Integrated Safety - or Not! ...Plus 6 Comments; Do You Agree?


We’ve all heard lots of arguments both for and against a fully integrated architecture for safety and general control. In the process world they’ve maintained a separate SIS (Safety Instrumented System) solution for safety creating a separate layer in their architecture for performing the safety functions. However, in the machine world when PLC’s were introduced in the 1970’s, standards groups rushed to exclude PLC’s from anything safety because the early technology wasn’t very reliable. Guess what happened?

Right, “anything safety” had to be hard wired relegating the safety functions to a separate layer and typically electromechanical devices. This is how the machinery world continued to live until 2002 when NFPA 79 changed allowing hardware / software devices designed, tested, and listed for safety applications. This change in the standard opened the door for options in technology, engineering, and design - to integrate safety - or not!

So, to answer the question today you have to look at your application and consider your options. Also, evaluate your risk assessment, the identified hazards, and what’s required to mitigate the identified hazards to tolerable levels. Layered safety and integrated safety are now options for you to consider along with your company’s safety policy, objectives, and business model.


Posted by J.B. Titus on August 14, 2009


September 2, 2009

In response to: Integrated Safety - or Not!fatcat commented:


As a designer I agree with the latest comment. As the are three approaches to minimize risk - inherently safe design measures, safeguarding and complementary safety measures, and information for use, the first and most important step in the risk reduation process is inherently safe design, because protective measures inherent to the characteristics of the machine are likely to remain effective, whereas experience has shown that ever well-designed safeguarding may fail or be violated and information for use may not be followed.

September 2, 2009

In response to: Integrated Safety - or Not!Celso Valdez commented:


Standars are very good start point to desing, machine, control sistem, SIS etc. Depending of the risk identified and the tolerance allowed by client to the risk and the size of the sistema or machine there are lots of safety devices and solutions to implement. So The core fact from my point of view is safety must be in mind anytime someone desing and contruct any sistem or machine and the new technologies, like smarts devices, control networks, control buses etc have lots of features which when used in accordance with standars can improve safety.

September 2, 2009

In response to: Integrated Safety - or Not!Stan Lichtenberg commented:


That is always a hard question. Do you add a PLC to a simple machine just to integrate safety or not? There is no hard and fast line that marks the crossing from 1 to another. But I have seen a PLC added for a couple limit switches and E-Stop buttons. Was that really necessary? In my work I usually am rebuilding older equipment and I present both systems where possible to the customer and let them decide.

September 2, 2009

In response to: Integrated Safety - or Not!Krzysztof Majczak commented:


Certainly, it’s always better to have options – one or another.

But from my perspective, the most important achievement of functional safety is introducing standards and methodology to approach safety. Thanks to 61508/62061, 13849 most of guess-work and wishful thinking have been eliminated. The process of DFS (in my terminology – design for safety) eliminates from start most of costly mistakes and makes safety an achievable goal.

September 2, 2009

In response to: Integrated Safety - or Not!haridoz commented:



September 2, 2009

In response to: Integrated Safety - or Not!Steve Ludwig commented:


We (Rockwell Automation) agree that the safety solution is dependent on the needs of the machine, which is why we provide a full range of safety solutions including component-based, programmable and integrated safety automation systems.

Machine builders should consider safety a core design function rather than an added function after design is complete. Designing safety and sustainability into the machine reduces risk and improves machine performance.

In less sophisticated applications, simple electromechanical devices may be perfectly adequate. However, more advanced machines can now leverage control architecture that performs multidiscipline control tasks, such as motion and safety in the same controller. These systems use the intelligence and diagnostics of the automation system to operate the machine in the most efficient manner, reducing nuisance shutdowns, waste and energy consumption for the end user, and reducing the design, manufacture, programming and start-up costs of the machine builder.

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