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TOP EVENTS CONSEQUENCE ANALYSIS MODELS Antony Thanos Ph.D. Chem. Eng. [email protected]PowerPoint Presentation

TOP EVENTS CONSEQUENCE ANALYSIS MODELS Antony Thanos Ph.D. Chem. Eng. [email protected]

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### TOP EVENTSCONSEQUENCE ANALYSIS MODELS Antony ThanosPh.D. Chem. [email protected]

This project is funded by the European Union

Projekat finansira Evropska Unija

Release

scenarios

Accident

type

Hazard Identification

Event

trees

Dispersion models

Release models

Consequence

results

Release

quantification

Fire, Explosion Models

Domino effects

Limits of

consequence analysis

- Pool fire
- Ignition of flammable liquid phase

Main consequence

Thermal radiation

Liquid fuel tank fire

- Pool fire characteristics
- Pool dimensions (diameter, depth)
- Confined pool (liquid fuels tank/bund fire) :
- Tank fire pool : diameter equal to tank diameter dimension
- bunds : pool diameter estimated by equivalent diameter of bund

- Confined pool (liquid fuels tank/bund fire) :

- Pool dimensions (diameter, depth)

- Pool fire characteristics (cont.)
- Pool dimensions (diameter, depth) (cont.)
- Unconfined pool (LPG pool from LPG tank failure –no dike present):
- Theoretically maximum pool diameter is set by balance of release feeding the pool and combustion rate from pool

- Unconfined pool (LPG pool from LPG tank failure –no dike present):

- Pool dimensions (diameter, depth) (cont.)

Release

to pool

Combustion

rate

- Pool fire characteristics (cont.)
- Pool dimensions (diameter, depth) (cont.)
- Unconfined pool :
Min : release rate (kg/sec)

Mcomb : combustion rate (kg/sec)

mcomb : specific combustion rate (kg/m2.sec)

- In real life, pool is restricted by ground characteristics. Typical values for assumed depth: 0.5-2 cm (depending on ground type, higher values reported for sandy soils)

- Unconfined pool :

- Pool dimensions (diameter, depth) (cont.)

- Pool fire characteristics (cont.)
- Flame height, inclination (angle of flame from vertical due to wind)
- Long duration (hours to days)
- Combustion rate

- Pool fire models
- Combustion rate per pool surface on empirical equations (Burges, Mudan etc.)
- Example :

- Combustion rate per pool surface on empirical equations (Burges, Mudan etc.)

- Pool fire models (cont.)
- Combustion rate for liquids not exceeding 0.1 kg/m2.sec. Upper range for low boiling point hydrocarbons
- Flame dimension from empirical equations (Thomas, Pritchard etc.)
- Example, Thomas correlation :
- Big pools : Hf/Dp in the range of 1-2

- Pool fire models (cont.)
- Point source model (cont.)
- No flame shape taken into account
- A fraction of combustion energy is considered to be transmitted by ideal point in pool center

- Point source model (cont.)

Thermal radiation

transmitted

semi spherically

- Pool fire models (cont.)
- Point source model (cont.)
- Increased inaccuracies near pool end (important for Domino effects)

- Point source model (cont.)

Flame height

Pool depth

- Pool fire models (cont.)
- Solid flame radiation model, radiation emitted via flame surface

- Pool fire models (cont.)
- Solid flame radiation model (cont.)
- Calculation based on :
- flame shape (usually considered cylinder -tilted or not-),
- distance from flame (View Factor),
- emissive power (thermal radiation flux at flame surface)

- Calculation based on :

- Solid flame radiation model (cont.)

- Pool fire models (cont.)
- Solid flame radiation model (cont.)
- Calculation equation :

- Solid flame radiation model (cont.)

- Pool fire models (cont.)
- Solid flame radiation model (cont.)
- View Factor : function of distance of receptor from flame and flame dimensions. Different equation for different flame shapes
- Transmissivity coefficient : Absorbance of thermal radiation by atmosphere components - e.g. humidity, CO2 –
- Correlation with relative humidity (R.H.) level and distance to “receptor”)
- High R.H, low transmissivity coefficient
- More important for far-field effects (due to increased distance)

- Solid flame radiation model (cont.)

- Pool fire models (cont.)
- Solid flame radiation model (cont.)
- Emissive power :
- Depending on pool size, substance
- For big pools, soot formation (20 kW/m2), masking of flame, significant reduction of average flame emissive power

- Emissive power :

- Solid flame radiation model (cont.)

