Coupling PyroSim Fire Results and Pathfinder Movement

Reading Time: 4 minutes
Created with software version: 2020.1

1. Introduction

We have begun coupling PyroSim fire results with Pathfinder movement. The first major task was to create a Results Viewer that could merge and display PyroSim and Pathfinder results simultaneously. That has largely been completed. We have also completed limited capability to calculate the Fractional Effective Dose (FED) as occupants move through changing CO, CO2, and O2 concentrations. Future development will use PyroSim results to alter occupant movement and decision making within the Pathfinder simulation. In this post, we demonstrate the capability currently available in Pathfinder 2018.1 and PyroSim 2017.2. See the post Manually Coupling FDS and Pathfinder to Respond to Smoke for instructions on how to link fire simulation output with evacuation simulation movement.

The video below displays fire, smoke, and the evacuating occupants. They first meet in the conference room and then exit the building. FED is calculated for selected occupants as they evacuate. Two occupants wait 90 seconds before evacuating.

The Fractional Effective Dose (FED) for one of the occupants that delayed 90 seconds before evacuation is shown below in Figure 1.

plot graph coupling fed
Figure 1. Fractional Effective Dose (FED) calculation for occupant that delayed 90 seconds before evacuation

2. Simultaneous Display of Evacuation (Pathfinder) and Fire (PyroSim) Results

If the user only wants to display the PyroSim and Pathfinder results simultaneously, run the Results Viewer and open both the Pathfinder results (*.PFR file) and the PyroSim results (*.SMV file). You can offset the PyroSim results display time in the FDS Preferences dialog on the Analysis menu.

3. Using Fire Results to Calculate FED During Evacuation

To calculate FED during evacuation, the required data must be saved during the PyroSim simulation and this data must be accessed as part of the Pathfinder simulation. We describe the steps to do this below.

3.1. Background for Calculation of Fractional Effective Dose

The Pathfinder calculation of Fractional Effective Dose (FED) uses the equations described in the SFPE Handbook of Fire Protection Engineering, 5th Edition, Vol 3, Chapter 63, pages 2308-2428 (SFPE 2016), shown below in Fractional Effective Dose Equations. The implementation uses only the concentrations of the asphyxiant gases \(CO\), \(CO_{2}\), and \(O_{2}\) to calculate the FED value (see the Pathfinder Technical Reference Manual for details).

Fractional Effective Dose Equations
\[FED_{tot} = FED_{CO} \times VCO_2 + FED_{O_2}\]

In this calculation, \(FED_{CO}\) is a function of \(CO\), activity level, and exposure time. Below 5% concentration, \(CO_{2}\) does not have toxic effects, but it stimulates breathing which increases the rate at which the other fire products are taken up, so \(V_{CO_{2}} \) modifies \(FED_{CO}\). \(FED_{O2}\) is a function of time and accumulates when \(O_{2}\) is less than 20.9%. Note that this calculation does not include the effect of hydrogen cyanide \(HCN\). Also, it is the same approach taken in the FDS+EVAC simulator.

3.2. Preparing the PyroSim Calculation

Pathfinder accesses the PyroSim fire data by reading the Plot3D data file written by FDS. To write this data, in PyroSim:

  1. On the Output menu, click Plot3D Data.
  2. Select [Species: CARBON DIOXIDE] Volume Fraction, [Species: CARBON MONOXIDE] Volume Fraction, and [Species: OXYGEN] Volume Fraction.
  3. Set the Output Interval to 10 seconds. Plot3D data files can become large and Pathfinder interpolates between data sets, so 10 seconds is adequate.
  4. Run the PyroSim simulation

3.3. Preparing the Pathfinder Calculation

We now tell Pathfinder to access the Plot3D data and calculate FED for selected occupants:

  1. On the Simulation menu, click Simulation Parameters.
  2. On the FDS Data tab, click Enable FDS Integration.
  3. Select the Smokeview file written during the PyroSim simulation. This will be located in the results folder and will be a name with an SMV file extension. The FED Output parameter will change to Enabled.
  4. Now, select an occupant. Click More. In the Additional Occupant Parameters dialog, click the Output tab and click Print CSV Data. Select Yes.
  5. Repeat for a limited number of occupants. A csv file will be written for each occupant, so limit the number of occupants to less than 50.
  6. Run the Pathfinder simulation.

3.4. Display Results

To display results:

  1. In Pathfinder, run the Results Viewer. This will display the evacuation results.
  2. In the Results Viewer, on the File menu, click Open Results and select the Smokeview file (SMV file extension).
  3. Select the results you wish to display.
  4. Open an occupant CSV file to plot the FED.

4. Future Development

As noted, the current capability represents the first steps toward full coupling between the fire and evacuation simulations. Future development will include navigation to avoid fire and smoke, change in speed due to smoke, dynamic display of exposures, and the ability to track exposure for all occupants.

To download the most recent version of Pathfinder, please visit the Pathfinder Support page and click the link for the current release. If you have any questions, please contact

5. Bibliography

SFPE. 2016. SFPE Handbook of Fire Protection Engineering. 5th ed. Springer-Verlag New York.

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