accident scenarios and top events antony thanos ph.d. chem. eng. antony.thanos@gmail
DESCRIPTION
This project is funded by the European Union Projekat finansira Evropska Unija. ACCIDENT SCENARIOS AND TOP EVENTS Antony Thanos Ph.D. Chem. Eng. [email protected]. Project implemented by Human Dynamics Consortium Projekat realizuje Human Dynamics Konzorcijum. Risk Analysis Framework. - PowerPoint PPT PresentationTRANSCRIPT
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
This project is funded by the European Union
Projekat finansira Evropska Unija
Project implemented by Human Dynamics Consortium
Projekat realizuje Human Dynamics Konzorcijum
ACCIDENT SCENARIOS AND TOP EVENTS
Antony ThanosPh.D. Chem. [email protected]
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Risk Analysis Framework
HazardIdentification
HazardIdentification
Consequence Analysis
Consequence Analysis
Accepted Risk
NO
Risk reductionmeasures
END
AccidentScenariosAccidentScenarios
Accident ProbabilityAccident
Probability
RiskAssessment
RiskAssessment
YES
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection No unique approach within EU, as
for rest of Risk Assessment Methodology
Nevertheless, worst case scenarios are almost always required for :
oEmergency Response
oLand Use Planning reason
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, UK case :
• “representative” set of major accident scenario required
• minimum scenarios list examples referred in Assessment Guides (SRAG) for certain types of establishments (although probabilistic approach)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, UK case : (cont.) Example of scenarios list in HSE
SRAG for LPGs
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, Netherlands case Detailed guidance in Reference
Manual Bevi Risk Assessments, as part of QRA
Step 1 : Sub-selection method (based on TNO selection method)
Screening method (relative ranking)
Basic principle: Identification of “Containment Systems” which contribute most to external risk
Not scenario selection, but Containment systems selection
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, Netherlands case (cont.) Main criteria :
oEffects (1% lethality) extent out of fence (calculation of consequence required for worst case scenario for Containment) and/or
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, Netherlands case (cont.) Main criteria : (cont.)
oEstimation of effects based on selection method :
Indication number A (intrinsic hazard)
Q, quantity
O1, O1, O1 factors for
process conditions
G, limit value (10000 kg for flammables)
G
OOOQA 321
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, Netherlands case (cont.)
oSelection method : (cont.)Selection number S: (hazard level
at location -fence)
n : 2 for toxics,
3 for flammables and explosives
L : distance from fence (at least 8 points
examined)
S>1, candidate Containment Systems for inclusion in QRA
Comparison of S values for various
Containment Systems provides final selection
AL
Sn
100
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, Netherlands case (cont.)
Sub-selection method
overview
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, Netherlands case (cont.) Step 2 : Definition of Releases
oReleases to be included for selected Containment System based on tables per equipment type referring also frequency
oExample for gas containers
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, Netherlands case (cont.) Step 3 : Top events (scenarios)
defined on event trees for releases
oEvent trees included for main cases in Manual
Releases general cut-off limit :
oprobability > 10-9 per year
o1% lethality distance extending outside fence
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, Cyprus case Deterministic approach Generic minimum list of scenarios
oCatastrophic failure of vessels, tanks, pipes
oRupture of vessel/tank (hole with diameter equal to max pipe connected to tank/vessel), hole 20% of pipe diameter
oSmall leak in vessel tank, pipe (hole diameter 25mm or 50 mm)
Selection method for critical equipment (TNO Purple Book)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Scenarios selection, a few other EU Member States cases Italy (Hybrid approach)
oDecree for LPGs : Certain scenarios are excluded based on available measures
France (Hybrid approach)
oHigh consequence scenarios must be included in consequence analysis, even for low probability
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Typical release scenarios per equipment type failure : Pipes
oCatastrophic failure (Full Bore Rupture –FBR- or guillotine break)
oPartial failure (hole diameter equivalent to a fraction of pipe diameter, e.g. 20%)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Typical release scenarios per equipment type failure (cont.) : Pressure vessel (process vessel,
tank, tanker)
oCatastrophic failure: “instantaneous” rupture (complete release of content within short time e.g. 3-5 min)
oMechanical failure : equivalent hole set to e.g. 50 mm
oSmall leakage (e.g. corrosion), smaller hole with equivalent diameter of e.g. 20 mm
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Typical release scenarios per equipment type failure (cont.) : Pressure vessel connected
equipment
oRelease from PSV
oFailure of connecting pipes (as for pipes above)
Pumps/compressors
oRelease from PSV
oLeakage from seal (equivalent small hole diameter set, e.g. 20 mm)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Typical release scenarios per equipment type failure (cont.) : Atmospheric liquid fuel tanks
o Ignition in floating roof tank (tank fire)
o Ignition of constant roof tank (tank fire)
oFailure of tank with release to dike (bund) of tank and subsequent fire in dike (dike fire)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Worst case scenarios Although low probability expected,
indispensible for Land Use Planning and Emergency Planning
Worst case releases/scenarios to be provided for the different sections of Plant (type of activities) :
oEach Production Unit
oTank-farm
oMovement facilities (road/rail tanker stations, ports)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Worst case scenarios (cont.) Worst case releases/scenarios
within sections :
oCatastrophic failure of vessel (process vessel, tank, tanker) with maximum inventory size
