This project is funded by the European Union
Projekat finansira Evropska Unija
TOP EVENTS
CONSEQUENCE
ANALYSIS MODELS
Antony Thanos
Ph.D. Chem. Eng.
antony.thanos@gmail.com
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Consequence analysis framework
Hazard
Identification
Release
scenarios
Event
trees
Dispersion models
Consequence
results
Accident
type
Release models
Release
quantification
Fire, Explosion Models
Domino effects
Limits of
consequence analysis
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Pool fire
 Ignition of flammable liquid phase
Main consequence
Thermal radiation
Liquid fuel tank fire
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Pool fire characteristics
 Pool dimensions (diameter, depth)
o 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
Dp 
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by the European Union
4  Abund

Project implemented by Human
Dynamics Consortium
• Pool fire characteristics (cont.)
 Pool dimensions (diameter, depth) (cont.)
o 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
Release
to pool
This Project is funded
by the European Union
Combustion
rate
Project implemented by Human
Dynamics Consortium
• Pool fire characteristics (cont.)
 Pool dimensions (diameter, depth) (cont.)
o Unconfined pool :
M in  M comb  mcomb  A
Apool  V pool / Depth
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)
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.)
o Example :
Tb  Ta
Tb  Ta
m
0.001 H C
H v  C p (Tb  Ta )
(liquefied gases ) m 
0.001 H C
H v
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.)
o Example, Thomas correlation :


Hf
m


 42
 a g Dp 
Dp


0.61
Hf= flame height
Dp= pool diameter
m= specific comb.rate ρa= air density
g=gravity constant
o Big pools : Hf/Dp in the range of 1-2
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Pool fire models (cont.)
 Point source model (cont.)
o No flame shape taken into account
o A fraction of combustion energy is
considered to be transmitted by ideal point
in pool center
Thermal radiation
transmitted
semi spherically
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Pool fire models (cont.)
 Point source model (cont.)
f M H C t a
q
4  x2
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”
o Increased inaccuracies near pool end
(important for Domino effects)
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.)
o Calculation 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.)
o Calculation equation :
q  VF  E  ta
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.)
o 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
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Pool fire models (cont.)
 Solid flame radiation model (cont.)
o Emissive 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.)
o 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)
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Pool fire models (cont.)
 Solid flame radiation model (cont.)
o Emissive power : (cont.)
 One example of correlations available for max
emissive power :
m  Hc  f
Emax 
H
1 4 f
Dp
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.)
o Emissive power : (cont.)
 Final emissive power must take into account
smoke production. Example correlations :
E  Emax  (1  s)  Esmoke  s
E  140  e
0.12 D p
 20  (1  e
0.12 D p
)
s, smoke coverage of surface
Dp, pool diameter (m)
Esmoke, emissive power of smoke (kW/m2)
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Pool fire models (cont.)
 Solid flame radiation model (cont.)
o 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
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Pool fire models (cont.)
 UK HSE suggestions for LPGs :
o Emissive 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
Main consequence
Thermal radiation
Secondary consequences:
oFragments (missiles)
oOverpressure
LPG BLEVE (Crescent City)
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 m 3)
 Very high emissive power (in the order or 200350 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) :
D  5.8 m1 / 3
t  0.45 m1 / 3 m  30 tn
t  2.6 m1 / 6 m  30 tn
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)
Radius (max), m
Duration, sec
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by the European Union
ADL
TNO
AIChE
Aloha
122
112
110
106
16
14
16
13
Project implemented by Human
Dynamics Consortium
• Fireball/BLEVE characteristics and models (cont.)
 Radius and duration from correlations with tank
content, example (AIChE CCPS) :
D  5.8 m1 / 3
t  0.45 m1 / 3 m  30 tn
t  2.6 m1 / 6 m  30 tn
o t, duration (sec)
o m, mass (kg)
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
o radiation emitted via fireball surface,
o Usually 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)
q  VF  E  ta
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.)
o View Factor : function of distance of receptor
from flame and fireball radius
o Transmissivity 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)
E  235  Pv0.39
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
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
Main consequence
Thermal radiation
Propane jet flame test
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 15

d Ct
MWa
MW f
L= jet flame length
d= release point diameter
Ct= fuel content per mole in stoichiometric mix
of fuel/air
ΜWa= air molecular weight
MWf= fuel molecular weight
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  9.1 M
W  0.25  L
L= jet flame length
M= release rate (kg/sec)
W= jet radius at flame tip (m)
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Jet flame models (cont.)
 Point source models
o Single point : all energy is released from
flame “center”. Similar to relevant point
source model for pool fires
o Multipoint 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
o Radiation emitted via flame surface
o Calculation 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.)
o Calculation equation :
q  VF  E  ta
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
M  c
E  Fs
A jet
Fs  0.21 e
0.00323u j
 0.11
Fs= fraction of combustion energy radiated
uj= expanding jet velocity (m/sec)
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 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
100%
Centerline "ground" concentration (v/v)
0
10%
50
100
150
200
250
300
350
400
UFL
LFL
1%
1/2 LFL
0%
Downwind distance, x (m)
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
1/2 LFL
Crosswinf distance (CW)
50
44 DW
(UFL)
LFL
20 CW
(UFL)
UFL
128 DW
(LFL)
0
0
50
100
150
200
250
67 CW
(LFL)
204 DW
(1/2LFL)
94 CW
(1/2LFL)
-50
-100
Downwind distance (DW), x(m)
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 : neutral
 F : 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 :
o Wind speed referred in meteorological data
usually refer to measurement at 9-10 m
height
o Boundary 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.)
o Simplified function :
u z  uref
p, function of :
 z

