DESIGN FOR SAFETY
HAZARDS ANALYSIS (HAZAN)
HAZAN STUDY


STARTS WITH THE SAME INFORMATION
AND TEAM AS THE HAZOPS STUDY
EXAMINES THE RESULT OF FAILURE OF
EQUIPMENT OR CONTROLS




INDIVIDUAL - SINGLE JEOPARDY
MULTIPLE - DOUBLE JEOPARDY
CAN BE ORGANIZED WITH FAULT TREE
ANALYSIS (FTA)
ALSO CALLED QUANTITATIVE RISK
ASSESSMENT (QRA)
HOW MUCH SHOULD BE SPENT FOR
SAFETY?
 tx.technion.ac.il/~dlewin/054402/LECTURE_13.pdf -
WHAT KIND OF RISKS ARE
PRESENT?
 tx.technion.ac.il/~dlewin/054402/LECTURE_13.pdf
GENERIC FAULT TREE ANALYSIS FOR HAZAN WITH DOUBLE
JEOPARDY
PRIMARY
EVENT
CONTROL
RESPONSE
SECONDARY
EVENT
CONTROL
RESPONSE
CONTROL
SUCCEEDS
EVENT
OCCURS
CONTROL
FAILS
CONTROL
SUCCEEDS
CONTROL
SUCCEEDS
EVENT DOES
NOT OCCUR
CONTROL
FAILS
EVENT
OCCUR
S
CONTROL
SUCCEEDS
EVENT
OCCURS
CONTROL
FAILS
CONTROL
FAILS
CONTROL
SUCCEEDS
EVENT DOES
NOT OCCUR
CONTROL
FAILS
FAULT TREE SYMBOLS

FAULT TREES USE PROGRAMMING SYMBOLS FOR
EACH TYPE OF JUNCTION
EXAMPLE SHOWING
FAULT TREE FOR
LOSS OF COOLING
WATER SUPPLY DUE
TO FAILURE OF
ELECTRICAL POWER
SUPPLIES.
http://www.s-2s.org/modules.php?na
me=s2s_wp4&idpart=2
&op=v&idp=1476
SEE NEXT PAGE FOR
MORE DETAIL.
EXAMPLE SHOWING
FAULT TREE FOR
LOSS OF COOLING
WATER SUPPLY DUE
TO FAILURE OF
ELECTRICAL POWER
SUPPLIES.
http://www.s-2s.org/modules.php?nam
e=s2s_wp4&idpart=2&o
p=v&idp=1476
http://www.s-2s.org/modules.php?nam
e=s2s_wp4&idpart=2&op
=v&idp=1476
EXAMPLE SHOWING P&ID
DIAGRAM FOR COOLING
WATERSUPPLY
http://www.s-2s.org/modules.php?name=s
2s_wp4&idpart=2&op=v&idp
=1476
PROBABILITY ANALYSIS FROM
HAZAN

PROBABILITIES ARE MULTIPLIED FOR EACH
LEVEL OF JEOPARDY
–
–
FOR 2 EVENTS IN SERIES, EACH WITH A 0.5
PROBABILITY, PROBABILITY OF BOTH
OCCURRING IS 0.25
SEVERITY MUST ALSO
BE CONSIDERED AS A
FACTOR IN CONSIDERING
DOUBLE JEOPARDY
SITUATIONS
www.cobalt.chem.ucalgary.ca
PRIMARY SOURCES OF
CATASTROPHIC EVENTS









