An employee was adjusting a 30" diameter PVC vertical stand pipe. There were some bricks holding up the casting, acting as adjustment shims. The employee stepped on one of the bricks as he was going to take the casting off of the vertical stand pipe. The brick, which was now underneath his foot, was on a gravel base and rolled out from under his foot as he lifted the casting off of the pipe causing the employee to lose his balance. As he was falling, his right arm and shoulder area landed in the center of the vertical stand pipe and his right upper chest area landed on the sidewall of the pipe. He was hospitalized with broken ribs and a collapsed lung.