Two men were injured in the fire on Halesowen Road at about 2.20am on Sunday.
One of the men was found in a critical condition and taken to the Queen Elizabeth Hospital in Birmingham, while the other was treated for injuries not believed to be serious and taken to Russells Hall Hospital, West Midlands Ambulance Service said.
A man in his 40s who was taken to hospital with burns later died, police confirmed.
West Midlands Fire Service has now said the cause of the fire was accidental.
