A 37-year-old man working on a small stock car in Worcestershire was taken to hospital with burns after fuel in the machine caught fire.
He had just started up the vehicle, which is usually raced on grass, when the incident happened.
The man, from Gloucestershire, had "quite serious burns" to his legs, hands and wrists.
The accident happened in Buckle Street in Honeybourne, on Tuesday evening.
The man was taken to the burns unit at Selly Oak Hospital.