The lac Magnetic tank cars derailed and crashed into each other. I think about 50 died.
It derailed because it was left with insufficient handbrakes and no one to keep an eye on it. After it caught fire, the the fireman turned the engine off, loosing the air brakes and it coasted downhill until it couldn't make a turn.
The cause wasn't the condition of the rails, but the lack of care given in handling hazardous cargo.s