Industrial Safety & Maintenance
Tsegay G.
Department of Chemical Engineering
tsegay.gebrekidan@mu.edu.et
April 28, 2017
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Outline
1 Hazard and Operability Studies (HAZOP)
What is a HAZOP study?
Origin of HAZOP study
Objectives of a HAZOP study
Advantages and disadvantages of HAZOP
2 HAZARD ANALYSIS
Pitfalls of HAZAN
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What is a HAZOP study?
Systematic technique to IDENTIFY potential HAZard and OPerating
problems
Involves a multi-disciplinary team methodically "brainstorming" the
plant design
A qualitative technique based on "guide-words" to help provoke thoughts
about the way deviations from the intended operating conditions can
lead to hazardous situations or operability problems
A HAZOP study is an examination procedure.
Its purpose is to identify all possible deviation from the way in which
a design is expected to work and to identify all the hazards associated
with these deviations.
When deviation arise that results in hazards, action are generated that
require design engineers to review and suggest solutions to remove the
hazard or to reduce its risk to an acceptable level.
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Origin of HAZOP study
HAZOP were initially 0 invented 0 by ICI1 in the United Kingdom, but the
technique only started to be more widely used within the chemical process
industry after the Flixborough disaster in 1974.
This chemical plant explosion killed twenty eight people and injured scores
of others, many of those being members of the public living nearby.
Through the general exchange of ideas and personnel, the system was then
adopted by the petroleum industry, which has a similar potential for major
disasters.
This was then followed by the food and water industries, where the hazard
potential is as great, but of a different nature, the concerns being more to
do with contamination rather than explosions or chemical releases.
1
Imperial Chemical Industries
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Objectives of a HAZOP study
Safety Issues:
To identify scenarios that would lead to the release of hazardous or
flammable material into the atmosphere, thus exposing workers to in-
jury
To check the safety of the design
To improve the safety of an existing and or modified facility
Operability Issues:
To decide whether and where to build
To check operating and safety procedures
To verify that safety instrumentation is working optimally
To facilitate smooth, safe prompt start-up
To minimize extensive last minute modifications
To ensure trouble-free long-term operation
"Prevention is better than control"
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Philosophy - Hazard vs Operability
HAZOPs concentrate on identifying both hazards as well as operability
problems. While the HAZOP study is designed to identify hazards through
a systematic approach, more than 80% of study recommendations are
operability problems and are not, of themselves, hazards.
Although hazard identification is the main focus, operability prob-
lems should be identified to the extent that they have the potential to lead
to process hazards, result in an environmental violation or have a negative
impact on profitability.
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Philosophy - Hazard vs Operability
HAZOPs concentrate on identifying both hazards as well as operability
problems. While the HAZOP study is designed to identify hazards through
a systematic approach, more than 80% of study recommendations are
operability problems and are not, of themselves, hazards.
Although hazard identification is the main focus, operability prob-
lems should be identified to the extent that they have the potential to lead
to process hazards, result in an environmental violation or have a negative
impact on profitability.
Definition of Hazard & Operability
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.
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Benefits
The circumstances when HAZOPs are likely to produce benefits are:
during the design or installation of any new plant or process, or major
modification to an existing one;
when there are unique hazards such as environmental hazards and qual-
ity or cost issues associated with the operation;
following a major incident involving fire, explosion, toxic release etc;
and
to justify why a particular code of practice, guidance note or industry
code is not to be followed.
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When should a HAZOP be held?
During various stages of plant design
At the beginning of the project as a safety and environmental specifi-
cation
Towards the end of process definition, when the Process Flow sheets
are available as a Safety and Environmental Review
When P&IDs2 are at Approved for Design stage (Final design HA-
ZOP)
During construction site inspections ensure that recommendations arising
from the HAZOP or other safety and environmental reviews are being
implemented.
