Chemical Process Safety
Read Chapter 24: Turton’s Design Book
(Crowl & Louvar)
Chapter 11: Hazard Identification
Chapter 12: Risk Assessment
Guidelines for Hazard Evaluation Procedures,
3rd Ed., CCPS (John Wiley), 2008:
5.3; 7.0-7.5; ch 9
1
Introduction
SAFE PROCESS DEVELOPMENT
Synthetic
Desktop
organic
screening,
chemistry databases,
ideas
calculations
Discovery
research and
multiple
experiments
CHEMICAL
Desktop
studies
Micro and
mini scale
reactors
Automated
Calorimeters
and reactors
Automated
laboratory
reactors.
Process
optimization
Pilot plant
studies
PR O C E S S
Kinetics,
modelling,
simulation
LIFE
Scale up
and design
Industrial production.
Debottlenecking.
Optimization of
mature processes.
Retrofits.
CYCLE
Adiabatic HAZOP,
calorimeters HAZAN,
HAZID
Design reappraisal,
relief systems, dump and
quench tanks
Objective is to move from the earliest phases of research and development through to
full scale production in a confident, safe and cost effective manner
D. Crowl, notes
2
Figure 11-1 Hazards identification and risk assessment procedure. (Adapted from Guidelines for Hazards
Evaluation Procedures (New York: American Institute of Chemical Engineers, 1985), pp. 1–9.)
3
Process Hazard Analysis – Many Options
1.
2.
3.
4.
5.
6.
7.
What-If
Checklist
What-If/Checklist
FMEA – Failure Mode & Effects Analysis
FTA – Fault Tree Analysis
Hazards Surveys
HAZOP – Hazards & Operability study
4
Process Hazard Analysis – Many Options
1.
2.
3.
4.
5.
6.
7.
What-If
Checklist
What-If/Checklist
FMEA – Failure Mode & Effects Analysis
FTA – Fault Tree Analysis
Hazards Surveys
HAZOP – Hazards & Operability study
5
1. What-If Analysis
• Unstructured method for considering results
of unexpected events
• Uses questions beginning with "what-if“
• Not concerned with "how" failures occur
• Purpose is to identify problems that could
lead to accidents
• Results in a list of potential problem areas
and suggested mitigation methods
6
What-If Example
LNG Vaporizer
What if:
(a) Water flow is stopped?
(b) LNG flow is stopped?
(c) Natural gas temperature is too low?
(d) Water flow is too low?
(e) Water pressure is too high?
(f) A tube leaks into the shell?
(g) Inlet water temperature is too low?
D. Crowl, notes
7
What-If Example
LNG Vaporizer
What-If
Consequence/ Hazard
Recommendation
Water flow is stopped?
Water in shell freezes and
may rupture shell; natural
gas temperature too low.
Automatic interlock to
stop LNG flow if water
flow is stopped.
LNG flow is stopped?
Not Hazardous
None
Natural gas temperature is Downstream piping may Monitor gas temperature;
become embrittled.
too low?
low temperature alarm.
Water flow is too low?
Natural gas temperature
Monitor flow rate; low
may be too low; water may
flow alarm.
freeze in tubes.
D. Crowl, notes
8
6. Hazards Surveys
Can be simple like inventory of hazardous
chemicals
More rigorous procedures:
- Dow Fire & Explosion Index
- Dow Chemical Exposure Index
9
6. Hazards Surveys: Dow Fire &
Explosion Index
• Complex and detailed procedure carried out by an individual
• Rates relative hazards of storing, handling, processing flammable
and explosive materials
• Systematic approach independent of judgmental factors
• Break the process down into units or sections, e.g. the reactor,
storage tank or a pump
• Use experience to select the units or sections that have the highest
likelihood of a significant hazard (too many to cover all); may use
checklist approach to choose
• Define the material factor (what chemicals are being used); in general, higher
the value the more flammable / explosive
• Adjust this with various penalties based on conditions such as storage above
normal boiling point, exothermic reaction, etc
• Then take credits for safety procedures and safety systems
• Finally arrive at a number that rates the hazard; compare with table /
experience
10
6. Hazards Surveys: Dow Fire &
Explosion Index
Dow Fire & Explosion Index standard form; C&L Fig 11-3
Penalties
MF
F1
Material factor
General Process
Hazards Factor
Penalty factors
F2
Special Process
Hazards Factor
D. Crowl, notes
11
6. Hazards Surveys: Dow Fire &
Explosion Index
Dow F&EI - Determining the degree of hazard,
Table 11-2
F&EI index value
1 – 60
61 – 96
97 – 127
128 – 158
> 158
Degree of hazard
Light
Moderate
Intermediate
Heavy
Severe
D. Crowl, notes
12
7. Hazard and Operability (HAZOP) Study
HAZOP is a Structured "What If" Type of Study
• Objectives
- Identify Hazards
- Identify Operability Problems
• HAZOPs Use Team Approach
• Multi-Disciplinary
• Guide word based
• Structured and Systematic
13
Hazards and Operability Study
Investigative Process
• Select study nodes
–
–
–
–
–
Major process vessels
Major process lines connected to process vessels
Pumps and compressors
Heat exchangers
Major support systems
• Pick a process parameter
- Flow, level, temperature, pressure, volume, pH,
concentration, agitation, etc
14
Hazards and Operability Study
Investigative Process (Cont’d)
• Apply guide words to process parameters
– Determine deviation from design
– Determine consequences of deviations
– Evaluate consequences
• Typical causes of deviations
– Hardware failures
– Human error
– Outside forces
– Unanticipated process state
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Hazards and Operability Study
Investigative Process (Cont’d)
• Suggested actions
– Change in design
– Change in equipment
– Alter operating procedures
– Improve maintenance
– Investigate further
• HAZOP Follow-up
– Assign responsibility for carrying out recommendations with
agreed timetable
– Refer recommendations to appropriate managers
– Evaluate and review
• Record keeping
– Copy of all data used
– Copy of all working papers
– HAZOP worksheets
16
Hazards and Operability Study
Guide Words and Their Meanings
Simple words or phrases used to qualify the intention and associated
Guide Words
& Symbols
Application
to Input in
Material
parameters
order
to Desired
Activity
toApplication
discover
deviations.
