The evaluation of the adequacy of fire safety distances is conducted if the project type “Fire Safety Distances” is selected.
In such a project, the heat flux is measured in Buildigs that do not have Fire sources or elements with the “On Fire” property enabled. The heat flux is measured on the surface of all elements with the Material property (material elements).
The measurement of heat flux on the surface of OBST elements corresponding to material elements is enabled via the BNDF parameter group in the FDS file.
&BNDF QUANTITY='INCIDENT HEAT FLUX'/
The QUANTITY parameter in the BNDF parameter group indicates that the heat flux falling on the surface will be measured.
By default, as adopted in FDS, specifying the BNDF parameter group causes measurements to occur on all surfaces present in the computational domain. To disable measurements on all surfaces, specify the BNDF_DEFAULT parameter as .False. in the MISC parameter group.
&MISC BNDF_DEFAULT=.False./
To enable measurements on a specific element, the BNDF_OBST parameter is added to the OBST parameter group.
&OBST FYI='Zdanie 2 Stena 7' XB=9.5,10.5,22.5,23,0,5.8 SURF_ID='6' BNDF_OBST=.True./
The FYI parameter in the OBST parameter group contains the name of the building and the material element to which this OBST element belongs.
After the simulation, Fenix+ 3 allows you to view a heat flux graph for any material element on which measurement was conducted. At each moment in time, the maximum flux value on the element’s surface is taken.
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You can set the critical heat flux density value for the material in the Substance and Material Editor.
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The critical flux value in a window opening, according to [12], is assumed to be 15 kW/m².
The maximum permissible heat flux value is calculated, according to [12], as 0.8 of the critical value.