PACE 60-year Anniversary Series: Safety Systems
Safety is an issue that you could be excused for taking for granted in 2013. Every industrial employee going to work in a plant today is afforded the peace-of-mind of a number of codes and regulations that stipulate worker, process and equipment safety.
But it hasn't always been this way: once upon a time workers – not employers – were responsible for the safety of their own bodies and that of the machines they used. In fact, industrial safety as we know it didn't really start taking shape until the last few decades.
While rules surrounding the use of rudimentary safety measures, for example hard hats, boots and gloves, have been around since the early 1900s, the first electrical safety systems only began appearing in Australian factories approximately 25 years ago.
According to Machine Safety By Design managing director, Frank Schrever, safety relays and presence sensing systems began surfacing via machinery imported from Europe around the late 1980s. Though some safety light curtains were being manufactured in Australia at the time, it took another decade for safety features to begin making their way in to control systems.
“Safety in terms of machine control systems really started to take off in the late 1990s after the appearance of the first edition of AS 4024 Safeguarding of Machinery in 1996”, Schrever told PACE.
Schrever is a trainer and consultant in machine safety, and also chairman of the Australian standards committee SF041 for the AS 4024 series of standards. Schrever was responsible for starting the Australian subsidiary of Germany company, Pilz, in 1998.
“In 1999 it was clear that not many people really understood what risk assessment, let alone safety-related control systems really meant. If a machine had been stopped by the safety system because a dangerous fault had been detected, the safety system was usually blamed, cursed and bypassed to keep the process running,” recalled Schrever.
“I witnessed people attacking the safety relay with a shifting spanner because it was seen as the culprit – not the saviour – in those years. The prevailing attitude was that this whole safety business was ridiculous, and ‘we've never done it like that before and we’re OK’.
"Wider awareness of the role design plays in safety and the standards governing this, not to mention stronger legislation, has changed this attitude throughout the manufacturing world over the last 14 years.”
In 1987 Pilz developed the first emergency stop safety relay, called the PNOZ, to protect man and machine.
In Schrever’s opinion, a revolution in safety systems occurred in the early 2000s when low-cost safety programmable logic controllers (PLC) entered the market, teamed with the advent of safe fieldbus communication systems.
“This has enabled designers to apply sophisticated safety control to even fairly low-cost machinery,” he explained. Some companies have also started to develop safe vision systems that can ‘view’ a three-dimensional space and slow or shut down machinery if a person is seen to be getting too close.
“There are also big changes in the interlocks being used; 15 to 20 years ago, if a guard interlock was used, it was probably a mechanical roller cam-style device. These days, transponder-style systems, which integrate a radio frequency tag, are becoming common and available from many manufacturers.
“They have the advantage of being more difficult to defeat, resistant to environmental effects, able to be integrated into electro-magnetic and mechanical guard-locking systems and overcome most of the failure modes of the older-style mechanical interlocks.”
For Schrever, the more recent bid to harmonise Australia’s occupational health and safety legislations has been another significant change which has lead to safety compliance being a top priority for industry.
“Although not yet complete (Victoria and Western Australia have not yet adopted the harmonised legislation), the key principles that affect machine safety are now identical in all states and territories,” Schrever said.
“I refer to the risk control hierarchy, which requires risk control by engineering means before reliance on administrative control and personal protective equipment, and the guarding hierarchy, which establishes an excellent principle for selection and design of guards.
“In essence, this states that interlocked guards should always be examined first, and only if found to be not reasonably practicable can the designer move onto bolted guards and presence sensing systems – in that order. This does force the practitioner to understand the motivation personnel may have for entering the machine and design accordingly.”
For Rockwell Automation commercial marketing specialist, Helder Paulini, the integration of safety features into process control products and automation systems has been a major milestone in safety-related systems during his 18 years in the automation industry.
“My first experience applying safety products was in association to our variable-speed drive products with ‘Integrated Safe Torque Off’ features, and this dates back to the mid-2000s,” Paulini told PACE.
“A major milestone then came in 2005 when Rockwell Automation introduced the first SIL3-rated Allen-Bradley GuardLogix controller, integrating safety into our control architecture.”
The advent of the PLC in the early 2000s was a major turning-point in the history of plant safety, allowing designers to apply sophisticated safety control to even low-cost factory machinery.
Paulini agrees that the institution’s move to standardise on safety regulations over the last two years is a step in the right direction for both plant-owners and companies making industrial equipment.
“Decades ago, we would rely on the presence of redundant components for machinery safety, and regulations were close to none. Nowadays, we are seeing global standards for safety regulations, and products are receiving certification to comply with these regulations,” he said.
“The past couple of years have seen serious changes in regulations/laws in several countries concerning safety in different industry environments and, as a consequence, companies will have to adjust their sites to meet these new regulations.”
Programmable safety systems
Honeywell Process Solutions (HPS) Principal Consultant, Safety and Advanced Applications, Bob Weiss, agrees that the advent of programmable PLCs represented a major turning-point in the adoption of safety products and systems in industrial plants.
Weiss is a Certified Functional Safety Expert and a TÜV Functional Safety Expert, serving on the Standards Australia subcommittee responsible for the functional safety standards AS61508 and AS61511, and has been working in the processing industry for 40 years.
“My experience includes installing some of the first programmable safety systems in Australia and the development of international company standards for safe use of programmable electronic systems,” he told PACE.
Weiss began using relay-based process safety systems back in the late 1980s, but switched to programmable safety systems when they began to appear on the market a year or two later.
“At the time, relay-based systems were considered to be very reliable by the industry so there was somewhat of a reluctance to move to using programmable safety control systems,” he explained.
“However, the introduction of independent certification for programmable safety systems provided the industry with assurances to the system’s reliability, and their take-up in the early 1990s was rapid. From around 2000, international standards IEC61508 and IEC61511 codified good practice in using programmable safety systems.
“More recently, there has been a move towards more flexible safety PLC architectures. For example, both 1oo2D and 2oo4D architectures can achieve a safety integrity level of SIL 3 but selection of the more economical 1oo2D can save money if achieving maximum plant availability is not a priority, for example for batch processes.
“Also, highly-distributed architectures are now becoming more common, allowing some safety functions to be implemented in field junction boxes. Simpler and more robust functional integration with control systems, whilst preserving independence and reliability of the safety functions is also now commonplace.”
According to Weiss, there is a significant difference between the relay-based systems previously used and the programmable safety systems widely used in the industry today, “where we take for granted low spurious trip rates, self-documenting programs and easy integration with control systems,” he said.