- Pool fire models (cont.)
- Solid flame radiation model (cont.)
- Emissive power : (cont.)

- Solid flame radiation model (cont.)

- Pool fire models (cont.)
- Solid flame radiation model (cont.)
- Emissive power : (cont.)
- Experimental Gasoline pool examples :
Dp=1 m, E=120 kW/m2

Dp=50 m, E= 20 kW/m2

- Medium to low emissive power for big pools (thermal radiation flux, up to 60 kW/m2 for liquid fuels)
- LPGs, LNG, provide higher emissive power (up to 150-270 kW/m2 for LPG, 250 kW/m2 for LNG)

- Experimental Gasoline pool examples :

- Emissive power : (cont.)

- Solid flame radiation model (cont.)

- Pool fire models (cont.)
- Solid flame radiation model (cont.)
- Emissive power : (cont.)
- One example of correlations available for max emissive power :

- Emissive power : (cont.)

- Solid flame radiation model (cont.)

- Pool fire models (cont.)
- Solid flame radiation model (cont.)
- Emissive power : (cont.)
- Final emissive power must take into account smoke production. Example correlations :
s, smoke coverage of surface

Dp, pool diameter (m)

Esmoke, emissive power of smoke (kW/m2)

- Final emissive power must take into account smoke production. Example correlations :

- Emissive power : (cont.)

- Solid flame radiation model (cont.)

- Pool fire models (cont.)
- Solid flame radiation model (cont.)
- Emissive power : (cont.)
- Please be careful !!!!
- Make sure radiation fraction used is in-line with experimental data if available
- Evaluate calculation results for emissive power with experimental results, if available

- Please be careful !!!!

- Emissive power : (cont.)

- Solid flame radiation model (cont.)

- Pool fire models (cont.)
- UK HSE suggestions for LPGs :
- Emissive power : 200 kW/m2 over half flame height

- Some conservative assumptions
- For unconfined LPG cases, for theoretical pool calculation :
- butane fire instead of similar propane release (lower boiling rate, higher pool diameter
- low ambient temperature examined (as above)

- Low relative humidity examined (high transmissivity coefficient)

- For unconfined LPG cases, for theoretical pool calculation :

- UK HSE suggestions for LPGs :

- Pool fire models (cont.)
- Example results for propane pool fire Dp=10 m, wind speed 5 m/sec T=25 °C (confined fire, Aloha),
- flame height Hf : 21 m
- combustion rate M : 400 kg/min

- Example results for propane pool fire Dp=10 m, wind speed 5 m/sec T=25 °C (confined fire, Aloha),

- Pool fire models (cont.)
- Example results for Methanol tank, Dtank=20 m, H tank=20 m, T= 25 C°, atmospheric conditions D5, 2 in hole on tank shell at ground level (burning unconfined pool, Aloha)
- pool diameter Dp = 27 m
- flame length : 11 m

- Example results for Methanol tank, Dtank=20 m, H tank=20 m, T= 25 C°, atmospheric conditions D5, 2 in hole on tank shell at ground level (burning unconfined pool, Aloha)

- Fireball, BLEVE (Boiling Liquid Expanding Vapour Explosion)
- Rapid release and ignition of a flammable under pressure at temperature higher than its normal boiling point

Main consequence

Thermal radiation

Secondary consequences:

- Fragments (missiles)
- Overpressure

LPG BLEVE (Crescent City)

- Fireball/BLEVE characteristics
- Very rapid phenomenon (expanding velocity 10 m/sec)
- Limited duration (up to appr. 30 sec, even for very large tanks)
- Significant extent of fireball radius (in the order of 300 m for very big tanks, ≈ 4000 m3)
- Very high emissive power (in the order or 200-350 kW/m2)
- No precise capability for prediction of when it will happen (usual initial step for tanks exposed to heat -pool fire, jet flame-, opening of PSVs)

- Fireball/BLEVE characteristics and models (cont.)
- Radius and duration from correlations with tank content, example(AIChE CCPS) :
- t, duration (sec)
- m, mass (tn)
- No significant deviations for various correlations available, example results for full propane tank BLEVE (100 m3)

- Radius and duration from correlations with tank content, example(AIChE CCPS) :

- Fireball/BLEVE characteristics and models (cont.)
- Radius and duration from correlations with tank content, example(AIChE CCPS) :
- t, duration (sec)
- m, mass (kg)

- Radius and duration from correlations with tank content, example(AIChE CCPS) :

