When Michael Miller, business development manager for safety business at Rockwell Automation, explains what functional safety is, he drills the idea into his audience.  “An excellent example of how functional safety has developed in industry is a regular drill,” he explains.

Thirty years ago a drill was made out of metal.

“Well, metal’s not a real good thing to have in your hands when the other end of it is 115 volts,” he laughs. “You’ve got quite a shock hazard there.”

So what was done?

Manufacturers added a third prong, which was supposed to be grounded, so if there were ever a short, the user wouldn’t get electrocuted. The problem was, 30 years ago, the overwhelming percentage of receptacles was two pronged. So users cut the third prong off. “That’s an example of how safety was added, but because of circumstances, a good idea went bad,” says Miller. “So let’s just go back a decade.”

Ten years ago, virtually all the drills were made out of Lexan®, a polycarbonate resin thermoplastic, so the potential for electrical shock was greatly reduced. “They designed safety into the device, so it would greatly reduce the possibility of electrocution,” says Miller. “It’s still possible, but highly unlikely.”

“Now look at today’s drills,” Miller continues. “They’re still made out of plastic, but now they’re DC: it’s impossible to get a life-threatening shock from the device. That’s the definition of functional safety: safety that is designed inherently into the device (italics added). It’s designed in, not added on.”

Functional Safety and Sustainability
According to Miller, two questions are asked about machines today: How can we make them sustainable? How can we make them safer?
 

“They’re not really two different things,” says Miller. “If I design safety into the machine—or give the operator freedom to access the machine, but access it only in a safe way, preventing unexpected start-ups, unexpected movement of any kind—I’m functionally designing safety into that machine. This allows all the features of sustainability, including longer product life, regulatory compliance, and improved productivity. It also addresses all the issues related to safety, such as reducing accidents and injuries, driving down health benefit costs, and mitigating general operational risk.”
 

So safety, when designed in, actually improves machine operation while keeping operators free from unwarranted hazards. Miller emphasizes that this is throughout the whole system, and the whole life lifecycle of the system. “When a machine is conceived, safety is designed into the idea,” he says. “There’s only one way to design it, and that’s the safe way. Safety isn’t an afterthought. Safety isn’t an add-on. It’s integral to the way the machine works, the way it is set up, the way it is maintained. That’s the only way to do it.”

Typically there is some type of requirement—a legal or industrial standard—that drives the requirements around the development and functionality of a machine. As part of the design process, hazards that may be present will be analyzed. “Obviously, the first thing to do is to try to design them out,” says Miller.

If this can’t be done, ways must be found to detect them or mitigate them to an acceptable level of risk. The risk assessment drives the functionality of a safety circuit design, not only from a control perspective, but also for the way machines are operated, manuals are written, and signage designed and posted. Everything is done to mitigate hazards and to maintain that mitigation throughout the lifecycle of the equipment.
    From this point, requirements are taken—typically called a safety requirement specification—and used to design the circuit, assess and secure the proper components, and document the process, from design, through installation and acceptance, to future repairs or changes. “If a change is made, we can go back, reevaluate the risks and hazards involved, and mitigate them, always adhering to the core requirements that remain in place,” explains Miller. “So it continues the lifecycle of a machine or system.”

During this process, notes Miller, users and OEMs alike keep a close eye on costs.

“One thing under scrutiny is how to incorporate safety without unduly affecting the overall costs of an installation,” he says. “Is this cost-effective? How will the safety function impact overall productivity? These are the types of questions customers want to have clear and positive answers to.”

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