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.

----
The Fire Science Show is produced by the Fire Science Media in collaboration with OFR Consultants. Thank you to the podcast sponsor for their continuous support towards our mission.

A tool doesn’t become a global workhorse because it’s clever. It becomes a workhorse when different labs can run it, calibrate it, compare it, and trust it. It is a very long road from the invention to widespread use. And I got the chance to discuss the path of how the Cone took off with Dr. Marc Janssens, who is a key figure in this story - he was even jointly co-awarded the Phillip DiNenno Prize together with dr Vyto Babrauskas, for his efforts on developing, standardizing and promoting the Cone.

Marc takes us back to the early days of reaction-to-fire testing, when heat release rate measurement was messy, methods differed by country, and oxygen consumption calorimetry still had to prove itself. He was sent on a mission to find a heat measuring device, and shares on what was available back then.

Later in the episode we dig into the questions raised: is a 10 by 10 cm specimen too small, what does “scaling” really mean, and how do you avoid fooling yourself when you try to turn cone calorimeter curves into real-fire predictions. We also get into why the cone’s controlled heat flux and feedback control mattered so much, and how interlaboratory round robin studies turned uncertainty into precision statements that standards could stand on.

From there, the conversation opens up into what cone calorimetry enabled: faster R&D for products, smarter screening ahead of costly room corner testing, and a path to modeling. Marc shares how cone calorimeter data supports fire modeling efforts, including flame spread approaches in FDS, and why validation at larger scales still matters. The episode lands with a powerful case study: performance-based, risk-informed nuclear power plant fire safety, where cable tray fire spread scenarios depend on models fueled by cone calorimeter measurements of cable insulation.

If you are a daily user of a Cone, an engineer who depends on high quality models and data, or simply want to hear about the history of our discipline... this one is for you.

----
The Fire Science Show is produced by the Fire Science Media in collaboration with OFR Consultants. Thank you to the podcast sponsor for their continuous support towards our mission.

A fire scene looks like a puzzle, but it’s a puzzle where the pieces melt, burn, and get hauled away before anyone can measure them. On the 25th anniversary of 9/11, I sit down with Professor Vincent Brannigan to ask a questions - does a fire investigation truly use the scientific method, or are we doing something else and calling it science?

Vincent brings a rare mix of experience as a fire protection engineer, a lawyer who has seen cases up close, and a historian of science who cares deeply about how we justify knowledge in court. We talk about the World Trade Center collapse, what made investigation so difficult, and how code and design assumptions (like fireproofing priorities and sprinklers) shape outcomes long before any investigator arrives. From there, we get precise about language: what a hypothesis is, what makes a scientific hypothesis testable, why a theory is not a casual idea, and why “proof” is the wrong word in most scientific and forensic contexts.

Then we take the discussion into the context of NFPA 921 directly. We explore why much of forensic fire reasoning is abductive inference (the Sherlock Holmes style of “best explanation”), why that can be useful, and why it becomes dangerous when it’s presented as if it carries the repeatability of lab science. We dig into witness statements, models and simulations, experiments that actually help, and the uncomfortable gap between “possible,” “probable,” and “true” when the courtroom demands answers.

If you care about fire investigation, forensic fire science, expert testimony, and how fire engineering knowledge becomes evidence or a foundation of new code recommendations, this conversation will sharpen how you think and how you write.

----
The Fire Science Show is produced by the Fire Science Media in collaboration with OFR Consultants. Thank you to the podcast sponsor for their continuous support towards our mission.