We have a few large grain bins at our facility that have 24" round access doors on the sides.
These doors actually consist of two doors (see attached pic - sorry it's so small, that's all I can find)...an outer door that is very flimsy, and an inner door that is heavy duty. The inner door swings inward, so it is not able to be opened until the grain level inside is below about 4' or so. The outer door doesn't really have much for a latch or a place to lock it, and it's so thin and flimsy that it could easily be bent open if someone was sufficiently driven to do so.
We could obviously put just a tamper-evident seal on the flimsy outer door...but is that really sufficient? No one would be able to access the grain until it was below the 4' mark because they couldn't open the inner door...but if the grain is below 4', they could access it quite easily. Sure, we'd know the seal was broken...but we also have a shallow pile of grain (which, with a 27' bin, is still a significant amount!) that we must now treat as though it's contaminated.
We came up with an idea to modify the inner door to effectively lock it, but it would take some cutting, welding, etc. - before we do that, we wanted to hear if anyone else had any other thoughts or ideas.
FYI - we're not third-party certified, just FSMA-compliant (or trying to be...)