The fire broke out around 1 a.m. in a second floor office at Norquay Technology on the 800 block of West Front Street. Their website indicates they are a commercial manufacturer of chemical products.
The fire was placed under control at 1:20 am.
"During overhaul, we did have minor extension to one of the labs here at Norquay, and we discovered various chemicals in there," explained Chester Fire Commissioner William Rigby.
Ten Chester firefighters and three employees were exposed to the chemicals.
Delaware County Hazmat and Emergency Management teams were called to the scene.
Teams in bubble suits went inside to assess the chemicals.
A decontamination trailer was set up.
Each person went in one side to be washed and out the other. Their clothing and gear were lined up and later loaded and sent for environmental testing.
Ambulance by ambulance rolled the ten firefighters and three employees to three area hospitals for evaluation, as a precaution. None were showing symptoms. All were released within hours.
The investigation into the cause of the fire continues.
Authorities have not said what chemicals were involved, but said there was no threat to the public.
"They secured everything. An environmental company will come in now and clean up. We're getting ready to turn the building back over to Norquay," Rigby said.
Norquay has not responded to request for comment.