The previous article “Considerations for electrical system safety for the refurbishment of container ship-to-shore cranes” (see PTI 33) presented a procedure for the risk analysis prior to the refurbishment of an obsolete control system. ISO12100, ISO14121 were introduced in order to provide a guideline for the risk analysis.
Aspects from IEC60204-32 where quoted which regulate the realisation of the electrical circuit for power supply and control. Feedback from readers brought about the questions as to what degree the application of the ISO and IEC standards as quoted in the article is a must.
ISO 12100 clearly describes the strategy for risk reduction. The standard describes safety measures as a combination of three steps taken by the designer and the user in order to deem the machine’s risk level as acceptable:
1) The machine builder should make a safe design of the machine where foreseeable risks are taken into consideration, which in the standard is pointed out as inherently safe design measures.
2) If from step one and due to the limits and operation of the machines residual risk remains or arises, safeguarding and complementary protective measures should be put in practice to limit the risk.
3) For some type of machine or operation not all risk can be reduced, therefore the operator, end-user or public should be informed about the residual risk on the machine, which in the standard is pointed out as ‘Information for use.’
It has to be observed that this is a hierarchical structure and these steps are needed to be taken in the order described and that under no circumstances one step should replace the other. This means that in order to provide an acceptable level of safety in the machine all three steps have to be achieved, making the machine, the persons, and the environment around safe even from unexpected operation of the machine.
And in case it is not achieved the information of residual risk should be readily available. Risk management and safety is a joint procedure between the machine’s designer and the user, where local legislation should be observed and the use of standards as tools to produce a safe operation of the machine should prevail.
