Consequence Assessment

Report
PIPELINE QRA SEMINAR
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
1
CONSEQUENCE ASSESSMENT
INTRODUCTION
• Release of material
Fire
• Release of Gas
• Jet fire
• Release of Liquid
• Pool Fire
• Release of Twophase
• Flash fire
• BLEVE
• Gas dispersion
• Explosion
• Human vulnerability
• Escalation
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
2
CONSEQUENCE ASSESSMENT
RELEASE OF HYDROCARBON GAS
Releases from gas inventories are governed by the following equation
for the initial release rate:
 1
Q 0  C D  A  P0  Z
where
Q0:
initial release rate (kg/s)
CD:
discharge coefficient
A:
area (m²)
P0:
initial pressure (Pa (N/m²))
M:
molecular weight of the gas (kg/kmol)
: ratio of ideal gas specific heats (1.3 for
methane)
R: universal gas constant (8314 J/(kg mol∙K))
T0: initial temperature (Kelvin)
Z 
M
RT
0


2


  1


 1
Following values of CD have been
recommended:
•
•
•
•
Sharp thin edged orifices: 0.62
Straight thick edged orifices: 0.82
Rounded orifices: 0.96
Pipe rupture: 1.00
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
3
CONSEQUENCE ASSESSMENT
RELEASE OF HYDROCARBON GAS
For METHANE a simple approximation is as follows:
Q 0  D ( mm )
2
 P ( bar )  10
4
Where
D:
leak area (mm2)
P: pressure (bar)
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
4
CONSEQUENCE ASSESSMENT
RELEASE OF HYDROCARBON GAS
Typical gas leak sizes for oil and gas installations:
Item
Leak sizes in mm
< 10
10 <25
25<50
50<75
75<100
>=100
N/A
Actuated Block Valve,
D <= 3"
87%
7%
0%
0%
7%
0%
0%
Actuated Block Valve,
3" < D <= 11"
68%
9%
14%
0%
0%
0%
9%
Actuated Block Valve,
D> 11"
83%
17%
0%
0%
0%
0%
0%
Flanges, D <= 3"
78%
10%
8%
2%
1%
1%
0%
Flanges,
3" < D <= 11"
84%
5%
4%
1%
0%
6%
0%
Flanges, D> 11"
85%
4%
0
4%
0%
7%
0%
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
5
CONSEQUENCE ASSESSMENT
RELEASE OF HYDROCARBON GAS
Examples of release rates (CD=0.62, =1.3)
Pressure
barg
D=1 mm
Release rate
D=8mm
Release rate
D=37.5mm
Release rate
1
0.000 kg/s
0.011 kg/s
0.234 kg/s
5
0.000 kg/s
0.032 kg/s
0.699 kg/s
15
0.001 kg/s
0.085 kg/s
1.861 kg/s
30
0.003 Kg/s
0.164 Kg/s
3.605 kg/s
45
0.004 kg/s
0.243 kg/s
5.348 kg/s
60
0.005 kg/s
0.323 kg/s
7.092 kg/s
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
6
CONSEQUENCE ASSESSMENT
RELEASE OF HYDROCARBON GAS
Decaying releases
Pressure decay as a function of leak size - including the effect of blowdown
(for 25 m³ gas inventory at a HP compressor, 63.9 barg, MW=18.3)
Small
Small with blowdown
Medium
Medium with Blowdown
Large
Large with blowdown
Limit
000 s
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
7
CONSEQUENCE ASSESSMENT
RELEASE OF HYDROCARBON GAS
Releases from liquid inventories are governed by the following
equation.
Q0  C D  A
2  l ( P0  P a )   l g  h 
Q0:
initial release rate (kg/s)
CD:
discharge coefficient (typical values 0.62-0.8)
A:
area (m²)
: liquid density (kg/m3)
P0:
initial pressure (Pa (N/m²))
Pa:
atmospheric pressure (105 Pa)
g: acceleration due to gravity (9.81 m/s2)
h: height of the liquid surface above the hole (m)
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
8
CONSEQUENCE ASSESSMENT
RELEASE OF HYDROCARBON GAS
Two Phase:
Release of two-phase flows will have a release rate between that for gas and that for liquid.
