extinguished. >> the fireman who was walking down escalator number 6 and looked across to escalator number 4, approximately one minute before flashover, had described the fire as being relatively small. >> but then, the fire spread across the steps, the bottom of the trench. it could only draw oxygen from one direction, from below. this was the trench effect. >> the flames were deflected into the trench and began to flow up the treads, the risers, and exposing the balustrades to very high levels of heat flux. >> from there, the hot gases are going up the escalator trench ahead of the flame. they're heating the wood quite considerably. it gets quite hot, even though there's no flame there. >> it's sucking up the air from below like a chimney would, which is what it needs to do, and that would tend to flatten the flames down in the early