Steel Buildings in Europe

Part 7: Fire Engineering 7 - 48 It is also still possible to choose to follow a two-zone or a one-zone strategy for the entire duration of a fire. With these strategies, the whole simulation is made considering two or one zones, from the initial time to the end of the calculation. No modification of the rate of heat release is made, except via the combustion models. Localised fire 2 zone model roof  g Beam Hasemi method’s   20°C z  g 2-zone model  at beam level x Figure 6.1 Combination of two-zone model with Hasemi method’s Some of the more complex zone models allow radiation calculations between the upper layer and room objects. They may also allow multiple fire plumes and multiple compartment analysis with mass exchange between each compartment (see Figure 6.2). The input data are usually the room geometry, room construction (including all walls, floors and ceilings), number of vents (or holes) and their sizes, room furnishing characteristics, and fire data (such as RHR curve, pyrolisis rate, combustion heat of fuel). The output data are usually the prediction of sprinkler and fire detector activation time, time to flashover, upper and lower layer temperature, smoke layer height, and species yield. The fire load can be considered to be uniformly distributed if the combustible material is present more or less over the whole floor surface of the fire compartment and when the fire load density (quantity of fuel per floor area) is more or less uniform. By contrast, the fire load should be “localised” if the combustible material is concentrated on quite a small surface compared to the floor area with the rest of the floor area being free of fuel. An essential parameter in advanced fire models is the rate of heat release. For design it is common practice to refer to the values given in EN 1991-1-2. For irregular or complex building geometry, complex ventilation systems, or where more detail is required on convective or radiant heat exposure levels at specific targets, the use of a field model should be considered.