CFD Investigation of Large Scale Pallet Stack Fires in Tunnels Protected by Water Mist Systems

Abstract

A series of full-scale fire suppression tests was conducted at the San Pedro de Anes test tunnel facility near Gı´jon, Asturias, Spain in February 2006. The fuel was wooden pallets or a mixed load of wood and high density polyethylene pallets. Fire protection was provided by water mist systems in different configurations. Because of facility restrictions, some scenarios of great interest, such as a free burn fire, could not be investigated. However, in order to complement the experimental results, a number of computational fluid dynamics simulations were conducted on a 140 m section of the tunnel facility. The Fire Dynamics Simulator, version 4, was used for the numerical investigation. An algorithm was developed to allow the fire to spread along the top of a series of pallet loads in such a way that the measured heat release rate was reproduced. Verification and validation studies confirmed that the model predicted the measured ventilation speeds and peak temperatures. The agreement between the simulations and the field measurements was very good prior to activation of the water mist. Back-layering was modeled well. After activation of the mist, the simulations predicted a large drop in gas temperatures, and retreat of the back-layer, but under-predicted the thermal cooling by the water mist downstream of the fire. With the suppression system, high temperatures and heat fluxes were limited to the immediate vicinity of the burning pallets. The model was then used to simulate a free burn fire in the tunnel. The simulation demonstrated the catastrophic conditions created by an unsuppressed fire in a tunnel when compared against the thermally managed conditions under suppressed conditions.

Quantification of Energy Balance during Fire Suppression by Water Mist in a Mid-scale Test Tunnel

“…This numerical tool is widely used in the fire community, generally to evaluate fire consequences in buildings. FDS has also been used to simulate tunnel fires, especially by McGrattan and Hamins [19], Cochard [20] and Mawhinney and Trelles (see [21] and [22]). The ability of current version of FDS to reconstruct the fire environment from a test performed within the one third test tunnel used here (with a longitudinal velocity too low to prevent back-layering effect and without water mist application) has been presented in details in [15].…”

Testing Water Mist Systems Against Large Fires in Tunnels: Integrating Test Data with CFD Simulations

“…The choices made in the selection of the computational grid in these simulations were at the limit of what was practical. Refer to the JFPE article [12] for a more complete discussion. The referenced article notes that the chosen resolution is below the calculated spatial uncertainty based on the estimates of the HRR uncertainty.…”

“…Results of a simulation for an un-suppressed fire, which could not be tested, are presented to illustrate the benefit of using the partially-validated model to better understand the performance of the suppression system. A complementary paper will be published in a separate journal (Journal of Fire Protection Engineering) to provide more detailed information on the FDS4 model [12].…”

“…A separate paper has been prepared as a complement to this one to present the CFD work in more detail, which will be published in the Journal of Fire Protection Engineering (JFPE) [12]. The goal of the current article is to provide synopses of the methodology used to reproduce the HRR of a decomposing, collapsing fuel load and of the approach used to model a high-pressure water mist system.…”

A study for a fire spread mechanism of residential buildings with numerical modeling

“…These days, improvement of computing performance leads to studies on the large fire phenomenon, such as prediction of effusive flame from a building balcony [6] and numerical analysis on the building collapse of World Trade Center 5 [7] and, in particular, research to verify the numerical analysis on the large space like-tunnel and atrium [8][9][10] are under study. In addition, researches deducing advanced numerical analysis results through improved modelling [11][12][13] and research predicting the performance of active systems, like smoke control facilities and sprinkler installation, based on the numerical analysis [14][15][16] are actively being conducted.…”