A pre-commissioning study reviews plant procedures and perform a
conventional safety audit Once operational, an audit of plant and
procedures at regular interval ensures ongoing safety awareness
2
process and instrumentation diagram
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HAZOP study of existing plant
Can be done at any time
Mainly used to improve operating procedures or when modifying plant
Sometimes used to identify possible improvements in plants where ac-
cident or incident rate is abnormally high
Can be used in conjunction with plant safety audits
Needs exceptional care to fully define the scope and aims of the study
Despite detailed operation knowledge, much of the original design in-
tent is often unknown
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Simple Example of a HAZOP Study
Diammonium Phosphate (DAP) Production: Phosphoric acid and
ammonia are mixed, and a non-hazardous product, diammonium
phosphate (DAP), results if the reaction of ammonia is complete. If too
little phosphoric acid is added, the reaction is incomplete, and ammonia is
produced. Too little ammonia available to the reactor results in a safe but
undesirable product.
Both chemicals will be used in large quantities and in concentrated form.
Due to the highly corrosive nature of both chemicals, the project team was
assigned to investigate the hazards posed to staff from the reaction
resulting from study line 1 (phosphoric acid delivery line).
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Cont
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HAZOP Study Report on line 1 of DAP
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Preliminary HAZOP Example
Refer to reactor system shown in the fig-
ure.
The reaction is exothermic. A cooling
system is provided to remove the excess
energy of reaction. In the event of cool-
ing function is lost, the temperature of
reactor would increase. This would lead
to an increase in reaction rate leading to
additional energy release.
The result could be a runaway reac-
tion with pressures exceeding the burst-
ing pressure of the reactor. The temper-
ature within the reactor is measured and
is used to control the cooling water flow
rate by a valve.
Perform HAZOP Study
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Preliminary HAZOP on Reactor - Example
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Preliminary HAZOP on Reactor - Answer
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HAZOP: The Critical Success Factor
The HAZOP process is based on the principle that a team approach to
hazard analysis will identify more problems than when individuals
working separately combine results.
The HAZOP team is made up of individuals with varying backgrounds and
expertise.
The expertise is brought together during HAZOP sessions and through a
collective brainstorming effort that stimulates creativity and new ideas, a
thorough review of the process under consideration is made.
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HAZOP Terminology-1
HAZOP Terminology-2
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HAZOP Terminology-3
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HAZOP Terminology-4
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HAZOP Methodology - Content
HAZOP Study Planning and Preparations
HAZOP Study Team - Role and Responsibilities
Meeting Arrangements
Reporting and Follow-up
HAZOP Guidewords;
Possible Causes & Consequences
Plant; Safeguards & Action Required
Working Session 2: Chemical Plant
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HAZOP Planning and Execution
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HAZOP study team
Independent leader (e.g., not from plant studied)
Preferred but complete independence not essential
Project engineer
Provide engineering input
Operations representative
Plant operation
Discipline engineers
Process
Instrument/ electrical
Mechanical/ maintenance
HAZOP minute recorder
One of the above
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Responsibility of HAZOP Team Members
HAZOP leader - The leader should be independent (i.e. has no
responsibility for the process and/or the performance of operations)
Plan sessions and timetable
Control discussion
Limit discussion
Encourage team to draw conclusion
Ensure secretary has time for taking note
Keep team in focus
Encourage imagination of team members
Motivate members
Discourage recriminations
Judge importance issues
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Checklist for HAZOP Leader
Always prepare study program in advance.
Agree on the format or form to be used.
Prepare follow up procedures.
Brief members about HAZOP during first meeting.
Stop the team trying to redesign the process. HAZOP is a team exer-
cise.
Do not let anybody (including the leader himself to dominate).
If conflict arises, handle with care.
Avoid long discussions by recording areas which need to be resolved
outside meeting.
Leader must be strong, yet diplomatic. Speak clearly. Make you point.
Better have experience working as team member previously.
Do not skip anything...some time small things may cause big accident.
