How can a machine control system designer consider that "reasonably foreseeable human error during operation does not lead to hazardous situations"?

The obligation to consider 'reasonably foreseeable misuse' related not only to control systems but is reflected in the general principles of the "Essential Health and Safety Requirements". The term 'reasonably foreseeable misuse' means the use of machinery in a way not intended in the instructions for use, but which may result from readily predictable human behavior.

While similar principles are enunciated in other standards including EN ISO 12100, this statement is particularly onerous. The control system designer needs to be conscious of the risk assessment and the measures for risk reduction that are dependent on the control system. The ease ofuse and ergonomics of the machine interface and its relationship to the control system are critical. Studies show that the probability of a safety system being "bypassed" is proportional to the "benefit" of bypassing the system. Therefore to avoid predictable behavior of system bypass, the design of the safety system should be considered in a manner where machine operators do not benefit or gain incentive from bypassing safety systems. Intelligent safety concepts including zoned safety systems, boundary less guarding, safe mode enabling and safe monitoring of machine parameters should be considered by the control system designer.

What are the important changes impacting machine control systems?

The obligations on machine control system designers are more explicitly and in some cases more stringently defined. Consider the following:
"Control systems must be designed and constructed in such a way as to prevent hazardous situations from arising. Above all, they must be designed and constructed in such a way that:

• they can withstand the intended operating stresses and external influences
• a fault in the hardware or software of the control system does not lead to hazardous situations
• errors in the control system logic do not lead to hazardous situations
• reasonably foreseeable human error during operation does not lead to hazardous situations."

These requirements restate with clarity that a failure of or any other cause in a machine control system should not lead to a hazardous situation. The new wording reflects the state of the art in control system technology, where there is a distinction between software and hardware.

How can I manage situations where there are different assessments of the same risk by different machine builders?

Machine risk assessment is part qualitative, part quantitative requiring judgment by competent persons. Consequently there is likely to be a dispersion of the results achieved by different manufacturers or their authorized representatives when carrying out a risk assessment on the same or similar equipment. With the strength of the obligation in the directive machine builders may expect that machinery buyers and statutory authorities will seek more opportunity to examine the procedures followed, the assumptions and judgments made, and the results achieved.

Additionally the demands on machine builders to provide more detailed instructions will provide traceability between Risk Assessment and Instructions.

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Whatever the reason for undertaking a formal risk assessment on machinery or work equipment, Pilz consultants can provide an impartial service. Risk assessments are encountered in almost every walk of life, even for crossing the road. But when it comes to machinery, a formal risk assessment needs certain requirements to be fulfilled, and the person performing the risk assessment must be competent to do so.

While some companies have personnel who are competent to perform formal risk assessments on machinery, others appreciate that they lack the competence and therefore need support from consultants. There are also occasions when companies are busy and do not have the resources available when required, or they may choose to use an independent service provider for this critical task.

For any of these scenarios, the consultancy division of Pilz Automation Safety L.P. can undertake risk assessments on machines or machine designs in accordance with the requirements of relevant standards. Each assessment identifies the hazards present, estimates and evaluates the risks, and determines and outlines the measures that may be applied to reduce the risks to acceptable levels.

As part of the risk assessment, the consultants identify applicable standards, regulations and best industry practices, prepare a statement of the machine’s limits, and examine all hazards throughout the relevant machine lifecycle phases.

Because Pilz consultants have decades of experience of machine safety, their advice related to risk-reduction measures is particularly useful. This is in contrast to some other consultants that can highlight problems but are unable to advise on pragmatic, cost-effective risk-reduction measures.

Furthermore, if the client requires ongoing support, Pilz can provide engineering services to take the safety concept forward, and even supply products to implement a safety-related control and monitoring system. Alternatively, the client can take the consultants’ risk assessment report and carry out the necessary work in-house or work with a third-party supplier or system integrator of their choice.

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