The fire, at the Boland's car dismantlers on Nevinstown Lane, on the Old Swords Road, broke out just before midnight and was still being tackled this morning.
The scrapyard was said to contain a lot of petroleum-based chemicals, as well as gas cylinders.
Fire brigade sources feared there could have been some leakage into drains around the site during the fire.
At one point there were seven fire tenders and a tanker pumping water onto the flames.
Two foam tenders from Dublin Airport were also brought to the scene to try to smother the fire.
There was extensive damage to the site, which operates as a vehicle dismantling plant under a disposal licence.
It also runs a 24-hour vehicle recovery service. There were no reports of any injuries but the Environmental Protection Agency as well as local authority management were expected at the site today once the fire was out.
As well as investigating how the fire started, they will also determine if there are any adverse effects on the local environment as a result of the blaze.
Gardai closed the Old Swords Road between the Airside Industrial Estate junction and the Cloghran roundabout while the fire crews attended the scene.
The road was closed under the advice of the chief fire officer due to risks from gas cylinders at the plant.
Traffic diversions were in place while the road was closed.
A spokesperson for Boland's car dismantlers said that they had "no comment" to make.