The initial conditions for fire simulation are a group of various physical values that are used in the simulation process. Some of these values can be set in the application interface, while other values are used by default and cannot be changed.
Temperature - the ambient temperature. The default value is 20°C.
Background Pressure - the atmospheric pressure. The default value is 101325 Pa (760 mm Hg).
Relative Humidity - the ratio of the mass fraction of water vapor in the air to the maximum possible fraction at a given temperature. The default value is 40%.
Temperature Gradient - the change in air temperature with an increase in height.
On average, the temperature changes (decreases) by 0.06 °C every 100 meters. The temperature gradient is usually used to simulate open high-rise domains.
Room Temperature is the initial air temperature inside the room space. See the Room section.
By default, Fenix+ 3 uses the Room Temperature parameter for all rooms, except for those where a different value is specified in the properties. This condition is met only if the Account for Temperature parameter is checked in the properties of such rooms. See details in the Room section.
The Temperature, Background Pressure, Relative Humidity parameters in the FDS file are represented in the MISC group by the TMPA, P_INF, and HUMIDITY parameters:
&MISC HUMIDITY=40 P_INF=101325 TMPA=20 VISIBILITY_FACTOR=2.38 MAX_LEAK_PATHS=1 BNDF_DEFAULT=.False./
For a description of the VISIBILITY_FACTOR parameter in the MISC group, see the Visibility section. For a description of the MAX_LEAK_PATHS parameter in the MISC group, see the Pressure section. For a description of the BNDF_DEFAULT parameter in the MISC group, see the Heat Flux on Enclosures section.
The Temperature Gradient is set using the LAPSE_RATE parameter in the WIND parameter group:
&WIND LAPSE_RATE= -0.006