- Fireball/BLEVE characteristics and models (cont.)
- Mass in fireball calculations :
- Typically whole tank content (worst case approach.)
- Netherlands (BEVI method) : gas phase + 3 x flash fraction of liquid phase at failure pressure.
- For typical failure pressure in LPGs with hot BLEVEs, results to whole tank content
- For propane at usual atmospheric conditions, results to whole tank content

- Mass in fireball calculations :

- Fireball/BLEVE characteristics and models (cont.)
- Solid flame model
- radiation emitted via fireball surface,
- Usually fireball considered as sphere touching ground (conservative approach, adopted by UK HSE)

- Solid flame model

Evolution of fireball/BLEVE

- Fireball/BLEVE characteristics and models (cont.)
- Solid flame radiation model (cont.)
- Calculation based on :
- sphere shape at contact with ground,
- distance from fireball (sphere View Factor),
- fireball emissive power (thermal radiation flux at fireball surface)

- Calculation based on :

- Solid flame radiation model (cont.)

- Fireball/BLEVE characteristics and models(cont.)
- Solid flame radiation model (cont.)
- View Factor : function of distance of receptor from flame and fireball radius
- Transmissivity coefficient : as in pool fire case

- Solid flame radiation model (cont.)

- Fireball/BLEVE characteristics and models (cont.)
- Emissive power in fireball calculations :
- Correlations are available for emissive power calculation based on :
- vapour pressure at failure conditions (AIChE CCPS)
Pv, vapour pressure at failure (MPa)

- and/or mass involved, duration, size of fireball

- vapour pressure at failure conditions (AIChE CCPS)
- Experimental data provide values up to 350 kW/m2
- UK, HSE suggestion >270 kW/m2

- Correlations are available for emissive power calculation based on :

- Emissive power in fireball calculations :

- Fireball/BLEVE models (cont.)
- Example results (full 100 m3 propane tank BLEVE, Aloha)
- But, duration is only 13 sec. For limit values set in TDU (not in kW/m2), the relevant thermal radiation flux limit must be calculated

- Example results (full 100 m3 propane tank BLEVE, Aloha)

- Fireball/BLEVE models (cont.)
- Example results (full 100 m3 propane tank BLEVE, Aloha) (cont.)
- For t=13 sec,
- 1500 TDU corr. to 35 kW/m2
- 450 TDU corr. to 14 kW/m2
- 170 TDU corr. to 6.9 kW/m2

- For t=13 sec,

- Example results (full 100 m3 propane tank BLEVE, Aloha) (cont.)

- Jet flame
- Ignition of gas or two-phase release from pressure vessel

Main consequence

Thermal radiation

Propane jet flame test

- Jet flame characteristics
- Results as outcome of gas or two phase releases of flammable substances
- Cone shape
- Long duration (minutes to hours, depends on source isolation)
- Very high emissive power (in the order or 200 kW/m2)
- Soot expected, but not affecting radiation levels

- Jet flame models
- Combustion rate determined by release rate
- Dimensions from empirical equations. Example of simplified Mudan-Cross equation
L= jet flame length

d= release point diameter

Ct= fuel content permole in stoichiometric mix

of fuel/air

ΜWa= air molecular weight

MWf= fuel molecular weight

- Jet flame models (cont.)
- Dimensions from empirical equations. Example of simplified Considine-Grint equation for LPGs
L= jet flame length

M= release rate (kg/sec)

W= jet radius at flame tip (m)

- Dimensions from empirical equations. Example of simplified Considine-Grint equation for LPGs

- Jet flame models (cont.)
- Point source models
- Single point : all energy is released from flame “center”. Similar to relevant point source model for pool fires
- Multipoint source : several point along jet trajectory taken into account

- Point source models

- Jet flame models (cont.)
- Solid flame radiation model
- Radiation emitted via flame surface
- Calculation based on :
- shape (cylinder, tilted or not)
- distance (View Factor)
- emissive power

- Solid flame radiation model

- Jet flame models (cont.) (cont.)
- Solid flame radiation model (cont.)
- Calculation equation :

- Solid flame radiation model (cont.)

- Jet flame models (cont.)
- Solid flame radiation model (cont.)
- View Factor : function of distance of receptor from flame and flame dimensions for shape assumed
- Transmissivity coefficient : as in pool fires, fireball/BLEVE
- Emissive power : Estimated by flame dimension (surface) and energy released
E= Emissive power (kW/m2)

M= release rate (kg/s)

ΔΗc= combustion energy (kJ/s)

A= jet surface area, m2

Fs= fraction of combustion energy radiated

uj= expanding jet velocity (m/sec)

- Solid flame radiation model (cont.)

