Tank Spacing Using
Radiant Heat Modeling
How Realistic are the Models?
Kris Thorsteinsson
ΔP Risk Inc.
www.deltaprisk.com
Pool Fire Models Based on Fire Tests
„
„
„
„
Flames from large hydrocarbon
fires are modeled as a mainly
smoke-obscured sooty portion
with a luminous lower band and
periodic luminous spotting
throughout
Luminous flame areas have a
surface emissive power (SEP) of
about 140 kW/m² and smokecovered areas a much lower SEP
of about 20 kW/m²
Researchers noted the
”unintuitive” effect that as the
diameters of medium / heavy
hydrocarbon pool fires increase
the radiative fraction or % of
luminous flame to total flame
surface decreases
They developed formulae relating
diameter to radiative fraction
(Fs), e.g., a 15m crude oil pool
fire has an Fs of 17% and an
average SEP of 40 kW/m2
10/Jan/2007
ΔP Risk Inc.
2
Pool Fire Model SEP Calculations
„
„
„
Calculations using Mudan & Croce formulae result in hydrocarbon
pool fires with diameters of 30 m and higher modeled as essentially
all smoky, with very little luminous flame.
40m and larger fires modeled with <1% luminous flame
Average SEP is close to the value for smoke of 20 kW/m², very
much less than the value for luminous flame of 140 kW/m²
D(m)
SEP (kw/m2)
1
2
3
5
10
15
20
30
40
50
70
100
126.4
114.4
103.7
85.9
56.1
39.8
30.9
23.3
21.0
20.3
20.0
20.0
10/Jan/2007
Fs (radiative
fraction)
0.90
0.82
0.74
0.61
0.40
0.28
0.22
0.17
0.15
0.14
0.14
0.14
ΔP Risk Inc.
% flame
% soot or smoke
88.69%
78.66%
69.77%
54.88%
30.12%
16.53%
9.07%
2.73%
0.82%
0.25%
0.02%
0.00%
11.31%
21.34%
30.23%
45.12%
69.88%
83.47%
90.93%
97.27%
99.18%
99.75%
99.98%
100.00%
3
Large Tank Fires
„
„
„
„
Accepted fire models
for these large tanks
would calculate a
radiative fraction of
<1%
i.e. <1% of flame
surface on average
is comprised of
luminous flame, or
>99% of flame is
hidden by smoke on
average
These photos
suggest a more
realistic Fs of 30%+
Also noted is the
upwind effect of a
higher % of luminous
flame, possibly
outweighing the
flame tilting effect
10/Jan/2007
ΔP Risk Inc.
4
Significance of Model Accuracy
„
„
Thermal radiation
modeling for tank layout
and spacing is
recommended by
insurance / risk
management (e.g. GE
GAP) and industry (e.g.
Energy Institute /
Institute of Petroleum)
guidelines
Emergency response
plans, fixed and
portable fire-fighting
provisions and tertiary
containment systems
may be based on
reliable modeling
10/Jan/2007
ΔP Risk Inc.
5
Singapore 1988 Straight Run Naphtha
Tank Fire – Escalation by Radiant Heat
„
„
„
„
„
Tank #1 full surface fire underway,
little or no wind
Tank #2 at left, 21m from Tank #1
starting to burn at rim seal area
after 2 hours
A Mudan & Croce based model
(using default SEP and radiative
fraction values) indicates only 4
kW/m2 at Tank #2, and 8 kW/m2 at
5m distance from Tank #1
Other models and observation
suggest 25-30 kW/m2 radiation
level at Tank #2 which is more
realistic given the fire spread
The Singapore Tank Fire
Protection study indicated
adjacent tank fire escalation at 0.5
Diameter separation in 2.8 hours
10/Jan/2007
ΔP Risk Inc.
6
Possible Explanations for Higher Observed
SEP in Tank Fires v Pan Test Fires
„
„
„
„
Heat feedback from the fire to
the flammable material has a
great effect on vaporization
rate and fire intensity
Tank shell heating up and
radiating back into the fire
would progressively increase
with time
A partial chimney effect may
occur increasing turbulence
and overall oxygenation above
the tank shell
The rate of burning eventually
becomes more like volatile
light end hydrocarbons which
typically do not demonstrate
reduced Fs with increasing
diameter
10/Jan/2007
ΔP Risk Inc.
7
References
„
„
„
„
„
„
“Fire Hazard Calculations for Large Open Hydrocarbon
Fires” Mudan & Croce, 1984
TNO Yellow Book “Methods for the Calculation of
Physical Effects” CPR 14E 3rd Edition 1997
“Fire Precautions at Petroleum Refineries and Bulk
Storage Installations” Energy Institute / IP, 2nd Edition
2007
GE GAP 2.5.2 “Oil & Chemical Plant Layout &
Spacing”, 2001
“Investigation of a Naphtha Storage Tank Fire” Baker
Engineering & Risk, 2004
“Thermal Radiation from Large Pool Fires” NIST 2000
10/Jan/2007
ΔP Risk Inc.
8