This document provides an overview of Hazard and Operability (HAZOP) studies, which are a technique used to identify potential hazards and operability problems in processes. It describes the origins, purpose, methodology, and typical components of a HAZOP study. Key aspects covered include identifying potential deviations from normal operating conditions using guidewords, determining causes and consequences of deviations, evaluating existing safeguards, and developing recommendations to address identified hazards. The document also outlines the HAZOP process, including defining nodes to segment the system, assigning a team to conduct the study, and systematically analyzing each node using guidewords across parameters.

1. HAZOP STUDY
HAZard and OPerability
An introduction

2. Content
 History
 Purpose
 Hazards
 Deviations
 Parameters
 Guidewords
 Consequences
 Safeguards
 Application
 HAZOP in Dow
 HAZOP Process
 Nodes
 Starting the Study
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3. Origins of HAZOP
 Concept dreamed up by Bert Lawley at I.C.I.
in the late 1960’s
 Result of a desire to have structured check
on P. & I.D.s
 Spread through I.C.I. in early 1970’s
 Endorsed by the “Health and Safety
Directorate” of the U.K. government
 NL, Belgian and U.K. etc. governments have
adopted HAZOP
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4. HAZOP in the 1980’s
 U.K. HSE and the Dutch Arbeidsinspectie
began to mandate HAZOP as part of Safety
Report for “Seveso Directive”
 I.C.I. by this time were doing HAZOP on
“everything”
 Dow incorporated in its Risk Management
process based on its own criteria (focusing
on highest risk)
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5. Purpose of HAZOP
 To identify credible causes, consequences
and safeguards before INCIDENTS occur
 To define recommendations to minimize the
HAZARD by eliminating or controlling the
cause or providing “lines of defence”
 Provide compatible information for
subsequent Process Safety efforts (i.e.
LOPA scenarios)
 Comply with regulatory Process Safety
requirements
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6. Scope of HAZOP
 Review is limited to the piping,
instrumentation and equipment shown on
the P&ID’s (do not re-design)
 Review is limited to deviations from normal
operations
 Impact of process unit on the utility systems
or other process units will be noted as
requiring further study
 Primary intent is to identify hazards and
define action items for additional safeguards
if appropriate
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7. HAZARDS
 Fire and Explosion
 Reactive Chemicals Incidents
 Toxic Exposure
 Corrosion
 Radiation
 Vibration
 Mechanical Hazards
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8. “Deviations”
 Hazards are caused by DEVIATIONS
from the DESIGN INTENTION
 HAZOP is a method for generating
these “DEVIATIONS” using “GUIDE
WORDS”
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9. Study is based on
“PARAMETERS”
 Flow
 Temperature
 Pressure
 Level
 Composition
 Agitation
 Anything it is important to control
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10. In combination with “GUIDE
WORDS”
 “No”
 “Less”
 “More”
 “Reverse”
 “Instead of ” or “Other than” (e.g.
something else or wrong composition)
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11. Combinations of parameters and
guide words are “DEVIATIONS”
 No flow
 Less flow
 More flow
 Reverse flow
 Flow of something not planned
 More temperature
 Less temperature
 And so on…...
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12. Deviations are logical
combinations like...
 More temperature
 Less pressure
Ignore illogical combinations like….
X Reverse temperature
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13. Determining the causes for a
deviation
 Consider only the causes that originate within the node
(consequences may be outside of the node)
 Deviations could be caused by:
 Equipment or process control failure
 Human error
 Loss of utilities
 External events such as fire
 Long term processes, e.g. erosion, corrosion, coking
 If process instrumentation crosses a node boundary, control
malfunction is considered a cause in both nodes
 Deviations that require the simultaneous occurrence of two or
more unrelated causes are not considered
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14. Consequences
 Describe all consequences, even those that propagate outside
the node.
 Consequences may include:
 Personnel injury
 Environmental damage
 Equipment damage
 Property loss
 Extended downtime
 Operability/Quality problems
 Consequences are described assuming there are no
safeguards
 Describe consequences as a chronological sequence of
events
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15. Safeguards
 Safeguards may include:
 Equipment design
 Instrumentation (control, alarm and shutdown)
 Pressure relief devices
 Administrative procedures
 Only list those instrument systems that have at least
an alarm as a safeguard
 Control instrumentation must automatically correct
or mitigate a process deviation
 Operator training and administrative procedures
should be listed provided they are part of ODMS
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16. What can HAZOP be applied
to?
 Continuous processes
 Batch processes
 Operating procedures
 Maintenance procedures
 Any operation where the Design Intention is
defined and deviations are possible
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17. Recommendations
 Recommendations are made to:
 Eliminate a cause
 Prevent or mitigate the consequence
 Reduce the likelyhood that the hazard will occur
 Examples of recommendations include:
 Equipment/instrumentation changes/additions
 Further study needed
 Inspection and maintenance
 Training
 Administrative systems to manage hazards
 Verification of design assumptions
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18. HAZOP Process
Team maximum 6 persons from (example):
 run plant engineer
 programmer
 process control
 process chemist
 shift operations team member
 study leader/facilitator
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19. Nodes
 P&ID’s for the process are broken into manageable
sections called nodes
 Nodes generally consists of unit operations and
associated piping and connect to upstream and
downstream units
 Nodes are defined by the HAZOP team and can be
redefined as needed
 A “Global issues” node can be included to capture
hazardous events that can impact the entire process
unit. For example:
Loss of containment
Sampling
Utility failure
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20. Typical nodes
E 201
R 201
P 201
NODE 1
NODE 2
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21. Nodes
 There is no “right” way to define nodes
 Usually start with a small node
 As experience builds, move to a larger node
 Follow the leader’s intuition
 If the team gets bored, the node is probably
too small
 If the team gets confused, the node is
probably too big
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22. Starting the study:
 The most knowledgeable person describes
the INTENTION of the node
 Composition (which chemicals are in the
equipment)
 Flow, temperature, pressure, phase,
quantity, agitation etc
 …. Anything important to the process
 Leader records for study team reference
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23. Start with Deviation “No Flow”
 Team gives all the causes for no flow in the
lines and equipment inside the node
 Leader prompts their thinking
 Team can add but not delete
 These causes are recorded in software
package
 The library in the software can be consulted
for possible additional causes
 When the ideas “dry up” move on to
CONSEQUENCES
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24. Team decision on “ACTION”
column
 Team may decide if any new action is
needed
 Can record any protective devices or
alarms which become active e.g. PSV’s
 Can refer decision outside the team
 Can refer serious consequences for
“consequence analysis”
 MUST NOT REDESIGN THE PLANT in
the Hazop study session!!
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25. After “no flow”
 Repeat exercise for “less flow”
(usually similar to “no flow”
 Repeat exercise for “more flow”
 Repeat exercise for “reverse flow”
 Repeat exercise for “composition”
(other than expected material
composition)
 UNTIL “FLOW” is completely studied
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26. After “flow”
 List causes for “more temperature”
 proceed to consequences for “more
temperature”
 repeat all steps as for flow
 when temperature is studied, go to pressure
 after pressure, consider other parameters,
e.g. agitation (use design intention as a
guide)
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27. When parameters are all done
for node 1
 Repeat whole process for node 2
 And all the other nodes defined in the
study scope
 List actions and responsibility for follow
up
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