- Jet flame models conservative approaches
- Examination of horizontal jet
- Produce more extended thermal radiation zones
- Have direct effect via impingement in near by equipment

- Wind speed (for models taking into account flame distortion due to wind) :
- Vertical jets : High wind speed (UK HSE suggestion 15 m/sec)
- Horizontal jets : Low wind speed (UK HSE suggestion 2 m/sec)

- Examination of horizontal jet

- Jet flame models example results (cont.)
- Example results, 2 in hole in top of propane tank/gas phase, vertical jet (Aloha)

- Vapour cloud dispersion (cont.)
- Extent of cloud : dimensions, downwind/crosswind till specific endpoints (concentration)

- Vapour cloud dispersion (cont.)
- Endpoints :
- Toxics : several toxicity endpoints (e.g. IDLH, LC50)
- Flammables : LFL, ½ LFL
- Deaths expected within cloud limits where ignition is possible (Flash fire) due to thermal radiation and clothes ignition
- Reporting of LFL, ½ LFL is for theoretical extend of cloud, as no ignition is assumed on cloud path
- Very extended clouds expected for LPGs, especially in catastrophic failure cases (in the order of 500-1500 m)

- Endpoints :

- Vapour cloud dispersion (cont.)
- Endpoints : (cont.)
- Flammables : (cont.)
- Usually ignition sources outside establishment premises limit actual cloud
- Protection zones not justified to take into account flammable dispersion till LFL, ½ LFL

- Flammables : (cont.)

- Endpoints : (cont.)

- Vapour cloud dispersion (cont.)
- Example results for LPG dispersion (SLAB) at ground level centerline

- Vapour cloud dispersion (cont.)
- Example results for LPG dispersion (SLAB) (cont.) at ground level

- Vapour cloud (gas) dispersion (cont.)
- Release conditions affecting dispersion :
- substance properties (Boiling Point etc.)
- pressure, temperature at containment
- release rate and area
- release point height
- release direction (upwards –PSV-, horizontal)

- Release conditions affecting dispersion :

- Vapour cloud (gas) dispersion (cont.)
- Meteorological conditions affecting dispersion :
- atmospheric stability class (A-F),
- wind speed,
- air temperature,
- humidity (for some substances reacting with water as for example HF or other polar substances : SO2, NH3 etc.)
- Type of area : rural/industrial/urban, roughness factor

- Meteorological conditions affecting dispersion :

- Vapour cloud (gas) dispersion (cont.)
- Atmospheric stability :
- Expression of turbulent mixing in atmosphere. Related with atmospheric vertical temperature gradient (dT/dz)

- Atmospheric stability :

- Vapour cloud (gas) dispersion (cont.)
- Atmospheric stability : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Atmospheric stability : (cont.)
- Usually attributed to standardized class A-F (Pasquill)
- A : unstable, in combination with high winds favors dispersion
- D : neutral
- F : stable, minimum mixing in atmosphere

- Other parameter to attribute atmospheric stability, Monin-Obukhov length (positive for stable conditions, negative for unstable conditions)

- Usually attributed to standardized class A-F (Pasquill)

- Atmospheric stability : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Atmospheric stability : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Atmospheric stability : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Wind speed :
- Wind speed referred in meteorological data usually refer to measurement at 9-10 m height
- Boundary layer effect (variation of speed with height)

- Wind speed :

- Vapour cloud (gas) dispersion (cont.)
- Wind speed : (cont.)
- Simplified function :
p, function of :

- stability class
- surface roughness

- Simplified function :

- Wind speed : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Wind speed : (cont.)
- Variation with stability class for rural environment :

- Wind speed : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Meteorological conditions :
- Typical set under interest in Safety Reports :
- D5 : stability class D, uref=5 m/sec (unstable conditions)
- F2 : stability class D, uref=2 m/sec (stable conditions). Worst case for extent of vapour cloud, especially in heavy gas dispersion

- Typical set under interest in Safety Reports :

- Meteorological conditions :

- Vapour cloud (gas) dispersion (cont.)
- Type of surroundings : rural/industrial/urban
- Refers to variation of height in elements of surrounding
- Usually attributed via “roughness factor”

