Explosion-Protection Fit for Paint – Explosion-Protected Products for Paint Shops

Author / Editor: Alexander Aust* / Dr. Jörg Kempf

The specialist in electrical explosion protection Pepperl+Fuchs now certifies its electrical explosion protection products for paint shops. The basis for this certification is a new standard sheet for regulating test methods for paint-wetting-impairment substances.

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PWIS is the acronym for paint-wetting-impairment substances. Silicones were the first substances to be identified as detrimental in this way. This is one reason why we still incorrectly refer to the absence of silicone as a measure of whether products are approved for use in paint shops. Many plants still apply standards that require products to be free of silicone if they are to be approved for operational use. However, PWIS not only covers silicones but also substances such as mineral and synthetic oils, fats, and release agents made from plasticizers, and the abrasion of plastics such as polyethylene.

Chemical substances of this kind are ubiquitous and present in many products. They pose a huge risk in paint shops, since they prevent proper adhesion during the painting process. Even small quantities of PWIS substances often make it impossible to achieve a uniform paint coating, and may lead to cratering or uneven layers. Such defects mean reworking or scrapping products, or — in the worst-case scenario — stopping production altogether. It goes without saying that companies operating paint shops want to avoid such costly quality issues. This is why customers make sure the equipment that they purchase is suitable for its intended purpose. Suppliers must provide evidence that the chosen products do not release PWIS.


Until 2018, there was no standardized method of classifying the products. No distinction was made on the basis of operating location and risk potential, meaning that the plant’s own tests were all carried out to the highest possible specifications. During tests, for example, components were rinsed with solvents, even though compressed air was used at the operating location. Tests also involved the heating of components in ovens (“tempering”, to use the industry term), even though the client intended to use the product at room temperature. This focus on worst-case scenarios entailed very high approval costs, and in many cases still does.

Last year, industry experts worked with the German Fraunhofer IPA (Fraunhofer Institute for Manufacturing Engineering and Automation) and the Surface Technology Department of the VDMA (German Mechanical Engineering Industry Association) to develop a single set of PWIS rules (German: LABS conformity) for standardized tests. The aim of the new VDMA 24364 standard sheet is to solve this problem and simplify processes for everyone involved. The standard is intended to make it easier for customers to obtain evidence that the products on offer are suitable for use in paint shops. It outlines a general procedure for testing products to determine whether they contain paint-wetting-impairment substances.

Standard Sheet for Simpler PWIS Certification

Practical experience shows that the requirements to be met by a specific product cannot be described in generalized terms. Many factors determine the criteria that should be applied to the relevant component: the nature of the component, the materials used to produce it, the products that it will come into contact with, and — in particular — the operating location and the area in which it will be used. The PWIS regulations drawn up by the Fraunhofer IPA and the VDMA, set out in the VDMA 24364 standard sheet, initially classify hazards. Allowing customers to categorize and assess products on the basis of the relevant operating location and type of use makes it easier for them to obtain evidence that the product offered is suitable for use in paint shops.

Paint shops are divided up into different PWIS-critical zones, similar to the zones of explosion protection areas. The PWIS relevance of a component is determined by assigning the component to its future operating location. Multiple product groups assigned to these different zones are also described in detail. Determining factors include whether the product will come into contact with certain chemical substances and how it will be used in the future. For example, products are included in product group A if they come into direct contact with the paint, the solvent, or the substrate to be painted. Products belong to product group C if they are used to control the painting process and do not come into direct contact with aggressive materials.

Specific Tests According to Zone and Test Class

After classifying the product according to zone and product group, a further classification into test classes can be carried out to determine what kind of test is appropriate for the product group and how it should be carried out.

In the case of product group A, for example, a choice must be made between test classes A1/rinsing off of all product surfaces, A2/rubbing off with solvent, and A3/immersion in solvent. This principle is described in detail for each product group and the associated test class. A clear description is provided of the test criteria and the test process to be used.

If a manufacturer intends to certify its products for various potential uses, the test classes can of course also be combined. Therefore, manufacturers can certify their products in a targeted manner for specific application areas. The precisely defined test methods make it easy for paint shop employees to determine whether the product is suitable for the intended purpose. Product requirements can be defined in an easily understandable manner in order to standardize approval specifications. The certificate contains details of specific conditions for approval of the relevant product. Uniform PWIS certification guarantees the highest possible level of transparency and reliable approval processes. Standardization significantly reduces the costs incurred by both sides.

The approval specifications are also relevant to explosion-protected areas of the paint shops. The strict requirements that must be met to achieve PWIS compliance also apply to electrical equipment used in gas and dust explosion protection atmospheres.

To meet these specific requirements, Pepperl+Fuchs has certified selected products from its extensive portfolio for use in paint shops in accordance with the requirements of the VDMA 24364 standard sheet. Terminal boxes, control panels, and control units that are certified for Ex Zones 1, 2, 21, and 22 have also been approved for test classes A1 and B2. Pepperl+Fuchs therefore offers a wide range of options for the electrical connection and control of plants and machines. The approval covers products used in Zone 1 that come into direct and indirect contact with paints and solvents.

* * A. Aust is Product Marketing Manager Electrical Explosion Protection Equipment & Solutions, Pepperl+Fuchs, Mannheim/Germany. Contact: Phone +49-621-776-2222