Movable Guards
Movable guards can translate, rotate, or translate AND rotate in combination to provide access to the hazard area. The closure of the guard closes the e-stop circuit. Opening the guard opens the e-stop circuit (“e-stop” includes all actions associated with an e-stop action, including air dump) and stops the machine. The closure of the guard itself cannot restart the
machine. The machine requires an overt action to restart from the open guard condition. The interlock must not be easily defeated by mislocation, substitution, or other means. Movable guards must not pinch, shear, crush, or otherwise harm the user. Guard weight must be considered in the design. Guards under free fall (hinged or sliding) must not create a dangerous condition to the user, or damage to the guard. Sliding or rolling guards must not create debris through wear that can contaminate the product contact zone (EN 953 3.5, 5.1.1, 5.5.5, 6.4.3.1), (ASME B20 5.11.3, 5.11.4).
Preferred Form:
a) Sliding guards preferred over lifting guards.
b) Single-piece guards.
c) Guards with handles that are formed into or welded to the door rather than attachments to thebdoor. If slots are used, EN 294 must be considered for relationship of the opening with the distance to the hazard. Slots are not permissible for radiation guarding.
d) Guards that avoid tracks or other structures that accumulate debris.
e) Interlocks that are safety-rated and can be integrated into the safety circuit.
f) Clear material or open-mesh (consider openings to permit observation of the process).
g) Static dissipative to prevent accumulation of charge.
Shield Guards
Shield guards are used to inhibit access to a hazard area when a traditional fixed or movable guard is an unrealistic solution. The most common example of this is the area around a rejector, where packages require paths into and away from the reject area to properly function. The shield guard is used as a last resort and should not be used if a fixed or movable guard is
a better solution.
Shield guards are a last alternative to a fixed or movable guard remedy. The shield guard should be as extensive as possible to inhibit access to the hazard area. It should also be used to warn the user of the extent and level of the hazard area. A shield guard must be considered as an area where integration guarding and instructions for personnel may be required by the user.
Shield guards are a recognized safety device per ASME B20. The ASME standard recognizes that there are situations where a fixed or movable guard is not a practical solution, and the alternative is generally no guard.
