Five Hampton Inn occupants were treated at the hospital, and one was unresponsive when the hotel was evacuated Monday night, Fire Chief Greg Neely said. An investigation revealed a carbon monoxide leak from a pool heater.

Neely's description of symptoms matched the description of carbon monoxide poisoning symptoms provided by the Center for Disease Control and Prevention.

A total of 33 people were evacuated from the hotel, north of U.S. 412 near Signature Plaza.

Emergency responders forced their way into one room when its occupant didn’t respond while evacuating the hotel, Neely said.

Four people were transported to Siloam Springs Regional Hospital. One went to the hospital by private vehicle, Neely said.

About 25 occupants were relocated to Best Western in West Siloam Springs, Okla., Neely said.

Some returned to Hampton Inn after the hotel reopened at 3:30 a.m. Tuesday, said April Gibson, general manager of Hampton Inn. Others stayed at Best Western.

The cause of the incident was traced to a swimming pool heater, Neely said. It was emitting elevated levels of carbon monoxide.

“We will have someone on the property today to verify the source, and repairs will be made immediately,” Gibson said. “The pool is out of order until further notice.”

The first call related to the incident was made at about 8:30 p.m. Monday when a 54-year-old man reported he was dizzy and had a rapid heart rate, Neely said.

About two hours later, another person reported similar symptoms.

Emergency responders determined the larger scope of the incident and called the gas company for assistance.

An investigation led them to the pool heater, Neely said.

Carbon monoxide is an odorless and colorless gas that is produced whenever a fossil fuel is burned, according to the Centers for Disease Control and Prevention.

“The most common symptoms of CO poisoning are headache, dizziness, weakness, nausea, vomiting, chest pain and confusion,” the CDC website shows. “High levels of CO inhalation can cause loss of consciousness and death.”