As a precautionary move during the leak, emergency workers closed down the South Loop for around 15 to 20 minutes.
"Propylene is like propane," said Bruce Clawson with the Texas City Office of Emergency Management. "It's fairly light and can get away from you. It did not exit the plant."
Officials say there was no danger to the community, and no shelter in place was issued. So far, there have been no reports of any injuries.
It's not known what caused the leak, but the unit was starting back up when the leak occurred.