How to choose the right parts for machine guarding?
To safeguard or not to safeguard? Or more precisely: use a physical guard or use safe presence detection?
The answer is probably both, but it does bring up the question of the design, selection and implementation of physical protection and what the designer of a machine guarding system has to consider.
At a first glance, physical guarding seems to be the simplest option: Machine guarding can help reduce the footprint of the production area, protect the operator from hazards and prevent material from leaving the guarded area. However, it is not as simple as just buying some fencing and placing it around the machine.
Machine guarding with ISO 14120 and IS0 12100
IS0 14120 (2015) Safety of machinery – Guards – General requirements for design and construction of fixed and movable guards. This standard describes the general requirements for the design, construction and selection of guards intended to protect persons against mechanical hazards.
The entire risk assessment must comply with 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 appropriate protection solutions.
If the risk assessment (RI&E) shows that physical shielding must be used, ISO 12100 describes the following categories:
- Fixed guards
- Movable guards
- Adjustable guards
- Interlocking movable guards
- Interlocking movable safety guards
- Interlocking and start-up devices.
These are all defined in ISO 12100 and their application is described in ISO 14120.
What are interlocking guards? These are guards that fulfil the following conditions:
- The machine is isolated until the guard is closed.
- A stop command is given if the guard is opened while the machine is running
Allow dangerous functions to operate only when the guard is closed.
- The stop command generated by a locked guard, for example by a safety switch, can be provided with lock-out (LOTO), since these padlocks can mechanically prevent the guard from closing and the machine from starting.
Impact testing of guards
An often overlooked component when selecting guards is impact testing, the guard should ensure that an operator cannot enter the guarded area from the outside until it is safe to do so and that operators standing outside the guarded area are protected from being dislodged or ejected from
For peace of mind, the guard must be able to withstand not only general wear and tear, but also shock and vibration from equipment such as forklifts passing through the facility, without compromising the safety of the machine.
The new annexes (B and C) to ISO 14120, which provide a methodology for both projectile and pendulum tests, offer clarification for both manufacturers and end users. Although ISO 14120 explicitly excludes interlocking devices from its area of application, it is difficult to imagine that such safety devices would be fitted that could not pass the same tests. Therefore, an interlocking device as part of the interlocking shield should not be a weak link in the event of an impact.
Example: 1600J Impact test Fortress amGard Pro safety switch with Troax ST30 machine guard (fitted with USP mounting brackets).