A small fire on the roof of the National Ambulance Service caused the building to be evacuated.
The blaze at the HSE building on Belgard Sqaure in Tallaght has now been extinguished by members of the Dublin Fire Brigade.
Smoke from the fire had got into the ventilation system which circulated in some rooms.
No injuries have been reported and the fire service says there has been no damage to the building.
There was no disruption to HSE services during the incident.
Red line Luas services were temporarily suspended between Belgard and Tallaght.