As regards to mechanical fault exclusion, the requirement of “defeating of guards prevention” is clearly highlighted in the harmonised standard “UNI EN ISO 14119 Interlocking devices associated with guards" and is reminded in UNI EN ISO 13849 "Safety-related part of control systems" Access’ exclusive Gamma Locks are designed to prevent such defeating of guards. Gamma Locks are stainless steel with an aluminium cover and are an integral part of the accidental locking prevention device.
In example 1 it is quite obvious how easily a common lock can be removed from the outside simply by removing the Allen screw hence compromising the guard’s safety function. With Access’s Gamma Lock, instead, it is impossible to reach the fixing screws (example 2) when the door is closed. The lock can be assembled and adjusted only when the door is open (example 3) If last-generation sensors have been installed on the door, it would be even more nonsensical that these could be removed along with the door component they are associated to by using any simple tool.
Example 4 (easily removable screws) Example 5 (not accessible screw) Example 6 (screws accessible only with open door)
In example 4 fixing screws are externally accessible and the switch can be easily removed which clearly violates the obligations set in standard UNI EN ISO 14119 "Interlocking devices associated with guards". Example 5, instead, fixing screws cannot be reached when door is closed. The lock can be assembled and adjusted only when the door is open (example 6). Gamma Door systems has been created to overcome all critical issues which typically affect those guard designs which do not take current regulations into account.
All Access’s door accessories have been designed to meet the requirements for the prevention of defeating guards by substituting standard screws with knurl nut systems which cannot be unscrewed when the door is closed.
Example 7 (easily removable screw) Example 8 (hinge with knurl nuts) Example 9 (hinge with knurl nut)
Example 7 shows how the door fixing screws can be easily reached at any time. This means the panel can be totally removed hence nullifying the safety function of the guard and its associated interlocking device. Examples 8 and 9 show Access’s knurl nuts fixing solutions applied to hinges. When the door is closed the screws cannot be reached and therefore cannot be removed.
The question you should raise is not why Access doors are more expensive, but if the doors you are using now are really safe.