A fire in road tunnel can be dangerous and lead to serious consequences if not addressed
appropriately. In a tunnel fire incident, creating a smoke free path for motorist evacuation
and facilitating fire fighters to access the fire is critical for fire and rescue operations. A
means of achieving this is to use ventilation fans to blow sufficient air down the tunnel
ensuring no back-layering of smoke occurs upstream of the fire. The airflow necessary for
such operation is known as the critical velocity which is a function of a number of factors
includes; heat release rate, tunnel geometry, tunnel gradient etc. Among these parameters,
the heat release rate is the most difficult to identify as this value is dependent on the types
of vehicles, number of vehicles involved, the type of cargo and the quantity of cargo
carried by these vehicles. There are also other factors such as the influence of ventilation
condition, tunnel geometry and the use of legislation (to restrict hazardous vehicles
entering in tunnel) that could affect the heat release rate in a tunnel fire. The number of
possible fire scenarios is numerous.
Based on current practise, fire size selection for most tunnel ventilation design often
references various guidelines such as NFPA 502, BD78/99 or the PIARC technical
committee report. The heat release rate, particularly for goods vehicle recommended by
the guidelines varies from 20 to 30 MW. However, recent fire tests conducted in the
Runehamar tunnel experiments indicate a higher heat release rate. These experiments
suggest that heat release rate guidelines for goods vehicles might be underestimated. An
ideal means to estimate the heat release rate in the tunnel is to use the oxygen consumption
calorimetry technique. However, this approach is generally expensive, logistically
complicated to perform and it is often not feasible to conduct such tests for a tunnel project
at the initial design stage simply because the structure and systems are not ready for such
activities.
This research thesis presents an approach to establish a design fire in a road tunnel
particularly the peak heat release rate for emergency tunnel ventilation system design. The
analysis consists of two stages; stage one involves the use of a probabilistic approach (risk
analysis) to identify the potential cause and type of vehicle which could result in a tunnel
fire. Findings from the risk analysis are used in stage two in which Computational Fluid
II
Dynamics (CDF) modelling is used to establish the heat release rate in the tunnel
considering factors such as fuel load, ventilation condition, tunnel geometry and ignition
location. The Fire Dynamics Simulator (FDS 4.0.7), a CFD model of fire-driven fluid flow
is used for the analysis and an urban road tunnel project in Singapore is used to illustrate
this methodology.
Other topic related to this research work includes the reconstruction for the Runehamar
tunnel fire test using numerical approach to calibrate the FDS simulation model. The used
of Probabilistic Bayesian approach and CFD approach using FDS to estimate the heat
release rate in the tunnel is also investigated in this thesis. The effect of vehicle fire spread
in road tunnel and numerical simulation of road tunnel fires using parallel processing is
presented. Preliminary work in using FDS5 for tunnel simulation work is discussed as part
of the research work in this project.
| Identifer | oai:union.ndltd.org:canterbury.ac.nz/oai:ir.canterbury.ac.nz:10092/2863 |
| Date | January 2009 |
| Creators | Cheong, Mun Kit |
| Publisher | University of Canterbury. Civil and Natural Resources Engineering |
| Source Sets | University of Canterbury |
| Language | English |
| Detected Language | English |
| Type | Electronic thesis or dissertation, Text |
| Rights | Copyright Mun Kit Cheong, http://library.canterbury.ac.nz/thesis/etheses_copyright.shtml |
| Relation | NZCU |
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