A tight, historic cellar. Arched ceilings. Long corridors. Tiny shafts. We faced a design wall: to keep routes tenable, we needed twice the extraction that the building could carry. At that point, I've failed as an engineer - I've reached my limit and could not find a solution.

Some time later, a solution appeared in my head from nowhere —what if the fan changed with the fire? Not in a crude on-off way, but by tracking temperature, exploiting density changes, and chasing constant mass flow instead of fixed volume.

We unpack the moment this clicked, the fan physics behind it, and why hotter smoke can actually make extraction easier if you use the margin correctly. You’ll hear how we oversized the fan, ran it at a lower frequency in ambient, then ramped as temperatures rose to keep kilograms per second steady. That adaptive control boosted cubic meters per second right when the layer needed support, eased plug-hole entrainment, and stabilised makeup air velocities. We walk through the thermodynamics, the electrical and pressure implications, and how these pieces form a practical control strategy for retrofits and new builds.

To ground the idea, we share two paths to proof. First, CFD with user-defined control that reads gas temperature each time step and updates fan frequency with smoothed delays to prevent oscillations—capturing the real feedback loop between fire and system. Then, full-scale container burns with live control showed the same trends from 20 to over 500 degrees: falling duct pressures, lower fan power at heat, and the headroom to increase volumetric extraction without breaking limits. 

Thinking about it now, this idea is a part of many other concepts that I describe together. To show a way how we come from the simple framework—Smoke Control 1.0 (empirical, static), 2.0 (CFD-informed, still static), into a new smoke control 3.0 (adaptive, feedback-driven)—and explore how this thinking can reshape underground venues, car parks, tunnels, pressurisation, and natural ventilation.

If you care about safer evacuation, smaller shafts, lower velocities, and systems that work with physics rather than against it, this story is for you. Subscribe, share with a colleague who designs smoke control, and leave a review with your toughest question so we can tackle it next.

Reading material:

- Can smoke control become smart?

- Transient characteristic of the flow of heat and mass in a fire as the basis for an optimised solution for smoke exhaust

- Smart Smoke Control as an Efficient Solution for Smoke Ventilation in Converted Cellars of Historic Buildings

----
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.