Machine safety needs holistic approach

Despite the increasing amount of legislation and the global harmonisation of standards in machinery safety, a significant number of fatal and non fatal accidents are still occurring each year.

More often than not, incident investigations discover several safety issues with equipment involved in the accidents - states David Collier, business development manager at PILZ Automation Technology

These issues originate in all phases of the life-cycle: specification, design, manufacture, use, modification, maintenance etc. It is, therefore, now increasingly apparent that legislation in itself is not enough; engineers need to have the competence and understanding to act in accordance with directives and standards. 

There are several European Directives that can apply to the safety of industrial machinery and equipment. However the two of most direct relevance are the Machinery Directive and the Use of Work Equipment.

The Machinery Directive (2006/42/EC) essentially states that it is the responsibility of the manufacturer or his authorised representative to ensure that equipment supplied is in conformance with the Directive. 

The “manufacturer” includes OEMs, but also, end users who build, significantly modify or integrate machines together. This Directive is enforced in the UK through Supply of Machinery (Safety) Regulations.

The Use of Work Equipment Directive (2009/104/EC), which is aimed at machine end-users, is intended to ensure employers take the necessary measures to ensure the safety, health and welfare of their employees.

This must be achieved through the use of safe systems of work to ensure a safe working environment as well as risk assessments of machinery and proper validation and maintenance activities. In the UK it is implemented as the Provision and Use of Work Equipment Regulations (PUWER).

The requirements of the regulations are mandatory under UK Law, and a presumption of conformity with them can be met through the use of standards harmonised to these Directives.

There are many standards, and they change over time, so finding your way through them can be challenging.

Both of the above Directives state that validation tests should be carried out with the highest degree of professional integrity and technical competence.

Employees with responsibility for machinery safety – often multi-tasking – are increasingly expected not only to have, but also to prove, competence. 

Companies, therefore, require consistent safety philosophies, that include not only provision of safe machines, but also training of key employees with responsibility for worker safety and for safe control systems.

These may be engineering managers, supervisors, design engineers, health and safety officers, risk managers, and anyone with input into machine design, operation and maintenance.

The person developing the overall safety concept needs to have an in-depth knowledge of the relevant legislation, regulations and standards, as well as the appropriate safety technologies.

Fit-for-purpose machinery safety training courses can provide a valuable supplement to practical machinery-based experience, which itself is something that is only attainable over time & under the right circumstances.

Although competence is a legal requirement for an engineer who is tasked with validating plant and machinery, this should not be the only reason to become certified.

Employees who have been working for  a number of years undertaking risk assessments or designs to mitigate risks, claiming to have seen ‘everything’ may not initially see an advantage from a certification. 

However, the ability to ‘prove’ knowledge through certification from internationally recognised organisations increases the engineers value as a company asset and take their careers to the next level.

Safe control or functional safety on machinery is covered by EN ISO 13849-1 (with its Performance Levels, PL a to PL e) or EN 62061 (with its Safety Integrity Levels, SIL 1 to SIL 3).

Some companies offer training which takes the approach that all hazards need to be covered by safety functions and safety devices using IEC 62061 and ISO 13849-1 – given the advancement of safety devices over recent years it is often possible to do so.

This approach, however, does not follow best practice as outlined in EN ISO 12100. Functional safety should only be considered when a risk assessment has been completed, all risk elimination measures have been considered and protective measures, such as the use of fixed and moveable guards, are to be implemented.

The so-called “Three Step Approach” as outlined in EN ISO 12100 requires that elimination or substitution of the hazard must be investigated first, and only where this is not possible, should engineering measures such as safety measures be considered.

The hierarchy of risk reduction is: Change Design – eliminate hazard; Protective measures – safeguarding (including functional safety); and Warning – information for use Once a decision to implement safeguards has been agreed there are a number of standards to be considered.

Only once the decision to use control functions, such as interlocking of guards or light curtains, as part of the hazard mitigation strategy has been taken can the functional safety requirements are specified, verified and validated using EN ISO 13849-1 or EN 62061.

Functional safety needs to address all technologies, be it electrical, hydraulic or pneumatic and cover all safety aspects from sensing devices, control circuit to the machine actuators.

Ensuring machine safety requires knowledge of all applicable machine safety legislation and standards, risk assessment, risk mitigation strategies, machine guarding, functional safety and administrative measures is required.