Manually Coupling FDS and Pathfinder to Respond to Smoke

A long-term development goal has been to fully couple the PyroSim/FDS fire results with Pathfinder evacuation. A first step toward this goal is the capability to display both fire and evacuation results in the same results viewer. However, full coupling of the two simulations has not been completed. In the interim, it is possible to run the fire simulation, monitor the reduced visibility due to smoke, and then manually use that information to slow and re-direct occupants in response to the fire. This provides an example.

Walking Speed as a Function of Visibility

We will use visibility to slow the walking speed of occupants. To do this, we will measure visibility at different location in the PyroSim/FDS model. The measurements will be located in the evacuation path. A local speed factor will be calculated as a function of time using the measured visibility at that location. The occupants will then slow their speed and adjust their paths using these speed reductions.

Walking Speed in Smoke: Representation in Life Safety Verifications by K. Fridolf, D. Nilsson, H. Frantzich, E. Ronchi, and S. Arias gives a function of walking speed as a function of visibility. In the paper, they use this as absolute walking speed, but we will treat this as a factor that slows the speed of each occupant. Their relation is given by equation 1: 


The speed factor is tabulated and shown in the graph below.

Speed factor
Figure 1: Speed factor as a function of visibility.

Fire Simulation

The fire model we will use for this example includes a room with a fire and a door that connects to a hallway. Occupants enter and then choose between two exits. At first, they use the nearest exit, but as the smoke slows their local velocity, they will choose to exit from the further exit. Figure 2 shows the geometry of fire simulation and Figure 3 shows the location of the devices that measure visibility. These were positioned at 2 m height. The fire is a 200 MW fire that ramps to full value at 60 seconds.

Perspective view of fire simulation
Figure 2: Perspective view of fire simulation


Visibility measurement devices
Figure 3: Location of visibility measurement devices.

Visibility measurement devices output data to a csv file. In PyroSim, on the Analysis menu, click Simulation Parameters. Click the Output tab and set the Device write interval to a value that will result in a reasonable number of data points in the csv file (I used a 1 second interval for a 120 second simulation). After the simulation, open the csv file and use equation 1 to calculate the speed factor as a function of time based on the visibility. Figure 4 shows part of a spreadsheet that does this calculation. Figure 5 plots the speed factors.

speed factor
Figure 4: Typical calculation of speed factor using measured visibility.


Calculated speed factors
Figure 5: Calculated speed factors.

Evacuation Simulation

We import the PyroSim model into Pathfinder and extract the floor. Add the entrance and exit doors. We then divide the floor into rooms that correspond to the device locations we used to measure visibility. Connect these rooms by doors. Select a room, then edit the speed modifier using the data calculated in the spreadsheet, Figure 6. 

speed modifier in Pathfinder
Figure 6: Defining speed modifier in Pathfinder.

Run the simulation. At first the occupants enter, walk past the room with the fire, and exit using the closest exit. At about 70 seconds, the occupants start to use the farther exit. This is because the occupants recognize that their speed in the hallway is slowed due to the smoke and that the further exit would be faster.

Speeds contours
Figure 7: Speeds contours of occupants.

Figure 8 shows the occupants with smoke displayed soon after it becomes better to use the further exit. 

occupants with smoke
Figure 8: Occupants shown with smoke.


This post has demonstrated a manual approach to link fire simulation output with evacuation simulation movement. In this case, visibility was used to change the walking speeds. This resulted in occupants choosing a different (longer) evacuation route. The user also has the option to completely prevent entry into a room (or through a corridor section) by closing doors at any time in the simulation.

Admittedly, this manual coupling is not automatic. However, it does demonstrate a work-around that is currently available. 

Download Input Files

You can download the input files used in this post.

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