About us ... Interfaces & Sensors Potentially EXplosive ATmospheres Services & Developments Technical topics  

  Last updated on 05/04/2019    (©  2001 - 2020   TECHNETEA) French

Logo Technetea

To successfully carry out
an ATEX approach

Electronics Engineering

Any manufacturer who starts an ATEX project shall sooner or later contact a certifying laboratory. The first contact, especially if it is the first time that this context is approached, is often the occasion of big discoveries :

"- But why isn't it possible to do that way ?!"

"- From an electrical point of view you have to think your equipment differently, and also redefine the mechanical protection."

"- But it's absolutely impossible to redesign the equipment differently ! It's the only way !"

And the extent of the problem appears fully when the manufacturer adds : "It's out of question to restart the project from scratch, the date of going into production is set and we are already late !"


Before arriving to that,

It will never be repeated enough, that an equipment which is not designed from the beginning for a use in potentially explosive atmospheres, has thereafter very little chance to be able to be adapted for a use in this context.

An ATEX project proceeds in four stages :

1)  the ATEX feasibility study

2)  the design and ATEX study on technical documents

3)  the ATEX assessment of the prototype

4)  the writing of the final documents and the issue of the ATEX certificate

Stage 1 : The ATEX feasibility study

This stage begins with the drafting of a short document with a maximum of two pages, which will be used as a support for a discussion with an ATEX certifying laboratory.

The feasibility study is carried out upstream of the project, and during this phase it is not at all necessary to provide an electrical schematic, but only to have a good definition of the project with technical ideas as clear as possible, and also to imagine some more options and technical fallback solutions to be able to feed the discussion.

The feasibility study must certainly not be disregarded ; if it is seriously carried out, at the end of the discussion the ATEX technical solution will inevitably appear.

Looking to get in contact with a certifying laboratory is essential ; but if need be, it can also be done indirectly through a design office (e.g. TECHNETEA ...). It is necessary to keep in mind that the role of the certifying laboratory is not to provide the technical solutions but only to check if those proposed are in accordance with the requirements of the ATEX standards ; on the other hand, it is the role of the manufacturer or the design office to propose and find those solutions.

The document called "Feasibility Study" helps to establish the framework of the project, it must contain the following information :

- What is the use of the equipment ? Where is it installed ? How it is fixed ?

- How is it used ? Who is authorized to operate on the installation ?

- the ATEX Zone where the system is installed

- the ATEX gas Group and the ATEX temperature classification

- the ATEX type of protection which is considered

- the physical characteristics of the area where the material is installed

- particular recommendations

- the operating temperature range

- a brief description of the equipment, electrical as well as mechanical

- a diagram representing the connections with the other elements of the installation, and the ATEX Zones where they are installed

- the caracteristics of the power supply

- the types of the sensors which are connected. Are they ATEX certified ? Which ATEX type of protection do they use ?

- the types of the connectors

- a first idea of how the equipment will be constructed : SMD (Surface Mounted Devices), assembly, coating, enclosure, ...

Also remember to collect the datasheets of all the specific technical components which are used, in particular the ATEX certificates and the instructions manuals of the sensors.

Stage 2 : The design and the ATEX study on technical documents

After a preliminary technical study, the procedure must be initiated very early with the certifying laboratory, on the basis of a clear electrical schematic, a bill of materials, and a document called the Safety Analysis in which the designer justifies each point in relation with the ATEX type of protection which is used : the maximum voltages, the maximum powers, the calculation of the factors of safety required by the standards, the choice of the components and limiting devices, etc ...

It is always preferable that the technical choices are assessed and approved by the certifying laboratory in parallel with the design stage. Indeed, it would be completely ineffective to go too far in designing the project, if a technical main point were rejected ; a test failure can anytime completely ruin the project and make it return to its starting point.

Any point of the design involving high currents, capacitors-inductors couplings, must in case of doubt be taken into account to request for assessment to the certifying laboratory. The same process must be applied for the thermal tests, which can affect the layout on the printed circuit boards, the size of the heat sinks, and the ATEX temperature classification.

Do not forget : to discuss the enclosure, the arrangement of the elements inside the equipment, the enclosure material ; to enquire about the tests which will be carried out on the materials and the structures of the housing, on the sealing, on the coatings, ... ; to try to do in advance some tests internally if possible, or to request for preliminary tests to the certifying laboratory ; to plan the tests far in advance ; to do simulation tests ; to deal the assessment tests cautiously to avoid flashbacks.

During this stage, the transmitted documents are referenced in an index ; they constitute the bundle of design documents including :

- a documents index

- electrical schematics and mechanical drawings

- the bills of materials

- the safety analysis

- the datasheets of some special electrical components

- the datasheets of the materials

- if relevant, also reports of tests carried out internally

For its part, the certifying laboratory starts to gather the reports of the preliminary tests and assessments.

Stage 3 : The ATEX assessment of the prototype

This stage consists of tests on some finished parts of the equipment and finally on the prototype itself, as :

- measurements of clearances and separation distances, on the printed circuit boards

- temperature measurements on the final printed circuit board

- mechanical tests : drop tests, impact tests, wrench tests, IP code verification, endurance of the materials

- some assessments explicitly requested by the standards only on the complete equipment

All the conceivable tests must have been carried out during the previous stage to avoid a refusal at this point.

Stage 4 : The writing of the final documents and the issue of the ATEX certificate

All the documents provided till now were only related to the design phase, and are not part of the formal request for the ATEX certificate ; another set of documents is to be edited :

- the descriptive note : it describes the components and the materials which constitute the equipment, with a specific formalism rather like a declaration.

- schematics and drawings, with required information in relation to the ATEX type of protection

- the instructions manual and the declaration of conformity

Those official documents are dated and signed by the legal representative of the requesting company, and as this CEO said to the executive director when he saw him signing the ATEX documents : "Well !!! That way, you are the one who goes to jail if there's a problem !"

For its part, the certifying laboratory draws up its assessment report and again after internal verifications, finally delivers the ATEX certificate of the equipment.



A certification procedure can be stopped at the end of stage 1, if the goal is only to make a preliminary study. It can also be stopped at the end of stage 2, if the goal is to validate a technical subset for a future study ; in this case the certifying laboratory can deliver an informal document specifying that the set of transmitted documents has been assessed in accordance with the requirements of the standards, and that on this basis, nothing has been pointed out which could then prevent an ATEX certification.

It would be completely wrong to think that a certification is only a matter of procedure, ATEX is primarily a very meticulous technical approach ; but it would be just as wrong to think that a certification procedure is long and expensive. About cost saving and time reduction, there is only one rule : to be methodical.

The method described on this page is the one widely used ; even those who are perfectly familiar with designing for ATEX, and maybe it would be better to say, especially them, do not take the risk to do differently.