Putting safety first

Though none would deny its importance, operator safety is a feature of machinery probably less talked about than, say, line performance, output and cost efficiencies. But the topic has risen up the agenda. Safety component suppliers are now are working to help meet new requirements for functional safety, and machine suppliers, being aware of the changes, can take advantage of the benefits.

Automating processes that allow powerful, flexible and reliable operation is a step towards improving safety on the factory floor. But taking the human away from the machine only removes the risk. The hazard remains as operator intervention is sometimes needed.Increasingly complex and programmable technologies in use for safety-related control systems has led to obsolete safety standards such as EN 954-1 (ISO 13849-1: 1999) and a change to the familiar system of ‘categories’.

Two ‘new generation’ standards for machine safety related control systems are IEC/EN 62061 and EN ISO 13849-1:2008. Both offer a time-sensitive level of integrity in a safety system and can be used to show compliance with the European machinery directive. They have new classification systems: IEC/EN 62061 uses SIL (Safety Integrity Level) and EN ISO 13849-1 uses PL (Performance Level).

Whether to apply the SIL and PL variation will depend on which is best for a particular application. In general, users familiar with EN 954-1 categories and use relatively straightforward conventional safety functions should follow EN ISO 13849-1 (PL). If required to use SIL, or an application uses complex multi conditional safety functionality, EN/IEC 62061 may be most suitable. EN ISO 13849-1 covers all technologies whereas EN/IEC 62061 only covers electrical based systems.

Both require some calculations based on reliability data that safety component manufacturers can supply. A calculation tool SISTEMA, by the German body for occupational safety and health (BGIA), provides for EN ISO 13849-1. TUV Rheinland has produced a calculation tool for EN/IEC 62061.

“Machine safety is total linkage of safety and productivity,” says Derek W Jones, safety business development manager at Rockwell UK. “Automation, whilst it keeps an operator out of the way under normal circumstances, can make operator intervention, when it is needed, complex.”

Understanding the human side of automation is crucially important to safer processes says Mr Jones: “Safety is in the head. It’s about human behaviour, analysing it and logically moving forward.”

An operator can ‘interrogate’ a machine that is doing something too fast and potentially avert an accident, he adds. “This capability to interrogate down to user level is a built in and an essential part of Rockwell architecture.”

A two-tier approach to ensuring operator safety is based on machine design and installation, and user responsibility, says Ian Murgatroyd, Rockwell Automation’s European product manager - Safety Components. In the first instance, a manufacturer must risk-assess all phases of a machine’s life. Thereafter, the user must offer training, instruction on safe use, maintenance and satisfy rules on personal protective equipment (PPE).

“Productivity is what companies are paid on. Safety systems that report faults and reduce downtime allow machinery to be more productive,” concludes Mr Murgatroyd.