Written by Kieran Fallon, a Chartered Engineer and Fellow of Engineers Ireland with over 30 years’ experience in electrical design and ATEX installations. He sits on the NSAI Committee responsible for Irish & IEC Standards associated with Hazardous Areas (ATEX). Kieran works for the DPS Group, a global consulting, engineering and construction management company.
Any engineer or electrician working on the design or installation of electrical systems needs to be competent. This is especially true when working with potentially explosive atmospheres. It is expected that such an ATEX professional would maintain, or have access to, a reference library including IEC / NSAI standards.
The key reference document used to be the ET 105 document, however the National Rules for Electrical Installations in Hazardous Areas ET 105:2011 has been withdrawn for some time now. It has been replaced with a number of separate documents including I.S. EN60079I.S. EN 60079–14 (Part 14) which provides a common installation standard for ATEX installations in Ireland.
I.S. EN 60079-14, Explosive atmospheres – Part 14: Electrical installations design, selection and erection
I.S. EN 60079-17, Explosive atmospheres – Part 17: Electrical installations inspection and maintenance
I.S. EN 60079-19, Explosive atmospheres – Part 19: Equipment repair, overhaul and
I.S. EN 60079–25, Explosive atmospheres – Part 25: Intrinsically safe electrical systems
IEC TS 60079-32-1 Electrostatic hazards, guidance
I.S. EN 80079–36 Explosive atmospheres – Part 36: Non-electrical equipment for explosive atmospheres – Basic method and requirements
I.S. 60079-10-1, Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres
I.S. 60079-10-2, Explosive atmospheres – Part 10-2: Classification of areas – Combustible dust atmospheres.
I.S. 10101, National Rules for Electrical Installations
NSAI Initial Inspection Guidance Document (due for publication 2021)
I.S. EN 60079-14
The I.S. EN 60079 Part 14, as with the complete I.S. EN 60079 series, deals only with electrical installations, mechanical installation requirements are included in the I.S. EN 80079 series of standards. The installation designer is however expected to be familiar with both electrical installation requirements and mechanical installation requirements.
As would be expected, considering its title, Part 14 addresses each of the ATEX protection types under the headings of design, selection and installation. Statutory requirements for substitution, control and mitigation measures which, must be considered under the ATEX worker safety directive, are repeated. Part 14 also defines documentation required for an installation including the Verification Dossier (similar to the Explosion Protection Document in European Community jurisdictions) and ATEX Hazardous Area Classification. Part 14 is explicit on the requirements for documenting an installation and includes sample initial inspection schedules. A comprehensive initial testing document is currently under development and is due to be published early 2021. It will address in detail the requirement that before plant or equipment is brought into service, it must be given an initial detailed inspection.
Personnel competency is addressed in Part 14 which requires that those responsible for the design of installations and the installation works associated with them have an in-depth knowledge of the equipment and protection types. It should be noted that work is in progress in the IEC Committees to develop a specific ATEX competency document, IEC TS 60079–44, which will address this subject in more detail. The competency of the designers and installers must be verified, and this verification recorded. Establishing competency and keeping records of same is not unique to Part 14 or ATEX installations and as there are already well-established procedures within the Irish construction industry in particular associated with BCAR, emergency lighting (I.S. 3217) and fire detection systems (I.S. 3218). Setting out the requirements for competency in a specific standard should establish a common assessment of ATEX professional’s training, qualifications and experience. Currently, for installations in Ireland, competency should be recorded on the project test certificate, the typical contents of which are available on the Health and Safety Authority website. However, a template for recording the initial detailed inspections of an ATEX installation is underway.
Earthing and bonding are addressed in detail in Part 14. Bonding of cable screens and armour where the only bonding point is outside the Hazardous Area for example a control room, is addressed (the bonding point of the cable must be cross bonded to the earthing system in the Hazardous Area). Electrostatic hazards are not addressed within Part 14 and the ATEX professional must refer to another part of the 60079 suite of documents, i.e. I.S. EN 60079–32-2 and S.R. CLC/TR 60079–32-1.