The fraction that flashes is related to fraction of gas at atmospheric conditions compared to
the overall release.
xg 
mg
mg  ml
Where:
mg: mass of gas
ml:
mass of liquid
The models for calculating two-phase flows are very complex and normally calculations are
performed using computer programmes.
Phase equilibrium affected by air
All methane - Butane
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
9
CONSEQUENCE ASSESSMENT
GAS DISPERSION
Open field dispersion of gas clouds not impinging on large obstacles generally consist of three
sections, each dominated by its own mechanism.
1. This is the first section near the release point; Mixing of air into the jet, due to
momentum of the release and shear forces at the edge (Cone shape)
2. The next section; Velocity of the release has been reduced and mixing of air
into the cloud due to the wind velocity – Especially for cross wind releases
3. Gaussian dispersion of the gas cloud due to ambient turbulence
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
10
CONSEQUENCE ASSESSMENT
GAS DISPERSION
Gas release from a inventory with a pressure of 45 barg through an 8 mm leak (0.36 kg/s). The release
occurs in the downwind direction and the wind speed is 1.5 m/s.
Red:
concentrations above the upper flammable limit (UFL)
Yellow:
contractions at or below the UFL
Green: concentrations at or above lower flammable limit (LFL)
Blue:
concentrations at or below 50% LFL
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
11
CONSEQUENCE ASSESSMENT
GAS DISPERSION – WIND SPEED
At high wind speeds the gas cloud will be more diluted as
Distance to LEL
more air will be entrained.
The dilutions are
more pronounced
for the 50% LFL
conc. of gas
PHAST calculations
at 1.5 m/s, 6 m/s
and 10 m/s wind
speeds, with
stability class F, D
and D respectively.
Hole size
mm
1
8
37.5
Pressure
barg
1
15
30
45
60
1
15
30
45
60
1
15
30
45
60
Release rate
kg/s
2.04E-04
1.88E-03
3.72E-03
5.62E-03
7.57E-03
1.31E-02
1.21E-01
2.38E-01
3.59E-01
4.85E-01
2.87E-01
2.65E+00
5.23E+00
7.90E+00
1.06E+01
1.5F
m
0.06
0.32
0.52
0.61
0.71
1.08
3.16
4.43
5.06
6.02
4.88
14.36
22.41
30.13
36.84
6D
m
0.06
0.30
0.48
0.58
0.65
0.97
2.54
3.61
4.52
4.94
4.25
11.58
19.27
26.82
32.59
10D
m
0.06
0.29
0.46
0.56
0.62
0.89
2.41
3.13
4.15
1.34
3.74
9.61
17.00
23.71
30.42
Distance to 50 %LEL
1.5F
m
0.21
0.72
1.08
1.25
1.47
2.15
5.67
7.82
9.52
11.39
8.75
36.37
54.89
71.39
87.67
6D
m
0.19
0.61
0.93
1.11
1.22
1.72
4.56
5.71
6.81
7.81
6.27
29.96
51.99
70.11
86.37
10D
m
0.19
0.58
0.84
1.03
1.15
1.42
3.92
5.19
5.82
6.60
5.39
25.83
48.92
67.74
85.29
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
12
CONSEQUENCE ASSESSMENT
GAS DISPERSION –
WIND DIRECTION
Neutral
buoyancy
•
•
•
The dispersion of the gas cloud is
affected by the wind in the 2nd and
3rd section with low velocity for the
gas plume.
Accordingly the direction of the
wind compared to the gas release
will influence the shape of the gas
cloud.
Analyses of upwind releases
computer simulations will have to
be made using Computational Fluid
Dynamics
Buoyant
Heavy
Upwards vertical release, zero
wind speed.
Upwards vertical release, finite
wind speed.
Downwards vertical release, zero
wind speed.
Upwards vertical release, finite
wind speed.
Horizontal release, zero wind
speed.
