Comment by tialaramex

It's an addiction, they're compelled to smoke, and so at the edges of the area they'll light up.

That's how the Kings Cross Fire started. Escalator full of potential fuel, smoker drops a used match, it falls inside the machine, fire. It wasn't legal technically to be smoking on that escalator, but it would have been legal in a few paces so "everybody" did it. The investigators found signs that such fires had likely started or almost started many times before, the disaster was just that this time it burned for long enough to create a pool of extremely hot gas flowing up the inclined ceiling for the escalator, and we got to discover the Trench Effect in the least fun way possible.