Hazard: Any operation that could possibly cause
a catastrophic release of toxic, flammable or
explosive chemicals or any action that could
result in injury to personnel.
Operability: Any operation inside the design
envelope that would cause a shutdown that
could possibly lead to a violation of
environmental, health or safety regulations or
negatively impact profitability.
What is HAZOP?
Hazard and operability (HAZOP) methodology is a
Process Hazard Analysis (PHA) technique used for
studying the hazards of a system, and its operability
problems, by exploring the effects of any deviations from
design conditions.
HAZOP is one of the best and most rigorous techniques
for identification of hazard and operability problems in a
chemical plant.
Who carries out hazop?
HAZOP is carried out by a team. The usual team is as
follows:
Hazard study leader
Commissioning manager
Plant manager
Project engineer
Process engineer
Control/Electrical engineer
Research Chemist (if new chemistry is involved)
When to perform HAZOP?
The HAZOP study should preferably be carried out as early
in the design phase as possible. On the other hand; to carry
out a HAZOP we need a rather complete design. As a
compromise, the HAZOP is usually carried out as a final
check when the detailed design has been completed.
A HAZOP study may also be conducted on an existing facility
to identify modifications that should be implemented to
reduce risk and operability problems.
PREREQUISITES FOR HAZOP
As a basis for the HAZOP study the following information
should be available:
Process flow diagrams (PFDs)
Piping and instrumentation diagrams (P&IDs)
Plant Layout diagrams
Material safety data sheets (MSDS)
Provisional operating instructions
Heat and material balances
Equipment data sheets
Start-up and emergency shut-down procedures
Phases of hazop
Pre-meeting phase
• Collection of data about facility viz. PFDs, P&IDs,
Plant layout, Chemical hazard data
• Identification of team members
Meeting phase
• Division of plant in sections or nodes
• Deviations, causes, consequences & protective
systems are identified
Post-meeting phase
• Discussions are recorded
• Actions are followed-up & report is issued
HAZOP procedure
1. Divide the system into sections (i.e., reactor, storage)
2. Choose a study node (vessel, line, operating instruction).
3. Describe the design intent of the study node.
4. Choose a process parameter.
5. Apply a guide word to the process parameter to suggest
possible deviations.
6. Determine possible causes & find protective systems.
7. Evaluate the consequences of the deviation (if any).
8. Recommend action (what? by whom? by when?)
9. Record all information.
10. Repeat procedure until all guide words, all applicable process
parameters & all study nodes have been considered.
Guide Words Used for the HAZOP
GUIDE
MEANING COMMENTS
WORDS
The complete
No part of the design intention is achieved,
NO, NOT, NONE negation , ex. No
but of the intention nothing else happens.
flow
MORE, Quantitative Applies to quantities such as flow rate and
HIGHER, increase, ex. High temperature and to activities such as heating
GREATER temp. and reaction.
Quantitative Applies to quantities such as flow rate and
LESS, LOWER decrease, ex. Low temperature and to activities such as eating
temp. and reaction.
All the design and operating intentions are
Qualitative
AS WELL AS achieved along with some additional activity,
increase
such as contamination of process streams.
Qualitative Only some of the design intentions are
PART OF
decrease achieved, some are not.
GUIDE
MEANING COMMENTS
WORDS
Most applicable to activities such as flow or
The logical chemical reaction. Also applicable to
REVERSE
opposite of substances, for example, poison instead of
antidote.
No part of the original intention is achieved –
Complete
OTHER THAN the original intention is replaced by
substitution
something else.
Too early or in the
SOONER THAN Applies to process steps or actions.
wrong order
Too late or in the
LATER THAN Applies to process steps or actions.
wrong order
In additional Applies to process locations, or locations in
WHERE ELSE
locations operating procedures.
ADVANTAGES DISADVANTAGES
1. Structured and systematic 1. No means to assess hazards
approach involving interactions between
2. Helpful when confronting different parts of a system or
hazards that are difficult to process.
quantify: 2. Highly time consuming
Hazards rooted in human 3. Team members often divert
performance and into endless discussions of
behaviours details.
Hazards that are difficult to 4. No means to assess
detect, analyse, isolate, effectiveness of existing or
count, predict, etc. proposed safeguards.
3. Built-in brainstorming 5. The success of a HAZOP study
methodology depends greatly on the ability &
4. Multidisciplinary study experience of the study leader
5. Comprehensive methodology and the knowledge, experience
6. More simple and intuitive and interaction between team
members.
Hazop case study: example
Materials A and B are continuously transferred by pump
from their respective supply tanks to combine and form a
product C in the reactor.
Suppose that A always has to be in excess of B in the reactor
to avoid an explosion hazard. The part of the system selected
for examination is the line from the supply tank holding A to
the reactor, including pump A. The intent for this part is to
continuously transfer material A from the tank to the reactor
at a rate greater than the transfer rate of material B.
HAZOP Worksheet
GUIDE ELEMENT DEVIATION POSSIBLE CONSEQUENCES ACTIONS
WORD CAUSES REQUIRED
NO Material A No flow Supply Tank No flow of A into Installation of a
A reactor low-level alarm on
is empty tank A & low-level
Explosion trip to stop pump
B
MORE Material A More flow Filling of Tank will overflow Installation of
tank into bounded area high-level alarm
when
insufficient
capacity
exists
LESS Material A Less flow Low level in Inadequate net Low-level alarm on
tank positive suction head tank A
Possible vortexing &
leading to an
explosion
Inadequate flow
TYPICAL HAZOP WORKSHEET
