Paragraph 3 Stability of supporting structure

be suitable and of sufficient strength and rigidity for the purpose for which it is being used;

in the case of a wheeled structure, be prevented by appropriate devices from moving inadvertently during work at height;

in other cases, be prevented from slipping by secure attachment to the bearing surface or to another structure, provision of an effective anti-slip device or by other means of equivalent effectiveness;

be stable while being erected, used and dismantled; and

when altered or modified, be so altered or modified as to ensure that it remains stable.