hazop & check list
TRANSCRIPT
C. S. Howat - Hazard & Operability - © 20021
INTRODUCTIONTO
PROCESS HAZARD EVALUATION&
Hazard and Operability Studies (HazOp)
Plant & Environmental Safety
Colin S. ‘Chip’ Howat Ph.D.
Kurata Thermodynamics Laboratory
Department of Chemical & Petroleum Engineering
University of Kansas
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Lecture: One to Two Class Periods
Title: Process Hazard Identification and HazOp
Thought: I don’t like work - no man does - but I like what isin work - the chance to find yourself. Your ownreality - for yourself, not for others - what no otherman can ever know.
Joseph Conrad, Heart of Darkness, 1902
Question: What are the implications of: ‘What you don’thave can’t leak’ and ‘People who aren’t therecan’t be injured’?
Purpose: Introduce hazard evaluation procedures and introduce Hazard & Operability Studies
Objective Synthesis and Evaluation
Introduction to Process Hazard Evaluation & Introduction to Process Hazard Evaluation & HazOpHazOp
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Outline
• Purpose of Hazard Evaluation• Introduction to Risk Assessment• Types of Hazard Identification Procedures• Focus on Two Methods• Focus on Identification
HazOp
•Focus on Identification
Checklist
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• Input Information
• Batch v. Continuous
• Input-Output Structure
• Inherent Safety Structure
• Recycle Structure
• Separation Structure
• Heat Integration Structure
• Process Control Structure
We have discussed the steps of process synthesis, in general. Again this is nota step-by-step procedure. But it does give a rough guide to what needs to beconsidered during the development of the base case, in particular, and of anydesign tier, generally. The steps are given below. The focus of this talk is toaddress the beginnings of Hazard Identification. Recall that the purpose ofof Inherent Safety is to reduce or eliminate the hazard. In order to do thatwe need to know what the hazards are and where they exist in the process.
ProcessDesign &ProcessAnalysis
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Inherently Safer Processes StrategiesInherently Safer Processes Strategies
MINIMIZE Use smaller quantities of hazardous substances.
SUBSTITUTE Replace a material with a less hazardous substance.
MODERATE Use less hazardous conditions, a less hazardous formof a material, or facilities which minimize the impactof a release of hazardous material or energy.
SIMPLIFY Design facilities which eliminate unnecessary complexityand make operating errors less likely, and which areforgiving of errors which are made.
As a refresher, the strategies that we have for inherent safety are listed below from the previous lecture. After we identify our hazards during synthesis and analysis, we can incorporate these strategies into developing the recycle, separation, heat integration and process control structures.
Chemical manufacturing processesChemical manufacturing processeswhich reduce or eliminate hazards associatedwhich reduce or eliminate hazards associated
with the materials and operations of the processwith the materials and operations of the processsuch that this is permanent aresuch that this is permanent are
INHERENTLY SAFER.INHERENTLY SAFER.
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Purpose of Hazard Evaluation
‘A hazard is an inherent physical or chemical characteristic that has thepotential for causing harm.’ Guidelines for Hazard Evaluation Procedures
We need to identify and evaluate the significanceof Hazardous Situations.
Hazard Evaluation Procedures are an organized effort to identify and analyze the significance of hazards.
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RISK = PROBABILITY * CONSEQUENCE
Probabilistic Risk Assessment
• Identify Hazard
• Identify Scenario
• Determine Event Probability
• Determine Event Consequences
Introduction to Risk Assessment
For the purposes of this course, we are primarily interested in identifying the hazard, and then, subsequently, we are interested in identifying scenarios, determining probabilities and determining consequences.
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System Description
Hazard Identification
Scenario Identification
Event Probability Event Consequence
Risk Determination
Acceptable?No
Re-DesignSystem
Risk Assessmentis an integral partof the design,start-up, operationprocedure.
Our first emphasis in synthesisis to try to eliminate or reducethe hazard during the processprocess design stage. Oursecond emphasis is to try toeliminate the hazard once theplant is in operation. So, our focus is on inherent safety. Nevertheless, when hazards still exist in the design and operation, there is the potentialthat they can escape and causeharm.
Once the hazard is identified,we attempt to identify accidentor excursion scenariosso that we can determine therisk.
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Types of Hazard Identification Procedures
The successful Hazard Evaluation program meets the following:
• The need for risk information has been met;
• The results are of high quality and are easy for decision makers to use;
• The study has been performed with the minimum resources needed.
