Neighbours saw the man rolling round on fire on the grass in Swinderby Garth, on the city's Bransholme estate, yesterday afternoon.
They rushed out to help extinguish the flames with wet towels.
Humberside Fire and Rescue said the fire involved fuel being decanted from a motorbike.
The man suffered 45 per cent burns and was taken to the specialist burns unit.
The fire had damaged a windowsill and fascia of his house.