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HAZOP: Hazard and Operability StudyHAZOP: Hazard and Operability Study
[email protected]/jnawrocki/models/
Models and Analysis of SoftwareLecture 11
Copyright, 2003 Jerzy R. Nawrocki
IntroductionIntroduction
HAZOP: HAZard and OPerability study; ICI Chemicals, UK, ‘70
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
IntroductionIntroduction
HAZOP: HAZard and OPerability study
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
Heating installationHeating installationRadiation therapy machineRadiation therapy machine
Electron accelerator
IntroductionIntroduction
HAZOP: HAZard and OPerability study
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
Railway crossingRailway crossing Aircraft control systemAircraft control system
IntroductionIntroduction
HAZOP: HAZard and OPerability study
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
Existing New
IntroductionIntroduction
HAZOP: HAZard and OPerability study
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
Heating installationHeating installationRadiation therapy machineRadiation therapy machine
Electron accelerator
~ 200 rad up to 50 oC
IntroductionIntroduction
HAZOP: HAZard and OPerability study
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
Therac-25 accident [Leveson93]Therac-25 accident [Leveson93]
Electron accelerator
15 000 rad
Heating installationHeating installation
90 oCAuch!
IntroductionIntroduction
HAZOP: HAZard and OPerability study
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
Heating installationHeating installation
90 oCElectron accelerator
15 000 rad
Radiation therapy machineRadiation therapy machine
H.= A set of conditions that can lead to an accident [Leveson91]
IntroductionIntroduction
HAZOP: HAZard and OPerability study
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
Oh God!
IntroductionIntroduction
HAZOP: HAZard and OPerability study
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
The computer doesn’t work!
IntroductionIntroduction
HAZOP: HAZard and OPerability study; ICI Chemicals, UK, ‘70
Aim: ‘identifying potential hazards and operability problems caused by deviations from the design intent of both new and existing process plants’ [Lihou03].
Performed by a team of multidisciplinary experts.
Structured brainstorming process.
IntroductionIntroduction
Process description
How deviations from the design intent can arise?Can they impact safety and operability?
What actions are necessary?
IntroductionIntroduction
.. the great advantage of the technique is that it encourages the team to consider less obvious ways in which a deviation may occur (..) In this way the study becomes much more than a mechanistic check-list type of review. [Lihou03]
KeywordsKeywords
Primary keywords: a particular aspect of a design intent (a process condition or parameter).
Safety: Operability:
Flow IsolateTemperature Start-upPressure ShutdownLevel MaintainCorrode InspectAbsorb DrainErode Purge... ...
Can corrosion bea design intent?
KeywordsKeywords
Secondary keywords: possible deviations (problems)NoNo
Less
More
Reverse
Also
Other
Fluctuation
Early
Late
They tend to be a standard set.
NoNo: The design intent is almost eliminated (blocked) or unachievable.
Examples:
Flow/No
Isolate/No
KeywordsKeywords
Secondary keywords: possible deviations (problems)No
LessLess
More
Reverse
Also
Other
Fluctuation
Early
Late
LessLess: Value of a parameter described by a primary keyword is less than expected.
Examples:
Flow/Less
Temperature/Less
KeywordsKeywords
Secondary keywords: possible deviations (problems)No
Less
MoreMore
Reverse
Also
Other
Fluctuation
Early
Late
MoreMore: The parameter value is greater than expected.
Examples:
Temperature/More
Pressure/No
KeywordsKeywords
Secondary keywords: possible deviations (problems)No
Less
More
ReverseReverse
Also
Other
Fluctuation
Early
Late
ReverseReverse: The opposite direction of the design intent.
Examples:
Flow/Reverse
Isolate/No
KeywordsKeywords
Secondary keywords: possible deviations (problems)No
Less
More
Reverse
AlsoAlso
Other
Fluctuation
Early
Late
AlsoAlso: The design intent (primary keyword) is OK, but there is something extra.
Examples:
Flow/Also = contamination
Level/Also = unexpected material in a tank
KeywordsKeywords
Secondary keywords: possible deviations (problems)No
Less
More
Reverse
Also
OtherOther
Fluctuation
Early
Late
OtherOther: The design intent occurs but in a different way.
Examples:
Composition/Other = Unexpected proportions
Flow/Other = Product flows where it is unexpected
KeywordsKeywords
Secondary keywords: possible deviations (problems)No
Less
More
Reverse
Also
Other
FluctuationFluctuation
Early
Late
FluctuationFluctuation: The design intent achieved only part of the time.
Examples:
Flow/Fluctuation = Sometimes flows, sometimes not.
Temperature/Fluctuation = Sometimes hot, sometimes cold.
KeywordsKeywords
Secondary keywords: possible deviations (problems)No
Less
More
Reverse
Also
Other
Fluctuation
EarlyEarly
Late
EarlyEarly: The design intent appears too early.
Examples:
Flow/Early = The product flows too early.
Temperature/Early = The intended temperature (high or low) is achieved too early.
KeywordsKeywords
Secondary keywords: possible deviations (problems)No
Less
More
Reverse
Also
Other
Fluctuation
Early
LateLate
LateLate: Opposite to early.
