafe situations •Credits for control and mitigation • Produces a number - the bigger the number the greater the hazard. • Only considers flammable materials • Not effective for procedures. Dow Fire and Explosion Index 32
- 33. 33 Dow Fire & Explosion Index
- 34. • Considers toxic materials only. • Includes simple source and dispersion models. • Not effective for procedures. Dow Criteria: If sum of F&EI and CEI > 128, then more detailed hazard review procedure required. Dow Chemical Exposure Index (CEI) 34
- 35. Mond Index Objectives of Mond Index To Identify, Assess and Minimize potential hazards on chemical plants units for new and existing processes About Mond Index Index primarily concerned with fire and explosion problem. Toxicity is considered only as possible complicating factor. Method gives credits for plant safety features (both hardware and software). Mond Index 35
- 36. Mond Index Procedure 1. Divide plant into units and each unit is assessed individually 2. Select ion of key material present in the unit. – Key material is the most dangerous chemicals (inherent properties), which higher possibility for combustion, explosion or exothermic reaction. 3. Calculation of Factors – Material Factor, B – Special Material hazards, M – Special Process hazards, S – Quantity Hazards, Q – Layout Hazards, L – Acute Health Hazards, T 4. Calculation of Indices - Dow Index (D), Fire Index (F), Explosion Index (E), Overall Hazard Rating (R). 36
- 37. The most important criteria - overall hazard rating, R Overall Hazard Rating Category 0-20 Mild 20-100 Low 100-500 Moderate 500-1100 High (group 1) 1100-2500 High (group 2) 2500-12,500 Very high 12,500-65,0000 Extreme > 65,000 Very extreme Mond Index Criteria 37
- 38. HAZID 38
- 39. HAZID • Performed by a team of multidisciplinary experts • The analyses are carried out based on area by area basis – It is focusing on location of the process • The discussion proceeds through the installation’s modules or operations using guide words to identify potential hazards, its causes, and possible consequences • The outcomes are summarised in HAZID Log Sheet 39
- 41. HAZID Guidewords – Port Facility 41
- 42. HAZID Log Sheet Ref No Guide word Hazard Description Conse- quences Risk Potential Safeguards /mitigating features Action / comment cons Freq 42
- 43. HAZOP 43
- 44. HAZOP • Performed by a team of multidisciplinary experts • The process is divided into distinct subsections or nodes – It is focusing on plant component/equipment • On each node, detailed brainstorming is conducted facilitated by a HAZOP Leader – Based on the design intent of each equipment specified by the node, possible deviations are examined, aided by guidewords and process parameters – Causes, consequences are identified and existing protection prescribed by the design are assessed. Based on these, recommendations are put forward • The outcome is summarized in a HAZOP Log Sheet 44
- 45. HAZOP Guidewords • 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 happen – Contamination, corrosion, sand deposits etc 45
- 46. 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 • 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 46
- 47. LOPA 47
- 48. LOPA • LOPA is a semi-quantitative risk analysis technique that is applied following a qualitative hazard identification tool such as HAZOP. • Similar to HAZOP LOPA uses a multi-discipline team • LOPA can be easily applied after the HAZOP, but before fault tree analysis • LOPA focuses the risk reduction efforts toward the impact events with the highest risks. • It provides a rational basis to allocate risk reduction resources efficiently. • LOPA suggests the required Independent Layer of Protection (IPL) required for the system to meet the required Safety Integrity Level (SIL) 48
- 49. LOPA Methodology • There are five basic steps in LOPA: 1. Identify the scenarios 2. Select an accident scenario 3. Identify the initiating event of the scenario and determine the initiating event frequency (events per year) 4. Identify the Independent Protection Layers (IPL) and estimate the probability of failure on demand of each IPL 5. Estimate the risk of scenario 49
- 50. LOPA 50
- 51. LOPA Consequence & Severity Initiating event (cause) Initiating event challenge frequency /year Preventive independent protection layers Probability of failure on demand (PFD) Mitigation independent protection layer (PFD) Mitigated consequen ce frequency /year Process design BPCS Operator response to alarm SIF (PLC relay) iJ i i I i ij J j I i C i PFD PFD PFD f PFD f f ... 2 1 1 i event initiating for C e consequenc against protects that IPL jth the of demand on failure of y probabilit i event initiating for requency frequency i event initiating for C e consequenc for frequency ij I i C i PFD f f 51
- 53. FMEA – Failure Modes, Effects Analysis • Performed by a team or a single analyst • Systematic review – Considers each component in turn – Subjectively evaluates effects of failure • Based on tabular format • FMECA includes critical analysis 53
- 54. FMEA – Failure Mode Keywords • Rupture • Crack • Leak • Plugged • Failure to open • Failure to close • Failure to stop • Failure to start • Failure to continue • Spurious stop • Spurious start • Loss of function • High pressure • Low pressure • High temperature • Low temperature • Overfilling • Hose bypass • Instrument bypassed 54
- 55. Example: FMEA on a Heat Exchanger Failure Mode Causes of Failure Symptoms Predicted Frequency Impact Tube rupture Corrosion from fluids (shell side) H/C at higher pressure than cooling water Frequent – has happened 2x in 10 yrs Critical – could cause a major fire Rank items by risk (frequency x impact) Identify safeguards for high risk items 55
- 57. Fault Tree Analysis • Provides a traceable, logical, quantitative representation of causes, consequences and event combinations • Not intuitive, requires training • Top-down analysis • Graphical method that starts with a hazardous event and works backwards to identify the causes of the top event • Intermediate events related to the top event are combined by using logical operations such as AND and OR. • Not particularly useful when temporal aspects are important 57
- 59. FTA Procedure m ake decision: acceptable ? identifytopevent construct thefault tree analyzequalitatively analyzequanitatively accept system Y E S N O developim provem ents
- 60. FTA Nomenclature