Inspectors sent to the mine to look at the extent of the rock fall.
It was out of service at the time of the incident, being prepared for maintenance.
Factors could include wear from weather, more traffic than the bridge was originally built to sustain.
Contained highly radioactive wastes left over from production of plutonium for nuclear weapons.
All of those killed were workers hired by various subcontractors.
Labourers were building a circular cooling tower at a power plant.
Currently serving 24 years for spectacular collapse of Houston-based.
Heavy iron equipment on upper floor may have caused the collapse.