1. HAZOP Introduction
Zhang Wei, Wu Zhangjin
zhangwei06@lzu.cn, tunzhj03@lzu.cn
Distributed & Embedded Systems Lab
Lanzhou Universtiy, P.R.China
dslab.lzu.edu.cn

2. Contents 1
Contents
• Summary of HAZOP Analysis
• Limitation of the HAZOP Technique
• Procedure for HAZOP Analysis
• HAZOP about Stepper Motor Demo
• Reference
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3. Summary of HAZOP Analysis 2
Summary of HAZOP Analysis
• What is HAZOP
• Brief summary of characteristics
• Most common uses
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4. Summary of HAZOP Analysis 3
What is HAZOP
A Hazard and Operability (HAZOP) study is a structured and systematic
examination of a planned or existing process or operation in order to
identify and evaluate potential hazards and operability problems. Or to
ensure the ability of equipments in accordance with the design intent.
The HAZOP analysis technique uses a systematic process to indentify
possible deviations from normal operations and ensure that appropriate
safegurads are in place to help prevent accidents. It uses special
adjectives combined with process conditions to systematically consider
all credible deviations from normal conditions. The adjectives, called
guide words, are a unique feature of HAZOP analysis.
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5. Effects 4
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6. Summary of HAZOP Analysis 5
Brief summary of characteristics
• A systematic, highly structured assessment relying on HAZOP guide
words and team brainstorming to generate a comprehensive review
and ensure that appropriate safeguards against accidents are in place
• Typically performed by a multidisciplinary team
• Applicable to any system or procedure
• Used most as a system-level risk assessment technique
• Generates primarily qualitative results, although some basic
quantification is possible
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7. Summary of HAZOP Analysis 6
Most common uses
• Used primarily for identifying safety hazards and operability problems
of continuous process systems, especially fluid and thermal systems
• Also used to review procedures and sequential operations
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8. Limitation of the HAZOP Technique 7
Limitation of the HAZOP Technique
• Requires a well-defined system or activity
• Time consuming
• Focuses on one-event causes of deviations
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9. Limitation of the HAZOP Technique 8
Requires a well-defined system or activity
The HAZOP process is a rigorous analysis tool that systematically
analyzes each part of a system or activity. To apply the HAZOP guide
words effectively and to address the potential accidents that can result
from the guide word deviations, the analysis team must have access to
detailed design and operational information. The process systematically
identifies specific engineered safeguards (e.g., instrumentation, alarms,
and interlocks) that are defined on detailed engineering drawings.
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10. Limitation of the HAZOP Technique 9
Time consuming
The HAZOP process systematically reviews credible deviations, identifies
potential accidents that can result from the deviations, investigates
engineering and administrative controls to protect against the deviations,
and generates recommendations for system improvements. This detailed
analysis process requires a substantial commitment of time from both
the analysis facilitator and other subject matter experts, such as crew
members, engineering personnel, equipment vendors, etc.
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11. Limitation of the HAZOP Technique 10
Focuses on one-event causes of deviations
The HAZOP process focuses on identifying single failures that can result
in accidents of interest. If the objective of the analysis is to identify all
combinations of events that can lead to accidents of interest, more
detailed techniques should be used.
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12. Procedure for HAZOP Analysis 11
Procedure for HAZOP Analysis
• Definition of some useful items
• Define the system or activity
• Main process of the HAZOP Analysis
• Conduct HAZOP reviews
• Use the results in decision making
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13. Procedure for HAZOP Analysis 12
Definition of some useful items
• Node:
Node is some specific sections of the system in which (the
deviations of ) the design/process intent are evaluated.A node can
be a subsystem, a function group, a function or a subfunction.
• Deviation:
A deviation is a way in which the process conditions may depart
from their design/process intent.It is created by combining guide
words with process parameters resulting in a possible deviation from
design intent.
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14. Procedure for HAZOP Analysis 13
Definition of some useful items
• Process parameters:
The process parameters is the relevant parameter for the conditions
of the process.For example,voltage,data,direction,etc.
• Guide words:
The guide words, or secondary keywords,applied in conjunction with
a Primary Keyword,these suggest potential deviations or
problems.For example, less, more ,no ,reverse,etc.
