An employee was welding an 24-inch diameter flange to a pipe that was attached to a weld positioner. The flange and the pipe combined weighed approximately 1,500 to 1,600 pounds. The employee went into the pipe to check the completed partial weld on the opposite end of where the positioner was located. The employee's feet were hanging outside the open end of the pipe. The weld broke causing the pipe and the employee to fall to the floor. The employee's feet were caught between the beveled ended of the pipe and the floor. All of the employee's toes on his right foot were amputated and the big toe on his left foot was fractured.