Ex assemblies, Part 1
Regulations in the scope of validity of ATEX 2014/34/EU
The discussion about Ex assemblies is as old as the EU ATEX Directive, and now dates back almost 20 years (the first version of the Directive entered into force in 2003 as 94/9/EU).
When harmonising the single market regulations for the EU Member States, unresolved safety issues were also addressed. One of these issues concerned the clear discrepancy in the assessment of sources of ignition which may result from electrical equipment and those which arise from non-electrical equipment, such as machines or parts of these, for example gearboxes, couplings, etc.
While electrical equipment has been subjected to careful consideration, examination and ultimately regulations for around a century now (the first "Regulation for electrical equipment protected against firedamp" was published as VDI 0170 back in 1911), the same attention has not been paid to the requirements for non-electrical or mechanical equipment and components. We can only guess the reasons behind this now; the most likely explanation is that a related accident occurred, whereby with electrical equipment it was relatively simple to see the link between the functional performance parameters and the likelihood of occurrence of sources of ignition. This meant that this equipment could generally be regarded as a self-contained, assessable unit.
Nevertheless, mechanical parts can generally also pose a certain ignition hazard, for example in the form of frictional heat or mechanical impact sparks. The fundamentals of this were addressed in the explosion protection directives of what was then the German Professional Association of the Chemical Industry (Berufsgenossenschaft Chemie). Recognition of the fact that non-electrical sources of ignition can also be effective sources of ignition, in particular due to the high number of sometimes fatal explosion accidents, especially in the dust explosion area, ultimately led to the development mentioned at the beginning. Since the basic principles of European directives are based on conformity with the relevant "fundamental health and safety requirements", in order to implement these in practice through harmonised standards, European standards had to be drafted first. This was relatively straightforward and, once the ATEX Directive entered into force, the relevant standards from the series EN 13463 ff were in place in Europe. So far, so good. Like usual, the problems started when implementing the directive in practice, specially in cases involving a combination of electrical equipment and mechanical devices, such as pumps, fans, drives, etc.
Many designs of technical equipment, especially those of machines, were based on these combinations consisting of several devices, components and parts.
Most design engineers and machine builders are familiar with the Machinery Directive. A conformity process and the issuing of a declaration of conformity in accordance with the Machinery Directive have since become established measures for these products.
However, if the products are built for hazardous areas, many manufacturers are not aware that ATEX Directive 2014/34/EU applies to their product.
Another problem is posed by the requirements for the conformity assessment processes defined in the ATEX Directive, which are different for electrical and non-electrical devices (e.g. need to involve the notified test bodies).
Components could be placed on the market subject to the following formal conditions:
- Individual devices form an inseparable unit (e.g. split tube motor pump) (with regard to the explosion protection concept).
- Individual devices are clearly separable and fully assessed for conformity. Assembly does not result in any new source of ignition. In this case, the devices can be placed on the market as:
a) Separate devices ("combination of devices") or
b) An ATEX device (assembly)
- Individual devices are clearly separable and assessed for conformity, but assembling them results in a new source of ignition.
This takes us to Ex assemblies. The ATEX Directive itself does not include the term "assembly": It is derived from Article 2: "Definitions", which states: "'equipment’ means machines, apparatus, fixed or mobile devices, control components and instrumentation thereof and detection or prevention systems which, separately or jointly, are intended for the generation, transfer, storage, measurement, control and conversion of energy and/or the processing of material and which are capable of causing an explosion through their own potential sources of ignition". This takes us to the term "assembly", which is defined in greater detail in the ATEX Guidelines, § 44, which states: A product (1) consisting of two or more partial devices (2) and – if necessary – together with components (3) and other parts (4) which are connected together electrically or mechanically to form a complete functional assembly is covered by the scope of the ATEX Directive.
The person who combines the single devices and places the combination on the market is considered to be the manufacturer of the assembly. The manufacturer must meet all of the relevant requirements from ATEX 2014/34/EU for the assembly. The single devices and components selected, as well as the way in which they are assembled, may, however, result in specific characteristics that the manufacturer must be aware of:
a) The assembly consists exclusively of ATEX-compliant single devices and components which the manufacturer of the assembly supplies themselves or obtains from other manufacturers. In this case, the manufacturer may assume that all component parts are compliant. Their assessment of conformity is then limited to the examination of the configuration as a whole and the evaluation of risks, taking account of the intended use and possible interactions between the combined components. In the documentation that is to be supplied with the assembly, all separate ATEX devices, including the associated EU declaration of conformity, must be identifiable. If the manufacturer does not want to incorporate all the information about the individual devices used in their operating instructions, we recommend supplying all installation and operating instructions in order to ensure that the installed assembly meets all relevant requirements from Appendix II to the directive when operated as intended.