oCatastrophic failure of pipe : Full Bore Rupture (FBR)/Guillotine Break) for pipes, especially for movement facilities (import/export pipelines, hoses/loading arms)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Worst case scenarios (cont.) Worst case releases/scenarios
within sections :
oFor liquid fuels tanks, fire in :Largest diameter tankDike with largest equivalent
diameter
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Worst case scenarios (cont.) Worst case releases/scenarios
must take into account :
oDifferent operating conditions (P/T/phase) e.g. :
For liquefied gases piping, worst case is usually expected from liquid phase pipe failure
For LPGs, worst case is usually expected from pure propane compared to butane (due to higher pressure)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Worst case scenarios (cont.) Worst case scenarios selection
criteria (cont.) :
oDifferent operating conditions (P/T/phase) e.g. (cont.) :
Smaller tank of pressurized ammonia can produce more extended consequences than larger refrigerated ammonia tank
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Worst case scenarios (cont.) Worst case releases/scenarios
must take into account :
oDifferent substances, e.g. smaller tank of a very toxic substance can produce more extended consequence than a larger tank of a toxic substance
oProximity to site boundaries, especially if vulnerable objects are close
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Worst case scenarios (cont.) Worst case scenarios usual
convention : Only one failure can happen at a certain time
oNo simultaneous accidents expression, e.g. only single tank BLEVE in LPG tank farm at a time
oNo double containment failure, e.g. in refrigerated tanks with secondary containment only primary containment failure is taken into account, if no special reasons are present
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Hazard identification usually specify release expected and not final accident (top event)
• Example : Initial event (release) : failure of
LPG pipeline due to corrosion Top events:
o jet flame
ovapour cloud explosion
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Event Tree and Top Events Logic evolution of potential
outcomes (top event) of an initial event (release) identified
Usually used in categorisation of final accidents (top events) per initial release identified
Scenario evolution parameters (e.g. ignition) produce differences in top events
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Event tree and Top Events (cont.) Example: Gas phase release from
LPG tankPHASE
IGNITION CONFINEMENT TOP EVENT
DIRECT JET FLAME
GAS DELAYED NO CONFINEMENT FLASH FIRE
CONFINEMENT UVCE
NO IGNITION
SAFE DISPERSION
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Why Event Trees? Consequence analysis requires top
events to be identified
Technique in the borderline of hazard identification and consequence analysis
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Consequence analysis framework
Releasescenarios Release
scenarios Accident
typeAccident
typeEvent
trees
Releasequantification
Releasequantification
Hazard
Identification
Release models
Consequenceresults
Consequenceresults
Domino effectsDomino effectsLimits of
consequence analysis
Dispersion models
Fire, Explosion Models
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Main top event categories
Toxicdispersion
Toxicdispersion
ExplosionExplosion
FireFire
Hazardoussubstance
release
Initial event Top event
Toxic effectsToxic effects
OverpressureOverpressure
ThermalRadiationThermal
Radiation
Consequences
FireFire ThermalRadiationThermal
Radiation
Toxicdispersion
Toxicdispersion Toxic effectsToxic effects
FireFire ThermalRadiationThermal
Radiation
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Top events related with thermal radiation “Fire” categories:
Pool fire
FLEVE (fire ball)
Flash fire
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire Ignition of flammable liquid phase
Liquid fuel tank fire
Main consequenceThermal radiation
Main consequenceThermal radiation
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Jet flame Ignition of gas or two-phase
release from pressure vessel
Propane jet flame test
Main consequenceThermal radiation
Main consequenceThermal radiation
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball, BLEVE (Boiling Liquid Expanding Vapour Explosion)
Rapid release and ignition of a flammable under pressure at temperature higher than its normal boiling point
LPG BLEVE (Crescent City)
Main consequenceThermal radiation
Main consequenceThermal radiation
Secondary consequences: oFragments (missiles)oOverpressure
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball, BLEVE Mechanism (exposure of tank to fire)
Shell at gas phase collapses due to weakening and in combination to pressure increase. Massive release of tank content. Rapid evaporation and ignition of the whole tank content
GAS PHASELOW HEAT TRANSFER,LOW HEAT CAPACITY,
RAPID INCREASE OF SHELL TEMPERATURE,POSSIBLE FAILURE
LIQUID PHASEHIGH HEAT TRANSFER RATE,
HIGH HEAT CAPACITYRATHER LOW SHELL TEMPERATURE
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion Passive (neutral) dispersion
(Gauss) :
oRelease of gas with density equal or higher than air
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) “Positive” buoyant dispersion :
oRelease of gas at elevated temperature (e.g. flue gas at stack)
oTreated as special case of Gauss models (plume rise)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Heavy gas dispersion, e.g. liquefied
under pressure gas releases Common characteristic of
substances : Normal Boiling Point (BP) less
than ambient temperature and Pressure higher than ambient
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Typical example of heavy gas
dispersion, LPGs :
oPropane BP = - 42 °C
oButane BP = - 0.5 °C
and
ostorage at ambient temperature (high pressure), propane case : T = 17 °C, P = 6,7 barg
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Other examples of heavy gas cases
:
oAmmonia BP= -33°C and
Storage at ambient temperature, usually in bullets (high pressure : T = 15°C, P = 6,3 barg) or
Semi-refrigerated storage (T = 0 °C,
P = 3,2 barg), usually in spheres
oPropylene (BP = -47.7 °C) at semi refrigerated storage (T = 6°C, P = 6 barg)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Heavy gas dispersion case -
Released gas has lower density than air
Why heavy gas dispersion is different ?
