into the shaft at an angle and raced upwards. in the confined trench, the fire could only draw air from below, creating a draft. >> because the air can't come round the fire, it has to come effectively through the fire. >> investigators then ran a bigger test on a one-third sized model of the complete king's cross station. if the trench effect worked this time, it would prove their theory was right. >> in three or four seconds the flames were from upright, then lying along the escalator trench. from then on, it was just predicted which is very gratifying. >> it is clear the previously unknown phenomenon called the trench effect was real. >> now we understand. it's now all obvious. it fits together. the jigsaw fits together perfectly. >> the investigative team now