In addition to addressing each type of protection used in ATEX Hazardous Areas, Part 14 addresses the use of Ex Equipment not based on IEC standards. The procedure is effectively certification by the end user. In theory a similar route may be this available for ATEX installations but will apply Zone 2 or Zone 22 areas only since the ATEX directive prohibits certification of equipment in other zones by anyone other than Notified Bodies. The use of such equipment is restricted to items that cannot be obtained with ATEX certification. This of course does not apply to non-electrical equipment which, except combustion engines in Zone 1 and Zone 21, don’t need Notified Body Certification albeit that a dossier on them must go to the NB.
Repair of ATEX equipment is covered in I.S. EN 60079-19 but the selection of used and/or repaired equipment falls within the scope of Part 14. In ATEX areas, although not mentioned in the standard, use a of second-hand and repaired equipment is restricted to those items previously carrying ATEX certification.
Part 14 is not a ‘standalone’ set of installation rules and must be read in addition to I.S. 10101. Working on electrical installations subject to the National Rules for Electrical Installations is considered as Controlled Works by the Commission for Regulation of Utilities and as such may only be carried out by a competent REC (Registered Electrical Contractor). Definitions of Controlled Works and REC are available on the CRU website.
I.S. EN 60079 Part 17
As with Part 14, I.S. EN 60079-17 (Part 17) Electrical installations inspection and maintenance supplements the requirements of NSAI I.S. 10101:2020 The National Rules for Electrical Installations.
The primary objective of Part 17 is to ensure that the installations are maintained in a satisfactory condition for continued use within a hazardous area, either:
a) regular periodic inspections, or
b) continuous supervision by skilled personnel.
As with the Part 14 the inspection and maintenance regimes require the personnel are suitably qualified and competent.
Documentation and recording of inspection activities is an important requirement of any maintenance regime and is included in the scope of Part 17. Inspection is addressed for each type of ATEX protection with sample inspection, sheets included.
The Part 17 standard addresses the complex issue of inspection and verification of unmarked equipment. That is where the certification plate or markings on explosion protected equipment is missing or illegible. Alternative methods may be used to determine traceability to the certification details of the specific equipment. Use of an equipment tag to trace the original purchase paperwork is a typical route followed by inspection teams to establish details. Where it is not possible to establish thorough documentation or inspection the certification of an item of equipment an assessment, following the procedure within Part 17 may be followed.
S.R. CLC/TR 60079–32-1
Whereas Part 14 and Part 17 address the control of ignition sources associated with equipment in hazardous area and various forms of protection Ex-d, Ex-e, Ex-i etc. they do not address in detail the potential ignition due to static discharges. To assist with the control of static the NSAI has published guidance S.R. CLC/TR 60079-32-1 (Part 32) on how to avoid ignition hazards arising from static electricity.
Static electricity is generated by the contact and separation of solids e.g. the movement of conveyor belts; the flow of liquids or powders, and the production of sprays. The accumulation of electrostatic charge can give rise to hazards including ignition of explosive atmospheres. It is general good practice to minimise the use of insulating materials in hazardous areas. All metal and other conductive or dissipative material should be connected to earth. Capacitance is the key parameter that needs to be controlled. The maximum allowable capacitance of isolated items depends on the ignitability of the gases, vapours and dust and should be controlled or eliminated.
Isolated conductors such as metal tanks, tank structures or mobile vessels associated with liquid handling can be raised to high potentials by charges on the liquid. This can lead to spark discharges which are particularly hazardous because they can usually ignite flammable vapours.
People who are isolated from earth (typically due to insulating footwear or floor) can acquire and retain an electrostatic charge. Charging mechanisms include walking, handling plastics, standing close to highly charged objects.
