FDS User Guide: document FIRE ARRIVAL TIME and FIRE RESIDENCE TIME outputs

Author: ericvmueller

Manuals/FDS_User_Guide/FDS_User_Guide.tex

@@ -11222,6 +11222,10 @@ \subsection{Extinction}
 \label{info:extinct_out}
 In combustion, knowing if, when, or where chemical reactions have been extinguished is important. The output quantity \ct{EXTINCTION} tells the user whether or not combustion has been prevented by the extinction routine. By default, \ct{EXTINCTION} = 0, which means that the FDS extinction routine has not prevented combustion. An \ct{EXTINCTION} value of 1 means that the routine has prevented combustion. The criteria for an \ct{EXTINCTION} value of 1 is the presence of fuel and oxidizer without any energy release. An \ct{EXTINCTION} value of -1 means that there is either no fuel or no oxidizer present.
 
+\subsection{Fire spread over a surface}
+\label{info:fire_spread_output}
+In some cases it can be useful to output timings related to the spread of fire over a surface. For example, when modeling wildland fires the shape and spread of the fire front can be very important. For this reason, two specialized output quantities are available as boundary files (Sec.~\ref{info:BNDF}) or as measurements from devices places on a solid boundary (Sec.~\ref{info:DEVC2}). These are \ct{FIRE ARRIVAL TIME} and \ct{FIRE RESIDENCE TIME}. The \ct{FIRE ARRIVAL TIME} quantity outputs the time at which the gas-phase cell adjacent to the solid exceeds a threshold for heat release rate per volume (\ct{HRRPUV}) and the \ct{FIRE RESIDENCE TIME} gives the cummulative time over which the threshold is exceeded during the simulation. The chosen threshold is the same as used by smokeview for rendering \ct{HRRPUV}, as described in Sec.~\ref{info:SMOKE3D}. In the case of a level set simulation (Sec.~\ref{info:level_set}), the \ct{FIRE ARRIVAL TIME} can be computed directly from the level set value and the \ct{FIRE RESIDENCE TIME} comes from the spread-rate adjusted burning duration of the fuel, as described in Sec.~\ref{level_set_fuel_model_1}. These two quantities are cummulatively populated over time such that a full picture of the fire spread can be obtained from relatively infrequent outputs - theoretically only one snapshot at the end of the simulation is required.
+
 
 \newpage
 
@@ -11449,6 +11453,8 @@ \section{Solid Phase Output Quantities}
 \ct{ENTHALPY FLUX WALL}                        & Section~\ref{info:enthalpy_flux}              & \unit{kW/m^2}           & B,D          \\ \hline
 \ct{TOTAL HEAT FLUX}                           & Section~\ref{info:heat_flux}                  & \unit{kW/m^2}           & B,D          \\ \hline
 \ct{EMISSIVITY}                                & Surface emissivity (usually constant)         &                    & B,D          \\ \hline
+\ct{FIRE ARRIVAL TIME}                         & Section \ref{info:fire_spread_output}         & \si{s}             & B,D          \\ \hline
+\ct{FIRE RESIDENCE TIME}                       & Section \ref{info:fire_spread_output}         & \si{s}             & B,D          \\ \hline
 \ct{GAS DENSITY}                               & Gas Density near wall                         & \si{kg/m^3}        & B,D          \\ \hline
 \ct{GAS TEMPERATURE}                           & Gas Temperature near wall                     & $^\circ$C          & B,D          \\ \hline
 \ct{HEAT TRANSFER COEFFICIENT}                 & Section \ref{info:convection}                 & \si{W/(m^2.K)}     & B,D          \\ \hline