This trail of breadcrumbs has led us back to ISO 13849-1:2006, Safety of Machinery – Safety-Related Parts of Control Systems. This new standard is the basis for the PL and B10d ratings you see on many safety devices today. The ratings are ranked “a” through “e” in increasing risk to the operator, with “e” being the greatest risk. Within this standard, the EN-954 categories for circuit types survive, but are only part of the implementation. More common-sense approaches are allowed, taking into account variables such as mean time to dangerous failure (MTTFd) for devices, monitoring devices for failure, circuit types (cat.1-4), and even those hazards which cannot be guarded without impeding the work to be done (such as PPE, signage, training, etc.). All of these are on the table if the situation supports them. ISO 13849-1:2006 was developed with the support of ANSI, as this organization supplied representative engineers to help with development of this standard. ANSI is a contributing member of ISO standards development and adoption boards.
A few years ago, I was working with an internal integration group for a manufacturing company which had facilities in many domestic and international locations. One of the initiatives I had undertaken was to redevelop procedures for assessing safety hazards on automated equipment.
Within the field of manufacturing automation, we face hurdles unique to the ways industrial control systems communicate. This often leads to piecemeal approaches to communication architecture development and installation. With a careful approach, legacy communication systems can be converted to higher performing systems, capable of providing connectivity without sacrificing security.
Over the range of projects we work on, we find ourselves constantly shifting focus from very distant overhead views to the minutest details. For the most part, we tend to relate the big picture information effects to big picture decisions. After all, little detail oriented decisions really only affect a component level change. While we certainly do not hold these guidelines to be law, these concepts oftentimes cloud our judgment and narrow our view of root cause options. Sometimes something small can have a big picture effect.