Transcript Slide 1

Computational modelling as an
alternative to full-scale testing for
tunnel fixed fire fighting systems
Kenneth J. Harris & Bobby J. Melvin
Parsons Brinckerhoff
Sacramento, CA USA
E-mail: [email protected]
Presented By Aaron McDaid
Key modeling bases
Fundamental energy analysis can be used to estimate
water application rates.
Subroutines that model the key elements of solid and
liquid vaporization have been written.
Subroutines that model the key elements of combustion
energy have been written.
Dynamics of Fire and Extinguishment
Water Application Rate Equation
Comparison of two identical fire test set-ups
Flaming Radiative Heat Flux & Pyrolysis Model
Common Heat Flux Levels
Source
Irradiance of sun on the earth’s surface
Minimum for pain to skin (relatively short exposure)
Minimum for burn injury (relatively short exposure)
Usually necessary to ignite thin items
Usually necessary to ignite common furnishings
Surface heating by a small laminar flame
Surface heating by a turbulent wall flame
ISO 9705 room-corner test burner to wall 100 kw
ISO 9705 room-corner test burner to wall 300 kw
Within a fully-involved room fire (800-1000 C)
Within a large pool fire (800-1200 C)
kW/m2
≤1
~1
~4
≥10
≥20
50-70
20-40
40-60
60-80
75-150
75-267
Description of LTA Fire Tests
LTA
Test
No.
Activation
Time after
60 C
Peak
FHRR
(MW)
Target
Max Target
Ignited? Heat Flux
(kw/m2)
1
Water
Application
Rate
(mm/min)
12
4 min
37.7
No
2
2
8
4 min
44.1
Unknown
7
0
none
150
Unknow
n
Yes
225
Tabulation and comparison of fuel quantities
Model Values
Wood
Plastic
Total
Volume (m3)/%
7.6/82
1.7/18
9.3
Test
Values
80/20
Mass (kg)/%
3,410/67
1,711/33
5,121
5,000
Energy (GJ)/%
58.0/61
37.6/39
95.6
99.2
Total inc. Target
(GJ)
117
Fuel Properties
Wood
Property
(11)
(12)
Specific Heat
~1.5-2.0
2.5-7.4
(12)
DF
2.2-4.0
Thermal
Conductivity
0.12
.19-2.08
.23-.80
Density
600
354-753
455-502
(13)
(14)
(15)
(16)
1.2-2.0
2.2
0.23
300-550
450
Heating Rate
Heat of Reaction
Heat of
Combustion
5
16003500
17000
16002900
1600
17000
Specific Heat
1.4-1.5
Thermal
Conductivity
.17-.19
Density
11501190
Plastic
Value Used
.92-2.3
1.4
0.17
570-3900
Heating Rate
1000
5
Heat of Reaction
800-6400
1500
Heat of
Combustion
1400047000
22000
Comparison of model and test results for
unsuppressed fire
Comparison of model and test results for 12
mm/min. suppressed fire
Peak heat flux and FHRR for various leakage rates
120
40
100
35
30
80
FHRR
25
60
20
15
40
Heat flux
10
20
5
0
0
2
4
6
8
Water Application Rate (mm/min)
10
12
0
Peak FHRR (MW)
Peak Net Heat Flux kW/m2
45
Comparison of model and test results for
unsuppressed and 12 mm/min. suppressed
fire
Dynamics of Fire and Extinguishment
Water application rate for external heat flux only
Vaporized water heat flux
Water Application Rate 2 mm/min
Water Application Rate 4 mm/min
Main/Target Rate 4/0 mm/min
Conclusion
o Computer modelling provides a more cost-effective means of demonstrating
proposed system performance.
o The fuel vaporization process is well-defined in fire science and the computer
models can be set up to utilize this approach.
• Some significant differences in modelling are required for this approach.
• The fuel properties and structure must be explicitly defined.
o Comparison with a test is beneficial to calibrate the model.
• Modelling of the unsuppressed fire in particular can produce results very close to
that shown in testing.
• Modelling of fire suppression can provide results that give a reasonable degree of
confidence of what can be expected of the system.
o Computer modelling can be used to model the interaction of water and fire for
design purposes, making individual full-scale testing unnecessary and making
FFFS more likely to be implemented in road tunnels.
o Pyrolysis-based input rather than fire heat release rate input should be used to
more accurately model the effects of water and fire interaction.
Fire Sprinkler International
Thank you
FSI 2014
22