Horizontal release, wind speed in
direction of release
Horizontal release, wind speed in
direction opposed to release
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
13
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
Following conditions in relation to loss of hydrocarbon containment with subsequent events such as fire and
explosion can be a threat to human health
•
•
•
High air temperature
Radiation
Toxicity
• H2 S
• Combustion products (smoke)
• Oxygen depletion
•
Explosion
• Overpressure
• Missiles
• Whole body displacement
•
Obscuration of vision
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
14
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
High air temperature
High air temperature can cause skin burns, heat stress, and breathing difficulty.
The table indicates the effects of elevated temperatures.
Temperature (°C)
Physiological Response
127
Impeded breathing
140
5-min tolerance limit
149
Oral breathing difficult, temperature limit for escape
160
Rapid, unbearable pain with dry skin
182
Irreversible injury in 30 seconds
203
Respiratory tolerance time less than four minutes with wet skin
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
15
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
Radiation
• The pathological effects of thermal
radiation on humans are progressively:
Pain  First degree burns  Second
degree burns  Third degree burns 
Fatality
• The combination of effect and time of
exposure can be summed up in
“Thermal Dose”:
I:
t:
Thermal
Radiation
(kW/m²)
Effect
1.2
Received from the sun at noon in summer in northern Europe
2
Minimum to cause pain after 1 minute
Less than 5
Will cause pain in 15-20 seconds and injury after 30 seconds exposure
Greater than
6
Pain within approximately 10 seconds, rapid escape only is possible
12.5
Significant chance of fatality for medium duration exposure.
* Thin steel with insulation on side away from the fire may reach
thermal stress level high enough to cause structural failure
25
* Likely fatality for extended exposure and significant chance of fatality
for instantaneous exposure
* Spontaneous ignition of wood after long exposure
* Unprotected steel will reach thermal stress temperature that can
cause failure
35
* Cellulosic material will pilot ignite within one minute’s exposure
* significant chance of fatality for people exposed instantaneously
intensity (kW/m2)
time (s)
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
16
CONSEQUENCE ASSESSMENT
RADIATION DESIGN EXAMPLE
The height of the flare stack is determined based
on requirements to radiation at various locations as
per API 521.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
17
CONSEQUENCE ASSESSMENT
RADIATION CONSIDERATIONS
• Wind
• Sun
• Crane, if present
• Roads and walkways
• Offices
• Working areas
• Muster area
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
18
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
Toxicity - H2S
Hydrogen Sulphide is considered a broad-spectrum poison mostly affecting the nervous
system.
Hydrogen Sulphide has a very distinctive smell of rotten eggs, but at higher concentrations
theConc.
sense of smell
is paralysed.
Physical
properties
ppm
0.02 – 0.03
Odour threshold
1
Weak smell
5
Distinguishable smell
30
Sense of smell is paralysed
Conc.
Effects on humans
500 - 1000
1000
1000 – 1200
> 2000
Conjunctivitis
Objection to light after 4 hours exposure
Objection to light, irritation of mucous membranes, headache
Slight symptoms of poisoning after several hours
Pulmonary oedema and bronchial pneumonia after prolonged
exposure
Painful eye irritation, vomiting
Immediate acute poisoning
Lethal after 30 to 60 minutes
Acute lethal poisoning
ppm
20 - 30
50
150 – 200
200 – 400
250 - 600
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
19
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
Toxicity – Combustion products
Smoke from hydrocarbon fires contains various combustion products:
•
Carbon monoxide
•
Carbon dioxide
•
Oxides of nitrogen
•
Ammonia
•
Sulphur dioxide
•
Hydrogen fluoride
The concentration of the various components depends on the
material being burnt, the amount of oxygen present and the
combustion temperature
Gas
Concentration in smoke (%)
Well ventilated fire
Under ventilated fire
Gas fire
Liquid fire
Gas fire
Liquid fire
CO
0.04
0.08
3
3.1
CO2
10.9
11.8
8.2
9.2
O2
0
0
0
0
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
20
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
Toxicity – Combustion products – Effects on human health
CO2
CO
Conc.
Effects
Conc.
Effects
1,500
ppm
Headache after 15 minutes, collapse after 30
minutes and death after 1 hour.
20,000 ppm (2%
v/v)
2,000
ppm
Headache after 10minutes, collapse after 20
minutes and death after 45 minutes.
