About a dozen workers at Rhode Island Resource Recovery Corp. in Johnston were sickened by fumes Wednesday morning.
The RIRRC said a worker saw smoke on the sorting line in the Materials Recycling Facility and the building was evacuated.
"There's one container that came through that there was a safety issue with. Out of a million containers that come through on a daily basis," said Gary Maddocks, chief of security for RIRRC.
Officials said 14 people were sent to hospitals complaining of breathing problems, nausea and heart palpitations. Rhode Island Hospital said it received 11 patients, who were decontaminated and evaluated for various complaints.
The Associated Press reported that a container holding the unknown product went through a shredding machine.
RIRRC Executive Director Michael OConnell said this kind of incident is preventable if people follow the rules of recycling.
"Only to put into their bin the things that belong into the bin. You can see what can happen if you put something dangerous in there. It can potentially do harm to the worker. That's why we're adamant about only putting into the recycling bin what belongs there," OConnell said.
The RIRRC said the Materials Recycling Facility was shut down for the day while it tries to identify the substance.