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Responsibility of HAZOP Team Members
Process Engineer
HAZOP Secretary Provide a simple description
Take adequate notes Provide design intention for each
Record documentations process unit
Inform leader if more time re- Provide information on process
quired in taking notes conditions and design conditions
If unclear, check wording before
writing Plant Engineer or Manager
Produce interim lists of recom- Provide information on compatibil-
mendations ity with any existing adjacent plant
Produce draft report of study Provide details of site utilities and
services
Check progress of chase action
Provide (for study on existing plant)
Produce final report
any update on maintenance access
and modifications
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Cont
Shift Operating Engineer or Supervisor
Provide guidance on control instrumentation integrity from an operat-
ing experience view point
Provide (for study on existing plant) information on plant stability at
the specified control parameters
Provide information on experienced operability deviations of hazard
potential
Mechanical Design Engineer Instrument Engineer
Provide specification details Provide details of control philosophy
Provide vendor package details Provide interlock and alarm details
Provide equipment and piping lay- Provide info on shutdown, safety
out information features
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Chemist
Provide details of process chemistry
Provide details of process hazards (polymerisations, byproducts, corro-
sion etc)
Project Engineer
Provide details of cost and time estimation and also budget constraints.
Ensure rapid approval if required
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Required information
P & IDs
Process flow diagrams
Heat and Material Balances
Layouts
Logic Diagrams
Equipment Data Sheets
Material Hazard Data Sheets
Hazardous area Layouts
Modes of operation to consider
The following modes of plant operation should be considered for each node:
Normal operation
Emergency shutdown
Reduced throughput operation
Commissioning
Routine start-up
Special operating modes
Routine shut-down
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HAZOP meeting
Proposed agenda:
Introduction & presentation of participation
Overall presentation of the system/operation to be analyzed
Description of the HAZOP approach
Presentation of the first node or logical part of the operation
Analyze the first node/part using the guide-words and parameters
Continue presentation and analysis (steps 4 & 5)
Coarse summary of findings
Focus should be on potential hazards as well as potential operational
problems.
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Sequence for conducting a HAZOP Study
Flow diagram for the HAZOP analysis - The parameter-first approach
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How to be a good HAZOP participant
Be active: Everyone contribution is important
Be to the point. Avoid endless discussion of details
Be critical in a positive way - not negative, but constructive
Be responsible. He who knows should let the other know
HAZOP recording
The findings are recorded during the meeting(s) using a HAZOP work-
sheet, either by filling in paper copies, or by using a computer connected
to a projector (recommended).
The HAZOP worksheet may be different depending on the scope of the
study - generally the following entries (columns) are included
Ref. no Consequences
Guidewords Safeguards
Deviations Actions required (or, recommendations)
Possible causes Actions allocated to (follow up responsibility)
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Process HAZOP worksheet
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Guidewords/Keywords
The basic HAZOP guide-words are:
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Additional guidewords
Process parameter
Process parameter may generally be classified into the following groups:
Physical parameters related to input medium properties
Physical parameters related to input medium conditions
Physical parameters related to system dynamics
Non-physical parameters related to batch type process
Parameters related to system operations
These parameters are not necessarily used in conjunction with guide-words
Instrumentation Maintenance
Relief Safety/contingency
Startup/shutdown Sampling
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Examples of process parameter
Flow Composition pH
Pressure Addition Sequence
Temperature Separation Signal
Mixing Time Start/stop
Stirring Phase Operate
Transfer Speed Maintain
Level Particle size Service
Viscosity Measure Communication
Reaction Control Absorb
Isolate Corrode Drain
Vent Erode Purge
Inspect Separate (settle, filter, centrifuge Maintain
Start-up Reduce (grind, crush, etc) Shut-down
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Guidewords + Parameter
Causes of Deviations - 3 Types
Human error: which are acts of omission or commission by an operator, designer, construc-
tor or other person creating a hazard that could possibly result in a release of hazardous or
flammable material.
Equipment failure: in which a mechanical, structural or operating failure results in the
release of hazardous or flammable material.
External Events: in which items outside the unit being reviewed affect the operation of the
unit to the extent that the release of hazardous or flammable material is possible. External
events include upsets on adjacent units affecting the safe operation of the unit (or node)
being studied, loss of utilities, and exposure from weather and seismic activity.
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Consequences & Safeguards
All consequences of any credible causes of a release that are identified
by the group must be determined in order to:
help to determine a risk ranking in HAZOPs where multiple hazards are
uncovered by the group so that priority can be established in addressing
the hazard.
help make the determination as to whether a particular deviation results
in an operability problem or hazard.
