Substantial modification of machinery: when does the operator become the manufacturer?

What is a substantial modification?

The Machinery Directive 2006/42/EC itself does not define the term. The principle follows from the European interpretation (among others in the European Commission's Blue Guide): a product that is modified after it has been put into service in such a way that its performance, purpose or type is substantially altered may be regarded as a new product and must then meet the requirements of the applicable harmonisation legislation afresh.

For machinery in Germany, this question is given concrete form by the interpretation paper of the Federal Ministry of Labour and Social Affairs (BMAS) on the subject of the “substantial modification of machinery” from 2015 (GMBl 2015, p. 183). It was drawn up with the participation of the Federal Institute for Occupational Safety and Health (BAuA), the authorities of the federal states, the German Social Accident Insurance (DGUV) and the German Engineering Federation (VDMA), replaces the previous version from 2000 and is the authoritative interpretation aid of German market surveillance.

The starting point of the paper: every modification to a machine, for example through a performance increase, a change of function or a change of the intended use (such as other process materials, conversions, interventions in the safety technology), must first be examined for its safety-relevant effects. Two questions are decisive: does the modification create a new hazard? Does it increase an existing risk?

Important: there is no blanket threshold, neither a percentage of the conversion costs nor a list of components that automatically makes a modification “substantial”. What is required is a safety assessment in each individual case: an expensive conversion can be uncritical, while a small intervention in the safety control system can have far-reaching consequences.

Distinction: maintenance and replacement of identical parts

Not every intervention on an existing machine triggers the check in the first place. The BMAS paper expressly clarifies that the following measures do not constitute a substantial modification:

• the replacement of components with identical components or with components of identical function and identical safety level (classic maintenance and repair that restores the original condition),
• the installation of protective devices that raise the safety level of the machine and do not enable any additional functions beyond that. Anyone who makes an existing machine safer does not thereby become the manufacturer.

Two qualifications: “identical” is to be understood narrowly. If a worn relay control is replaced by a freely programmable safety PLC with new operating modes, the check for new hazards is reopened. And regardless of product law, the employer remains obliged under occupational health and safety law: after every change to a machine (not only after substantial modifications), the workplace risk assessment under Section 3 of the German Ordinance on Industrial Safety and Health (BetrSichV) must be reviewed and, where necessary, the operating instructions for employees adapted.

The BMAS test scheme step by step

The interpretation paper describes a decision scheme with which you evaluate every modification systematically. The examination can be carried out methodically using the procedures of the risk assessment per EN ISO 12100. As soon as one of the questions ends with the result marked in green, there is no substantial modification:

In summary: if the machine is safe after the modification without additional measures, or if simple protective devices restore the safe condition, there is no substantial modification. Only if neither applies is the modification substantial.

The consequences: the operator becomes the manufacturer

If a substantial modification exists, the machine is treated in law like a new machine. The person responsible for the modification takes on the role of the manufacturer: the operator who carries out the conversion itself, just as much as a contracted retrofit service provider. Who bears the manufacturer's responsibility should therefore be clearly settled by contract before the conversion. In concrete terms, the manufacturer's role means:

• Essential health and safety requirements: The substantially modified machine must meet the requirements of Annex I of the Machinery Directive, and as a whole, not only in the converted area.
• Risk assessment: A risk assessment per EN ISO 12100 must be carried out and documented for the modified machine.
• Conformity assessment procedure: The appropriate procedure must be run through again; for Annex IV machinery a notified body may have to be involved.
• Technical file: The technical file must be compiled for the modified condition. In practice this is the biggest hurdle when the original manufacturer's documents are missing or incomplete.
• Operating instructions and warnings: Operating instructions for the modified machine must be provided; remaining residual risks must be pointed out.
• Declaration of conformity and CE marking: Finally, the manufacturer draws up the declaration of conformity and affixes the CE marking to the substantially modified machine.

For linked installations, the same yardstick applies to the assembly of machinery: if the modification affects only a part of an installation, it must be checked what effects it has on the installation as a whole. If the modification and its effects on the assembly are substantial, there is a substantial modification of the entire installation.

What changes with the Machinery Regulation from 2027?

From 20 January 2027 the Machinery Regulation (EU) 2023/1230 replaces the Machinery Directive 2006/42/EC. For the subject of this article that is a turning point: for the first time, substantial modification is then defined in law across the Union, in Article 3 point (16) of the Regulation. Until now the assessment rested solely on national interpretations such as the BMAS interpretation paper.

Under this definition, a substantial modification is a physical or digital modification of machinery after it has been placed on the market or put into service, which is not foreseen or planned by the manufacturer, which affects its safety by creating a new hazard or by increasing an existing risk, and which requires

• the addition of guards or protective devices to the machine the processing of which necessitates a modification of the existing safety control system, or
• the adoption of additional protective measures to ensure the stability or mechanical strength of the machine.

In substance, the Regulation thus essentially adopts the logic of the German test scheme: if a protective measure that does not intervene in the safety control system is sufficient, there is no substantial modification. Three points are new or expressly regulated:

• Digital modifications count too: Software changes (for example an update that unlocks new functions or alters safety functions) can also trigger a substantial modification.
• Clear allocation of obligations: Whoever carries out a substantial modification is considered a manufacturer under Article 18 of the Regulation and is subject to the manufacturer's obligations of Article 10, from the risk assessment to CE marking. Non-professional users who modify their own machine for their own use are exempt.
• Relief for installations: If the risk assessment shows that the modification affects only part of an assembly of machinery, the obligations are limited to the parts affected. Machines in the installation that are not affected do not have to be checked and documented again.

In practice: until the beginning of 2027 the BMAS paper remains the authoritative guidance in Germany. Anyone who builds their assessment scheme on it today will largely work correctly under the new Regulation as well, but should expressly include software changes in the assessment.

Typical practical cases from mechanical engineering

Whether a substantial modification exists is always a decision in the individual case. The following constellations show what matters in common conversions:

Recommendation: document the assessment, even without a substantial modification

The most common omission in practice is not the wrong assessment but the missing one. If, years after a conversion, an accident occurs or market surveillance makes an enquiry, you must be able to prove that the modification was checked and why it was classified as not substantial. Robust documentation comprises at least:

• the description of the existing machine and its condition before the modification (type, year of construction, existing protective devices),
• the modifications carried out in detail (what was changed mechanically, electrically, in the control system and in software),
• the risk consideration of the modification per EN ISO 12100: new hazards, changed risks, evaluation of the existing and, where applicable, supplemented protective measures,
• the reasoned result (substantial modification yes/no) with date and responsible person.

You need this documentation in both cases: if a substantial modification exists, it is the entry point into the conformity procedure. If not, it is your evidence and at the same time a sensible basis for the workplace risk assessment under the BetrSichV that is required anyway.

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