To guard or not to guard? Or to be more precise, to use physical guarding or presence sensing safety devices?
The answer is probably both, but it raises the question about the design, selection and implementation of physical guarding and what the designer of a machine safeguarding system needs to consider. At face value physical guarding seems the easy option, it can help reduce the manufacturing footprint, protect the machine operator from hazards, and prevent egress of material from the safeguarded space. However, it is not as simple as just buying some fencing and installing it around the machine.
Guarding using ISO 14120 and ISO 12100
IS0 14120 (2015) Safety of Machinery – Guards – General Requirements for design and construction of fixed and moveable guards is the standard to turn to. It specifies the general requirements for the design, construction and selection of guards provided to protect persons from mechanical hazards.
As with the whole safeguarding process the starting point should, however, be ISO 12100 (2010) General principles for design — Risk assessment and risk reduction. This standard guides the reader through the risk assessment process and the selection of safeguarding methods.
If the risk assessment leads the designer to the selection of guards then ISO 12100 breaks them into the following: categories, fixed, movable, adjustable, interlocking, interlocking with guard locking and interlocking with start function. These are all defined in ISO 12100 and their application detailed in ISO 14120.
In general, if you are asking “What are interlocked guards?” they are those that:
– Ensures a machine cannot operate until a guard is closed.
– Provides a stop command if the guard is opened while machine is operating.
– Allows hazardous functions to operate when the guard is closed.
The stop command from the interlocked guard makes them a popular option for implementing proactive inhibit functions – as individually applied padlocks or personnel keys can mechanically block the guard from being closed and prevent the reset of machinery .
Guarding Impact Testing
On often overlooked area of guarding selection is impact testing. Guarding should both ensure an operator cannot enter the safeguarding space from the outside until it is safe to do so and protect operators stood outside the guard from projectiles and emissions from within.
For peace of mind aside from general wear and tear guarding should be able to resist impacts from equipment, such as forklifts moving about the facility, without compromising on the machine’s safety.
The new Annexes (B and C) of ISO 14120, providing methodology for both projectile and pendulum tests provide much needed guidance for manufacturers and users alike. Whilst ISO 14120 specifically excludes interlocking devices from its scope it is difficult to imagine fitting such devices that cannot withstand the same impact testing. An interlock device as part of the interlocked guard should not be the weak link when it comes to impact.