Firefighters respond to reports of an explosion outside Chicago's Soldier Field, where the Autism Speaks Walk event was taking place on Saturday.
Video shows shows one of the sponsors' tents on fire.
Firefighters say when the tent caught fire it also caused a propane tank to explode.
A 60-year-old man was taken to a hospital for smoke inhalation and is said to be in good condition.
No other injuries were reported.
No word what caused the tent to catch fire.
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