Iarnód Éireann has launched an investigation into an incident on a Cork to Dublin train that resulted in smoke entering the train through the air-conditioning system.
The 7.30 service ran into problems last Sunday between Charleville and Limerick Junction.
Smoke and a pungent smell passed through the train, causing panic among some passengers.
Iarnód Éireann said it was caused by a brake disc problem. They have launched an investigation, but say they are happy that safety was maintained, despite a two-hour delay in the journey.