b) The assembly consists of a modular system of components, which must be specially selected and configured for a specific purpose. The combination required for a specific application can also be assembled by the user or the installer from the "modular system" offered by the manufacturer. All components have a valid EU declaration of conformity. A manufacturer who offers this kind of "modular system" can also assume that all components are compliant. Out of all possible and useful assembly variants, they must choose the configuration that is least favourable from an explosion protection perspective. For this variant, they must identify the additional explosion risks resulting from intended operation and any interactions and evaluate these as part of the conformity assessment ("worst-case scenario"). In the EU declaration of conformity and the operating instructions that are to be supplied with the "modular system", all separate ATEX devices, including the associated EU declaration of conformity, must be identifiable. The manufacturer also has to provide instructions for selecting and combining modules correctly and the required installation and operating instructions in order to ensure that the installed assembly meets all relevant requirements from Appendix II to the directive when operated as intended.
c) The assembly contains component parts with ATEX declaration of conformity as well as those without proven conformity. In this case, the conformity assessment covers components without conformity assessment as well as all potential explosion risks resulting from intended operation and interactions between the individual components. The documentation to be supplied is listed in a).
d) This is a modular system like the one described in b), with component parts which have their own declaration of conformity, as well as those without a conformity assessment.
As for b), the "worst-case scenario" must also be considered here and a conformity assessment must be performed for all component parts which have not yet been assessed. The documentation to be supplied is described in b).
In practical applications, however, unfortunately misunderstandings often arise when it comes to interpreting the requirements of the directive. The examples below describe typical cases of errors which are ostensibly criticised by users of process systems. These users face the obvious dilemma of requiring specific machines and devices for their processes while they themselves also have to comply with the requirements for operational explosion protection, i.e. the German Hazardous Substances Ordinance (Gefahrstoffverordnung). The EU Directive on which the German Hazardous Substances Ordinance (Gefahrstoffverordnung) is based, 1992/92/EC, governs the assignment of devices as defined by Directive 2014/34/EU to the zones defined by the user. This directive fundamentally requires the devices used from the relevant device category to meet the requirements of Directive 2014/34/EU. Deviations from these requirements are only possible by means of the user's explosion protection document and are the user's responsibility.
- Machine and device builders are mainly active in "standard" industrial areas. Devices for operation in hazardous areas are an exceptional case in their business activities. This is why they look for suitable, experienced partners, e.g. for configuration with explosion-protected electrical equipment. Alongside the correct marking of the electrical explosion protection type, this partner will then also incorrectly state this on the rating plate for the product as a whole. By doing so, they overlook the fact that the supplier of the explosion-protected components does not bear manufacturer responsibility for the product as a whole, e.g. the machine. This responsibility is borne by the manufacturer of the machine, who must ensure that the requirements for the conformity assessment for their machine are met. In particular, they must check whether the machine as a whole is considered to be a device within the scope of the ATEX Directive. When placing the product as a whole on the market, the manufacturer also has to prove that they have implemented the conformity assessment in accordance with ATEX 2014/34/EU and also in accordance with all other applicable EU directives, e.g. for machines. The EU declaration of conformity must also clarify conformity with the requirements of other applicable EU directives.
- If the risks outlined below may arise, the manufacturer of the assembly must reconsider and design and build the machine according to the principle of integrated explosion protection. This means that it is not enough to only use ATEX-certified equipment and machine parts, as in case a). Instead, the manufacturer of the assembly must check whether the combination and any possible interactions between the components could have a negative impact on overall explosion protection. Some examples of risks that may arise are listed below:
a) Mechanical influences: High levels of vibration in equipment or design elements such as motors or gearboxes may affect the fatigue strength of structures or the tightness of conduits and fittings, if the equipment or design elements are not secured properly or if the suspension is inadequate. Potential consequences include the release of combustible materials, frictional heat at unwanted movable parts or even mechanical sparks due to material fractures.Thermal influences: Extreme heating, etc.
b) Temperature fluctuations may significantly impair the material properties (strength, insulation characteristics, etc.), especially of plastic parts, in the long term. Attention must also be paid to low temperatures, e.g. due to poor insulation of liquefied gas pipelines.
c) Electrical influences: Insufficient clearance between live conductors or between conductors and external conductive parts can lead to inductive and/or capacitive coupling of stray currents. It is especially critical to be aware of this in the case of intrinsically safe electrical circuits, as this can render their entire explosion protection ineffective.
d) Negative impact of necessary organisational measures: Unsuitable assembly may make necessary regular test and maintenance measures difficult or even impossible.
Marking of typical assemblies
When assembling equipment certified in accordance with 2014/34/EU with different explosion protection properties, the properties which apply to the entire assembly and represent the lowest level of protection must be stated, as is illustrated by the following examples from the guidelines for 2014/34/EU relating to marking. The examples below also describe the cases in which the assemblies are used at the interfaces with different zones or with the non-Ex area.
The types of protection should be stated in the operating instructions, especially for complex assemblies. This is clearer and easier to understand than providing this information on the rating plates. Rating plates already contain a multitude of information in a relatively small area.
However, the option of stating types of protection on the rating plate is not fundamentally excluded and should be considered when having this information on the assembly itself would provided added value. These details must always be included in the operating instructions. This may be the case, for example, where there is the possibility of interactions between the individual component parts of the assembly, which must be prevented by correct handling.
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