6 replies to this topic

[Omega Lim]

Hi,

 

I am currently using a metal detector to detect foreign material (Ferrous, Non-Ferrous, and Stainless Steel) in flour.

What is the critical limit size (mm) of Ferrous, Non-ferrous, and Stainless Steel that I should set for the Metal Detector.

 

Thank you.

[gfdoucette07]

Omega,

 

There are several factors to also consider

 

Pipe diameter

Density of your material

Flow rate

Accuracy of  your unit

 

The vendor of your product should be able to assist with these answers but most  places I have seen are between 1.5 & 2.5MM depending on the above factors.  Hope this is a place to start

 

G

[Charles.C]

Hi Omega,

 

Ideally the answer is, of course, zero, since no metallic contamination is optimum. If otherwise the product may be considered "dangerous" or possibly considered not "dangerous" but "unwholesome" and therefore equally rejectable.

(A haccp critical Limit is usually, theoretically, based on "safety" but may be effectively superceded by "Regulatory").

 

A suggested most conservative, operational, answer for your own instrument is -

 

the Critical Limit equals the Limit of Detection (LOD) for the specific food matrix involved / specific test piece material involved-accessible /given Machine settings.

 

So, briefly, using a standardised Procedure/Machine settings, you start with an easily, consistently, detectable (certified) test piece size of defined material, (eg SS)/given food matrix-packaging. Then proceed with smaller test sample sizes until an "unsatisfactory" result is obtained. The penultimate test size to the "unsatisfactory" sample represents the LOD for the conditions of the test series.

 

Whether the above will be Regulatorily/ auditorially acceptable may depend on aspects additional to the practical elements in previous post such as location/industry/FS Standard.

 

There are many similar queries to yr own on this forum. Numbers which were found to be "acceptable" vary considerably. The discussions  include several threads related to the US Baking Industry.

[JSayreQS]

I'm in a similar business. For our metal detectors, we have the smallest Stainless Steel test piece available that can register every time on the verification step. When we validated, we set the machine to the sensitivity that allowed us to get this reading every single time. Then we moved on to the Non-Ferrous and got the smallest size that read with the Stainless Steel sensitivity setting. For the Ferrous, we got the same size as the Non-Ferrous. Our test pieces are 1.5mm Fe, 1.5mm Non-Ferrous, and 1.8mm SS. The important thing is that you have reasoning and rationale to support why you choose to validate for this size. There are a lot of factors to consider though. The aperture of the machine is set for a round piece. If metal is introduced, will it be round? Or will it be misshaped and one side might be larger than the other. When I discuss our metal detection with customers, I use the following rationale:

 

The validation of the lone CCP (metal detection) in the plant is based off of our risk assessment, metal detector capability, and historical data.  

 

The most likely risk of metal contamination in our system has been determined to be ferrous metal.  Our metal detectors have been set at a sensitivity which targets ferrous metal at the lowest detectible size.  Detection of non-ferrous and stainless steel is subsequently set to the best capability of the unit.  Dependent on aperture size, and frequency of operation, all sensitivity information is expressed in diameters of spherical samples. Non spherical objects such as wires will exhibit an orientation effect, i.e. they can be more easily detected in certain axis. If the diameter of the wire is less than the spherical sensitivity setting the sample may not be detected in all orientations.  Based upon the speed of product through the aperture and the aperture diameter, we have determined that the best standards to suit our purpose are the use of 1.5mm Fe, 1.5 mm Non-Ferrous, and 1.8mm Stainless Steel.

 

All metal detection limits (1.5mm Fe, 1.5mm Non-Ferrous, and 1.8mm Stainless Steel) are well below the FDA guidance for the at-risk range of “hard and sharp foreign objects” of  7.0mm to 25mm. 

 

Additionally, annual validation of the metal detector units capability is performed by an external service provider to confirm performance criteria are being met.

[Charles.C]

I'm in a similar business. For our metal detectors, we have the smallest Stainless Steel test piece available that can register every time on the verification step. When we validated, we set the machine to the sensitivity that allowed us to get this reading every single time. Then we moved on to the Non-Ferrous and got the smallest size that read with the Stainless Steel sensitivity setting. For the Ferrous, we got the same size as the Non-Ferrous. Our test pieces are 1.5mm Fe, 1.5mm Non-Ferrous, and 1.8mm SS. The important thing is that you have reasoning and rationale to support why you choose to validate for this size. There are a lot of factors to consider though. The aperture of the machine is set for a round piece. If metal is introduced, will it be round? Or will it be misshaped and one side might be larger than the other. When I discuss our metal detection with customers, I use the following rationale:

 

The validation of the lone CCP (metal detection) in the plant is based off of our risk assessment, metal detector capability, and historical data.  

 

The most likely risk of metal contamination in our system has been determined to be ferrous metal.  Our metal detectors have been set at a sensitivity which targets ferrous metal at the lowest detectible size.  Detection of non-ferrous and stainless steel is subsequently set to the best capability of the unit.  Dependent on aperture size, and frequency of operation, all sensitivity information is expressed in diameters of spherical samples. Non spherical objects such as wires will exhibit an orientation effect, i.e. they can be more easily detected in certain axis. If the diameter of the wire is less than the spherical sensitivity setting the sample may not be detected in all orientations.  Based upon the speed of product through the aperture and the aperture diameter, we have determined that the best standards to suit our purpose are the use of 1.5mm Fe, 1.5 mm Non-Ferrous, and 1.8mm Stainless Steel.

 

All metal detection limits (1.5mm Fe, 1.5mm Non-Ferrous, and 1.8mm Stainless Steel) are well below the FDA guidance for the at-risk range of “hard and sharp foreign objects” of  7.0mm to 25mm. 

 

Additionally, annual validation of the metal detector units capability is performed by an external service provider to confirm performance criteria are being met.

 

Hi JSayre,

 

Thks for the input/Risk Analysis.

 

Use of the FDA Guidance document/7-25mm range needs some caution since there are exceptions as detailed in the document. Other locations, eg Canada (max. 2mm), may have different viewpoints.

 

Certain variables seem to have particular importance as far as the LOD is concerned, eg see the attachment in this post (Pg 16) -

http://www.ifsqn.com...ted/#entry66632

 

The post following the above linked illustrates that higher limiting levels may be operationally encountered.

[Gerard H.]

Dear Omega,

 

In addition to the previous reactions, I would like to add the following tips to determine the sizes:

 

• Getting to the vendor will surely be helpful. Maybe they can also mention what's used in the flour industry.
• What is required in the customer specifications / requirement documents?
• The humidity of the flour (varieties) can play a role in the sensivity of the metal detector.
• Go for the minimal possible size, however without creating false positive results.
• Take care of needle shaped objects (such as wires), as mentioned above. They can pass a sieve, and if badly oriented, they also pass undetected through your metal detector.

Hope this will be helpful for you. In case of any questions or remarks, please let me know.

 

Regards,

 

Gerard Heerkens

[QIC]

Nice