50% increase in
breathing rate and
depth
30,000 ppm (3%
v/v)
3,000
ppm
Maximum “safe” exposure for 5 minutes,
danger of collapse in 10 minutes.
100% increase in
breathing rate and
depth
6,000
ppm
Headache and dizziness in 1 to 2 minutes,
danger of death in 10 to 15 minutes
12,800
ppm
50,000 ppm (5%
v/v)
Breathing becomes
laboured and
difficult
NOx, NH3, SO2, HF
Component
Effects
NOx
Strong pulmonary irritant capable of
causing immediate death as well as
delayed injury
NH3
Pungent, unbearable odour; irritant to
eye and nose
SO2
A strong irritant, intolerable well
below lethal concentrations
HF
Respiration irritants
Immediate effect, unconscious after 2 to 3
breaths, danger of death in 1 to 3 minutes.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
21
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
Toxicity – Oxygen depletion
• Normal air contains 21% oxygen, however during fire, part of or all the oxygen is used for combustion.
• At oxygen concentrations below 15 %, oxygen starvation effects such as increased breathing, faulty
judgement, and rapid onset of fatigue will occur.
Concentration of
oxygen in air
(%)
Responses
11
Headache, dizziness, early fatigue, tolerance time 30 minutes.
9
Shortness of breath quickened pulse, slight cyanosis, nausea,
tolerance time 5 minutes.
7
Above symptoms becomes serious, stupor sets in,
unconsciousness occurs, tolerance time 3 minutes
6
Heart contractions stop 6 to 8 minutes after respiration stops
3-2
Death occurs within 45 seconds
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
22
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
Explosion – Overpressure
•
Compression and decompression of a blast
Overpressure
[barg]
0.210
20% probability of fatality to personnel
inside
0% probability of fatality to personnel in
the open
0.350
50% probability of fatality to personnel
inside
15% probability of fatality to personnel in
the open
0.70
100% probability of fatality to personnel
inside or in unprotected structures
wave on the human body results in
transmissions of pressure waves through
the tissues.
•
Damage occurs primarily at junctions
between tissues at different densities;
Consequence
bone, muscle and air cavities.
•
Lungs and ear drums are especially
susceptible to the damaging effects of
overpressure.
Relatively high pressures are required for
fatalities, and these are often related to
missiles, collapse of buildings or drag force
effects, and knock over of personnel
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
23
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
Explosion – Missiles
• Missiles in terms of fragments can be loose items
or items that are broken loose by the blast and
conveyed by the drag forces.
• Broken glass can generates sharp missiles and
glass breaks at relative low pressures:
• 1% level glass breakage peak=0.017 bar
• 90% level glass breakage peak=0.062
Injury
Peak
overpressure
(bar)
Impact
velocity
(m/s)
Impulse
(Ns/m²)
Skin laceration threshold
0.07-0.15
15
512
Serious wound threshold
0.15-0.2
30
1024
Serious wound near 50%
probability
0.25-0.35
55
1877
Serious wound near
100% probability
0.5-0.55
90
3071
Mass of glass
fragments (g)
Impact velocity (m/s)
1%
50%
99%
0.1
78
136
243
0.6
53
91
161
1
46
82
143
10
38
60
118
bar
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
24
CONSEQUENCE ASSESSMENT
HUMAN VULNERABILITY
Explosion – Whole body displacement
The blast overpressure and the impulse can knock personnel over or literally pick personnel up and translate
them in the direction of the blast wave.
The head is the most vulnerable part of the body from the effects of the translation and subsequent impact
with a solid surface.
Total body impact tolerance
Related velocity (m/s)
Most “safe”
3.05
Lethality threshold
6.40
Lethality 50%
16.46
Lethality near 100%
42.06
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
25
CONSEQUENCE ASSESSMENT
FIRE
Chemical reaction
A hydrocarbon fire is a chemical reaction between the oxygen in the air
and the hydrocarbon molecules which requires energy to initiate the
reaction (ignition).