- Type of surroundings : rural/industrial/urban

- Vapour cloud (gas) dispersion (cont.)
- Type of surroundings (cont.)
- Conservative approach : open country (rural)

- Averaging time :
- Variation in time, due to turbulence, of wind characteristics :
- speed
- direction

- Variation in time, due to turbulence, of wind characteristics :

- Type of surroundings (cont.)

not exposed

x

T=0

average wind

direction

y

exposed

x

T=t

- Vapour cloud (gas) dispersion (cont.)
- Averaging time : (cont.)
- For continuous releases, concentration at constant location (x, y, z) is not constant

- Averaging time : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Averaging time : (cont.)
- increase of averaging time :
- plume boundaries widen
- concentration distribution flattens

- increase of averaging time :

- Averaging time : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Averaging time : (cont.)
- Very important to use averaging time in models, suitable to exposure time under interest
- Models may use parameters for certain averaging time, which might not be suitable for application in Safety Report. PLEASE ALWAYS CHECK !!!
- Gaussian models use implicit 10-min averaging time but…

- Averaging time : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Averaging time : (cont.)
- Toxics exposure usually under interest for period of 30 min (due to LC50 30 min endpoints etc.)
- Aloha-DEGADIS (Heavy Gas Dispersion) uses 5 min for toxics
- Ignition of flammable cloud is related with very low exposure time (time just for ignition to happen).
- Aloha-DEGADIS uses 10 sec for flammables (e.g. LPGs, no matter if toxic effect is examined)

- Averaging time : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Averaging time : (cont.)
- Example results for propane release from liquid phase piping (SLAB)

- Averaging time : (cont.)

Averaging time = 1 sec

Averaging time = 30 min

- Vapour cloud (gas) dispersion (cont.)
- Averaging time : (cont.)
- Reason for reporting both LFL, ½ LFL in flammable dispersion
- ½ LFL reporting contributes to uncertainty of averaging time (conservative approach)

- Reason for reporting both LFL, ½ LFL in flammable dispersion

- Averaging time : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Passive (neutral) dispersion (Gauss) :
- Release of gas with density equal or higher than air

- Passive (neutral) dispersion (Gauss) :

- Vapour cloud (gas) dispersion (cont.)
- Passive (neutral) dispersion (Gauss) :
- Basic characteristics:
- Maximum concentration at centreline
- Concentration reducing with increasing distance from source
- If release at ground level, maximum concentration at ground level

- Basic characteristics:

- Passive (neutral) dispersion (Gauss) :

- Vapour cloud (gas) dispersion (cont.)
- Passive (neutral) dispersion (Gauss) :
- Basic equation for point source continuous release

- Passive (neutral) dispersion (Gauss) :

u, wind speed at z (m/sec)

M, release rate flow (kg/sec)

Hd, active release height (m)

- Vapour cloud (gas) dispersion (cont.)
- Passive (neutral) dispersion (Gauss) : (cont.)
- σy, σz :
- functions of stability class with x and roughness factor
- usually given for 10-min averaging time
- proper correction of σy based on necessary averaging time is required

- σy, σz :

- Passive (neutral) dispersion (Gauss) : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Passive (neutral) dispersion (Gauss) : (cont.)
- Example results for dispersion for NH3 release by 2 in hole in 6 bar gas vessel, D5 (Aloha)

- Passive (neutral) dispersion (Gauss) : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Passive (neutral) dispersion (Gauss) : (cont.)
- Equations provided for point stationary source (no momentum)
- But jets of releases have significant momentum due to high velocity… modifications needed in model to take into account release momentum

- Passive (neutral) dispersion (Gauss) : (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Passive (neutral) dispersion (Gauss) : (cont.)
- For jets of releases modifications are needed, typical example : plume rise parameter to modify the release source point at downstream location

- Passive (neutral) dispersion (Gauss) : (cont.)

