Machine safety switches aren’'t no-brainers

A GOOD part of engineering involves conception, design and implementation of complex electrical and mechanical components, which become the machines we ship around the world. I’m involved with the safe operation of these machines, which are an integral part of manufacturing processes in the packaging, container and pharmaceutical industries.

The design of a new machine has inherent risk associated with its development. As such, the design of machine subsystems based on new technology comes with performance and safety risks that vary due to the nature of their complexity and their design role in the new machine.

An important part of engineering design is to minimize the risk associated with a machine’s operation and to ensure safety. This prevents product damage, possible product recalls, or machine problems that require repair expenses and equipment downtime. And, of course, the first priority is to prevent personal injury to the operators.

Consider this machine safety scenario: an engineer specifies safety components that he knows have a proven record of performance and reliability. You would expect that using this design convention would yield a minimal safety design risk.

Then, several weeks after a manufacturing run, and shipment and installation of his equipment at a customer site, he gets a phone call telling him a safety-interlock switch failed. Failed? Yes, failed as in, “when an operator opened the door, the machine was still in RUN mode.” Fortunately, there were no injuries. Your first thought is “someone ‘jumped’ the switch out,’ but it turns out the safety switch just failed.

Manufacturers of safety components pride themselves on their marketing rhetoric about reliability, and try to buy the confidence of design engineers. This confidence leads to brand identification and, ultimately, purchase of safety components from this manufacturer. The reliability of a safety-interlock switch should never appear as a concern above the design horizon. Now, it suddenly occupies the center of your radar screen. This kind of failure should be very disturbing for the component manufacturer, and can compromise the integrity of the OEM.

It really isn’t shocking that, even with the most due-diligent new designs, machines sometimes suddenly fail in the field. They don’t always perform as they did in the “lab.”

However, failure of a safety-interlock switch is inexcusable and, in my opinion, not an acceptable outcome. In this day and age, if an injury had occurred, in addition to that devastating event, imagine the liability lawsuits, workmen’s compensation, insurance increases, lost employment, etc.

It’s now commonplace to order from and deliver manufacturing components to all corners of the globe. There are almost as many different safety regulations as there are countries. By following proven safety guidelines and performing risk assessments, engineers can identify the machine hazards, analyze the consequences, and design accordingly.

Machine safety design is an extremely important issue with most engineers. We expend a lot of time and have a lot of pride in assuring that equipment is safety-compliant and will protect the operators.

Discovering that a particular safety switch is no longer compatible with a standard safety relay or simply no longer reliable should raise a red flag. We can’t assume all safety switches are created equal and that they’ll provide the necessary protection when duty calls. Sadly, a safety switch is, like any other component, prone to failure. Component manufacturers have to be aware that engineers want reliable components.

Scenarios in which safety-interlock switches fail should cause an engineer to reevaluate the priority given to the hazardous conditions of machine operation, and consider redundant backup. Specifying safety switches isn’t a no-brainer after all.

As an engineer, it’s always been exciting and a challenge to design and invent something new. It’s one thing for an engineer to err on a design specification, but it’s another issue entirely for an integral safety component to fail.

Finally, for the machine end user, when it comes to machine safety, never rely exclusively on a guarantee that any machinery is safe. You must perform your own safety inspections, and if you think that machinery isn’t safe to operate, then don’t use it.