1 CH4 + 2 O2  CO2 + 2 H2O + 809 KJ/mole
Convection
CO
Soot
Incomplete
Combustion
Conduction
Radiation
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
26
CONSEQUENCE ASSESSMENT
FIRE
Different types of fire:
•
Jet fire
•
Pool fire
•
Flash fire
•
Fireball/BLEVE
•
Explosion
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
27
CONSEQUENCE ASSESSMENT
FIRE
Radiation
The fraction of energy radiated from a fire depends on the type of fire, jet fire or
pool fire and the size of the fire.
Fractions of radiation for diffusion flames.
Gas
Methane
Butane
Natural gas
(95% Methane)
Burner diameter
(cm)
Fraction of heat
radiated
0.51
0.103
1.90
0.160
4.10
0.161
0.51
0.215
1.91
0.253
4.10
0.285
20.30
0.280
20.3
0.192
40.60
0.232
Fractions of radiation for jet fire
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
28
CONSEQUENCE ASSESSMENT
JET FIRE
Ignited high momentum and continuous release of flammable gas or liquid. These
fires are extremely violent with the formation of large turbulent flames, emitting
high levels of radiation.
Multiphase jet
fire test at
SpadeAdam
Jet fire in
terms of an
ignited gas
blowout in
Algeria
Rule of thumb
Flame size: Fl=18.5∙Q0.41
Fl: flame length (m)
Q: release rate (kg/s)
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
29
CONSEQUENCE ASSESSMENT
JET FIRE
Jet fire – Radiation
Jet fires have a very high heat output and the surface emissive power of the
flame can be as high as 300 to 400 kW/m².
Jet fire
For leaks
m>2
kg/s
For leaks
m > 0.1
kg/s
Local peak
heat load
350 kW/m²
250 kW/m²
Global
average
heat load
100 kW/m²
0
kW/m²
Radiation contours for 45
barg release through a
37.5 mm hole simulated
in PHAST
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
30
CONSEQUENCE ASSESSMENT
POOL FIRE
Release of flammable liquid, a two phase jet with rain out of oil or low
pressure two phase releases can lead to formation of an oil pool.
If ignited fumes evaporating from the oil pool will burn (low momentum).
The heat from the fire will cause more evaporation and cause the fire to
accelerate.
Pool fire test at SpadeAdam
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
31
CONSEQUENCE ASSESSMENT
POOL FIRE
Once the diameter of the pool has been established the
flame length can be derived from the following:
Flame size
The diameter of an unobstructed pool fire
on an even surface fed by a continuous
release:
4  Q
D 
  b

b
L / D  42  
0 .5
  a ( g  D )



0 . 61
L: flame length (m)
D: pool diameter (m)
b: masburning rate (kg/(m²∙s))
ρa: density of ambient air (kg/m³)
g: acceleration due to gravity (m/s²)
D: diameter (m)
Q: release rate (kg/s)
b: mass burning rate (kg/(s∙m²))
Substance
Mass burning rate Kg/(s∙m²)
Gasoline
0.05
Kerosene
0.06
Hexane
0.08
Butane
0.08
LNG
0.09
LPG
0.11
Crude oil
0.035 – 0.05
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
32
CONSEQUENCE ASSESSMENT
POOL FIRE
Pool fire radiation
Pool fires have a lower radiation than jet fires,
typically between 100 to 200 kW/m².
These pool sizes, flame sizes and
radiation distances have been calculated
by DNV programme: Flare [Guide].
The calculations are based on heptane
(C7) as the medium burning.
Proposed incident heat fluxes
[Scandpower]
Pool fires
Local peak heat load
150 kW/m²
Global average heat load
100 kW/m²
Release
rate
Pool
Flame
diameter length
kg/s
0.4
1.7
7
42
60
167
427
699
m
2.5
5
10
25
30
50
80
100
m
8
13
21
39
44
63
88
102
Tilt angle Surface
emissive
power
°
58
53
48
39
37
29
19
11
kW/m2
109
86
56
26
23
20
20
20
Distance
to 12.5
kW/m2
Distance
to 5
kW/m2
m
6.3
9.4
11
13.2
15.6
25.2
40.2
50
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
m
12
19
28
30
32
43
64
77
33
CONSEQUENCE ASSESSMENT
FLASH FIRE
•
Flash fires are slow burning gas clouds, where the flame front does not
accelerate to detonation (non-explosive combustion of a gas cloud)
•
The ignition point is typically at the edge of the cloud as the combustion zone
moves through the cloud away from the ignition point.