Modified

Original

- Vapour cloud (gas) dispersion (cont.)
- Flue gases dispersion
- Example : pool fire combustion products, e.g., SO2
- Special characteristics :
- Large area of source (e.g. tank area, bund area), (not point source). Modifications are available to models or sources are treated as point ones
- High temperature of flue gases
- Relevant plume rise equations provided for stacks (Briggs, Holland equations), provide unrealistic plume rise height

- Conservative approach, no plume rise, dispersion begins from flame end

- Flue gases dispersion

- Vapour cloud (gas) dispersion (cont.)
- Flue gases dispersion (cont.)
- Special atmospheric condition to be considered (temperature inversion conditions, trapped plume)

- Flue gases dispersion (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Plume rise effects
- Concentration at centrelines not continuously decreasing with distance
- Max concentration at centreline appears at distance from source

- Plume rise effects

- Vapour cloud (gas) dispersion (cont.)
- Plume rise effects (cont.)
- Example results from calculation of SO2 dispersion from dike fire of heating oil tank (D5, release rate 0.25 kg/sec SO2, dike equivalent diameter 66 m)

- Plume rise effects (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Heavy gas dispersion
- Special complex models
- CFD
- Box models (instant releases)
- Grounded plume models (continuous releases)

- Special complex models

- Heavy gas dispersion

- Vapour cloud (gas) dispersion (cont.)
- Heavy gas dispersion (cont.)
- Maximum concentration expected at centerline
- Concentration decreases with increasing distance
- More extended plume compared to neutral dispersion

- Heavy gas dispersion (cont.)

- Vapour cloud (gas) dispersion (cont.)
- Heavy gas dispersion (cont.)
- Meteorological data
- F2 produce more extended cloud

- Propane/butane cases
- same release source (e.g. same hole size) will produce more extended cloud for propane due to higher release rate

- Meteorological data

- Heavy gas dispersion (cont.)

- Vapour cloud (gas) dispersion models
- Heavy gas dispersion (cont.)
- Example results for propane release from 2 in hole in liquid phase of tank (D5) (Aloha)

- Heavy gas dispersion (cont.)

- Vapour cloud (gas) dispersion models
- Heavy gas dispersion (cont.)
- Example results for propane release from 2 in hole in liquid phase of tank (F2) (Aloha)

- Heavy gas dispersion (cont.)

- Vapour Cloud Explosion (VCE)
- Delayed ignition of flammable vapour cloud under partial confinement (obstacles within cloud) producing overpressure during flame front propagation

Main consequence

Overpressure

Secondary consequences:

- Fragments (e.g. broken glasses)

VCE results (Flixborough)

- Vapour Cloud Explosion (VCE) characteristics
- Very short duration (<1 sec)
- Models, high uncertainty due to several assumptions used in every model
- Type of models:
- CFD (FLACS, PHOENIX etc.)
- TNT blast charge (TNT equivalency)
- Air-fuel charge blast (Multi-Energy, Baker -Strehlow -Tang etc.)

- Vapour Cloud Explosion (VCE) models
- TNT equivalency model
- Simple, based on analogy with explosives effects
- A fraction of combustion energy released in cloud is attributed to produce overpressure
- The former energy fraction is recalculated as equivalent (on energy basis) mass of TNT
- The effects are defined based on known correlation of overpressure with TNT mass

- TNT equivalency model

- Vapour Cloud Explosion (VCE) models (cont.)
- TNT equivalency model (cont.)
- αe, refers to part of combustion energy released producing overpressure (1-10%)
- High uncertainty in both αe value and quantity of flammables (released mass –till what time ???-, mass within LFL-UFL) to be used
- Review on topic by TNO Yellow Book and AICheJ CCPS Guideline

- TNT equivalency model (cont.)

- Vapour Cloud Explosion (VCE) models (cont.)
- TNT equivalency model (cont.)
- Some comments/examples on selection of mass and αe :
- αe must be selected along with suitable flammable mass
- for αe1-5%, mass must not contain only the part of cloud in LFL-UFL section
- flammable mass must take into account not only gas but also liquid droplets (aerosol) in 2-phase releases
- Dow approach : mass defined by release rate and time to maximise LFL distance

- Some comments/examples on selection of mass and αe :

- TNT equivalency model (cont.)

- Vapour Cloud Explosion (VCE) models (cont.)
- TNT equivalency model (cont.)
- Some comments/examples on selection of mass and αe : (cont.)
- mass defined by time to reach ignition source or time to stop release (time for energizing isolation valves)
- HSE suggests TNT mass double the gas mass in confined areas

- Explosives blast and VCE present differences, as explosives have short duration higher shock wave peak values.
- TNT equivalency model is approximation of phenomenon based on statistical analogies

- Some comments/examples on selection of mass and αe : (cont.)

- TNT equivalency model (cont.)

- Vapour Cloud Explosion (VCE) models (cont.)
- TNT equivalency model (cont.)
- Overpressure calculated by diagram
for distances required

- Uncertainty on centre of explosion
to be considered

- Similar diagrams for positive phase
duration, impulse

- Overpressure calculated by diagram

- TNT equivalency model (cont.)

