Franklin, MA – Twelve people were taken to the hospital after a gas leak and carbon monoxide scare at a shopping plaza in Franklin Thursday morning.

Firefighters were called to 9 Round Kickbox Fitness in the Franklin Village Mall just after 9 a.m. and found high CO readings inside the gym and in the businesses next door and upstairs.

Twelve people were taken to Milford Hospital and are expected to be OK. The building was ventilated to remove the potentially deadly fumes.

Firefighters discovered dangerous levels of carbon monoxide throughout the building, up to 300 parts per million. “Normal is zero, so 300 is very significant,” said Franklin Fire Chief James McLaughlin.

The fire department believes the issue was caused by a boiler in the laundromat next to the gym. It was leaking gas and that created the sudden increase in carbon monoxide levels.

Teraisa Sabatini-Tucker, the owner of 9 Round, said she called Columbia Gas back on Monday after noticing a gas odor in the building. Testing was done and there were no issues again until the odor came back Thursday morning.

“I called the gas company and they responded within about 15 minutes,” she told WBZ-TV. “They got everybody out of our unit, as well as the adjacent units and upstairs as well, which I understand, they were reading very high levels upstairs.”

“I compliment the person who recognized the importance of calling the gas company early on, which got them here early on, and as soon as they saw that there was an issue, they immediately called us and got everything in motion very quickly, so the operation went very well,” Chief McLaughlin told reporters.

All of the businesses were able to reopen, but the laundromat will be without heat until the boiler is replaced.