On November 18, 1987, a small fire beneath a wooden escalator at King's Cross St Pancras station killed 31 people — and rewrote fire safety engineering worldwide. This video explains the trench effect, a previously unknown fluid dynamics phenomenon that investigators only identified after the disaster, using scale models and early CFD simulations to reproduce what witnesses described.

The counterintuitive physics is the heart of the story. Fires are supposed to rise vertically via buoyancy, but inside the 30-degree escalator trench, the flames lay flat against the incline. The Coandă effect pinned the hot gases to the wooden treads, while the confined geometry accelerated air along the slope. The result was a preheated fuel bed and a jet of flame that erupted into the ticket hall as a flashover — the "blowtorch" of the title.

What makes this a genuine engineering explainer rather than a disaster recap is the investigation methodology: how the Health and Safety Executive built a 1/3-scale model at Buxton, how the CFD results matched the physical tests, and how the discovery changed escalator materials, sprinkler codes, and smoking bans across the London Underground. Small channel, but the technical framing is solid and the accident-to-principle arc is well constructed.