- Vapour Cloud Explosion (VCE) (cont.)
- TNO Multi-Energymodel :
- Only confined areas of cloud are considered
- Partial explosions from confined areas expected
- Energy released assuming stoichiometric combustion, based on air contained in areas taken into account (average 3.5 MJ/m3 of air for most hydrocarbons) uniform concentration of flammable in confined areas assumed

- TNO Multi-Energymodel :

- Vapour Cloud Explosion (VCE) (cont.)
- TNO Multi-Energymodel : (cont.)
- Overpressure from Berg graph
using Sachs distance

- Overpressure from Berg graph

- TNO Multi-Energymodel : (cont.)

- Vapour Cloud Explosion (VCE) (cont.)
- TNO Multi-EnergyModel : (cont.)
- Similar graphs for positive phase duration, dynamic pressure
- Blast strength 10 : detonation, explosives case, not valid for VCEs as propagation of blast via detonation requires high homogeneity in cloud

- TNO Multi-EnergyModel : (cont.)

- Vapour Cloud Explosion (VCE) (cont.)
- TNO Multi-EnergyModel : (cont.)
- Disadvantage : complex empirical rules for (TNO Yellow Book, Assael) :
- definition of confined areas
- definition of successive or simultaneous blast in confided areas
- selection ofblast strength (confinement increase, increases blast strength

- HSE suggests blast strengths 2 and 7

- Disadvantage : complex empirical rules for (TNO Yellow Book, Assael) :

- TNO Multi-EnergyModel : (cont.)

- Vapour Cloud Explosion (VCE) (cont.)
- Baker-Strehlow-Tang model
- Similar principles as TNO Multi-Energy model
- confined areas only taken into account
- stoichiometry of air with fuel in confined areas

- Gas type “reactivity” (susceptibility to flame front acceleration) taken also into account along with obstacle density
- methane, CO : low reactivity
- H2, acetylene, ethylene/propylene oxide : high reactivity
- other substances : medium

- Similar principles as TNO Multi-Energy model

- Baker-Strehlow-Tang model

- Vapour Cloud Explosion (VCE) (cont.)
- Baker-Strehlow-Tang model (cont.)
- Flame speed defined by table on gas reactivity and confinement type

- Baker-Strehlow-Tang model (cont.)

- Vapour Cloud Explosion (VCE) (cont.)
- Baker-Strehlow-Tang model (cont.)
- Overpressure from graph using Sachs distance and flame speed
- Energy to be used double to actual as graph presents free air blast (not surface blast)

- Overpressure from graph using Sachs distance and flame speed

- Baker-Strehlow-Tang model (cont.)

- Vapour Cloud Explosion (VCE) (cont.)
- Example results for propane release from 2 in hole in liquid phase of tank (D5) (Aloha, Baker-Strehlow-Tang method)

Ignition time 2 min

Composite for unknown ignition time

- Pesticides fires and dispersion
- Variation of stored substances quantities within year due to seasonal production of some products.
- Evaluation of stored quantities distribution could be required to evaluate quantities to be taken into account in calculations.

- Some times, active substance stored in powder form
- Specific combustion rate rather low (TNO Green Book) : in the range of 0.02 kg/m2.sec

- Variation of stored substances quantities within year due to seasonal production of some products.

- Pesticides fires and dispersion(cont.)
- Special characteristic of pesticides : when burnt, not all substance is consumed, flue gases contain unburned pesticide substances (“survivor” fraction)
- In case of fire, dispersion of flue gases must examine :
- Combustion products (e.g. SO2, HCl, NO2 etc.)
- Unburned pesticide active substance

- Pesticides fires and dispersion(cont.)
- UK HSE suggests stoichiometric conversion of S, Cl to SO2 and HCl.
- Conversion ratios :
- C to CO : 5%
- N to HCN and NO2 : 5%

- According to TNO Green Book, formation rate of NO2, HCN and NO decreases with this order, Taking into account the similar toxicity of the former, conversion of N to NO2 only is conservative

- Pesticides fires and dispersion (cont.)
- Survivor fraction in flue gases : 0.5-10% of combustion rate of substance at source
- Lower survivor fractionfor high boiling point substances
- UK HSE suggests survivor fraction 10% otherwise justification must be provided

- Pesticides fires and dispersion (cont.)
- Especially in closed warehouse cases :
- what is plume rise for flue gases ??
- which is the combustion rate ??

