Chemcials are designated for use and those determined to present a food risk are to be locked up with restricted access. ID badges could be required, also included visitor badges. All visitors must be escorted (we also require all visitor and contractors watch our GMP training prior to entry). In some cases if you use helmets you can color code to show level of access granted or by some other designator. Access restricted areas may require a keycoded to pass through doors (especially good for a lab).
You could also go another step and provide training to your associates to show they were properly trained on what to look for in support of the food defense program once everything is written an approved.