A Delta flight that to Tulsa on Saturday after a dozen passengers fell ill with carbon monoxide poisoning.
However, a Delta spokesman said that plane had been tested for carbon monoxide since landing and no traces, or any other source of gas, were found.
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The flight had departed from Atlanta and was bound for Denver when several people showed signs of sickness, prompting the flight to divert to Tulsa.
Speaking to AJC.com, Tulsa Fire Department spokesman Stan May said the exposures were "very low level and their symptoms were they were drowsy, and a couple of them felt nauseous."
He suggested that it was possible an aerosol can in someone's luggage may have caused the issue.
He added: "It apparently wasn't caused by the airplane itself. Whatever it was had stopped off-gassing by the time we were called in to put the metres to it, because we didn't find it in the air, it was just detected it in the passengers".
Mel Gilles, a passenger travelling from Jacksonville, Florida, to her home in Boulder, Colorado, said she first noticed a flight attendant feeling ill.
She added: "At the same moment, about six people around me began to feel ill.
"Some put their heads down. Others asked for bags to throw up in. And then I noticed that a few rows in front of me, a couple of people were having problems as well."
The flight then diverted to Tulsa.
According to CN Traveller, other passengers had to disembark in Tulsa and go through a security checkpoint again before they were put on another flight to Denver later on Saturday.
A Delta spokesperson said: "Technicians continue to assess the original MD-90 out of an abundance of caution."