Dr Randy McDermott takes us behind the scenes of fire science's most critical software tool in this conversation about the Fire Dynamic Simulator (FDS) developed at NIST. As one of the developers, Randy offers valuable insights into how this essential modelling tool is maintained, improved, and adapted to meet the evolving challenges of the fire safety community.

The conversation begins with a look at the development process itself, based on a greater picture roadmap and also addressing practical issues reported by users. This balance between vision and responsiveness has helped FDS maintain its position as the gold standard in fire modelling. Randy unpacks the massive validation guide (over 1,200 pages) and explains how users should approach it to understand model capabilities and uncertainties.

The guide, along with all the validation cases, is available at Github repository here: https://github.com/firemodels/fds

Rather than blindly applying FDS to any problem, he emphasises the importance of identifying similar validated cases and understanding the limitations of the software for specific applications. The discussion tackles emerging challenges like battery fires and mass timber construction – areas where traditional fire modelling approaches face significant hurdles. Randy addresses the limitations of current models while outlining pathways for future development, including potential integration with external specialised models and improvements in chemistry modelling.

Finally, we also get to talk about computational costs and efficiency. As Randy explains the implementation of GPU acceleration and the challenges of incorporating detailed chemistry, listeners gain a deeper appreciation of the tradeoffs involved in advanced fire modelling.

Whether you're an FDS user, fire safety engineer, or simply curious about computational modelling, this episode offers valuable perspectives on the past, present and future of the tool that underpins modern fire safety science.

Oh, and Randy is not just an FDS developer - he is also a prolific researcher. You can find more about his scientific works here: https://www.nist.gov/people/randall-j-mcdermott

As always, MASSIVE THANKS TO THE NIST GROUP AND THEIR COLLABORATORS FOR BUILDING AND MAINTAINING THE SINGLE MOST IMPORTANT PIECE OF SOFTWARE WE HAVE!!! You guys are not thanked enough!

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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.

Four years ago, what began as a mission to preserve valuable fire safety engineering conversations has grown into a fairly large platform connecting professionals across 170+ countries. The journey to 200 episodes and nearly 200,000 downloads has been both challenging and deeply rewarding – in this episode, I share a bit about my journey, the state of things and the near future of the podcast.

*** Important notice: at the end of the show notes is a survey, and I would be thrilled if you participated in it. Back to the news post ***

Behind every weekly episode lies 10-12 hours of preparation, recording, and editing. From coordinating with international guests across time zones to balancing out the technical depth and accessibility, producing the Fire Science Show has become a finely-tuned process. Some recordings happen at 5 AM, some late at night, all to bring the most valuable fire science conversations to your ears.

This special anniversary episode pulls back the curtain on what makes the podcast work. You'll discover how episodes are created from concept to publication, learn about memorable moments (like the great LEGO collapse catastrophe during an interview with my podcasting idol Pat Flynn), and hear about challenges faced along the way. The most popular episodes – including fundamentals with Rory (2,500 listens) and timber fire safety with Danny Hopkin (1,800 listens) reveal what resonates most with our community of listeners. But all episodes are important, as they together create a space where complex fire science becomes accessible and engaging for professionals worldwide.

As we look toward the future, your input is essential. What topics should we cover? What format works best for you? The listener survey linked in our show notes is your chance to help shape the Fire Science Show's next chapter. Join us as we continue bridging the gap between cutting-edge research and practical application in fire safety engineering.

>>>> LINK TO THE SURVEY <<<<

Lastly, but also very important. Massive shout out to the OFR for making this journey possible. If not you, we would not be celebrating this anniversary. Thank you so much for your support to the concept of freely accessible high-quality CPD delivered to any part of the world, any time someone feels like it!

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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.

I've finally done it. We've repeated Jin's experiment! I thought I knew-it-all about that experiment, but boy... knowing and doing it are two different things. I can say, I've finally cleared my mind on some thoughts after this, which I am finally happy to share with all of you!

First things first, massive thanks to my partner in crime Wai-Kit Wilson Cheung, from the group of prof. Xinyan Huang, who was the man on the ground doing the experiments with me. Together we went further into this model, than ever before.

The revelations are far-reaching. We found that Jin used extraordinary lighting conditions—180 lux background brightness and impossibly bright signage—far from realistic building emergency conditions. Background brightness emerges as perhaps the most critical factor in determining what can be seen through smoke, with dramatic differences between light-emitting and light-reflecting signs. Most significantly, the experiment's careful constraint of sign size (using proportionally larger signs at greater distances) created elegant mathematics but removed a crucial real-world variable from the model.

These insights have profound implications. Engineers likely overestimate visibility in many scenarios, particularly with reflective signage. The widely used K-values (3 for reflective signs, 8 for light-emitting signs) appear reasonably conservative for typical building conditions, though higher values might be warranted in darker environments. Most provocatively, simply increasing sign size would almost certainly improve evacuation safety, yet our current models provide no mechanism to quantify this benefit.

Fire safety practitioners will find this episode transformative, offering both practical guidance and theoretical understanding. Should we stick with visibility distance or shift to smoke density as our primary metric? How can we balance lighting conditions to optimize visibility of both obstacles and signage? And most critically, how might next-generation visibility models better serve real-world building safety? These are things we currently work on.

If you look for reading, check the paper on the extinction coefficient by the German colleagues: https://arxiv.org/abs/2306.16182

If you strive for more podcast episodes:

• this one covers historical Jin's experiment: https://www.firescienceshow.com/162-experiments-that-changed-fire-science-pt-9-jins-experiment-on-visibility-in-smoke/
• this one is on soot and smoke: https://www.firescienceshow.com/163-fire-fundamentals-pt-11-soot-in-fire-safety-engineering/
• and this one our general thoughts about modelling visibility and new pathways we see forward: https://www.firescienceshow.com/030-visibility-prediction-framework-with-lukas-arnold/

The research was funded by the National Science Centre, Poland, based on a contract for the implementation and financing of a research project OPUS LAP No 2020/39/I/ST8/03159 and by Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under the project number 465392452, for the joint project: “Visibility Prediction Framework – a next-generation model for visibility in smoke in built environment”.

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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.