If an electrostatically charged person touches a conductive object (e.g. pipework, structural steel, metal vessel) a spark can occur at the point of contact. Such sparks, which are unlikely to be seen, heard or even felt by the person, can cause ignitions. Sparks from a person are capable of igniting gases, vapours and even some of the more sensitive dusts. It is very important that people who may be exposed to flammable atmospheres having Minimum Ignition Energy (MIE) < 10 mJ should be prevented from becoming electrostatically charged by being earthed. This is best achieved by having a conductive or dissipative floor and ensuring that people wear dissipative footwear.
I.S. EN 60079-25
Every component part and system (product) used in an ATEX Hazardous Area has associated with it calculations to prove the safety integrity of the system. For the majority of components these calculations are carried out by the manufacturer as part of Technical File submitted to the Notified Body for certification. Intrinsically safe systems are generally designed as part of the installation and the designer must produce calculations to prove the safety of the system. These calculations referred to as a Descriptive System Document (DSD) confirms power supply, acceptable inductance and capacitance, and cable parameters. Details of how to produce DSD is contained within Part 25.
Part 25 also requires that compliance of an intrinsically safe system is demonstrated by the consideration of the following:
a) correct ATEX hazardous area, zone, grouping and temperature class;
b) correct device for ambient temperature range;
c) comparison of input and output characteristics and parameters of the device;
d) cable parameters of the interconnecting wiring;
e) faults within cables containing a single multi-drop circuit;
f) faults within cables containing multiple intrinsically safe circuits;
g) suitability and influence of simple apparatus;
i) earthing and bonding.
I.S. EN 60079-10 (Part 10)
In the suite of EN 60079 standards two documents define the methodology for area classification. These documents I.S. EN 60079-10-1 and I.S. EN 60079-10-2 describe the procedures associated with the area classification for gas/solvent vapours and dusts/powders respectively.
Although hazardous area classification is carried out competent personnel with particular skills and training this it is important that designers and installers are aware of the methodology involved in the selection of zones. Hazardous area classification is a method of analysing and classifying the environment where explosive gas atmospheres may occur, to facilitate the proper selection, installation and operation of equipment to be used safely in that environment. The classification also takes into account the ignition characteristics of the gas, vapour or dusts. The properties of vapours and gases are available in another document I.S. EN 80079-20 (Explosive Atmospheres – Material characteristics for gas and vapour classification – Test methods and data). Hazardous area classification has two main objectives, the determination of the type of any zone, and the extent of the zone. It should be reviewed on a regular basis and generally recommended that an annual review take place.
Both ATEX legislation and standards require that installations should be designed, constructed, operated and maintained so that any releases of flammable substance, and consequently the extent of hazardous areas, are kept to a minimum, with regard to frequency, duration and quantity of a release.
In addition to general Hazardous Area Classification the concept of zone of negligible extent for gas and vapours is addressed. In some cases, a zone of negligible extent (NE) may arise and may be treated as non-hazardous. A zone of negligible extent would also imply either a negligible release rate or a negligible release quantity and considering the volume for dispersion. Such a zone implies that an explosion, if it takes place, will have negligible consequences.
I.S. EN 80079–36
It is essential that the designers and installers working with potentially explosive atmospheres are aware of the mechanical sources of ignition be taken into account in addition to the electrical sources of ignition. To assist with this the I.S. EN 80079 series of standards, which replaced I.S. EN 13463, address the requirements and protection concepts for mechanical explosion protected equipment. I.S. EN 80079-36 covers the basic requirements for design, construction and testing of most non-electrical equipment with potential ignition source.
More detailed guidance on ATEX compliant mechanical equipment can be found in other sections of I.S. EN-80079 addressing Nonelectrical type of protection constructional safety “c”, control of ignition source “b”, liquid immersion “k”.
Competency and Knowledge
Competency, for an ATEX professional, is generally taken as based on a combination of knowledge, training and experience. Some of the required knowledge is contained within the reference library maintained by the ATEX professional. This article seeks to outline some of the key documents which should be available to those working in ATEX environments.
Considering the high level of technical content within the standards there is little alternative to having access to current copies of the standards.
The standards referenced in this article can be purchased from the National Standards Authority of Ireland, NSAI.