The large fire at a Biffa building in Cardiff is suspected to have been accidental.
South Wales Fire and Rescue Service sent more than 10 crews to the blaze in Leckwith on Thursday and nobody was injured.
The fire sent thick black smoke billowing across parts of the city with crews battling for hours to extinguish the fire.
Images from the scene off Hadfield Road appeared to show damage to large parts of the site, which also suffered a large fire in 2017.
On Friday, a fire service spokeswoman said: "At approximately 11.49am on Thursday the 13th of May, we received reports of a commercial fire in Leckwith, Cardiff.
"Multiple crews and 13 appliances attended the scene and used specialists equipment to extinguish the fire.
"A stop message was received at approximately 4.27pm. The supposed cause has been suspected to be accidental."
A council worker from the tip next to the commercial unit said he first noticed the fire at 11.50am. He said there were huge flames through the building and coming through the roof.
During the incident, the fire service urged people in Leckwith to drive carefully as "smoke is drifting across the roadways".
A spokesman for Biffa said a full investigation is set to be carried out into the fire.
On Thursday, the company said: "We are aware of a fire incident at our site in Leckwith, Cardiff, which was reported this morning and is now under control. We are working with the South Wales Fire and Rescue service team and will be carrying out a full investigation into the incident. Thankfully, nobody has been injured."
