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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
TOP EVENTSCONSEQUENCE ANALYSIS MODELS
Antony ThanosPh.D. Chem. [email protected]
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
• 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
• Pool fire characteristics Pool dimensions (diameter, depth)
oConfined pool (liquid fuels tank/bund fire) :
Tank fire pool : diameter equal to tank diameter dimension
bunds : pool diameter estimated by equivalent diameter of bund
bund
p
AD
4
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire characteristics (cont.) Pool dimensions (diameter, depth)
(cont.)
oUnconfined 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
Combustionrate
Release to pool
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire characteristics (cont.) Pool dimensions (diameter, depth)
(cont.)
oUnconfined 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)
DepthVA
AmMM
poolpool
combcombin
/
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire characteristics (cont.) Flame height, inclination (angle of
flame from vertical due to wind) Long duration (hours to days) Combustion rate
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models Combustion rate per pool surface
on empirical equations (Burges, Mudan etc.)
oExample :
v
Cab
abpv
Cab
H
HmgasesliquefiedTT
TTCH
HmTT
001.0)(
)(
001.0
m = specific comb.rate (kg/m2.sec) Tb = Boiling point βρασμού (Κ) Ta = ambient temperature (K) ΔHc = Combustion heat (J/kg) ΔHv = latent heat (J/kg) Cp = liquid heat capacity (J/kg.K)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• 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.)
oExample, Thomas correlation :
oBig pools : Hf/Dp in the range of 1-2
61.0
42
pap
f
Dg
m
D
H
Hf= flame height Dp= pool diameter m= specific comb.rate ρa= air density g=gravity constant
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Point source model (cont.)
oNo flame shape taken into account
oA fraction of combustion energy is considered to be transmitted by ideal point in pool center
Thermal radiationtransmittedsemi spherically
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Point source model (cont.)
o Increased inaccuracies near pool end (important for Domino effects)
24 x
tHMfq aC
q = thermal radiation flux at “receptor” (kW/m2) f = thermal radiation fraction (0.1-0.4, depending on
substance and pool size. Big pools, low values) Μ = combustion rate (kg/s) ΔHc= combustion heat (kj/kg) ta = transmissivity coeff., x = distance of pool center from “receptor”
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model,
radiation emitted via flame surface
Pool diameter
Flame height
Pool depth
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model (cont.)
oCalculation based on : flame shape (usually
considered cylinder -tilted or not-),
distance from flame (View Factor),
emissive power (thermal radiation flux at flame surface)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model (cont.)
oCalculation equation :
atEVFq q = thermal radiation flux at “receptor” (kW/m2) VF = view factor for flame shape at receptor Ε = emissive power (kW/m2) ta = transmissivity coefficient
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model (cont.)
o View Factor : function of distance of receptor from flame and flame dimensions. Different equation for different flame shapes
o 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)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model (cont.)
oEmissive power : Depending on pool size, substanceFor big pools, soot formation (20
kW/m2), masking of flame, significant reduction of average flame emissive power
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model (cont.)
oEmissive power : (cont.)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model (cont.)
oEmissive 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)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model (cont.)
oEmissive power : (cont.)One example of correlations
available for max emissive power :
p
f
D
HfHcm
E41
max
Ε= emissive power (kW/m2) m= specific combustion rate (kg/m2.sec) ΔHc= combustion heat (kJ/kg) f = thermal radiation ratio Hf = flame length Dp = pool diameter
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model (cont.)
oEmissive 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)
)1(20140
)1(12.012.0
max
pp DD
smoke
eeE
sEsEE
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Solid flame radiation model (cont.)
