Production equipment sometimes undergoes modification. Reasons can include:

• Accommodating a new replacement part.
• Changing a tool to produce a different product.
• Conforming to a customer design change in the same product.
• Producing the new model of the same product (as is done in automotive).
• Improving throughput.
• Reducing the scrap rate.
• Improving energy efficiency.

These and many other reasons make equipment modifications fairly common in production plants. What may not be so common is ensuring that the operating and maintenance procedures are updated to reflect the change.

For example, a complex and failure-prone servo-driven system for clamping a work piece in place was replaced with a pneumatic equivalent that runs on plant air. Maybe it could have been replaced with a better servo-driven system, but it wasn’t. Now there’s a supply line that runs at 80 PSI, and there’s a different way that fingers can be pinched (or broken). There’s also an energy source that can drive particles into a person’s skin or eyes.

Pneumatic systems are not dangerous per se when the proper guards are in place and the correct safety procedures are followed. But in the absence of those, this modification creates a danger where one did not exist. Going the other direction, from pneumatic to electric, would also have created a danger where one did not exist if the necessary guards were not in place and the proper procedures were not followed. It does not matter what kind of modification is made — when the modification is made the safety parameters almost always change.

Depending on the circumstances, a given set of new safety parameters may be exceedingly difficult to accommodate. So before a modification is made, those parameters must be considered, and they must be reviewed after the modification is made.

Here are some questions to consider:

• Will a new interlock be created? Will an old one be removed? Will there be any effect on existing interlocks? Can the existing interlocks be implemented with the change that is intended, and if so what will that entail? What new interlocks should be created, due to this change? This set of questions also applies to permissives.
• What new eye hazards might be created, and how could those be mitigated from a design standpoint? The previous question also applies to each area of the body, including fingers, ears, lungs, feet, etc.
• What new electrical hazard might this create and how will that be mitigated? This also applies to other types of energy sources, including mechanical, kinetic, chemical, and thermal.
• What effect might there be on the egress path? On interference with the fire protection system? On emergency lighting? On access for first responders?

Sometimes a change simply is not worth the safety risks involved. At a factory that had an annealing line, the operators wanted their operator interface (OI) upgraded to a much larger touchscreen. When engineering responded that the OEM did not provide such an upgrade, the production superintendent insisted on getting it some other way. The original 8-in. touchscreen was replaced with a 21-in. touchscreen, which was heavier and bulkier so it required a new mounting system.

Productivity did not increase with the new OI, but there were two unintended safety problems. The first was the e-stop near the OI had to be relocated. The electrician who did the job moved it from the left side of the OI to the right side of the OI. This rendered it useless for its intended purpose. The other was the big touchscreen blocked much of what the operators should be looking at, so that change allowed dangerous operating conditions to escape early detection.

While plant engineering was able to solve the e-stop problem, there was no getting around the visual issues with the much larger touchscreen. When they consulted the OEM, an engineer there said this problem is why they chose the 8-in. screen to begin with and did not offer a larger one. After all that expense, including three ruined batches due to a previously preventable conveyor jam, they went back to the original OI.

Even something as “no brainer” as adding an infra-red window for thermography requires some forethought. It’s much safer than opening an enclosure, thus the “no brainer” part. But what if you locate the window such that the thermographer has to stand next to a bank of power factor correction capacitors to use it?

Adding an HVAC air intake vent? You don’t locate it next to an open cooling tower that has antifreeze in the water, and you don’t locate it near the vent for the battery room.

Installing a motor disconnect? Make sure you account for how it is designed to be used. Notice that the handle is on the left side of the enclosure. The operator stands to the left to operate the disconnect and uses his left hand. If the cover latch fails and the cover blows open due to an arc blast, the operator is out of the blast path. And worst case, he would lose his left hand and not his right (which would be really the worst case if he is left handed). If it seems like the only way you can mount the disconnect is so the operator must stand directly in front of it, then come up with another way to mount it. For example, instead of bolting it to the wall, try to bolt a stand to the floor at 90 degrees from the wall and mount it there.

Always answer the safety questions before making the modifications. It is safer that way — and usually less expensive.