Two men were in critical condition from carbon monoxide after they were found in a bus on the infield at Texas Motor Speedway, authorities said.
One person was taken by helicopter ambulance to a Plano hospital while the other man was taken to a local hospital.
The men were found in a converted bus which was parked on the infield near Turn 2 at the Texas Motor Speedway, 3545 Lone Star Circle. The area is for overnight campers.
They were discovered shortly before 9 a.m.
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The men were believed to be in the their 50s, authorities said.
“There was a generator under the bus and it appears that it was not properly vented,” said fire department spokesman Kyle Clay in a Sunday telephone interview.
No other injuries were reported.