oEmissive 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) UK HSE suggestions for LPGs :
oEmissive power : 200 kW/m2 over half flame height
Some conservative assumptions o 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)
o Low relative humidity examined (high transmissivity coefficient)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pool fire models (cont.) Example results for propane pool fire
Dp=10 m, wind speed 5 m/sec T=25 °C (confined fire, Aloha),
o flame height Hf : 21 m
o combustion rate M : 400 kg/min
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• 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)
o pool diameter Dp = 27 m
o flame length : 11 m
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 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)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball/BLEVE characteristics and models (cont.) Radius and duration from
correlations with tank content, example (AIChE CCPS) :
o t, duration (sec)
o m, mass (tn)
o No significant deviations for various correlations available, example results for full propane tank BLEVE (100 m3)
tnmmt
tnmmt
mD
306.2
3045.0
8.5
6/1
3/1
3/1
ADL TNO AIChE
Aloha
Radius (max), m
122 112 110 106
Duration, sec
16 14 16 13
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball/BLEVE characteristics and models (cont.) Radius and duration from
correlations with tank content, example (AIChE CCPS) :
o t, duration (sec)
o m, mass (kg)
tnmmt
tnmmt
mD
306.2
3045.0
8.5
6/1
3/1
3/1
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball/BLEVE characteristics and models (cont.) Mass in fireball calculations :
o Typically whole tank content (worst case approach.)
o 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball/BLEVE characteristics and models (cont.) Solid flame model
oradiation emitted via fireball surface,
oUsually fireball considered as sphere touching ground (conservative approach, adopted by UK HSE)
Evolution of fireball/BLEVE
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball/BLEVE characteristics and models (cont.) Solid flame radiation model (cont.)
o Calculation based on : sphere shape at contact with
ground, distance from fireball (sphere View
Factor), fireball emissive power (thermal
radiation flux at fireball surface) atEVFq
q = thermal radiation flux at “receptor” (kW/m2) VF = view factor ar receptor for sphere shape fireball Ε = emissive power (kW/m2) ta = transmissivity coefficient
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball/BLEVE characteristics and models (cont.) Solid flame radiation model (cont.)
oView Factor : function of distance of receptor from flame and fireball radius
oTransmissivity coefficient : as in pool fire case
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball/BLEVE characteristics and models (cont.) Emissive power in fireball
calculations :o Correlations are available for emissive
power calculation based on :
o vapour pressure at failure conditions (AIChE CCPS)
Pv, vapour pressure at failure (MPa)
o and/or mass involved, duration, size of fireball
o Experimental data provide values up to 350 kW/m2
o UK, HSE suggestion >270 kW/m2
39.0235 vPE
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball/BLEVE models (cont.) Example results (full 100 m3
propane tank BLEVE, Aloha)
o 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Fireball/BLEVE models (cont.) Example results (full 100 m3
propane tank BLEVE, Aloha) (cont.)
o 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
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
• 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Jet flame models Combustion rate determined by
release rate Dimensions from empirical
equations. Example of simplified Mudan-Cross equation
L= jet flame lengthd= release point diameterCt= fuel content per mole in stoichiometric mix of fuel/airΜWa= air molecular weightMWf= fuel molecular weight
f
a
MW
MW
Ctd
L 15
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Jet flame models (cont.) Dimensions from empirical
equations. Example of simplified Considine-Grint equation for LPGs
L= jet flame lengthM= release rate (kg/sec)W= jet radius at flame tip (m)
LW
ML
25.0
1.9
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Jet flame models (cont.) Point source models
oSingle point : all energy is released from flame “center”. Similar to relevant point source model for pool fires
oMultipoint source : several point along jet trajectory taken into account
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Jet flame models (cont.) Solid flame radiation model
oRadiation emitted via flame surface
oCalculation based on : shape (cylinder, tilted or not) distance (View Factor)emissive power
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Jet flame models (cont.) (cont.) Solid flame radiation model (cont.)
oCalculation equation :
atEVFq q = thermal radiation flux at “receptor” (kW/m2) VF = view factor for flame shape at receptor Ε = emissive power (kW/m2) ta = transmissivity coefficient
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Jet flame models (cont.) Solid flame radiation model (cont.)
