On May 23, 1999, about 0810 Eastern Daylight Time, a Balloon Works, Firefly-7, N9070T, was not damaged while landing in a field, near Gasburg, Virginia. The certificated pilot and one passenger were not injured. A second passenger was seriously injured. Visual meteorological conditions prevailed and no flight plan was filed for the local flight conducted under 14 CFR Part 91. In a written statement, the pilot reported that he was a participant in a hot air balloon race. A weather briefer was present for the race, and had launched a 12-inch helium weather balloon. The pilot was present with the weather briefer when the weather balloon was launched, and they observed the surface wind from 210 degrees at less than 5 knots, with no significant wind shifts up through 800 feet. The hot air balloon launched under light wind conditions, about 0745. As the balloon was approaching the first steerage, at about 50 feet above the ground, the pilot had to climb the balloon to 300 feet to complete the turn. During the climb, a windshear flattened out one side of the balloon, re-inflating a moment later, violently shaking the entire balloon. The pilot decided to abort the race, and informed the passenger that they would be landing in the first available field. A hay field was spotted about 4 miles ahead of the balloon, and the pilot maneuvered to it. The field was several hundred yards long, with power lines on the far end. Several other balloons had used the field to land, due to encountering the same type of winds. As the balloon neared the ground, the winds continued to blow, and the basket collided with a hay bail, at a speed of about 15 knots. Event officials, who were on the ground, and witnessed the accident, estimated the speed of the balloon at 20 knots. After impacting the hay bail, the basket touched down, dragged along the ground, and rolled over. The balloon then collapsed completely to the ground. An airport located 10 miles to the northwest, reported, clear skies, winds from 210 degrees at 6 knots.