tandards define the requirements by which we are to design, build, and implement industrial machine systems. They exist so people associated with the build, installation, operation, and maintenance of the equipment are assured of a safe piece of machinery.
We should remember that standards, although typically very good, are not perfect. They define general design requirements and work practices, but may not have the scope or detail for every application.
Some standards are straightforward. Selecting a wire size for a given ampacity is relatively easy, with little need to over-analyze. Other standards such as those dealing with how, or when to apply interlocks to guarding, or how long an off-delay timer setting needs to be in order to safely stop a spindle in a Category 1 stop situation, become a little more involved.
To complicate matters, there are standards from different authorities that cover the same ground. NFPA 79, the Electrical Standard for Industrial Machinery, is prevalent in the U.S. The International Electro-Technical Committee (IEC) publishes similar standards (IEC 60204-1) that have predominance in the European community. If an OEM builds equipment destined for a U.S. location, does that mean it can or should ignore IEC standards? The reality is that standards represent a set of minimum requirements to safely build and operate specified equipment.
But a minimum level of safety shouldn't be where our responsibility as design engineers ends. It is our responsibility to incorporate best practices and do proper "due diligence" to all our safety applications.
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"It is our responsibility as design engineers to incorporate best practices and apply proper 'due diligence' to all our safety applications."
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Take the case of an industrial OEM that sells machines in both U.S. and European markets. Its customers traditionally want control systems that closely follow the customer's local standards organization. Accordingly, the OEM builds its control systems to two different standards. The standards might call for different means of safeguarding an operator load door, for example. The European specification is more detailed and arguably more stringent.Now, if someone is injured while operating that machine,and the load door is suspect,the standards to which the machine was built will come into question. If the accident involved a U.S. customer and reached the courts, the plaintiff lawyer likely will question the OEM's decision to build to two different standards. If the European standard appears more stringent, then the question becomes why do European customers receive a "safer" machine? A jury might wonder why the OEM built to a "lesser" standard for the U.S. customer, especially if it is perceived the accident could have been avoided provided the "better" standard was applied.Recently, a machine tool builder I know received complaints from customers that the drain holes in the machine frame for channeling excess coolant tend to plug easily and overflow onto the floor. The machine tool builder recommended that its customer remove the fixed guards every week to clean the drain holes. The entire operation would take no more than an hour.
IN MANY INSTANCES, if a fixed guard requires the use of a special tool to remove, then the guard is not interlocked, as was the case with the fixed guards over the drain holes. Now, however, the machine builder is asking that the customer remove these panels on a regular basis, thereby making the frequency of exposure to the hazard greater.The OEM eventually decided to interlock the guard panels with the control system so the machine could not be started if the panels were not in place, and it would also stop the machine if the panels were removed while the machine was running. This machine builder found no code or standard that dictated this as a requirement, but felt the risk was high enough to warrant the additional safety interlocking.We are supposed to be experts in our field. If there is a better standard available to create a safer machine, we should apply it. If there is no standard available that we think meets our system safety requirements, we are expected to perform due diligence and incorporate a design that satisfies the safety requirements.Of course, this can be blown out of proportion and the line needs to be drawn at some point. Protecting against negligence, inattentiveness, ignorance, hardware failures, etc., is different than trying to protect against sabotage or willful acts to defeat a safety system.But due diligence needs to be done to provide adequate levels of protection for all persons associated with the equipment during normal use that includes reasonably foreseeable misuse.
Jason Christopher is a controls designer for Liberty Precision Industries, Rochester, N.Y., an integrator of high-volume manufacturing cells and systems. Learn more about Liberty at www.libertypi.com.