o View Factor : function of distance of receptor from flame and flame dimensions for shape assumed
o Transmissivity coefficient : as in pool fires, fireball/BLEVE
o 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)
11.021.0 00323.0
jus
jets
eF
A
cMFE
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Jet flame models conservative approaches Examination of horizontal jet
o Produce more extended thermal radiation zones
o 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)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Jet flame models example results (cont.) Example results, 2 in hole in top of
propane tank/gas phase, vertical jet (Aloha)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
END OF PART AEND OF PART A
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud dispersion (cont.) Extent of cloud : dimensions,
downwind/crosswind till specific endpoints (concentration)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud dispersion (cont.) Endpoints :
o Toxics : several toxicity endpoints (e.g. IDLH, LC50)
o 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)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud dispersion (cont.) Endpoints : (cont.)
o 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud dispersion (cont.) Example results for LPG dispersion (SLAB)
at ground level centerline
0%
1%
10%
100%
0 50 100 150 200 250 300 350 400
Downwind distance, x (m)
Cen
terl
ine
"gr
oun
d"
con
cen
trat
ion
(v/
v)
UFL
LFL
1/2 LFL
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud dispersion (cont.) Example results for LPG dispersion (SLAB)
(cont.) at ground level
-100
-50
0
50
100
0 50 100 150 200 250
Downwind distance (DW), x(m)
Cro
ssw
inf
dis
tan
ce (
CW
) 44 DW(UFL)
20 CW(UFL)
128 DW(LFL)
67 CW(LFL)
204 DW(1/2LFL)
94 CW(1/2LFL)
LFL
1/2 LFL
UFL
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Release conditions affecting
dispersion :o substance properties (Boiling Point
etc.)
o pressure, temperature at containment
o release rate and area
o release point height
o release direction (upwards –PSV-, horizontal)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Meteorological conditions affecting
dispersion :o atmospheric stability class (A-F),
o wind speed,
o air temperature,
o humidity (for some substances reacting with water as for example HF or other polar substances : SO2, NH3 etc.)
o Type of area : rural/industrial/urban, roughness factor
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Atmospheric stability :
o Expression of turbulent mixing in atmosphere. Related with atmospheric vertical temperature gradient (dT/dz)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Atmospheric stability : (cont.)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Atmospheric stability : (cont.)
o Usually attributed to standardized class A-F (Pasquill)
A : unstable, in combination with high winds favors dispersion
D : neutralF : stable, minimum mixing in
atmosphere
o Other parameter to attribute atmospheric stability, Monin-Obukhov length (positive for stable conditions, negative for unstable conditions)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Atmospheric stability : (cont.)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Atmospheric stability : (cont.)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Wind speed :
oWind speed referred in meteorological data usually refer to measurement at 9-10 m height
oBoundary layer effect (variation of speed with height)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Wind speed : (cont.)
oSimplified function :
p, function of :stability classsurface roughness
p
refrefz z
zuu
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Wind speed : (cont.)
o Variation with stability class for rural environment :
0
4
8
12
16
20
24
28
32
0 5 10 15 20 25 30 35
Height, m
Win
d v
elo
city
, m/s
ec
A C D E F
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Meteorological conditions :
o 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Type of surroundings :
rural/industrial/urbano Refers to variation of height in
elements of surrounding
o Usually attributed via “roughness factor”
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Type of surroundings (cont.)
oConservative approach : open country (rural)
Averaging time :
o Variation in time, due to turbulence, of wind characteristics :
speed
direction
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Averaging time : (cont.)
o For continuous releases, concentration at constant location (x, y, z) is not constant
y
x
x
T=t
T=0
not exposed
exposed
y
average winddirection
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Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Averaging time : (cont.)
o increase of averaging time :plume boundaries widenconcentration distribution
flattens
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Averaging time : (cont.)
