Providing Safety

EN ISO 14119

EN ISO 14119 Interlocking devices associated with guards

EN ISO 14119 describes the design requirements for minimising the override possibilities of safety switches.

The European Machinery Directive requires machinery to be fitted with safety components, such as safety switches and blocking devices.

The NEN/EN/ISO 14119:2013 also requires that machinery be designed to minimise the motivation for bypassing these safety mechanisms. This is in addition to the requirements of the ISO 1200s which state that the possibility of bypassing safety devices must be taken into account in the risk assessment.

ISO 14119 describes four steps to prevent safety switches and interlocking devices from being by-passed or over-ridden in a reasonably foreseeable manner.

The first step is to implement the basic measures, as described in paragraph 4 of the ISO 14119 – Requirements for the design and installation of safety devices with and without interlocking device. This states that Type 3 safety components (non-contact safety switches without coding) can only be used if it is reasonably foreseeable that they will not be overridden or tampered with.

No motivation for manipulation or an override?

If, after implementing these basic measures, it appears that there is no motivation for manipulation or an override, additional requirements are not necessary.

If it turns out that motivation for doing so remains foreseeable, the next step is to see if it can be eliminated or minimised. This can be done through design measures or alternative methods. In the latter case, these may be special modes of set-up, tool change, fault finding, maintenance or process observation.

If the motivation can be eliminated or minimised, additional measures are not required.

Finally, if the motivation for manipulation or overriding is still foreseeable, additional measures are required.

The following 4 steps are important and worth revisiting, this time as a flowchart.

Additional measures

If the motivation for overriding and/or tampering cannot be removed, ISO 14119 requires that additional measures should be taken in order to minimise the risk of overriding safety switches.

These additional measures are categorised as followed:

  • Prevent access to the safety switches by mounting out of reach or behind the guard.
  • Preventing the replacement of actuators, e.g. by the use of uniquely coded actuators.
  • Use of non-removable fastenings to prevent the removal of safety switches and actuators.
  • Using a control system to monitor interlocks to ensure correct operation.

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Why would an operator want to bypass a safety switch?

Motivation to manipulate has been an important issue in reformulating ISO14119 with considerable emphasis on additional measures to prevent manipulation.

The current standard defines non-removable operating tongues and excludes the use of safety screws. Significant efforts have been made to improve the existing table of requirements, but the focus remains on additional measures and not on addressing the underlying problem – why would an operator want to bypass a safety switch?

When considering additional measures, it is essential to follow the four-step approach, taking into account the following key question: “Does the motivation to bypass or tamper exist?” If it does not exist or can be eliminated, no additional methods are needed.

However, the reality is that eliminating the motivation to manipulate during the risk assessment can not only provide a safer working environment, but can also lead to productivity gains. Focusing only on making it more difficult to ‘defeat’ safety switches does not eliminate the problem but only treats the symptoms.