From the description of the processing line given by the OP, there would be no metal contamination large enough to be more than a low severity.
This is how I'm looking at it. All the suppliers of the products processed on this production line have metal detection
.. all suppliers have MDs that detect below the FDA's "hazard" limit (metal between 7 - 25 mm in any dimension). The only processing that happens prior to packaging is blending, and the ribbon blender is designed such that it should not introduce additional metal into the process i.e. there is no metal-to-metal contact that may create shavings, and there are no removable/breakable parts (that is, they aren't breakable with normal, reasonable use) in contact with the product. PMs are performed regularly, and pre-op inspections are in place prior to use (part of the inspection is looking at the condition of the blender, visible contamination, etc.). As has been noted, there is no history of the blender contributing to metal inclusion in the product.. we can't prove this based on the processing line in question, as it doesn't have MD (though we have never had complaints regarding metal with products processed on this line), but we do know from the lines that have
MD that the only metal we ever see is aluminum, which comes from a supplier that does not have metal detection
(I have confirmed this on a supplier audit, and have statements in writing). All of our equipment is S/S (the food contact points at least), so any aluminum is not from us. This supplier's product is not used on the line w/o MD. Also, we maintain an archive of any isolated metal picked up by the MDs - looking back at the archive, there is only one instance in 3 years of metal that came from our processes. This metal came from one of our vertical form-fill-seal machine - the most automated piece of equipment we have, with the highest likliehood of depositing metal in the product.
So, based on the historical evidence, the conditions of processing, our suppliers' metal detection, and our own PMs, storage controls, and GMPs (e.g. no items in pockets above waist, etc.), I would say that metal inclusion is low risk on this production line. However, despite this, I do think that metal detection
would be wise and beneficial to have on this production line just to have the added control and peace of mind. It just makes my job easier in the end :)
Yes, GMO is right - the powers that be are not willing to invest in MD for this line (or at least, not until the volumes increase), but I am also not interested in making a big to-do about this situation based on the low risk. Would I prefer to have it? Yes. Can I sleep at night without it? Yes - the risk, based on the evidence I have, is low enough to where I feel comfortable.. but I'd be lying if I said that having a MD wouldn't make me feel a bit better (even though they're of course not a fail-safe and have their own limitations).