have this installation of pipe for concrete pump
( change the concrete pump pipe to a new place ) but then the place that they want to install has the stair obstructed the way so it way necessary to move the stair out from the position in order to can install easily when after finished for installation of the concrete pump then they would pull up the stair up to installed as before by using the line to tied but because of the striding form have two floor so the workers must stand by the first floor for control the balance of the stair, immediately the stair fell blown the second floor to hit a worker who stand by the first floor and finally the stair and worker fell down together in to the floor or surface