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15. Procedure for HAZOP Analysis 14
Define the system or activity
• The system boundaries should be specified and clearly defined.By
doing these, analysts can avoid overlooking key elements at
interfaces
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16. Procedure for HAZOP Analysis 15
Main process of the HAZOP Analysis
• Divide the system into sections and develop credible deviations
• Determine the cause of the deviation and evaluate the
consequences/problems
• Find the safeguard which help to reduce the occurrence frequency of
the deviation or to mitigate its consquences
• Recommend some actions to against the deviation more effectively
• Record the information
• Repeat procedure
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17. Procedure for HAZOP Analysis 16
Divide the system into sections and develop
credible deviations
• So first we should divided the system into several sections and
choose one as a node.Of course we should know the design intent of
this node so that we could find the process parameters from it.After
that we should apply some guide-word to match these parameters
and both of them compose a deviation.
Guide Word + System Parameter = Deviation
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18. Effects 17
record the information
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19. Effects 18
procedure diagram
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20. Procedure for HAZOP Analysis 19
Conduct HAZOP reviews
• Introduce the team members
• Describe the HAZOP approach
• Conduct the analysis
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21. Procedure for HAZOP Analysis 20
Use the results in decision making
• Judge acceptability
• Identify improvement opportunities
• Make recommendations for improvements
• Justify allocation of resources for improvements
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22. HAZOP about Stepper Motor Demo 21
HAZOP about Stepper Motor Demo
• What is Stepper Motor Demo
• Specify the problems which include some issues
• Divide the system by interfaces
• Develop the deviations
• Analysis the interface 3
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23. HAZOP about Stepper Motor Demo 22
What is Stepper Motor Demo
Stepper Motor Demo is a RTLinux Application which controls the
running status of a small stepper motor. Our intent is to analysis the
Hazards and Operability of a system by analysising a actual example on
the stepper motor demo.
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24. HAZOP about Stepper Motor Demo 23
Specify the problems which include some issues
As a system with the motor, it may appear some problems as following:
• The motor burn down or cannot rotate forever
• The motor rotate too quick
• The motor do contrarily what you want it do,for the direction is
reverse
• . . .
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25. HAZOP about Stepper Motor Demo 24
Divide the system by interfaces
As the header file – smc 1500.h show, there are five different interfaces,
we can analysis them independently:
• void write lpt(struct motor t *motor);
• struct motor t stepper motor setup(int motor);
• void move steps(struct motor t *motor);
• void set stepper motor safe(struct motor t *motor);
• void stepper motor brake(struct motor t *motor);
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26. HAZOP about Stepper Motor Demo 25
Develop the deviations
According to the problems,we can develop the deviations like this:
parameters
/guide-
words
No,
Not,
None
Less,
Low,
Short
More,
High,
Long
Early
/Later
Before
/After
Faster
/Slower
Reverse
Power No
power
Under
voltage
Over
voltage
Voltage
change
suddenly
– – backflow
Step No step Less
steps
More
steps
Steps
take not
on time
Steps se-
quence is
disorder
Steps
take
faster/slower
–
Direction – – – – – – different
direction
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27. HAZOP about Stepper Motor Demo 26
Analysis the interface 3
We just analysise the interface 3 as an example:
HAZOP analysis of STEPPER MOTOR DEMO
3.0 void move steps(struct motor t *motor);
Item Deviation Causes Consequences Safeguards Recommandations
3.1 Over voltage The input power is too
high
The motor may be
burned down
1. install a voltmeter to
show the motor’s voltage
2. install a indica-
tor light, if the voltage
is larger than threshold
value, lighten it.
3.2 Under volt-
age
1. the wire become old,
the resistor is so big that
the voltage become small.
2. The parameter volt-
age in struct motor t was
small
the motor cannot
rotate normally, or
don’t have enogh
power to work.
1. install a voltmeter to
show the motor’s voltage
2. install a indicator light,
if the voltage is small,its
blink persistently
... ... ... ... ... ...
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28. Reference 27
Reference
• http://www.uscg.mil/hq/gm/risk/e-
guidelines/rbdm/html/vol3/08/v3-08-cont.htm
• Marvin Rausan, Hazard and Operability Study
• ...
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