o Very important to use averaging time in models, suitable to exposure time under interest
o Models may use parameters for certain averaging time, which might not be suitable for application in Safety Report. PLEASE ALWAYS CHECK !!!PLEASE ALWAYS CHECK !!!
o Gaussian models use implicit 10-min averaging time but…
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Averaging time : (cont.)
o Toxics exposure usually under interest for period of 30 min (due to LC50 30 min endpoints etc.)
o Aloha-DEGADIS (Heavy Gas Dispersion) uses 5 min for toxics
o Ignition of flammable cloud is related with very low exposure time (time just for ignition to happen).
o Aloha-DEGADIS uses 10 sec for flammables (e.g. LPGs, no matter if toxic effect is examined)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Averaging time : (cont.)
o Example results for propane release from liquid phase piping (SLAB)
-100
-50
0
50
100
0 50 100 150 200 250
Downwind distance (DW), x(m)
Cro
ssw
inf
dis
tan
ce (
CW
) 44 DW(UFL)
20 CW(UFL)
128 DW(LFL)
67 CW(LFL)
204 DW(1/2LFL)
94 CW(1/2LFL)
LFL
1/2 LFL
UFL
-100
-50
0
50
100
0 50 100 150 200 250
Downwind distance (DW), x(m)
Cro
ssw
ind
dis
tan
ce (
CW
) 28 DW(UFL)
10 CW(UFL)
86 DW(LFL)
47 CW(LFL)
136 DW(1/2LFL)
72 CW(1/2LFL)
LFL
1/2 LFL
UFL
Averaging time = 1 sec Averaging time = 30 min
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Averaging time : (cont.)
o Reason for reporting both LFL, ½ LFL in flammable dispersion
o ½ LFL reporting contributes to uncertainty of averaging time (conservative approach)
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Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) 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.) Passive (neutral) dispersion
(Gauss) :
oBasic characteristics: Maximum concentration at
centrelineConcentration reducing with
increasing distance from source
If release at ground level, maximum concentration at ground level
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Passive (neutral) dispersion
(Gauss) :
oBasic equation for point source continuous release
u, wind speed at z (m/sec)M, release rate flow (kg/sec)Hd, active release height (m)
2
2
2
2
2
2
2
)(
2
)(2
2),,( z
e
z
e
y
HzHzy
zy
eeeu
MzyxC
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Passive (neutral) dispersion
(Gauss) : (cont.)
oσy, 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
2.0
min10 min10
aver
y
ty taver
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Passive (neutral) dispersion
(Gauss) : (cont.)o Example results for dispersion for NH3
release by 2 in hole in 6 bar gas vessel, D5 (Aloha)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Passive (neutral) dispersion
(Gauss) : (cont.)
oEquations provided for point stationary source (no momentum)
oBut jets of releases have significant momentum due to high velocity… modifications needed in model to take into account release momentum
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Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Passive (neutral) dispersion
(Gauss) : (cont.)o For jets of releases modifications are
needed, typical example : plume rise parameter to modify the release source point at downstream location
Original
Modified
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Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Flue gases dispersion
o Example : pool fire combustion products, e.g., SO2
o 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 gasesRelevant plume rise equations
provided for stacks (Briggs, Holland equations), provide unrealistic plume rise height
o Conservative approach, no plume rise, dispersion begins from flame end
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Flue gases dispersion (cont.)
o Special atmospheric condition to be considered (temperature inversion conditions, trapped plume)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Plume rise effects
o Concentration at centrelines not continuously decreasing with distance
o Max concentration at centreline appears at distance from source
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Plume rise effects (cont.)
o 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)
0,0
0,2
0,4
0,6
0,8
0 1000 2000 3000 4000 5000 6000
Downwind distance (m)
Gro
und leve
l ce
ntr
eline c
once
ntr
ati
on
(mgr/
m3)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Heavy gas dispersion
oSpecial complex modelsCFDBox models (instant releases)Grounded plume models
(continuous releases)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Heavy gas dispersion (cont.)