HUMAN ERROR
MISLABELING
TRIP FAILURES
STATIC ELECTRICITY
WRONG MATERIAL OF CONSTRUCTION
FAULTY OPERATING PROCEDURES
UNEXPECTED REVERSE FLOW
COMPUTER CONTROL PROBLEMS
IGNORANCE
http://www.processforusability.c
o.uk/safety/images/larsen.jpg
INHERENT SAFETY
 OBJECTIVES
 ELIMINATE HAZARDS
– Eliminate the hazardous material
– Substitute a non-hazardous material
– Discontinue the operation
http://www.acusafe.com/Hazard_Analysis/Hazard
_Analysis-talks.htm#Talks%20and%20Papers
INHERENT SAFETY
 REDUCE CONSEQUENCES
– Reduce the quantity of the hazardous material
– Provide a curbed area with a drain to contain and
evacuate a spill
– and produce a smaller pool area of a spill
– Separate the operation by adequate spacing to reduce
exposure to adjacent operations and personnel
http://www.acusafe.com/Hazard_Analysis/Hazard_Analysi
s-talks.htm#Talks%20and%20Papers
http://altermondialisme.free.fr/monde/Etats_unis.jpg
INHERENT SAFETY
 REDUCE LIKELIHOOD OF INITIATION
– Reduce the potential for human error through
simplicity of design
– Control ignition sources
– Provide redundant alarms
http://www.acusafe.com/Hazard_Analysis/Hazard
_Analysis-talks.htm#Talks%20and%20Papers
INHERENTLY SAFE DESIGN
 GUIDELINES TO REVIEW PROCESS DESIGN
FOR SAFETY
–
–
–
–
–
INTENSIFICATION
SUBSTITUTION
ATTENUATION
LIMITATION OF EFFECTS
SIMPLIFICATION
 KLETZ, TREVOR, PLANT DESIGN
FOR SAFETY, HEMISPHERE
PUBLISHING 1991
INTENSIFICATION POLICIES
 REDUCE QUANTITIES OF MATERIALS IN THE
SYSTEM
 REACTORS
– TUBE FLOW VS. CSTR
– VAPOR PHASE VS. LIQUID PHASE
 DISTILLATION
– LIMIT INVENTORIES
– USE IN-COLUMN HEAT
EXCHANGERS
 HEAT EXCHANGERS
– SHELL & TUBE VS. PLATE
– PROCESS FLOW IN TUBES
http://www.inl.gov/featurestories/i/scwr.gif
INTENSIFICATION POLICIES
 STORAGE
– MINIMAL VOLUME
STORAGE TANKS
– PIPELINES
 NUMBER OF TRAINS
http://rphrm.curtin.edu.au/2006/iss
ue1/defense05.png
– SINGLE TRAIN HAS SMALLER OVERALL
INVENTORY THAN MULTIPLE TRAIN
– SINGLE TRAIN HAS FEWER LEAK POINTS
– SINGLE TRAIN HAS ECONOMY OF SCALE
SUBSTITUTION POLICIES
 USE LESS HAZARDOUS RAW MATERIALS
 USE LESS HAZARDOUS NON-REACTIVE
COMPONENTS
– REPLACEMENT OF CFCs IN REFRIGERATION
SYSTEMS AND AEROSOLS WITH HFCs AND N2
– USE OF SUPERCRITICAL CO2 IN PLACE OF
METHYLENE CHLORIDE FOR EXTRACTION
– USE OF WATER-BASED SOLVENTS FOR SEMICONDUCTOR PROCESSING
– USE STEAM AND WATER AS HEAT TRANSFER
MEDIA INSTEAD OF HYDROCARBONS
ATTENUATION POLICIES
 USE LESS HAZARDOUS CONDITIONS
FOR PROCESSES
– LOWER PRESSURES
– LOWER TEMPERATURES
– MULTIPLE STEPS
 NORMALLY COST EFFECTIVE SINCE
PROCESS CONDITIONS ARE CLOSER
TO AMBIENT
ATTENUATION POLICIES
 AMMONIA SYNTHESIS (KHARBANDA &




STALLWORTHY, SAFETY IN THE CHEMICAL
INDUSTRY, HEINMANN PROFESSIONAL
PUBLISHING,1988) N2 + 3H2 → 2NH3
1930’S CASALE PROCESS AT 450 – 600 atm
1950’S ICI PROCESS 300 – 350 atm
1960’S KELLOGG PROCESS 150 atm
1982 ICI AMV PROCESS 80 - 100 atm
http://www.topsoe.com/site.nsf/vIMAGESBYNAME/Ammonia28---PVCdiagram.gif/$file/Ammonia28---PVC-diagram.gif
KLETZ, TREVOR, PLANT DESIGN FOR
SAFETY, HEMISPHERE PUB, 1991
LIMITATION OF EFFECTS
 CHANGE PROCESS SEQUENCE TO
LIMIT HAZARDOUS CONDITIONS
– SEQUENCE OF PROCESSES
– NUMBER OF STEPS IN A SINGLE VESSEL
 USE OF SUBMERGED PUMPS TO
REDUCE LEAK IMPACTS
http://www.savinobarbera.com/images/istall
azione-pompa-immersa-bg.gif
SIMPLIFICATION POLICIES
 STRONGER EQUIPMENT TO REPLACE
RELIEF SYSTEMS
 MATERIALS OF CONSTRUCTION THAT
RETAIN DUCTILITY (LOW
TEMPERATURES)
 ELIMINATE EXCESS INSTRUMENTATION
 MINIMIZE NUMBER OF PIECES OF
EQUIPMENT BY COMBINING SERVICES
KLETZ, TREVOR, PLANT
DESIGN FOR SAFETY,
HEMISPHERE PUB, 1991
CLASS PROBLEM
 GIVEN: Automobile
 WANTED: Fault tree analyzing when auto
fails to start
 BASIS: Engine powered car with remote
starting switch
 SOLUTION: Present results as fault tree
chart. Estimate probability for each
component.