Electric.ie Jan/Feb 2021

46 ELECTRIC.IE • The Magazine & Website for the Irish Electrical Industry • 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. https://shop.standards.ie/ Industry News <<<Continued from page 45