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 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 SourcekW/m 2 Irradiance of sun on the earth’s surface≤1 Minimum for pain to skin (relatively short exposure)~1 Minimum for burn injury (relatively short exposure)~4 Usually necessary to ignite thin items≥10 Usually necessary to ignite common furnishings≥20 Surface heating by a small laminar flame50-70 Surface heating by a turbulent wall flame20-40 ISO 9705 room-corner test burner to wall 100 kw40-60 ISO 9705 room-corner test burner to wall 300 kw60-80 Within a fully-involved room fire ( C) Within a large pool fire ( C)75-267

Description of LTA Fire Tests LTA Test No. Water Application Rate (mm/min) Activation Time after 60 C Peak FHRR (MW) Target Ignited? Max Target Heat Flux (kw/m 2 ) 1124 min37.7No2 284 min44.1Unknow n 70none150Yes225

Tabulation and comparison of fuel quantities Model ValuesWoodPlasticTotalTest Values Volume (m 3 )/%7.6/821.7/ /20 Mass (kg)/%3,410/671,711/335,1215,000 Energy (GJ)/%58.0/6137.6/ Total inc. Target (GJ) 117

Fuel Properties Property(11)(12) D F (13)(14)(15)(16)Value Used Wood Specific Heat~ Thermal Conductivity Density Heating Rate 5 Heat of Reaction Heat of Combustion Plastic Specific Heat Thermal Conductivity Density Heating Rate 5 Heat of Reaction Heat of Combustion

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

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.

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