•
The flame front of the flash fire is relatively slow (10 m/s), and the duration of
flash fires are relatively short (10 to 15s) depending on gas cloud size
•
Combustion of the gas within the gas cloud will cause the cloud to expand up to
8 times it original size.
•
Heat flux experiments indicates that the maximum radiation from flash fires is
in the range of 160 to 300 kW/m².
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
34
CONSEQUENCE ASSESSMENT
FIREBALL / BLEVE
• A fireball is rapid turbulent
combustion of fuel in an
expanding and usually rising
ball of fire.
• Fireballs are often related
to the sudden release of
hydrocarbons due to failure
of a pressure vessel - Boiling
Liquid Expanding Vapour
Explosion (BLEVE)
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
35
CONSEQUENCE ASSESSMENT
FIREBALL / BLEVE
Flame size
The release material will be ignited by the external fire and a fireball
with intense radiation will occur. Moreover shock waves and
overpressure can be generated as a result.
The maximum diameter of the fireball can
be estimated by:
1 / 3
Dc  5 .8 m f
The duration of the fireball can be
estimated by:
1 /3
t c  0 . 45 m f
tc
1 /6
 2 .6 m f
for mf < 30,000 kg
for mf > 30,000 kg
Dc: maximum diameter (m)
mf: mass of fuel (kg)
tc: duration of combustion in seconds.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
36
CONSEQUENCE ASSESSMENT
FIREBALL / BLEVE
Radiation
The radiation from a fireball is very intense, experiments have shown
radiation levels between 320 kW/m² and 375 kW/m².
Reference
Fuel
Fireball
duration
[s]
Fuel Mass
[kg]
Fireball diameter
[m]
Emissive power
[kW/m²]
Johnson et al.
Propane
Butane
1000
4.5
56
320
Johnson et al.
Propane
Butane
2000
9.2
88
375
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
37
CONSEQUENCE ASSESSMENT
EXPLOSION DEFINITION
An explosion is the sudden, catastrophic, release of energy, causing a pressure wave
(blast wave).
• Explosion can occur without fire e.g. failure through overpressure.
• Explosion of flamable mixture is divided into deflagration and detonation.
• Detonation: Reaction zone propagates at supersonic velocity and the main heating
mechanism is shock compression.
• Deflagration: Reaction zone propagates at subsonic velocity but significant overpressure
can still be generated.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
38
CONSEQUENCE ASSESSMENT
EXPLOSION
A gas explosion is a rapid burning gas cloud where the flame front is accelerated generating shock waves
and overpressure.
In order for a vapour cloud explosion to occur in a hydrocarbon facility, four conditions have to be present:
1.
There has to be a significant release of flammable material
2.
The flammable material has to be sufficiently mixed with the
surrounding air
3.
There has to be an ignition source
4.
There has to be sufficient confinement, congestion or turbulence
in the released area
In explosions the (gas cloud) flame front will expand 8 to 9 times due to the heat of combustion.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
39
CONSEQUENCE ASSESSMENT
RULES OF THUMB APPLIED TO NINOTSMINDA
Leak D= 10 mm
P barg
Leak D= 30 mm
Flame m
Fireball-D
Flame m
Fireball-D
54
14
26
34
54
100
18
32
44
66
250
26
43
64
90
Fireball size assuming a 3 min. HC-release at the given pressures
and leak sizes.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
40
CONSEQUENCE ASSESSMENT
EXPLOSION
The effects of explosions can cause significant
damage.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
41
CONSEQUENCE ASSESSMENT
EXPLOSION
Gas cloud
The size of the gas cloud has a large effect on the peak pressure from an explosion.
The size of the cloud is dependent on several factors such as leak rate, ventilation rate etc. (section 2.2 in
notes).
