Physical protection devices must be located at a  sufficient distance from the hazard zone in machinery, if they have certain  openings. Determined distance, machine chassis, tensioning equipment, hair  driving systems, etc. must be provided with a physical protection. 

In  accordance with EN ISO 13857 standards, the safety distance depending on the openings of the physical protection devices is determined as follows. The specified  values are referenced for access from within the physical protection device  (CRT)