Category 3 Solutions1

For equipment being used in Zones 2 or 22 then an EU Notified Body or UK Approved Body does not need to issue Type Certificates or assess the solution. Category 3 equipment still needs to be compliant with the relevant Directives, Regulations and Standards and this can be declared by any ‘Competent’ person.
Known as ‘Self Certification’ this usually done by the supplier, system builder or manufacturer who must issue a Declaration of Conformity.

Unfortunately Category 3 solutions are regularly done incorrectly, usually through ignorance, bringing Competency into question with a consequent lack of confidence in the product or concept of 'Self Certification'.

Competent person

Competent Person

A competent person is someone who has sufficient training and experience or knowledge to carry out the assessment.
Competence is an attribute that is decision-specific, meaning that a person may be competent for some purposes and not for others.
For example, for a company with a track record of manufacturing hazardous area equipment would be generally be considered to have competent staff for similar equipment e.g. a hazardous areas enclosure manufacturer with there own certification for enclosures would probably be deemed competent to provide a Category 3 control panel solution as it is largely dependent on the enclosure certification

A company without experience of hazardous area solution and not holding certification type certificates in their own name would certainly require further investigation as to competence level.
A third party ‘expert’ could be used, but legal responsibility is primarily the person signing the Declaration of Conformity then the company directors. Of course using a recognised certifying company will mitigate some, but not all, risk.

Establishing competency is important to the end user as they have front end liability and use it to offset risk by to the Declaration of Conformity Signatory (and supplying company).



Declaration Requirements

Although a type certificate is the legal contract of compliance is the Declaration of Conformity which must be supported by a Technical File created with contents and procedures exactly the same as if it was being submitted to an approval body and the item marked the same including:

  • Full list of components with justifications for compliant.
  • Evidence of assessment and/or testing to the relevant standard(s)
    e.g. Temperature and power dissipation calculations,.
  • Unique part number or reference (often the Declaration of conformity Number.)
  • Item must have a fully compliant certification label(s).
  • Specific Hazardous area installation and usage instructions to be supplied with product

Category 3 Assemblies

For a fully intrinsically safe assembly using Ex i certified components (and simple apparatus) then a complete assembly certification is not usually required. However Descriptive System Documents for each I.S. loop are mandatory for all Hazardous Area Categories.
For all other protection methods an assembly certification is almost always required. All solutions are subject to the specific certification of its components or assessment in the technical file of uncertified components.

enclosure Examples are:

  1. HMI with certification Ex ec or similar
    Items such as Category 3 HMI’s2 often have special conditions attached to them typically “Must be mounted in a suitably certified enclosure".3 because they usually have unprotected connections at the rear.
    In this case No additional certification nor a new assembly certification label is required, the HMI certificate covers the required enclosure.
    In addition an Earth terminal could be added as it accepted that additional Earth Terminals do not affect certification.
  2. HMI with Terminals in the enclosure
    Add a single terminal (excluding Earth) then certification must apply to Enclosure, HMI and terminals and the assembly must have its own certification label albeit still Ex ec
  3. HMI with other certified components in the enclosure
    Again the assembly must have its own certification to include the specific protection methods4 of its contents e.g. Ex dec if it has Ex de lamps or pushbuttons

Optical Components
It is often overlooked but fibre optics are considered an ignition risk and must be certified. There is a protection method Ex op pr5, “Protected Optical regulation” which is based on the concept that there is no escape of radiation from the confinement. The confinement being the enclosure, therefore purely optical uncertified components can be included in the Category 3 assembly and suitably protected fibre optic cables used. The label will need to include this protection e.g. Ex  ec op pr.

Intrinsic Safety Associated Apparatus A full intrinsically safe solution does not require assembly certification but any associated apparatus within the assembly would generally require additionally Category 3 certification e.g. Ex ec Although it is perfectly acceptable to incorporate the intrinsically safe output into the assembly label e.g. Ex ec [ia]. It is also acceptable to not include the associated apparatus [ia] part on the enclosure label.
The Ex ec part is for the enclosure and contents, the Ex [ia] is relates the the circuit, independent of the enclosure protection and not germane to the assembly certification.


  1. . This is for UKEX and ATEX certification only. IECEX is product certification and therefore all equipment must be submitted for approval 

  2. A couple of manufacturers can supply Category 3 (or Cat 2) HMI’s which have full enclosed connections. 

  3. For most Category 3 solutions based on Ex n, Ex ec, Ex dc, or combinations.
    It is subject to the HMI certificate specification but a component approved enclosure, is normally sufficient. 

  4. If components use the older Ex na or Ex nc protection methods these can be included as Ex ec and Ex dc as the more recent version. 

  5. Other optical protection methods such as Ex op is (power limited) and Ex op sh can be used but they generally require certified components or are more difficult to demonstrate compliance.