Wildland-Urban Interface fires are a class of fires that deserves own models, own studies and a lot of research focus. This is what I discuss today with prof. Arnaud Trouvé from the University of Maryland, shortly before he has given his plenary talk at the recent Combustion Symposium in Kyoto. In this interview, Arnaud explains what makes wildland urban interface (WUI) fires and urban conflagrations so hard to predict, also with a focus on the combustion phenomena.

Arnaud is interested in how the fires spread from the wildlife into the urban areas, and how to model this spread. The state of the art models for fire spread are lacking in here, due to how they perceive a fire front as a "line", whereas in cities we are looking at collection of compartment-household fires that may last for hours, and create a burning area kilometre wide. Therefore, we need new modelling approaches, and we need them at three scales - the scale of vulnerabilities of a parcel, a parcel-to-parcel setups and whole community scales.

To improve the state of the art, he breaks the problem into the scales that matter: indoor fire dynamics (where CFD can estimate structure burning), parcel-level exposure (where fire penetration is the missing link), and community-scale fire spread (where reduced order models dominate because fuel and building maps are often coarse). We dig into the practical modeling mechanics behind WUI simulators: 2D spread on gridded maps, simplified radiation and flame shape models, probabilistic firebrand transport, and the limits of one-way coupling where wind is prescribed but not influenced by the fire.

We also discuss an important bottleneck: the data. Satellite observations often arrive with poor temporal resolution, and controlled full-scale experiments are rare, which makes validation and scenario selection painfully uncertain. We also discuss why windows and near-structure fuels can be a universal pathway for loss, and why the field needs stronger shared infrastructure and collaboration to move faster.

Congratulations on your plenary talk and thank you Arnaud for representing the fire community at the Combustion Symposium. Once Arnaud's plenary paper is published, I will update the show notes with a link!

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In todays episode of fire fundamentals we talk with Professor Elizabeth Weckman from University of Waterloo about advanced optical diagnostics that let fire researchers read temperature, chemistry, soot, and velocity from light without relying only on probes. We break down what cameras, infrared imaging, spectroscopy, lasers, and PIV can reveal, plus the calibration and interpretation pitfalls that can quietly ruin your data.

Things covered in this episode:
• why optical diagnostics are “non-intrusive” in practice and where they still perturb the flow
• limits of probe-based measurements in fire including spatial resolution and radiation errors
• using basic photography and video as a first diagnostic and as a planning tool
• calibration habits for cameras and why cheap, robust cameras are often a better choice for a fire laboratory
• infrared thermography for surface heating plus emissivity problems and practical coatings
• Schlieren imaging for density and temperature gradients and what it can and cannot imply
• point vs planar vs line-of-sight vs tomographic measurements and how “smearing” happens
• FTIR and absorption spectroscopy for pyrolysis gases, emissions, and toxic species
• chemiluminescence and laser-induced fluorescence to mark combustion and flame fronts
• Raman and CARS for temperature and concentration and why they are technically demanding
• soot diagnostics from light extinction to laser-induced incandescence and aging effects
• PIV basics, seeding challenges in fire, and what velocity fields unlock for validation

The episode is best enjoyed along Beth's paper from the IAFSS: Unravelling the mysteries of fire

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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.

The cone calorimeter sits in thousands of labs, shaping what we know about flammability, smoke production, and heat release rate. This essential piece of equipment comes with quite a story of how it was engineered or why its “obvious” design choices were anything but obvious. We wanted that history from the source, so we invited Professor Vyto Babrauskas to walk us through the decisions, constraints, and small breakthroughs that turned an idea into the most practical bench-scale fire test in common use today.

We dig into the 1970s research environment at NIST (then NBS), including the plastics-focused push that created funding, talent density, and the freedom to build new measurement tools. Vyto explains how the field moved from qualitative “widget tests” toward combustion-science thinking, and why oxygen consumption calorimetry was the turning point. We also talk about terminology and standardization, including how “heat release rate” became the key engineering variable for “how big is the fire,” and why that framing still guides modern fire modeling and performance-based design.

Then we get concrete: why the specimen is 100 by 100 mm, how the cone heater geometry was modified to keep combustion products flowing where they should, why adding feedback control was so important, and how ignition and smoke measurement evolved into the robust setup many of us take for granted under ASTM E1354 and ISO 5660. We also cover heat flux selection for realism, horizontal versus vertical orientation, and why some promising variants like controlled-atmosphere attachments never became widespread. The closing brings it back to today, including Vyto's critique of fire research (mainly in Li-ON batteries) that stops at plotting heat release rate curves without answering the deeper engineering and forensic questions.

If you would like to read more about the cone, I got you covered:

• https://www.nist.gov/nist-museum/cone-calorimeter-most-important-tool-fire-safety-science from the NIST Museum
• https://www.nist.gov/news-events/news/2022/03/happy-retirement-cone-calorimeter - a NIST note on the history of the cone
• https://www.jstage.jst.go.jp/article/fst/41/1/41_21/_article paper by Vyto Babrauskas on the early history of the cone.

Cover image credit: NIST, from the https://www.nist.gov/news-events/news/2022/03/happy-retirement-cone-calorimeter

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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.