A carbon monoxide incident sent 12 people to the hospital Thursday morning and forced the evacuation of a strip mall in Franklin, Massachusetts, fire officials said.
The incident happened just after 9 a.m. at Franklin Village Mall.
Fire officials said a malfunction of the furnace inside a dry cleaner was to blame.
"They call it the silent killer and it has to be taken extremely seriously," Franklin Fire Chief James McLaughlin said.
Thirteen ambulances were called to the scene after some people reported feeling dizzy and having headaches.
"I am a little shaken up by the whole thing but I am OK," 9Round 30 Min Kickbox Fitness owner Teraisa Sabatini-Tucker said.
She said she called the gas company when she arrived to work because she noticed the odor of rotten eggs.
"Honestly, I just had a friend of mine who said a rotten egg smell can indicate a gas problem," Sabatini-Tucker said.
As a result, six businesses were evacuated and 12 people were taken to an area hospital for treatment. Two others refused treatment, fire officials said.
Those taken to the hospital were expected to be OK, according to fire officials.
Sabatini-Tucker said fire officials were able to quickly assess the situation.
"(they) quickly identified there was something happening and asked us to leave the gym. They then evacuated adjacent neighbors. And when they went upstairs, that's when they found out there was some high levels upstairs and people weren't feeling so great up there," she said.
The scene has since been clear and the evacuated businesses have been allowed to return. The furnace at the cleaners, however, will not be able to be used until a technician looks at it, fire officials said.
"This is always an opportunity to remind the public of the importance of carbon monoxide meters. Carbon monoxide is colorless and odorless," McLaughlin said.