Abstract: Employee #1 was part of carpenter crew placing 8 by 16 ft concrete form sections at night to allow lane closure of a highway so a boom truck could lift and position form sections in order to pour a retaining wall below the highway. Employee #1 was approximately 12 ft above the ground on a Keller 20 ft aluminum extension ladder in nearly new condition, leaning against the form section being installed. A coworker was straddling the top of the form section at the other end, 8 ft away. Another coworker was at the top of the bank at the other end of the 2 by 4 brace Employee #1 was holding. Employee #1 was holding the brace in one hand and his hammer in the other hand. He was preparing to nail the brace to the form section when the panel of the form section shifted toward the ladder and the ladder moved. Employee #1 lost his balance and fell. He sustained a compound fracture to his right ankle and was hospitalized. The ladder did not fall.