If the team concludes from the consequences that a particular cause of
a deviation results in an operability problem only, then the discussion
should end and the team should move on to the next cause, deviation
or node.
If the team determines that the cause will result in the release of haz-
ardous or flammable material, then safeguards should be identified.
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Cont
Safeguards should be included whenever the team determines that
a combination of cause and consequence presents a credible process
hazard.
What constitutes a safeguard can be summarized based on the following
general criteria:
Those systems, engineered designs and written procedures that are de-
signed to prevent a catastrophic release of hazardous or flammable ma-
terial.
Those systems that are designed to detect and give early warning follow-
ing the initiating cause of a release of hazardous or flammable material.
Those systems or written procedures that mitigate the consequences of
a release of hazardous or flammable material.
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HAZOP Study Reporting
The report must be placed with the HSE(Health & Safety Executive)
Assessment and Control of Work and will largely consist of the record
sheet(s), however, the following information should be included:
An outline of the terms of reference and scope of the study.
A very brief description of the process which was studied
The procedures and protocol employed.
General comments.
Results. This usually states the number of recommended actions.
Appendices:
Master copies of the drawings studied.
Copies of technical data used.
Cause and Effect charts (i.e. matrices showing the executive action of
safety related instruments and trips).
Any calculations produced.
Relevant correspondence between departments, from contractor to ven-
dor, or client to contractor.
HAZOP study record sheets
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Case Study: Shell & Tube Heat Exchanger
Using relevant guide works, perform HAZOP study on shell & tube heat
exchanger
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HAZOP on Heat Exchanger: Answer 1
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HAZOP on Heat Exchanger: Answer 2
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Advantages of HAZOP
Systematic and comprehensive technique. A detailed plan for perform-
ing the technique is available which systematically applies guide words
and parameters to all the pipes and vessels in the process.
Examines the consequences of the failure. Thought should be given
by the assessment team to the consequences of the deviations identi-
fied. This aids in the production of recommendations for methods to
minimize or mitigate the hazard.
Disadvantages of HAZOP
Time consuming and expensive. Most plants contain a large number of
pipes and vessels each of which need to be examined by the application
of the various guidewords and parameters.
Requires detailed design drawing to perform the full study. To fully
perform the study the process has to be designed to such a level that
all the pipes and vessels are detailed with their operating conditions,
and control instrumentation.
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Outline
1 Hazard and Operability Studies (HAZOP)
What is a HAZOP study?
Origin of HAZOP study
Objectives of a HAZOP study
Advantages and disadvantages of HAZOP
2 HAZARD ANALYSIS
Pitfalls of HAZAN
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HAZARD ANALYSIS
Hazard analysis is the process of recognizing hazards that may arise from a
system or its environment, documenting their unwanted consequences and
analyzing their potential causes. The hazard analysis process commences
with a Preliminary Hazard Analysis (PHA) in the early stages of a project
and continues throughout the system products life cycle.
International standards define hazard analysis as follows:
The process of describing in detail the hazards and accidents
associated with a system, and defining accident sequences
Identify hazards through a systematic hazard analysis process encom-
passing detailed analysis of system hardware and software, the envi-
ronment (in which the system will exist), and the intended use or
application. Consider and use historical hazard and mishap data, in-
cluding lessons learned from other systems. Identification of hazards is
a responsibility of all program members. During hazard identification,
consider hazards that could occur over the system life cycle.
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Cont
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Hazard Analysis Objectives
The objectives of a hazard analysis are to:
Identify hazards. To determine the hazards and hazardous events of the equipment
under control and the control system (in all modes of operation), for all reasonably
foreseeable circumstances including fault conditions and misuse
Identify causes. To analyse the event sequences leading to the hazardous events
identified
Determine risks. To analyse the risks associated with the hazardous events.
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Hazard Analysis Objectives
The objectives of a hazard analysis are to:
Identify hazards. To determine the hazards and hazardous events of the equipment
under control and the control system (in all modes of operation), for all reasonably
foreseeable circumstances including fault conditions and misuse
Identify causes. To analyse the event sequences leading to the hazardous events
identified
Determine risks. To analyse the risks associated with the hazardous events.
