268 - Is critical velocity that critical?

Critical velocity is supposed to be the clean moment when tunnel smoke control flips from unsafe to safe. But after too many real projects and too many review battles, I am very sure that such a single number cannot be a sole proxy of what is safe or unsafe... So why it has so much power over my design? In this solo episode I walk through why critical velocity became the world's favorite proxy for tunnel fire safety: it’s simple, it’s calculable, and it gives verifiers something rigid to chec...