Water Application Rates for Fixed Fire Fighting Systems in Road Tunnels
Published: 14 April, 2010
Road tunnel deluge systems require substantial amounts of water, which can have significant impact on the storage, delivery and drainage systems. Fixed fire fighting systems (FFFS) are gaining attention as a means for providing an early response to a road tunnel fire. While these systems have been used for a considerable time in Japan and Australia, their incorporation into road tunnels in other parts of the world is now being evaluated. One of the major issues this paper explores is the water application rate.
The objectives and strategies, exposure protection, control of burning, suppression and extinguishment for an FFFS are identified. Fire point theory is then used to quantify the effects of water application rate on heat flux. Computational fluid dynamics (CFD) analysis using varying water application rates is then performed on shielded and unshielded stacked solid fuel packages that would represent a severe fire incident. The analysis showed that rather than being a continuum of performance, the effect of water application rate occurred in discrete effects. In other words, while some minimum water application rate would accomplish a certain objective, a marginally higher rate would not necessarily improve the situation. The application of significantly higher rates would move to a different objective, whereby again marginally higher increases would have little benefit. These confirm the application of fire point theory to assess how much water is sufficient to accomplish FFFS objectives. This now allows an objective to be identified within the overall framework of tunnel safety systems and the FFFS to be sized to accomplish that objective.
