We don't have our magnets as CCPs but that is because we have a metal detector at the end of the bagged line process.
One issue with having your magnet as a CCP is that it won't take out non-ferrous metal so you can't say that it is removing all metal. Also you have to have a critical limit which can be hard to define for a magnet. Furthermore do you have metal screen material in your sifters? Are those ferrous or nonferrous screens? If they are nonferrous the screen material may break apart and get into your product... please don't ask how I may or may not have knowledge of this issue. Though we have found that even "nonferrous stainless steel" can be attracted by a magnet just not strongly. Another issue is that your magnet will not detect if something falls into the product from your bagging line itself.
If your magnet is truly going to be a CCP it does have to be able to be opened, inspected, and cleaned at a determined frequency. Our magnets are CPs (or oPRPs in FSSC same thing different name) because of the issues listed above. However all of our magnets are pretty easy to open and inspect. We check those after every milled load of product.
Our flour may sit around for a short period of time in our warehouse (really just a large alcove) for a day or two before shipping but there are times we have to move them out the same day.
You should inspect the magnet at least once at the start of a load and once at the end of the load. That way if there is an issue it's only on that one load. I don't know how long your bagging runs are ours is about 2 to 2 1/2 hours. You could shut down bagging operations long enough to inspect it, which in a close easy to open and inspect magnet shouldn't take more than 5 minutes, and then be able to inspect it every hour or so.
The frequency of your CCP inspection is really determined by how much risk you want to put into your product. If you determine your product is at risk and you bagged out an entire load of flour then you have scrap that load and start over.
Edited by Mr. Incognito, 31 December 2014 - 01:43 PM.