On July 3, 1999, at 2129 eastern daylight time, an unmanned Adams A55S Balloon, N9808S, caught fire, drifted, and collided into a single family dwelling near Woodstock, Georgia. The personal flight was operated by the pilot under provisions of Title 14 CFR Part 91, and visual flight rules. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The commercial pilot was seriously injured and a passenger received minor injuries. The balloon was destroyed. The flight departed Alpharetta, Georgia, at 2000. According to the pilot, the balloon was picked up from a repair station earlier in the day and taken to a private residence where his instructor and another pilot could examine it. The pilot reported that the balloon was closely examined and carefully assembled. No mechanical problems were reported to have been found and inflation of the balloon was normal. A tether operation of standing and ascending to the extent of the 25 foot tether was conducted for about 45 minutes. The pilot reported that his son noticed fire dripping from the fitting that connects the main fuel line to the burner assembly. The pilot tried unsuccessfully to extinguish the fire with a glove while turning off the two fuel tanks. The pilot pushed his son from the balloon after the fire grew worse and the reduction of weight caused the balloon to ascend rapidly to the extent of the tethers. At this point, the pilot jumped from the balloon and fell 25 feet to the ground. The balloon remained tethered for about 15 to 20 minutes until the fire burned through the tether ropes. After breaking free from the tethers, the balloon ascended and drifted unmanned for about an hour before descending and colliding with a single family dwelling approximately 30 miles from the point of origin. Damages to the balloon included fire damage to the lower panels, burner assembly, hoses, and uprights. Examination of the fuel line fitting revealed a loose connection between the two threaded ends. According to the manufacturer of the fuel hose, it is produced for use in air conditioning applications and should never be used with LP gas.