Metal Detection CCP Validation Fact Sheet

The following explains what an example validation of the metal detector CCP would look like.

The hazard identified would be something like this:

‘Physical metal contamination of the dispatched finished product, due to inability to detect metal, caused by a faulty metal detector.’

The monitoring activity for the hazard would be to check that the metal detector is working at a set frequency.

So what would the critical limits for this monitoring activity be?

The ‘limit’ that is ‘critical’ (critical limit) is the point where you can guarantee safety.

For metal detection, this would be the test piece sizes. Because, if we take the 2mm stainless steel test piece as an example – you are in effect saying that you can guarantee that there will be no stainless steel in the product of 2mm or more in size. You cannot guarantee the safety of the product, if it was to contain stainless steel of less than 2mm.

Therefore, we need to validate the critical limits – i.e. the test piece sizes.

To do this we need to prove what are the smallest test piece sizes that can be achieved, in order to guarantee the consumer, the maximum safety level. Get help from your metal detector provider or contractor to run the trials, using a range of test pieces and work your way down from the larger sizes, until you get to a point where the test piece is not picked up each and every time. It is a good idea to send the test piece through at least 30 times to prove that it rejects every time. Once you’ve got the test pieces that you think you should use, repeat this again over at least 3 runs to show that it is consistent.

Before doing this though you need to work through the following, as it will affect how you do your trials.

There are other factors that need to be considered when validating, such as (this is not an exhaustive list and will vary depending on the CCP you are validating):

If equipment is being used (which in this case is the metal detector) – how does it work? Are there any functions of the equipment (the metal detector) that may vary and what impact will this have? What effects could the process have on the critical limits? What effects could the product have on the critical limits?

We go through the above questions and answer them in turn.

1. If equipment is being used (which in this case is the metal detector) – how does it work?

This will depend on what type of metal detector you have, for example a throat detector or a conveyor detector. We’ll focus on a conveyor detector for this example.

For a conveyor detector, the conveyor with the product on, runs directly through the metal detector – through the middle of what is called the search head.

The search head is the piece of the detector that picks up the signal transmitted from the metal as it passes through. It is this signal, if it is strong enough, that will cause the detector to reject the product or stop the detector if it’s a belt stop system.

It is important to know this, because you will need to use this information to determine whether you should test the product, with the test pieces on top of the product, on inside the product.

I’ll explain why. Below is a diagram of a standard metal detector, showing the conveyor running through the centre of the search head.

The green box is the search head. The arrows show the signal. The most difficult place for the detector to see, in the centre of the search head shown as a red dot. This is also shown from a side on view below. This is where you should put your test pieces, because if the detector can see them here, it’s proving worst case.

So if your product height on the conveyor means the top of the product is in line with the centre of the search head, you need to put your test pieces on top of the product. See below diagram.

However, if the height of your product, when sitting on the conveyor means the centre of the search head is in the middle of your product, you need to put your test pieces inside the product. See below diagram.

Determine this first, before carrying out any trials on the test piece sizes – as you’ll need to do the trials with the test pieces in the right place, to prove worst case and to mimic your monitoring method.

2. Are there any functions of the equipment (the metal detector) that may vary and what impact will this have?

If your detector has fail safe systems such as reject bin full, belt stop, reject confirmation etc you’ll need to know how each of these works, in order to ensure that your procedure covers tests of each. You’ll need to validate that these test procedures work by carrying out trials.

3. What effects could the process have on the critical limits?

In the case of metal detection, the speed at which the process is running can have a massive impact on the detector. The faster the product is going through it, the less likely the detector will pick up the test piece sizes you’ve determined. Therefore, you need to run your trials on the test piece sizes at worst case speed, i.e. the fastest speed you will run. You also need to make sure that you carry out your monitoring test at this speed.

Think about if there are any other process conditions that need to be included in your validation.

4. What effects could the product have on the critical limits?

Variations in product will have an effect on the detector, especially variations in moisture content. Review the product range that will be going through the detector to see if each one needs to be trialed (and set up for test) individually or if you can group them together.

Changes in product can cause false rejects - where the detector thinks there’s metal in the product but it’s the signal from the product itself that causes the reject. So, it’s really important to trial different batches of product, to make sure the detector only rejects product with metal in it (or the test pieces). Failure to do this, will mean that the team running the detector get used to false rejects and the confidence in the detector will be lost – when this happens you run the risk of product with metal being dispatched, as the team may think it’s just the detector playing up again.

In addition to this, we also need to validate how often the monitoring activity must take place. This is so that we can ensure that any defect product is still within our control, if the CCP monitoring activity fails. In the simplest terms work out how long it would take the product to get from the CCP, be dispatched and out of your control. For something like metal detection, it may be that the product may be sent into dispatch and put on a vehicle quite quickly, so the frequency of the tests may need to be quite high.

If you need any help with this fact sheet, do not hesitiate to get in touch on 01909 511252 or info@techni-k.co.uk

If you’ve found this fact sheet useful you may find out HACCP documentation pack helpful too.

It contains every that you need to create a first class HACCP that will pass any audit!

Take a look at www.techni-k.co.uk/BRC_HACCP