Hazard Analysis Context
A hazard analysis might be performed in one of the following contexts:
Development. Examining a system in development to identify and assess potential
hazards and eliminate or control them
Operations and management. Examining an existing system to identify and assess
hazards in order to improve the level of safety; formulating safety management
policy; training personnel; increasing motivation for efficiency and safety of operation
Certification. Examining a planned or existing system to demonstrate its level of
safety and to facilitate acceptance by a customer, a government safety authority or
the public.
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When is a Hazard Analysis Performed?
The synthesis of a safe design does not guarantee a safe working system.
Hazard analysis is therefore an iterative process that continues for the
life of a system.
The objective of progressive hazard analysis is therefore to identify and
mitigate hazards that can be introduced in the requirements, design,
development, testing, installation, commissioning, operation and
maintenance and disposal of a system.
Events that should trigger a hazard analysis are:
Concept definition
Requirements review
Design review
Design change review
Installation and commissioning plan review
Operating and support plan review
Decommissioning plan review.
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Preliminary Hazard Analysis Objectives
A Preliminary Hazard Analysis (PHA) is conducted in the early stages of a
project. Its objectives are to:
Identify known hazards
Determine the cause(s) of the hazards
Determine the effects of the hazards
Determine the probability that an accident will be caused by a hazard
Establish initial design and procedural requirements to eliminate or
control hazards.
Preliminary Hazard Analysis Non-objectives
A PHA does NOT:
Describe the details of how the hazards will be avoided or mitigated
Generate detailed safety requirements
Create strategies for implementing safety requirements.
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Hazard Analysis Inputs
The following items may be input into the hazard analysis process:
System Description - a description of the system under development
and the context under which it is to be used (e.g. functional model)
Safety Incident Logs - incorporating experience gained from previous
operation of the same or similar systems
Preliminary Hazard List - this is a list of hazards determined in a pre-
vious analysis
Hazard Checklist - this may exist for various industries that have codi-
fied the causes of safety incidents with the same or similar equipment
Customer Requirements - any pre-existing requirements specifications
and concept documents
Regulatory Requirements - constraints imposed by regulatory agencies
People at risk - A list of people who may be put at risk by the system
(e.g. general public, environment and workers).
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Hazard Analysis Process
A hazard analysis is performed with the following steps:
1 Define objectives
2 Define scope
3 Define and describe the system in terms of system boundaries and
information to be used in the analysis
4 Identify the hazards
5 Collect data. For example historical data, related standards and code
of practice, scientific tests and experimental results.
6 Perform qualitative ranking of hazards based on their potential effects
and their likelihood
7 Identify causal factors
8 Identify preventive or corrective measures and general design criteria
and controls.
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Hazard Analysis Techniques
Hazards may be realized or unrealized.
A realized hazard has happened in the past and can therefore be
identified from experience.
An unrealized hazard is a potential for a hazardous situation that has not
happened in the past but can be recognized by analyzing the
characteristics of an environment or failure modes of equipment items.
Hazard analysis techniques include:
Function Failure Analysis
Event Tree Analysis
Failure Modes and Effects Analysis
Fault Tree Analysis
Cause-consequence Diagrams
Hazard and Operability Studies.
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Hazard Analysis Output
The outcomes of the hazard analysis are documented in the Hazard Analysis
Report and a Hazard Log. Typical outputs are:
A summary of the process and techniques used
A consolidated hazard list
Hazard causes
The assumptions made during the analysis activity
Risk assessment.
How Hazard Analysis Outputs are Used
The outputs of a hazard analysis are used to:
Develop systems safety requirements
Prepare design descriptions
Prepare test plans
Prepare operational instructions
Prepare management plans.
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Pitfalls of HAZAN
1 Data may be inapplicable
2 Data apply to the past
3 Data affected by maintenance or operating policy
4 The impossibility low fractional dead time redundancy and diversity
5 More about common mode failures
6 Non-random failure
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THANK YOU
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