As far as I know and as I can see, there is mention of a specific thickness in the BRC norm. This was what I could find in the BRC standard:
"Where they pose a risk to product, glass windows shall be protected against breakage.".
In other words: adequate protection in case of a product risk. For the choice of the shatterproof film I should look for a one of very high quality, which doesn't degrade over the years (due to sunlight exposure, dust or humidity). It's valuable to gather opinions of other users of such shatterproof films, before buying.
I am unknown with the situation of your plant, however for the internal windows, a change from glass windows into polycarbonate ones can also be a solution.
I wish you very good luck with the BRC audit!