“Two people per parking space” is one of those default fire engineering inputs that we are very used to place into a model without really thinking much of it. But it is one of those defaults that show a huge richness once you dig deeper. Are all parking spaces taken? Are people in their cars? What are they doing? How long have they been there concurrently... We take that simple rule and pull on the thread until it turns into a full conversation about evidence, uncertainty, and what “credible maximum” should mean when you are designing for real-world risk.

Dr Mike Spearpoint from the OFR joins me to explain how occupant load values end up in codes, why they are so hard to interpret, and why “maximum possible” can push designs into unrealistic corners. Then we get practical: we build a static, risk-based method for car park occupant load using distributions for car park utilisation and people per vehicle, run it through Monte Carlo simulation, and talk about selecting percentiles like the 95th or 99th for design. If you work with evacuation analysis, performance-based fire engineering, or fire safety assessment, this is the kind of reasoning you can reuse anywhere.

In his consideration, Mike reaches something he calls the dynamic model: people are only briefly “in the car park” as they park, unload, walk to the destination, and leave. Because published data on “around-the-car” activity time is scarce, Mike measures it directly using public CCTV observations and turns it into a usable distribution.

Why did he do this? This is a part of a larger project on adequate fire resistance periods in car parks. We also connect utilisation to vehicle-to-vehicle fire spread and why those assumptions can ripple into design fires and structural fire resistance decisions for open-sided car parks.

If you are looking for the report itself with all the details, look here: https://www.gov.uk/government/publications/fire-safety-open-sided-car-parks

I'll make it easy for you, it starts at page 218 ;)

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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.

A fire strategy can be technically correct, but if the team building the building never truly understands it - goals and objectives may be missed. For the 250th Fire Science Show, we slow down and talk about the craft of communicating fire science to construction professionals so that the intent survives real projects, real deadlines, and real handovers.

This episode is an extended version of my talk I gave recently at the IAFSS Research Sub-Committee Workshop, which we have organised with Felix Wiesner, and I had a chance to talk along my friends - prof. Guillermo Rein, Birgitte Messerschmidt and dr Steve Kerber.

In this episode, we share why the biggest failures are rarely tiny compliance misses. The scary failures come from misread strategy, missing execution on site, and teams optimizing for the wrong target because we explained the “what” but not the “why.” From smoke zoning misunderstandings to the way product labels and ratings get interpreted, we unpack how simple miscommunication can create life-threatening conditions even when everyone is working hard.

Then we offer a practical framework built around three ideas: context, timeliness, and the way we speak. Context means understanding the building ecosystem: code and local planning, sustainability and energy efficiency, LEED or BREEAM certification pressures, business model realities, and aesthetics. Timeliness means matching our message to the building lifecycle, keeping high-level objectives clear early on, translating them into technical concepts during design, and only then driving into the technical detailing that makes compartmentation, egress, smoke control, and structural fire safety real. Finally, we get honest about what works: simple anchors like ASAT versus RSAT, consequence-focused language, and respectful collaboration, plus what breaks trust fast: jargon, paper-style writing, megawatt talk, and false certainty around “60 minutes” ratings.

Some other podcast recommendations after this one:

• https://www.firescienceshow.com/136-fire-fundamentals-pt-6-the-fire-automation-in-a-building/ what happens in a building during a fire?
• https://www.firescienceshow.com/246-fire-fundamentals-pt-20-fire-resistance-criteria-with-piotr-turkowski/ a wider view on the fire resistance
• https://www.firescienceshow.com/199-commercial-timber-guidebook-with-danny-hopkin-and-luis-gonzalez-avila/ commercial timber guidebook which is an example of excellent communication of fire safety concepts.

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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.

From the SFPE Performance Based Design Conference in Singapore, we sit down with Jonathan Hodges and Mark McKinnon (UL Research Institutes) and Christian Rippe (Jensen Hughes) moments after their case study presentation to break down a modern parking garage fire engineering workflow with a huge does of performance based and probabilistic approaches.

We talk about what changes when today’s vehicle fleet makes multi-vehicle fire spread more plausible, and why picking a single car fire curve can quietly bake bias into an entire performance-based design. The team shares how they use real incident data, vehicle size distributions, ignition location categories, and percentile-based heat release rate curves to build design fires that are transparent and defensible. We also dig into EV charging as an initiating mode, what the data can and cannot support, and how a “gap analysis” mindset helps practitioners avoid false precision.

Then we get into the risk machinery: scenario binning, frequencies, sprinkler reliability assumptions, and how CFD (FDS) fits when you cannot simulate 100,000 possibilities. Finally, we go structural with concrete spalling, thermal finite element modeling in Abaqus, and a scripted workflow that iteratively removes damaged concrete to understand how exposure evolves during long-duration multi-vehicle fires.

For this episode, there is a ton of resources. From Jonathan:

1. Reference for first design fire paper: https://doi.org/10.1016/j.firesaf.2024.104145
2. Reference for second design fire paper: https://doi.org/10.1016/j.firesaf.2026.104721
3. Reference for database paper: https://doi.org/10.1007/s10694-025-01701-5
4. Reference for number of parking garages: https://doi.org/10.1016/j.firesaf.2022.103565
5. Reference for ULRI vehicle fire data: https://doi.org/10.1016/j.dib.2026.112471
6. Reference for ULRI material database: https://materials.fsri.org/
7. Reference for NERIS: http://neris.fsri.org/
8. Reference for NFPA Vehicles data: https://www.nfpa.org/education-and-research/research/nfpa-research/fire-statistical-reports/vehicle-fires

And two from myself:

1. Outcomes of the massive fire with spalling in Warsaw https://doi.org/10.1016/j.firesaf.2025.104352
2. Open sided car park report by OFR https://www.gov.uk/government/publications/fire-safety-open-sided-car-parks/real-fires-open-sided-car-park-fire-resistance-introduction-and-conclusion

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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.