Although strong in compression, cast iron was known to be brittle in tension or bending. On the day of the accident, the bridge deck was covered with track ballast to prevent the oak beams supporting the track from catching fire, imposing a heavy extra load on the girders supporting the bridge and probably exacerbating the accident. Stephenson took this precaution because of a recent fire on the Great Western Railway at Uxbridge, London, where Isambard Kingdom Brunel's bridge caught fire and collapsed.