Iarnrod Eireann began an immediate investigation last night after two trains - one of them carrying the dangerous chemical, ammonia - collided in Dublin.
The crash happened in Glasnevin, near Cross Guns Bridge, shortly before 9 p.m. after three wagons on the ammonia train heading for Shelton Abbey became derailed.
The ammonia train's rear wagon, which was carrying a water tank, was struck by the engine of a Cork-bound freight train heading in the opposite direction.
Three tenders from Dublin Fire Brigade's Phibsborough station went to the scene but there was no spillage of ammonia, a natural gas compressed into liquid form.
None of the wagons derailed was carrying ammonia, an Iarnrod Eireann spokesman said. Two were unladen and the other was the water-carrying barrier wagon which was struck by the freight train. No one was injured in the incident.
Both trains, minus the derailed wagons on the ammonia train, were able to resume their journeys last night.
The spokesman said the remaining wagons would be cleared during the night so there would be no disruption of commuter services today.
Iarnrod Eireann investigating officers were at the scene last night to begin inquiries into the cause of the crash. A report will be made to the railways inspection officer at the Department of Public Enterprise, and to the Minister, Ms O'Rourke.