OK Guys!
I admit it, sometimes I can be such a dummy!
Today whilst checking out a couple of Chillers.
The type that have acoustic panels attached to their sides which are retained by 90 degree turn panel key locks.
Both Chillers in series with their controls at the end.
So I check the second one in and being happy with the view inside. I replace the end panel and lock into place.
I walk around the side of the chiller to check out the other end.
"Bang!" (a sheet of steel being dropped type bang) Plant dies!!!
"What the?" or words to that effect says I.

Walking back around to the end I had just left. I discovered said replaced panel leaning against the end of the 1st Chiller.

With its emergency stop in!
Hence the plant shutdown!
Being a remote plant room with no-one around, I was able to reset the stop and restart the plant before anyone even noticed.
So I wrote on my plant report that the Emergency stop had been tested.
Small positive from a negative I guess.
I must be getting old as I used to class them as "I want my Mom!" situations nowadays I blame myself.