oMaximum concentration expected at centerline
oConcentration decreases with increasing distance
o More extended plume compared to neutral dispersion
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.) Heavy gas dispersion (cont.)
oMeteorological dataF2 produce more extended
cloud
oPropane/butane cases same release source (e.g.
same hole size) will produce more extended cloud for propane due to higher release rate
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion models Heavy gas dispersion (cont.)
o Example results for propane release from 2 in hole in liquid phase of tank (D5) (Aloha)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour cloud (gas) dispersion models Heavy gas dispersion (cont.)
o Example results for propane release from 2 in hole in liquid phase of tank (F2) (Aloha)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
END OF PART BEND OF PART B
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
• Vapour Cloud Explosion (VCE) characteristics Very short duration (<1 sec)
Models, high uncertainty due to several assumptions used in every model
Type of models:o CFD (FLACS, PHOENIX etc.)
o TNT blast charge (TNT equivalency)
o Air-fuel charge blast (Multi-Energy, Baker -Strehlow -Tang etc.)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) models TNT equivalency model
oSimple, based on analogy with explosives effects
oA fraction of combustion energy released in cloud is attributed to produce overpressure
oThe former energy fraction is recalculated as equivalent (on energy basis) mass of TNT
oThe effects are defined based on known correlation of overpressure with TNT mass
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) models (cont.) TNT equivalency model (cont.)
o αe, refers to part of combustion energy released producing overpressure (1-10%)
o High uncertainty in both αe value and quantity of flammables (released mass –till what time ???-, mass within LFL-UFL) to be used
o Review on topic by TNO Yellow Book and AICheJ CCPS Guideline
TNT
ffeTNT Hc
HcWW
Wf= flammable in cloud WTNT= TNT equivalent mass (combustion energy basis) αe = TNT equivalency coefficient (energy basis) Hcf = combustion energy of flammables (kJ/kg)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) models (cont.) TNT equivalency model (cont.)
o Some comments/examples on selection of mass and αe :
αe must be selected along with suitable flammable mass
for αe 1-5%, 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) models (cont.) TNT equivalency model (cont.)
o 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
o Explosives blast and VCE present differences, as explosives have short duration higher shock wave peak values.
o TNT equivalency model is approximation of phenomenon based on statistical analogies
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) models (cont.) TNT equivalency model (cont.)
o Overpressure calculated by diagram
for distances required
o Uncertainty on centre of explosion
to be considered
o Similar diagrams for positive phase
duration, impulse
3TNTW
RR
HcTNT= combustion energy for TNT (4,680 kJ/kg) R = Hopkinson distance (m/kg0.33) R= distance from explosion centre
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) (cont.) TNO Multi-Energy model :
o Only confined areas of cloud are considered
o Partial explosions from confined areas expected
o 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) (cont.) TNO Multi-Energy model : (cont.)
oOverpressure from Berg graph
using Sachs distance
3
0PE
RR
E= combustion energy R = Sachs distance R= distance from explosion centre
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) (cont.) TNO Multi-Energy Model : (cont.)
o Similar graphs for positive phase duration, dynamic pressure
o Blast strength 10 : detonation, explosives case, not valid for VCEs as propagation of blast via detonation requires high homogeneity in cloud
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) (cont.) TNO Multi-Energy Model : (cont.)
o Disadvantage : complex empirical rules for (TNO Yellow Book, Assael) :
definition of confined areas definition of successive or
simultaneous blast in confided areas
selection of blast strength (confinement increase, increases blast strength
o HSE suggests blast strengths 2 and 7
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) (cont.) Baker-Strehlow-Tang model
o Similar principles as TNO Multi-Energy model
confined areas only taken into account
stoichiometry of air with fuel in confined areas
o Gas type “reactivity” (susceptibility to flame front acceleration) taken also into account along with obstacle density
o methane, CO : low reactivity
o H2, acetylene, ethylene/propylene oxide : high reactivity
o other substances : medium
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) (cont.) Baker-Strehlow-Tang model (cont.)