- Plume rise in warehouse flue gases
- For fire in full development plume rise might be high, but potentially low in initial phase of fire
- Typical equations fail, as producing unrealistic plume rise

- Especially in closed warehouse cases :

- Pesticides fires and dispersion (cont.)
- Combustion rate, affected by type of fire
- Roof collapse
- As in open area, fuel controlling
- High flue gas temperature

- Ventilation controlled
- roof intact, some window breakage (limited release area)
- fire rate controlled by availability of oxygen in warehouse
- low temperature of flue gases, low plume rise

- Roof collapse

- Combustion rate, affected by type of fire

- Pesticides fires and dispersion (cont.)
- UK HSE suggests :
- plume rise set at max 50 m
- calculations for source via a few m2 area of window (nevertheless, recognized as pessimistic), (NTUA methodology refers to 3 m2)
- special models

- UK HSE suggests meteorological condition to be examined as worst case ones :
- F2
- D5, D15 with low inversion height (400 m)

- UK HSE suggests :

- Pesticides fires and dispersion (cont.)
- NTUA methodology suggests the following cases :
- Roof collapse : flue gas rate 8 kg/m2.sec (per warehouse area), T=500 °C
- Ventilation controlled (roof intact) : flue gas rate 5 kg/m2.sec (per opening area, assumed 3 m2), T=140 °C

- NTUA methodology suggests the following cases :

- Pesticides fires and dispersion (cont.)
- NTUA methodology classification of fires (as per HSE FIRE Pest II computer program)

- Pesticides fire and dispersion (cont.)
- Survivor fraction according to NTUA methodology (as per HSE, Risk Assessment Method for Warehouses 1995)

- Accidents with effects to environment
- No mature and wide-used quantitative models for estimation of effects to environment
- Qualitative models (applied some times, examples :
- Energy Institute (ex. IP) Screening Tool
- Belgium (Flanders) Richtlijn Milieurisicoanalyse
- IPC Guidance Note on Storage and Transfer of Materials for Scheduled Activities, Irish EPA

- No unique approach in EU members (in many countries no specific approach) in relevant requirements

- Literature for Top Events Consequence Analysis Models
- Lees’ Loss Prevention in the Process Industries, Elsevier Butterworth Heinemann, 3nd Edition, 2005
- Methods for the Calculation of Physical Effects due to Releases of Hazardous Materials (Liquids and Gases), Yellow Book, CPR 14E, VROM, 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

- Literature for Top Events Consequence Analysis Models (cont.)
- Safety Report Assessment Guides (SRAGs), Health and Safety Executive, UK
- Risk Assessment Methods for Warehouses - Computer Program FIREPEST II, Health and Safety Executive, 1997
- Assael M., Kakosimos K., Fires, Explosions, and Toxic Gas Dispersions, CRC Press, 2010 Benchmark Exercise in Major Accident Hazard Analysis, JRC Ispra, 1991
- Rew P., Humbert W., Development of Pool Fire Thermal Radiation Model, HSE Contract Research Report 96, 1996
- McGrattan K., Baum H., Hamins A. Thermal Radiation from Large Pool Fires, National Institute of Standards and Technology, NISTIR 6546, Nov 2000
- Taylor J., Risk Analysis for Process Plant, Pipelines and Transport, E&FN SPON, 1994

- Literature for Top Events Consequence Analysis Models (cont.)
- Drysdale D., Fire Dynamics, J. Wiley and Sons, 2nd Edition, 1999
- Beychok M., Fundamentals of Stack Gas Dispersion, 3rd Edition, 1994
- C. Delvosalle, F. Benjelloun, C. Fiévez,, A Methodology for Studying Domino Effects, Faculté Polytechnique de Mons,Ministere Federal de l’;Emploi et du Travail, July 1998
- RIVM, Reference Manual Bevi Risk Assessments, 2009
- ALOHA, Users Manual, US EPA, 2007
- ALOHA Two Day Training Course Instructor's Manual
- Environmental risk assessment of bulk storage facilities: A screening tool, EI, 2009
- Richtlijn Milieurisicoanalyse, 2006

- Literature for Top Events Consequence Analysis Models (cont.)
- IPC Guidance Note on Storage and Transfer of Materials for Scheduled Activities, Irish EPA, 2004
- N. Markatos, NTUA, Chemical Engineering Department, Methodology of Assessment of Consequence from fire in Pesticide installations, 2001 (in Greek)

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