Selection of Hazard Evaluation Program
• The motivation for the study and types of results needed
• The type of information available, perceived risks, characteristics
• The resource availability and analyst/management preference
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Examples of Hazard Identification & Evaluation Procedures
• Safety Review -- Qualitative descriptions of potential safety problems
• Checklist -- Written list of items to verify status of system• Relative Ranking -- A strategy to compare systems for further
study• Preliminary Hazards Analysis -- General method to focus on system• What-if Analysis -- Brainstorming approach concerning
undesired events• What-if/Checklist -- Combined brainstorming/detailed list• Hazard and Operability Study -- Systematic method to identification• Failure Modes/Effects Analysis -- Tabulate equipment failure modes• Fault Tree Analysis -- Deductive approach from event to cause• Event Tree Analysis -- Inductive from initiating to all outcomes• Cause Consequence Analysis -- Combined Fault and Event Trees• Human Reliability Analysis -- Systematic evaluation of factors affecting
personnel
?
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Examples of Hazard Identification & Evaluation Procedures
• Safety Review -- Qualitative descriptions of potential safety problems
• Checklist -- Written list of items to verify status of system• Relative Ranking -- A strategy to compare systems for further
study• Preliminary Hazards Analysis -- General method to focus on system• What-if Analysis -- Brainstorming approach concerning
undesired events• What-if/Checklist -- Combined brainstorming/detailed list• Hazard and Operability Study -- Systematic method to identification• Failure Modes/Effects Analysis -- Tabulate equipment failure modes• Fault Tree Analysis -- Deductive approach from event to cause• Event Tree Analysis -- Inductive from initiating to all outcomes• Cause Consequence Analysis -- Combined Fault and Event Trees• Human Reliability Analysis -- Systematic evaluation of factors affecting
personnel
?
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Typical Uses of Hazard Evaluation Procedures
(Guidelines for Hazard Evaluation Procedures, p.77)
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So what is our focus?
The previous slide indicates that thechecklist procedure is applicable forconceptual design and operation. Checklists do give insight into the exploration step because they helpengineers consider initiating eventsbeyond intended performance. I have included checklist informationat the end of this talk.
The identification of toxicity, high pressure and high temperature hazards may be relatively straightforward. With that identification you can invoke the inherent safety strategies to reduce the hazard. Oftentimes, though, the hazard is not clearly evident. A formal method is useful to analyze the design as it evolves. This can be considered ‘routine operation’ in the previous table. The most widely used method for identifying hazards is the Hazard & Operability Study ~ HazOp, for short.
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Hazard and Operability Studies
Hazard and Operability Analysis was developed toidentify and evaluate safety hazards in a processplant and to identify operability problems which couldcompromise a plant’s ability to meet design productivity.
The purpose is to carefully review a process or operationin a systematic fashion to identify excursions whichcould lead to undesirable consequences. This gives insightinto the hazards that are present in the plant.
The results are identified hazards and operabilityproblems, recommended changes and studies etc.
These are typical requirements when analyzing an existing plant or new design. Accurate P&I’s , detailed process info, knowledge of instrumentation and operation etc. are required. The team requires design, operation, maintenance etc. experience.
We will be able to apply this method. It will guide us in selecting inherently safer strategies.
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HazOp Procedure
A HazOp Guide Word is combined with a Process Parameter to
Identify:
Deviations from intended design/operation
Causes of those deviations
Consequences of those deviations
Safeguards to prevent causes and mitigateconsequences of the deviations
Actions (recommendations) for design oroperation changes to avoid deviation
HazOp Studies do not provide insight into the probability or likelihood of the deviation.
Identificationis the focus!
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HazOp Guide Words
No or Not The complete negation of the intentionex. No flow to reactor
Less Quantitative decrease in the intentex. Less flow to the reactor
More Quantitative increase in the intentex. More flow to the reactor
Part of Qualitative decrease in the intentex. Part of the reactants to the reactor
As well as Qualitative increase in the intentex. Cooling water in the reactor
Reverse Logical opposite of the intentionex. Reverse flow into the reactor
Other than Complete substitutionex. Another material besides reactants in the
reactor
Other words may be more appropriate such as sooner for other than when considering time, higher instead of more when considering level, etc. --Consider the intent of the words.
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Common HazOp Parameters
Flow Frequency
Pressure Viscosity
Temperature Voltage
Level Information
Time Mixing
Composition Addition
pH Separation
Speed Reaction
This list is tailored to the task at hand -- not all used, more added as required.
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Preparing for the Review
HazOpReview
byTeam
Attitude MeetingLeadershipPreparation
Knowledge/Experience
Team’s HazOpExperience
Documentation Follow-up
Informationfor Study
Table
Deviation Causes Conseq. Safeguard Action
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HazOps require discipline. The use of the guide word must be strictly followed. Usually there is a moderator whose purpose is to keep the committee on task. As we have seen in our discussions, it is easy to drift to other topics or explore other ideas. In the context of the HazOp, this could lead to failure to identify the hazards in the process and to evaluate the systems in place the control the hazard.
