Smoke does not just slow people down, it changes what they believe is even possible. That simple idea is why we get so excited about pyFDS-Evac, an open source workflow that connects Fire Dynamics Simulator (FDS) results directly to modern evacuation modeling with JuPedSim. When the fire environment can remove an exit from view, reduce walking speed through extinction and soot exposure, or even incapacitate an agent, you stop “post-processing evacuation” and start modeling decisions that respond to conditions.

We sit down with Mohcine Chraibi from Forschungszentrum Jülich to unpack how their team builds pedestrian dynamics software that researchers can actually extend. We talk candidly about why legacy tools like FDS-Evac faded, why commercial evacuation software can feel like a black box when you need to publish and validate new ideas, and what it takes to keep an academic codebase alive. Mohcine walks us through the modular pipeline: run FDS as normal, read outputs through FDS Reader, compute sight lines and smoke effects with FDS VisMap, and drive agents with JuPedSim while pyFDS-Evac applies fire-driven behavior changes.

Then we go deeper into routing and wayfinding. You will hear how graphs and A-star pathfinding evolve toward flow-field methods, why “familiarity” and cognitive maps matter when occupants do not know the building, and what JuPedSim 2.0 aims to deliver next, including stairs, 2.5D to 3D buildings, and switching movement models by location.

If you care about fire safety engineering, evacuation simulation, pedestrian dynamics, or visibility in smoke, subscribe, share this with a colleague, and leave a review so more researchers and practitioners can find the tools and the ideas. What would you test first with an open FDS to evacuation pipeline?

Links to the good stuff:

Jupedsim the engine: https://www.jupedsim.org/
its webapp: https://app.jupedsim.org/

Youtube-playlist for jupedsim: https://www.youtube.com/watch?v=ekbvCdy1P3w&list=PLYiH62IDwy5fdFJRiGky0Hdq88xKwjayL

pyFDS-Evac: https://pedestriandynamics.org/pyFDS-Evac/

pyFDS-evac presentation from the visbility seminar https://pedestriandynamics.org/pyFDS-Evac/talks/visibility-seminar-2026/#/1

Cover image comes from the 1st video on the JuPedSim playlist - the Galton Board Walked by Pedestrians in JuPedSim, by Pedestrian and Fire Dynamics Channel on youtube.

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