1
Chemical Process SafetyRead 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
2
Introduction
Micro and mini scale reactors
Adiabatic calorimeters
Kinetics,modelling,simulation
Design reappraisal,relief systems, dump and
quench tanksDesktopstudies
Objective is to move from the earliest phases of research and development through tofull scale production in a confident, safe and cost effective manner
AutomatedCalorimetersand reactors
HAZOP,HAZAN,HAZID
Syntheticorganic
chemistryideas
Desktopscreening,databases,
calculations
Discovery research and
multipleexperiments
Automatedlaboratoryreactors.Process
optimization
Pilot plantstudies
Scale upand design
Industrial production.Debottlenecking.Optimization of
mature processes.Retrofits.
SAFE PROCESS DEVELOPMENT
C H E M I C A L P R O C E S S L I F E C Y C L E
D. Crowl, notes
3
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.)
4
Process Hazard Analysis – Many Options
1. What-If2. Checklist3. What-If/Checklist4. FMEA – Failure Mode & Effects
Analysis 5. FTA – Fault Tree Analysis6. Hazards Surveys7. HAZOP – Hazards & Operability
study
5
Process Hazard Analysis – Many Options
1. What-If2. Checklist3. What-If/Checklist4. FMEA – Failure Mode & Effects
Analysis 5. FTA – Fault Tree Analysis6. Hazards Surveys7. HAZOP – Hazards &
Operability study
6
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
7
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
8
What-If ExampleLNG Vaporizer
too low?
flow alarm.
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 become embrittled.
Monitor gas temperature; low temperature alarm.
Water flow is too low? Natural gas temperature may be too low; water may freeze in tubes.
Monitor flow rate; low
D. Crowl, notes
9
6. Hazards Surveys
Can be simple like inventory of hazardous chemicals
More rigorous procedures: - Dow Fire & Explosion Index- Dow Chemical Exposure Index
10
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
11
6. Hazards Surveys: Dow Fire & Explosion Index
Dow Fire & Explosion Index standard form; C&L Fig 11-3
Penalties Material factor
Penalty factors
Special ProcessHazards Factor
MF
F1
General ProcessHazards Factor
F2
D. Crowl, notes
12
6. Hazards Surveys: Dow Fire & Explosion Index
Dow F&EI - Determining the degree of hazard, Table 11-2
F&EI index value Degree of hazard
1 – 60 Light 61 – 96 Moderate 97 – 127 Intermediate 128 – 158 Heavy > 158 Severe
D. Crowl, notes
13
7. Hazard and Operability (HAZOP) StudyHAZOP 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
14
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
15
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
16
Hazards and Operability StudyInvestigative 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
17
Hazards and Operability Study
Guide Words and Their MeaningsSimple words or phrases used to qualify the intention and associated
parameters in order to discover deviations.Guide Words & Symbols
Application to Input Material Application to Desired Activity Further Applications
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.
Further intentions, e.g., sources or destination.
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.
18
19
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
20
HAZOP Example Worksheet
D. Crowl, notes
21W. Buck, SDSMT Seminar, 2012
22
Risk Matrix
B.K. Vaughen, PSM Overview, SACHE, 2012
Freq
uenc
y
Consequence
UnacceptableUndesirable Marginal
Risk = F x C
Acceptable
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
23
Risk Equation
B.K. Vaughen, PSM Overview, SACHE, 2012
Frequency x ConsequenceRisk =
Operational Discipline
Frequency x ConsequenceRisk =
Operational Discipline
FrequencyHow often the event may occur
- its likelihood is a “probability”
ConsequenceHow severe the event may be
- an undesired result of the event
24
Operational Discipline
B.K. Vaughen, PSM Overview, SACHE, 2012
The personal commitment of everyone to ensure theirpersonal and process safety by
1) performing their tasks correctly, and
2) recognizing, responding to and seeking help, as needed, to unanticipated situations or conditions.
OD
25
Operational Discipline
B.K. Vaughen, PSM Overview, SACHE, 2012
“Organizational” OD
Leadership FocusEmployee InvolvementPractice Consistent With
ProceduresExcellent Housekeeping
“Personal” OD
AwarenessKnowledgeCommitment
26
Risk Reduction
B.K. Vaughen, PSM Overview, SACHE, 2012
F x CRisk =
OD
F FrequencyEngineering and Administrative Controls
C ConsequenceInherently Safer ProcessesEmergency Response
Design Phase: the
best time to use ISP
27
Risk Reduction
B.K. Vaughen, PSM Overview, SACHE, 2012
OD Operational Discipline
Safety Culture Organizational OD Safety Behavior and Personal ODCommitment Characteristics
F x C Risk =
OD
28
Effect of Poor OD on Risk
B.K. Vaughen, PSM Overview, SACHE, 2012
Freq
uenc
yConsequence
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
UnacceptableUndesirable Marginal
Actual Risk
Perceived Risk
Risk = OD
F x C
Acceptable
29
Risk Matrix
W. Buck, SDSMT Seminar, 2012
30
PSM Systems
B.K. Vaughen, PSM Overview, SACHE, 2012
Designed to minimize process safety risk:
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)
Risk = OD
F x C
31
32B.K. Vaughen, PSM Overview, SACHE, 2012
33
Questions?