z
 ref




p
stability class
surface roughness
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 :
32
Wind velocity, m/sec
28
C
A
24
D
F
E
20
16
12
8
4
0
0
5
10
15
20
25
30
35
Height, m
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/urban
o 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.)
o Conservative 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.)
y
o For continuous releases, concentration at
constant location (x, y, z) is not constant
x
not exposed
T=0
average wind
direction
y
exposed
x
T=t
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.)
 Averaging time : (cont.)
o increase of averaging time :
plume boundaries widen
concentration 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 !!!
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
100
Averaging time = 1 sec
1/2 LFL
50
50
44 DW
(UFL)
LFL
20 CW
(UFL)
UFL
128 DW
(LFL)
0
0
50
100
150
200
250
67 CW
(LFL)
204 DW
(1/2LFL)
94 CW
(1/2LFL)
-50
Crosswind distance (CW)
Crosswinf distance (CW)
Averaging time = 30 min
1/2 LFL
28 DW
(UFL)
10 CW
(UFL)
LFL
86 DW
(LFL)
0
0
UFL
50
100
150
200
250
47 CW
(LFL)
136 DW
(1/2LFL)
72 CW
(1/2LFL)
-50
-100
-100
Downwind distance (DW), x(m)
This Project is funded
by the European Union
Downwind distance (DW), x(m)
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)
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.)
 Passive (neutral) dispersion (Gauss) :
o Release 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) :
o Basic characteristics:
Maximum concentration at centreline
Concentration 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) :
o Basic equation for point source continuous
release
C ( x, y , z ) 
M
2    y  z  u
e
  y2

 2 2
y





  ( z  H2e ) 2   ( z  H2e ) 2  

2 z
2 z


  e
 e




u, wind speed at z (m/sec)
M, release rate flow (kg/sec)
Hd, active release height (m)
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 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


t a ver
y
10 min
y
This Project is funded
by the European Union
 t aver
 
 10 min



0. 2
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.)
o Equations provided for point stationary
source (no momentum)
o But jets of releases have significant
momentum due to high velocity…
modifications needed in model to take into
account release momentum
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 For jets of releases modifications are needed, typical
example : plume rise parameter to modify the
release source point at downstream location
Modified
Original
This Project is funded
by the European Union
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 gases
 Relevant 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)
Ground level centreline concentration
(mgr/m3)
0,8
0,6
0,4
0,2
0,0
0
1000
2000
3000
4000
5000
6000
Downwind distance (m)
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium
• Vapour cloud (gas) dispersion (cont.)
 Heavy gas dispersion
o Special complex models
CFD
Box 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.)
o Maximum concentration expected at
centerline
o Concentration 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.)
o Meteorological data
F2 produce more extended cloud
o Propane/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 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 consequence
Overpressure
VCE results (Flixborough)
This Project is funded
by the European Union
Secondary consequences:
oFragments (e.g. broken glasses)
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
o Simple, based on analogy with explosives
effects
o A fraction of combustion energy released in
cloud is attributed to produce overpressure
o The former energy fraction is recalculated as
equivalent (on energy basis) mass of TNT
o The 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.)
WTNT   e
W f Hc f
HcTNT
Wf= flammable in cloud
WTNT= TNT equivalent mass (combustion energy
basis)
αe = TNT equivalency coefficient (energy basis)
Hcf = combustion energy of flammables (kJ/kg)
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
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.)
R
R
3
WTNT
HcTNT= combustion energy for TNT (4,680 kJ/kg)
R = Hopkinson distance (m/kg0.33)
R= distance from explosion centre
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
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.)
o Overpressure from Berg graph
using Sachs distance
R
R
E
3
P0
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.)
o Flame 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
This Project is funded
by the European Union
Composite for unknown ignition time
Project implemented by Human
Dynamics Consortium
• Pesticides fires and dispersion
 Variation of stored substances quantities within
year due to seasonal production of some
products.
o 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
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 :
o Combustion products (e.g. SO2, HCl, NO2
etc.)
o Unburned 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 :
o C to CO : 5%
o 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
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 collapse
 As in open area, fuel controlling
 High flue gas temperature
o 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
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)
Combustion
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
Low
13000 sec
Combustibles
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)
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
Liquid substance
(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, CCPSAICHE, 2000
 Guidelines for Consequence Analysis of Chemical Releases, CCPSAICHE, 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)
This Project is funded
by the European Union
Project implemented by Human
Dynamics Consortium