Pressure is mounting on Irish Rail to explain the “systems failure” which allowed the collapse of a bridge that had been deemed safe.

It emerged yesterday that the viaduct over the Broadmeadow Estuary in Malahide, Co Dublin, was due to undergo a full bridge inspection and assessment in October.

The company was warned about possible damage to one of the piers supporting the rail bridge five days before it collapsed, but no structural damage was found despite two inspections. Now there are political calls for explanations to the incident in which a disaster for commuters travelling home was narrowly avoided.

On Monday last week the leader of the Malahide Sea Scouts contacted the company with concerns about erosion to the piers.

The following day an engineer inspected the viaduct and found “no visible structural issues, and that all markings were cosmetic”, the company said yesterday.

Two days later a track monitoring vehicle travelled over the line. This records all dimensions of track, including levels and gauge, and would identify any deviations from normal conditions including those not visible to the naked eye. It found the railway was operating as designed.

Yet the following day the viaduct collapsed at 6.30pm, moments after a train passed over it.

Fine Gael said it was “unacceptable” that an underwater survey of the bridge was not conducted following the warnings and said Irish Rail would be asked to appear before the Dail Transport Committee to explain the “systems failure”.

“There are still many questions around the unanticipated collapse of the Malahide rail bridge that has increased public concern over the safety of similar bridges and of the inspection regime of railway infrastructure,” said FG transport spokesman Fergus O'Dowd.

However, Irish Rail insisted all safety procedures and inspection standards were followed. It believes erosion of the sea bed around the pier was the reason for the collapse.

Work on replacing the bridge will take an estimated three months.