The height of a perimeter fence needs to consider not just the height of the worker, but anything they are likely to be standing on. If a workplace provides portable steps, then the safeguarding provided will need to account for this additional potential reaching height.
Machine Safety Basics: Safety Control Systems
Safety control system means the machine logic that tells the motors, pneumatic/hydraulic valves, and other sources of hazardous motion that a door is open and someone is accessing the safeguarded space.
