Machine Safety: Integrated safety can learn from the 1960s

Machine safety thought leaders of tomorrow can learn from the evolution of machine guarding since the 1960s. Some safety was integrated even before PLCs.


Is there anyone in manufacturing today that remembers machine guarding in the 1960s? People who understand this evolution from the 1960s to today might be the thought leaders for tomorrow. Understanding this evolution is actually the basis for tomorrow’s machine safety. Previously, I’ve blogged about the evolution of machine safety using the graphic below. This graphic illustrates the unintended consequence of unplanned machine downtime and how technology has evolved for a fully integrated (machine control and the safety related parts) machine control system. Even before the advent of programmable logic systems (PLCs) some machine control and safety related parts were integrated.

Machine control technology landscape, according to JB Titus, Control Engineering Machine Safety Blog

So, here is where I date myself. When I started my first job out of college as an industrial engineer at an automotive assembly plant in 1968, we did not have a single PLC anywhere. Around 2,500 hourly employees per shift were producing 60 automobiles per hour or around 1200 automobiles per day. The plant was approximately 2 million square feet under roof, and there wasn’t even 15k of software involved in manufacturing. Every operation throughout the manufacturing process involved hard wiring, multi-conductor cabling and electromechanical devices. The machine control logic was accomplished via cabinets filled with relays and interconnection wiring. Trouble shooting a control system with 1,200 relays was a nightmare. And still, 1,200 automobiles were produced per day.

Since 1968 pre-dates the creation of OSHA by President Nixon, any machine safety or guarding of hazards was also as described above, hard guarding or common sense, in my opinion. So, as we began to install the first PLCs in the early 1970s, their machine control logic (software) looked almost like the “ladder logic” drawings used for relay control systems. Since these early PLCs needed time to evolve and improve their reliability the machine safety standards quickly updated to require that “everything safety” be hard wired. This action probably was warranted but in my opinion it caused the unintended consequence for 30 plus years of unplanned machine downtime. The “safety layer” of technology within the machine control architecture was almost frozen in time in contrast to general automation technology as shown in the graphic.

Since 2002 and the introduction of safety PLC technology the “safety layer” has quickly advanced and, in my opinion, actually caught up with and can be merged with general automation technology. And that’s why we call it – integrated safety.

Is anyone out there familiar with this short story? Has your experience been similar or different? Add your comments or thoughts to the discussion by submitting your ideas, experiences, and challenges in the comments section below.

Related articles linked at the bottom of this post include the following related topics:

Machine Safety: Year over year safety automation growth outpaces general automation

Machine Safety: Industry 4.0 and how it could impact machine safety

Machine safety: Executives balance risks, profits

Machine Safety: Managing operational risk 

Contact: for “Solutions for Machine Safety”.

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