oAt release point, pressure reduction occurs (from vessel pressure to atmospheric)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) General thermodynamics of heavy
gas dispersion
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Why heavy gas dispersion is
different ? (cont).
oGas phase release: Lower pressure incurs lower
temperature of gas (adiabatic expansion, Joule/Thomson effect). Colder gas has density higher than surrounding air (fells to ground).
Additional effect by entrainment of air in expanding gas and condensation of humidity
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Why heavy gas dispersion is
different ? (cont).
oLiquid phase release: Reduction of pressure causes
evaporation of liquid to gasEvaporation causes lower
temperature in both gas and liquid (equal to normal boiling point temperature, freezing effect)
Expanding liquid/gas entrains air who is getting cold by boiling, condensing also humidity
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Heavy gas dispersion : Vapour
cloud remains for long distance at ground level
Propane cloudHeavy gas behaviour
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Refrigerated gases not considered
in general as producing heavy gas dispersion :
oStorage at cryogenic conditions (close to normal boiling point, atmospheric pressure)
oExamples:Liquefied Natural Gas (LNG)Cryogenic ammonia
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Refrigerated gases (cont.)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Effects:
Toxic substances (e.g. HF) : toxic effect via inhalation
Flammables (Flash fire) : Ignition of cloud in area with no confinement (obstacles)
odeaths expected within cloud limits where ignition is possible (LFL-HFL), due to thermal radiation and clothes ignition
olow flame front propagation velocity (as per wind speed)
oinsignificant overpressure
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) Delayed ignition of flammable
vapour cloud under partial confinement (obstacles within cloud) producing overpressure during flame front propagation
Main consequenceOverpressure
Main consequenceOverpressure
VCE results (Flixborough)Secondary consequences: oFragments (e.g. broken glasses)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Explosion Explosion : General term for vapour
cloud ignition event, in which turbulence (necessary for combustion surface increase) leads to significant flame front propagation velocity and overpressure
oTurbulence sources:Leaks (release with jet
characteristics)Obstacles :
Equipment, e.g. air-coolersWalls, tanks, or other
confinement in space
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Explosion (cont.) Explosion feedback mechanism
High combustionrate
High combustionproducts volume rate
High heat release rate
Overpressure
Expandingflue gasesCombustion
Turbulence
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Deflagration Rather fast combustion rate Molecular diffusion limitation Small ignition energy requirements
(10-4 J for hydrocarbons) Flame front propagation velocity :
5-30 m/sec Flash fire : deflagration with no
flame front acceleration
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Detonation High ignition energy (106 J) Compression in flame front
exceeds autoignition temperature Supersonic flame front propagation
velocity. High overpressure produced Highly homogenous cloud required
– not feasible in real life
Explosives case
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Literature for Accident Scenarios and Top Events
Lees’ Loss Prevention in the Process Industries, Elsevier Butterworth Heinemann, 3nd Edition, 2005
Methods for the Determination of Possible Damage to People and Objects Resulting from Releases of Hazardous Materials , Green Book, CPR 16E, TNO, 1992
Guidelines for Chemical Process Quantitative Risk Analysis, CCPS-AICHE, 2000
Guidelines for Consequence Analysis of Chemical Releases, CCPS-AICHE, 1999
Guidelines for Evaluating the Characteristics of Vapour Cloud Explosions, Flash Fires and BLEVEs, CCPS-AICHE, 1994
Guidelines for quantitative risk assessment, Purple Book, CPR 18E, RVIM, 2005
RIVM, Reference Manual Bevi Risk Assessments, 2009
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Literature for Accident Scenarios and Top Events (cont.)
HSE, Safety Report Assessment Guide : LPG
Benchmark Exercise in Major Accident Hazard Analysis, JRC Ispra, 1991
Methodology for Evaluation of Safety Reports, Cyprus Ministry of Labour and Social Security, 2007 (in Greek)
Assael M., Kakosimos K., Fires, Explosions, and Toxic Gas Dispersions, CRC Press, 2010
Crowl D., Louvar J., Chemical Process Safety Fundamentals with Applications, Prentice Hall, 2nd Edition, 2002
Taylor J., Risk Analysis for Process Plant, Pipelines and Transport, E&FN SPON, 1994