While it is possible to apply HazOp to an entire process, it is typically applied to specific areas which have been prescreened for potential hazards.
In our case, we will be focusing on issues such as inventory, toxicity, reactivity, pressure and temperature. We will also be concerned with our control system ability to keep the process operating at intendedconditions as the base case evolves.
Basically, we take a very small section of the process to focus on at one time. We select the process parameter that we want to investigate and then select the menu of guide words that we wish to study. We then successively fill in HazOp forms for each guide word applied to each process parameter for each section of the plant that we might study. Finish one guide word before going on to the next.
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Example Problem
The reaction system shown below is exothermic. A cooling system isprovided to remove the excess energy of reaction. In the event thecooling function is lost, the temperature of the reactor would increase.This would lead to an increase in reaction rate leading to additionalenergy release. The result could be a runaway reaction with pressuresexceeding the bursting pressures of the reactor.
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Deviation Causes Consequences Safeguards Actions
Intent: Guide: Process Parameter:
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Deviation Causes Consequences Safeguards Actions
Intent: Guide: Process Parameter:
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Deviation Causes Consequences Safeguards Actions
Intent: Cooling Flow in Coils Guide: No Process Parameter: Cooling
No Cooling Plug in Line Temperature Increases None TemperatureAlarm
Blocked Line Possible RunawayRelief Valve
Pipe Breaks Broken Coils due toBlock in CW Low Flow
CV Fails Alarm
Controller Fails Study of WaterReactantInteraction
EmergencyShutdown
CW System Back up CWFails System
Air System Fail AFO Valve
Sewer Backs Up Filter on CW
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HazOp
Hazard & Operability Studies will help us identify the principal hazards in our plant. We can use thisidentification to invoke the Inherent Safety Strategies to reduce the hazards and to invoke High Reliability SystemTheory to evaluate Layers of Protection.
Remember, while HazOp’s identify hazards, they donot give insight into the probability that they will escape and cause harm.
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Checklists
Process Hazard Checklists
Another method to identify hazards is the process safety checklist. While the literature calls this hazard identification, the use of ‘hazard’ in this context is broader than the specific definition that I want us to use for Inherent Safety.
Ø This is a list of items that the reviewer needs to consider.Ø This list contains itemizes problems and failures.Ø The items on the list may or not apply to the situation.Ø The list acts as a reminder to stimulate thought.Ø The list can be used for:
Conceptual DesignPilot Plant OperationDetailed DesignConstructionStart upRoutine OperationModification/ExpansionDecommissioning
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Checklists
The checklist reminds the reviewer or operator of potential problem areas.
A check-off is required. For a checklist to be effective the reviewer or operator must respond.
Further Study RequiredDoes Not ApplyCompleted
All controls fail safe?
The following is an example from Crowl & Louvar.
ACTION REQUIRED!
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Further Study RequiredDoes Not ApplyCompleted
General Layout
1. Areas properly drained?2. Aisle ways provided?3. Fire walls, dikes and special guardrails needed?4. Hazardous underground obstructions?5. Hazardous overhead restrictions?6. Emergency accesses and exits?7. Enough headroom?8. Access for emergency vehicles?9. Safe storage space for raw materials and finished products?
10. Adequate platforms for safe maintenance operations?11. Hoists and elevators properly designed and safeguarded?12. Clearance for overhead power lines?13.14.15.
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Further Study RequiredDoes Not ApplyCompleted
Buildings
1. Adequate ladders, stairways and escape-ways?2. Fire doors required?3. Head obstructions marked?4. Ventilation adequate?5. Need for ladder or stairway to roof?6. Safety glass specified where necessary?7. Need for fireproofed structural steel?8.9.
10.11.12.13.14.15.
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Further Study RequiredDoes Not ApplyCompleted
Process
1. Consequences of exposure to adjacent operations considered?2. Special fume or dust hoods required?3. Unstable materials properly stored?4. Process laboratory checked for runaway explosive conditions?5. Provisions for protection from explosions?6. Hazardous reactions possible due to mistakes or contamination?7. Chemistry of processes completely understood and reviewed?8. Provisions for rapid disposal of reactants in an emergency?9. Failure of mechanical equipment possible cause of hazards?