Design Intent
The intended material including
quantity, chemical composition and
input physical condition.
The intended activity. May be
one major and one or more
dependent minor activities.
NO
The intended material is not present
but no substitute material present.
The intended activity does not
occur but no direct substitute
activity takes place.
MORE
A greater quantity of material than
intended, e.g., "Higher Pressure".
A greater activity than intended,
e.g., flow rate, pressure rise, heat
input, chemical reaction, duration
of activity etc.
LESS
A lesser quantity of material than
intended, e.g., weight or volume.
Lower physical condition, e.g.,
"Lower Pressure".
A lesser activity than intended,
e.g., flow rate, pressure rise, heat
input, chemical reaction, duration
of activity etc.
Further Applications
Further intentions,
e.g., sources or
destination.
17
18
HAZOP Example
• Chemistry is such that concentrations of B must not
exceed that of A
• First Study Node - pipeline from suction side of pump
that delivers A to the reaction vessel
• First Guide Word - No to design intent of transfer A
• Causes of Deviation
–
–
–
–
Supply tank is empty
Pumps fail to run
Pipeline is fractured
Isolation valve is closed
• Consequences
– Excess of B over A could lead to an explosion
• Recommendation
– Install interlock device on pump B into reactor
19
HAZOP Example Worksheet
D. Crowl, notes
20
W. Buck, SDSMT Seminar, 2012
21
Risk Matrix
Frequency
Consequence
Negligible
Marginal
Serious
Critical
Catastrophic
Frequent
D
C
B
A
A
Probable
D
D
B
B
A
Occasional
D
D
C
B
B
Remote
D
D
D
C
B
Improbable
D
D
D
D
C
Unacceptable
Undesirable
Marginal
Risk =
F x C
Acceptable
B.K. Vaughen, PSM Overview, SACHE, 2012
22
Risk Equation
Risk =
Frequency x Consequence
Operational Discipline
Frequency
How often the event may occur
- its likelihood is a “probability”
Consequence
How severe the event may be
- an undesired result of the event
B.K. Vaughen, PSM Overview, SACHE, 2012
23
Operational Discipline
OD
The personal commitment of everyone to ensure their
personal and process safety by
1)
performing their tasks correctly, and
2) recognizing, responding to and seeking help,
as needed, to unanticipated situations or
conditions.
B.K. Vaughen, PSM Overview, SACHE, 2012
24
Operational Discipline
“Organizational” OD
Leadership Focus
Employee Involvement
Practice Consistent With Procedures
Excellent Housekeeping
“Personal” OD
Awareness
Knowledge
Commitment
B.K. Vaughen, PSM Overview, SACHE, 2012
25
Risk Reduction
Risk =
F
F x C
OD
Frequency
Engineering and Administrative Controls
C
Consequence
Inherently Safer Processes
Emergency Response
Design Phase:
the best time
to use ISP
B.K. Vaughen, PSM Overview, SACHE, 2012
26
Risk Reduction
Risk =
F x C
OD
OD Operational Discipline
Safety Culture
Organizational OD
Safety Behavior
and Personal OD
Commitment
Characteristics
B.K. Vaughen, PSM Overview, SACHE, 2012
27
Effect of Poor OD on Risk
Frequency
Consequence
Negligible
Marginal
Serious
Critical
Catastrophic
Frequent
D
C
B
A
A
Probable
D
D
B
Occasional
D
D
C
B
B
Remote
D
D
D
C
B
Improbable
D
D
D
D
C
Unacceptable
Undesirable
Marginal
Acceptable
Actual
Risk
B
A
Perceived Risk
Risk =
F x C
OD
B.K. Vaughen, PSM Overview, SACHE, 2012
28
Risk Matrix
W. Buck, SDSMT Seminar, 2012
29
PSM Systems
Designed to minimize process safety risk:
Risk =
F x C
OD
There is always some level of risk
Our PSM-related risk reduction efforts are compared and
evaluated against other potential business risks (i.e.,
environmental, operational, maintenance, quality and financial)
B.K. Vaughen, PSM Overview, SACHE, 2012
30
31
B.K. Vaughen, PSM Overview, SACHE, 2012
32
Questions?
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