[00:00] As fans crowded onto the escalator, their combined weight increased the load on the main motor, and eventually it hit a tipping point and the motor started accelerating uncontrollably. Safety sensors in the machine noticed this sudden change and triggered two things in short succession.
[00:16] First, the power to the motor was cut, and immediately after that, the main brake engaged. Two massive arms clamped down on the drum to lock it in place and avert a runaway. This brake should have had enough stopping power to bring the fully loaded escalator to a halt, even under the massive strain.
[00:34] But it didn't. Tests after the incident showed that its braking force was far too low, around 37% of the manufacturer's specification. The weakened brake struggled to slow the spinning motor and the escalator's downhill acceleration continued.
[00:49] This is when the last line of defense kicked in. When the escalator's speed rose by more than 20%, the auxiliary brake triggered, driving steel wedges into a disc on the driveshaft.
[01:01] But when investigators opened up this brake, they were shocked. The final mechanical backstop had been partially disabled. Someone had physically tied plastic straps around one of the two brake wedges and rendered it useless.