I realise that my proposal makes "sheet" redundant; I'll come to that in a moment.

I can't find any reference anywhere to an "occupational and industrial safety sheet", and if that were what it meant there would surely be an example somewhere. There are certain types of standard data safety sheets (SDS):
https://en.wikipedia.org/wiki/Safety_data_sheet

But OIS quite often stands for operating instruction sheet:
http://www.acronymattic.com/Operation-Instruction-Sheet-(OIS...

And I think that's probably what it stands for here.

See the following Ford Motor Company document:

"Operator Instruction Sheets (O. I. S.)
OIS and JSAs will be maintained via a computer data base for operations within a zone and/or department. Employees and/or work groups will have access to these documents and may determine if, and/or where they desire to maintain them, as long as they are maintained in an orderly manner."
Note that they are associated with JSAs (Job Safety Analysis: https://en.wikipedia.org/wiki/Job_safety_analysis ).
In the same document "OIS sheet" is used, even though OIS has been defined as operating instruction sheet:
"Ensure complete and current OIS/JSA sheets are available for every job."
"This quality stop button procedure is not intended to include Delta items that are covered under processes which should be outlined in each operator’s OIS sheet."
"The following items will be included in this discussion:
1. The existing OIS/JSA sheet."
http://local249.org/wp-content/uploads/2013/05/2015-Local-Ag...

So we can see here that the redundancy "O(perating) I(nstruction) S(heet) sheet" does occur. I think people are so used to using the abbreviation that it doesn't strike them.

So are operating instruction sheets filled in? Apparently yes, at least to some extent; they are revised. And they are associated with safety:

"If necessary, review the safe operating instruction sheet prior to starting the task to remind everyone of the proper technique. [...]
Always review/revise the safe operating instruction sheet."
http://www.asse.org/assets/1/7/RandyDeVaulArticle.pdf?ref=ps

So I think this is probably what your document is referring to.