10. Hazards possible from gradual or sudden blockages in piping?11. Hazards possible from gradual or sudden blockages in equipment?12. Public liability risks possible from sprays, fumes, mists or noise?13. Provisions made for disposal of toxic materials?14. Material safety data sheets available for all chemical species?15. Hazards possible from simultaneous loss of two or more utilities?
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Further Study RequiredDoes Not ApplyCompleted
Process (cont.)
16. Hazards involved in sewering materials?17. Safety factors altered by design revisions?18. Consequences of reasonably worst incident reviewed?19. Consequences of combination of incidents reviewed?20. Process diagrams correct and up-to-date?21.22.23.24.25.26.27.28.29.30.
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Further Study RequiredDoes Not ApplyCompleted
Piping
1. Safety showers and eye baths required?2. Sprinkler systems required?3. Provisions for thermal expansion?4. All overflow lines directed to safe areas?5. Vent lines directed safely?6. Piping specifications followed?7. Washing-down hoses needed?8. Check valves provided as needed?9. Protection and identification of fragile pipe considered?
10. Possible deterioration of exterior of piping by chemicals?11. Emergency valves readily accessible?12. Long and large vent lines supported?13. Steam condensate piping safely designed?14. Relief valve piping designed to prevent plugging?15. Drains to relieve pressure on suction/discharge of process pumps?
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Further Study RequiredDoes Not ApplyCompleted
Piping (cont.)
16. City water lines not connected to process pipes?17. Flammable fluids feeding prod units shut off from safe distance?18. Personnel protective insulation provided?19. Hot steam lines insultated?20.21.22.23.24.25.26.27.28.29.30.
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Further Study RequiredDoes Not ApplyCompleted
Equipment
1. Designs correct for maximum operating pressure?2. Corrosion allowance considered?3. Special isolation for hazardous equipment?4. Guards for belts, pulleys, sheaves and gears?5. Schedule for checking protective devices?6. Dikes for any storage tanks?7. Guard rails for storage tanks?8. Construction materials compatible with process chemicals?9. Reclaimed and replacement equipment checked structurally?
10. Reclaimed/replacement equipment checked for process pressures?11. Pipelines independently supported to relieve pumps?12. Pipelines independently supported to relieve other equipment?13. Automatic lubrication of critical machinery?14. Emergency standby equipment needed?15.
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Further Study RequiredDoes Not ApplyCompleted
Venting
1. Relief valves or rupture disks required?2. Materials of construction corrosion resistant?3. Vents properly designed? (Size, direction, configuration)4. Flame arrestors required on vent lines?5. Relief valves protected from plugging by rupture disks?6. Telltale pressure gauges installed between rupture disk/relief valve?7.8.9.
10.11.12.13.14.15.
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Further Study RequiredDoes Not ApplyCompleted
Instrument and Electrical
1. All controls fail safe?2. Dual indication of process variables necessary?3. All equipment properly labeled?4. Tubing runs protected?5. Safeguards for process control when instrument out of service?6. Process safety affected by response lag?7. Labels for all start-stop switches?8. Equipment designed to permit lockout protection?9. Electrical failures cause unsafe conditions?
10. Sufficient lighting for both outside and inside operations?11. Lights provided for all sight glasses, showers and eye-baths?12. Breakers adequate for circuit protection?13. All equipment grounded?14. Special interlocks needed for safe operation?15. Emergency standby power on lighting equipment required?
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Further Study RequiredDoes Not ApplyCompleted
Instrument and Electrical (cont.)
16. Emergency escape lighting required during power failures?17. All necessary communications equipment provided?18. Emergency disconnect switches properly marked?19. Special explosion proof electrical fixtures required?20.21.22.23.24.25.26.27.28.29.30.
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Safety Equipment
1. Fire extinguishers required?2. Special respiratory equipment required?3. Diking material required?4. Colorimetric indicator tubes required?5. Flammable vapor detection apparatus required?6. Fire extinguishing materials compatible with process materials?7. Special emergency procedures and alarms required?8.9.
10.11.12.13.14.15.
Further Study RequiredDoes Not ApplyCompleted
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Raw Materials
1. Any materials and products require special handling equipment?2. Any raw materials/products affected by extreme weather
conditions?3. Any products hazardous from a toxic or fire standpoint?4. Proper containers being used?5. Containers properly labeled for toxicity, flammability,
stability, etc.?6. Consequences of bad spills considered?7. Special instructions needed for containers?8. Special instructions needed for storage and warehousing
distributors?9. Does warehouse have operating instructions covering
each product?10.11.
Further Study RequiredDoes Not ApplyCompleted
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Checklists are not a substitute for amore rigorous approach. However,
they can be a constant reminderto reviewers of items to consider for
the situation at hand. They can be usedas a stimulant for more formal studies.