Ten people were taken to hospital after a gas leak at a factory in Wigan.
About 230 workers were assessed by paramedics after the factory on Dobson Park Industrial Estate was evacuated at 18:35 GMT on Tuesday.
Fire crews wearing breathing apparatus isolated the leak from inside the building before midnight, said Greater Manchester Fire and Rescue Service.
"The air quality has been tested by monitoring systems and there is no cause for concern", it said.
Firefighters "worked closely with the onsite engineer to isolate the plant system to prevent a further leak", a statement from the brigade said.
Ten people were taken to hospital "as a precaution", it added.
The industrial estate, in the Ince-in-Makerfield area, is home to a number of manufacturing and industrial units.