Wood is a unique material with respect to fire. Despite being combustible, it is a stable structural element when confronted with flame due to its low thermal conductivity and characteristics of its chemical degradation (Pyrolysis). The level of fire resistance is determined by the mass, size, and configuration of the constructive elements used.

Fig.1 Some types of horizontal timber claddings.

 

When wood is used as a cladding material, takes the form of boards, plates, or other thin strips, therefore its behavior is subject to its combustibility. This risk is why building fire-safety codes and regulations in many countries have been increasingly restricting the use of combustible claddings.

Fig.2 Left. Computational domain and contents of the fire scenario.
Right. Geometric description of the scenarios. (A) Horizontal projection of 80 cm depth.
(B1and B2) Two singular facade designs.

In this study we used modeling techniques and computer fire simulations to evaluate the influence of facade configuration on fire trajectory and the level of protection it can offer at the facade surfaces.

Fig.3 Left. Detail 1. Lintel and horizontal projection (eave).
Right. Details 2 and 3. Singular design elements.

The study results has made it possible to draw a number of conclusions, the following are some of them:

  • The facade geometry of buildings can influence greatly on the behaviour of fire and its propagation.
  • The horizontal projection (non-combustible material) acts as a flames deflector. Therefore, this projections (eaves) help to prevent the fire spread through combustible materials cladding such as wood.
Fig.4 Temperature distribution graphics. Side view.
Top. Different horizontal projection sizes. Bottom. Singular designs of façade.
  • The horizontal projections greater than 80 cm are appropriate to reduce the heat flow on the surface of the facade.  When the risk is greatest, for example due to the size of the windows may be necessary to increase to 120 cm depth in order to minimize the incidence of heat flux on the facade.
  • The combination of horizontal projections and sloped surfaces could be a good option to minimize the risk of vertical fire spread. This type of configurations deserves to be further explored.
Fig.5 Left. Graphics of fire spread through large windows.
Right. And through small windows.

 

  • The windows size is an important issue in the fire spread control through the facades. The small windows reduce the risk of spread because the emitted heat flux is lower in comparison to large windows.

The study was performed using field models of computational fluid-dynamics. Particularly through the software:  Fire Dynamics Simulator (FDS) to solve numerically the mathematical integration models, PyroSim for the graphical interface, and Smokeview for viewing the results.

 

Abstract of paper “Computer-Simulation Research On Building-Facade Geometry For Fire Spread Control In Buildings With Wood Claddings” presented by Giraldo P., INCAFUST ‘s researcher, at The World Conference on Timber Engineering. Auckland, New Zealand. 2012.

 

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