The incident began around 4:10 a.m. at the Coopers Creek Chemical Corporation plant on the 800 block of River Road in Upper Merion Township.
Officials said a small fire started in a boiler room, then spread to a large tank holding coal tar or creosote.
Fire officials gave all the all-clear around 7:30 a.m. They said there was no threat to the community.
No injuries were reported.
The hazmat situation shut down River Road (Route 23) for close to three hours.