Examples:
Level/Late = The inteded level in a tank is achieved too late.
KeywordsKeywords
Secondary keywords: possible deviations (problems)No
Less
More
Reverse
Also
Other
Fluctuation
Early
Late
Are all combinationsof keywords meaningful?
Temperature/No ???
Corrode/Reverse ???
Methodology – Report formatMethodology – Report format
Deviation Cause Consequence Safeguards Action
E.g. Flow/No
Potential cause of the
deviation
Consequences of the cause
and the deviation itself
Any existing devices that prevent the
cause or make its
consequeces less painful
Actions to remove the
cause or mitigate the
conse-quences
Methodology – The processMethodology – The process
Select a section of the plantSelect a section of the plant
For each primary keyword relevant for the plant:For each primary keyword relevant for the plant:
For each relevant secondary keyword:For each relevant secondary keyword:
Think of significant consequences and record them;Record any safeguards identified;Think of any necessary actions and record them;
Think of significant consequences and record them;Record any safeguards identified;Think of any necessary actions and record them;
For each discovered cause for the deviationFor each discovered cause for the deviation
Deviation Cause Consequence Safeguards Action
Flow/No Problem...
The HAZOP teamThe HAZOP teamOptimal: 6 peopleMaximum: 9 people
Equal representation of customer and supplier
Experts from a range of disciplines
Team composition: questions raised during the meeting should be answered immediately.
Chairman and secretary
Preparatory workPreparatory work
1. Assemble the data
2. Understand the subject
3. Subdivide the plant and plan the sequence
4. Mark-up the drawings
5. Devise a list of appropriate keywords
6. Prepare table headings and an agenda
7. Prepare a timetable
8. Select the team
The reportThe report
• Scope of the study
• Brief description of the process under study
• Keyword combinations and their meanings
• Description of the Action File (contains Action Response Sheets reporting on the actions performed to reduce the risks; initially empty)
• General comments (what was unavailable or not reviewed, what the team was assured of)
• Results (the number of recommended actions)
UML-HAZOPUML-HAZOP
J.Górski, A.Jarzębowicz
Technical University of Gdańsk
Wykrywanie anomalii w modelach obiektowych za pomocą metody UML-HAZOP, IV KKIO, Best Paper Award
Detecting Defects in Object-Oriented Diagrams Using UML-HAZOP, FCDS, vol. 24, No. 4, 2002.
Strengths of UML-HAZOPStrengths of UML-HAZOP
• UML
• Defect detection in UML diagrams
• A structured review method for UML diagrams guided by keywords (NO, MORE, LESS, ..)
• An interesting checklist for UML diagrams
• Experimental evaluation shows that the method is quite efficient (defects detected per unit of time)
Weaknesses of UML-HAZOPWeaknesses of UML-HAZOP
Limited to class diagrams only.
Limited to two kinds of relationships in class diagrams, Association and Generalization, from which 10 primary keywords are derived.
In the presented experiments all the analysis was performed by one reviewer whilest HAZOP relies on multidisciplinary teams.
IntroductionIntroduction
.. the great advantage of the technique is that it encourages the team to consider less obvious ways in which a deviation may occur (..) In this way the study becomes much more than a mechanistic check-list type of review. [Lihou03]
Weaknesses of UML-HAZOPWeaknesses of UML-HAZOP
Limited to class diagrams only.
Limited to two kinds of relationships in class diagrams, Association and Generalization, from which 10 primary keywords are derived.
In the presented experiments all the analysis was performed by one reviewer whilest HAZOP relies on multidisciplinary teams.
The method lacks analysis of possible consequences of an identified defect (anomaly).
SummarySummary
HAZOP is a structured HAZOP is a structured brainstorming method for risk brainstorming method for risk analysis.analysis.
It can be applied in different It can be applied in different contexts (eg. UML-HAZOP)contexts (eg. UML-HAZOP)
It goes well with other analysis It goes well with other analysis methods, eg. fault tree analysis methods, eg. fault tree analysis (AND/OR trees of faults)(AND/OR trees of faults)
Used by: UK Ministry of Defence, Used by: UK Ministry of Defence, Motorola, chemical companies, etc.Motorola, chemical companies, etc.
BibliographyBibliography
[Lihou03][Lihou03] Mike Lihou, Hazard & Operability Mike Lihou, Hazard & Operability Studies, Lihou Technical & Software Services, Studies, Lihou Technical & Software Services, www.lihoutech.com/hzp1frm.htm, 3.06.2003. , 3.06.2003.
A very good introduction to HAZOP.A very good introduction to HAZOP. [Leveson91][Leveson91] N. Leveson, S.Cha, T.Shimeall, N. Leveson, S.Cha, T.Shimeall,
Safety verification of Ada programs using Safety verification of Ada programs using software fault trees, software fault trees, IEEE SoftwareIEEE Software, July 1991, , July 1991, 48-59.48-59.
FTA templates for Ada programs.FTA templates for Ada programs. [Leveson93][Leveson93] N. Leveson, C. Turner, An N. Leveson, C. Turner, An
investigation of the Therac-25 Accidents, investigation of the Therac-25 Accidents, ComputerComputer, July 1993, 18-41., July 1993, 18-41.