The original TNT equivalent of a gas
cloud can be approximated by the
following formula:
w TNT  10    w HC
wTNT: weight of TNT (kg)
wHC: weight of hydrocarbon released
(kg)
η: yield factor (3-5% [GexCon])
This model does not account for the
geometrical congestions such as
congestion and confinement
Harrison and Wickers revised the TNT model to
account for severe congestion:
w TNT
 0 . 16 V ( kg )
V: the smaller of either total volume of the
congested area or the volume of the gas cloud
(m3)
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
42
CONSEQUENCE ASSESSMENT
EXPLOSION
Type of gas
The composition of the gas cloud affects the strength of the explosion as
methane is less reactive than propane and ethane.
Explosion pressure
for natural gas
depending on
methane
concentration
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
43
CONSEQUENCE ASSESSMENT
EXPLOSION
Gas concentration
Hydrocarbon gasses can burn in an interval from LEL to UEL, below or above the gas is too lean and too rich
to actually burn. The optimal concentration for combustion is where the gas balances the available oxygen in
the air (stoichiometric concentration).
Explosion pressure as
function of concentration of
the gas cloud [Design].
The Equivalence Ratio (ER)
is defined as follows:
ER 
( Fuel / Oxygen
( Fuel / Oxygen
) Actual
) Stoic hiome
tric
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
44
CONSEQUENCE ASSESSMENT
EXPLOSION
Congestion
Turbulence is a key factor in accelerating the flame front travelling through the gas cloud during an
explosion. Obstacles in the gas cloud will generate turbulence as the cloud expands due to the combustion,
and the more obstacles the more turbulence and hence higher explosion pressures
Confinement
The more confined, the less area to
relieve the pressure
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
45
CONSEQUENCE ASSESSMENT
ESCALATION
Temperature
Yield stress
Time
Ignited gas blow out
GSF Adriatic at the Temsah platform of the coast of Egypt
BLEVE
Escalation to platform leading to
loss of both rig and platform
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
46
CONSEQUENCE ASSESSMENT
ESCALATION EXAMPLES
• Small fire spreads into a large fire
• Jet fire causes BLEVE or major pool fire
• Jet fire causes loss of structural integrity or prevent escape.
• Explosion leading to loss of integrity in neighbouring areas or loss of
safety functions.
• Ship collision or dropped object leads to HC release.
• Etc.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
47
CONSEQUENCE ASSESSMENT
ESCALATION PREVENTION
The main thing in process safety design is to prevent hydrocarbon
release and if released to prevent ignition. However if this occurs anyway
escalation shall be prevented.
• Fire zoning
• Blast walls
• PFP and AFP
• Blowdown and ESD segregation
• Layout
• Etc.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
48
CONSEQUENCE ASSESSMENT
PIPELINE SAFETY ZONES
Governed by local
legislation.
Local legislation and guidelines
typically rely on the guidelines
issued by GPTC (Gas Piping
Technology Committee), API
and ASME.
A risk assessment will always
have to be part of the safety
zoning.
Typical safety zoning
ROW typically varies
between 18 m and 36 m
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
CONSEQUENCE ASSESSMENT
EXAMPLE FROM RINGSTED, DENMARK (WEST-EAST PIPELINE)
Pipeline D = 30”, Pipeline pressure P = 80 barg
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
CONSEQUENCE ASSESSMENT
NEIGHBOURING DISTANCES FROM PIPELINE (RINGSTED, DK)
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
CONSEQUENCE ASSESSMENT
POSSIBLE CATASTROPHIC SCENARIO AND CONSEQUENCES
With an Ø 75 mm breach, rule of thumb calculation gives:
Jet Flame Size = 100 m (impinging on all nearby residences).
If release lasts for 3 minutes and ignites, the resulting fireball will have a diameter of
133 m (intolerable to closest residents).
Legally, Ringsted pipeline complies with technical and legal requirements.
QRA is a tool to evaluate and support what in the end are POLITICAL DECISIONS to
proceed with construction within questionable, high-risk and/or consequence areas.
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
END OF CONSEQUENCE
ASSESSMENT
INOGATE PIPELINE QRA SEMINAR
SEPTEMBER 8-12, 2014
53

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