SQF has requirements for this:
Jewelry and hard objects in pockets (12.3.4)
Do not wear jewelry on the hands, wrist, neck, or ears that cannot be cleaned and sanitized and then secured to your person. Do not carry objects in your outside pockets. Plain wedding bands are acceptable but not recommended (220.127.116.11).
Basically nothing can be dangling or exposed that might present a risk to the product. It is as simple as making it part of your SOP. No keys or other materials exposed on your person in the production areas or storage areas that could present a risk for contamination of the product.
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