The derailment of a passenger train at Lytham, Lancashire, England occurred when the front tyre of the locomotive fractured.
The building was completely demolished and coals from the grate ignited a carriage.
The defect probably formed during the steel casting operation, and became critical as the tread was worn away.
All the other wheels from the same batch were removed from service and broken up, but no other cavities were found in the treads.
The drop in failure rate was due to the introduction of the monobloc steel wheel and better inspection and maintenance methods.