oFlame speed defined by table on gas reactivity and confinement type
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Vapour Cloud Explosion (VCE) (cont.) Baker-Strehlow-Tang model (cont.)
o 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)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pesticides fires and dispersion Variation of stored substances
quantities within year due to seasonal production of some products.
oEvaluation 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• 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 :
oCombustion products (e.g. SO2, HCl, NO2 etc.)
oUnburned pesticide active substance
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pesticides fires and dispersion (cont.) UK HSE suggests stoichiometric
conversion of S, Cl to SO2 and HCl.
Conversion ratios :
oC to CO : 5%
oN 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pesticides fires and dispersion (cont.) Survivor fraction in flue gases :
0.5-10% of combustion rate of substance at source
Lower survivor fraction for high boiling point substances
UK HSE suggests survivor fraction 10% otherwise justification must be provided
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pesticides fires and dispersion (cont.) Especially in closed warehouse cases :
o what is plume rise for flue gases ??
o which is the combustion rate ?? Plume rise in warehouse flue gases
o For fire in full development plume rise might be high, but potentially low in initial phase of fire
o Typical equations fail, as producing unrealistic plume rise
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pesticides fires and dispersion (cont.) Combustion rate, affected by type of fire
o Roof collapseAs in open area, fuel controllingHigh flue gas temperature
o Ventilation controlledroof intact, some window breakage
(limited release area)fire rate controlled by availability of
oxygen in warehouselow temperature of flue gases, low
plume rise
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pesticides fires and dispersion (cont.) UK HSE suggests :
o plume rise set at max 50 m
o calculations for source via a few m2 area of window (nevertheless, recognized as pessimistic), (NTUA methodology refers to 3 m2)
o special models UK HSE suggests meteorological condition
to be examined as worst case ones :
o F2
o D5, D15 with low inversion height (400 m)
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pesticides fires and dispersion (cont.) NTUA methodology suggests the following
cases :
o Roof collapse : flue gas rate 8 kg/m2.sec (per warehouse area), T=500 °C
o Ventilation controlled (roof intact) : flue gas rate 5 kg/m2.sec (per opening area, assumed 3 m2), T=140 °C
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pesticides fires and dispersion (cont.) NTUA methodology classification of fires
(as per HSE FIRE Pest II computer program)
CombustiblesCombustion rate
Duration
High intensity fire
Flammable liquids (product solutions in solvents) purring in floor and pool fire.Inert “technical” substances or products containing significant percentage of flammable solvents
High 6500 sec
Medium intensity fire
Inert “technical” substances or products containing significant percentage of flammable solvents
Medium 7000 sec
Low intensity fire
Inert “technical” substances or products in flammable packaging
Low13000
sec
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Pesticides fire and dispersion (cont.) Survivor fraction according to NTUA
methodology (as per HSE, Risk Assessment Method for Warehouses 1995)
Solid substance
Liquid substance
Liquid substance
(2)
Liquid substance
particles <2 mm, high storage height (1)
cans < 10kg, large
storage height (1)
cans < 10kg, small storage
height (1)
metal drums
High intensity fire
10 10 0.5 10
Medium intensity fire
5 5 0.5 4
Low intensity fire
2 2 0.5 1
(1) Medium and large storage height : > 2 m, small storage height: < 2 m
(2) Same for particles <2 mm and small storage height
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• Accidents with effects to environment No mature and wide-used
quantitative models for estimation of effects to environment
Qualitative models (applied some times, examples :
o Energy Institute (ex. IP) Screening Tool
o Belgium (Flanders) Richtlijn Milieurisicoanalyse
o 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• 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
This Project is funded by the European Union
Project implemented by Human Dynamics Consortium
• 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)