Potentially Explosive Atmospheres

BS 5345. General Recommendations—Code of Practice for Selection, Installation and Maintenance of Electrical Apparatus for Use in Potentially Explosive Atmospheres. BSI, U.K. 

HS(Gj22 Electrical apparatus for use in potentially explosive atmospheres... 

Withdrawn) 1989 AMD 3 Code of practice for selection, installation and maintenance of electncal apparatus for use m potentially explosive atmospheres (other than mining applications or explosives processing and manufacture). Part 1 General recommendations (AMD 7871) dated 15 September 1993. Withdrawn, superseded by BS EN 60079-14 1997 (Withdrawn) 1978 AMD 1 Code of practice for selection, installation and maintenance of electncal apparatus for use m potentially explosive atmospheres (other than mining applications or explosives processing and manufacture). Part 6 Recommendations for type of protection. Increased safety (AMD 5557) dated 30 November 1989. Withdrawn, superseded by BS EN 60079... 

AMD 2 Electrical apparatus for potentially explosive atmospheres - General requirements (AMD 10552J dated August 1999. Partially superseded BS EN 50014 1993 which remains cuiTcnt... 

AMD 1 Electrical apparatus for potentially explosive atmospheres- Intrinsic safety i (AMD 10040J dated June 1998. Read with BS EN 50014 1993... 

BS5501 Electrical apparatus for potentially explosive atmospheres. 

When installing conductive nonmetallic piping and metallic pipe with nonmetallic linings, consideration should be given to the need to provide electrical continuity throughout the system and to grounding requirements. This is particularly critical in areas with potentially explosive atmospheres. 

The main issue here as regards to SRVs is the Guidelines on the Application of Directive 94/9/EC of 23 March 1994 on the approximation of the laws of the Member States concerning equipment and protective systems intended for use in potentially Explosive Atmospheres Second edition - July 2005. The paragraph affecting SRVs is the section on what is called simple products (including simple valves), which remains in the guidelines and reads as follows ... 

Due to the quite different structures of industrial plants equipped with electrical installations, there are different probabilities for the existence of potentially explosive atmospheres formed by gas-air, vapour-air or dust-air mixtures. With respect to economical reasons, the types of explosion protection for electrical apparatus and systems will depend strongly on the explosion risk at the installation point. It is very unusual to construct and build all explosion protected electrical apparatus in such a manner that they can operate permanently in a surrounding hazardous atmosphere with combustible gases, vapours and dusts in air. The common way is to classify different areas in industrial plants according to the probability for the existence of a hazardous atmosphere and to establish adequate types of explosion protection. In other words, industrial plants with potentially explosive atmospheres are divided and classified into zones. ... 

SC 31-9 Electrical apparatus for the detection and measurement of combustible gases to be used in industrial and commercial potentially explosive atmospheres... 

One of the primary contents of the Treaties of the European Community (EC) is the elimination of trade barriers for technical equipment. These barriers have been based on different technical standards (and their legislation) in the member states of the EC. Referring to article 100 of the Treaties of the EC, some directives have been issued in order to harmonize the standardization for technical products (explosion protected electrical apparatus and systems, elevators). These directives describe precisely the technical requirements and list the relevant standards, in the field of explosion protection CENELEC Standards exclusively. Directive 82/130/EEC refers to mines endangered by firedamp and/or combustible dusts, and Directive 76/117/EEC covers areas hazardous due to potentially explosive atmospheres. The member states of the EC shall transform these directives into their national legislation within 18 months. 

Table 3.8 List of notified bodies in the European Union for type testing and certification of electrical equipment for potentially explosive atmospheres...

EIZulBergV [9], issued by the Federal Minister for Economic Affairs, covering areas in coal mines endangered by firedamp, and areas hazardous due to potentially explosive atmospheres in the field of mining (except coal mines), with the exception of surface installations. 

A main effort to facilitate international trading and commissioning of electrical apparatus for use in (potentially) explosive atmospheres has been undertaken the so-called IECEx-Scheme the IEC Scheme for Certification to Standards for Safety of Electrical Equipment for Explosive Atmospheres eliminates the need... 

Table 5.1 Types of protection electrical apparatus for potentially explosive atmospheres (zone 1)...

An enclosure whose interior is filled with air (without any combustibles) or inert gas, e.g. nitrogen, argon, carbon dioxide or sulphur hexafluoride showing a positive pressure differential to the environmental potentially explosive atmosphere, indicates the very general principle of pressurization. The same concept is applied to clean rooms in semiconductor manufacturing or in pharmaceutical production. Gases, vapours, mist or even dust are prohibited to penetrate into the interior of such a clean room or pressurized enclosure. 

Caution needs to be taken with local pressure variations of the environmental atmosphere. A well-known example is the outlet side of an external cooling fan of a surface-cooled motor or generator (see Fig. 6.15). At this point, the environmental potentially explosive atmosphere shows an increased pressure, which shall be overcompensated by an adequate internal overpressure. The p-standards ask for a minimum overpressure of 50 Pa (=0.5mbar) for Group I p-apparatus or Group II p-apparatus in zone 1. 

So, a purging process (performed with the protective gas maintaining the positive pressure differential during operation) shall flush the hazardous mixture inside the p enclosure before energizing the apparatus. More precisely during the purging process, and with air as protective gas, the potentially explosive atmosphere inside the enclosure shall be diluted to a safe value of gas concentration, i.e. 25 per cent of LEL, or, with inert gas as protective gas, the oxygen content of the atmosphere inside the enclosure shall be reduced to 2 per cent (v/v). 

To enable an effective purging, the protective gas flow direction during purging should support the escape of the unwanted atmosphere by an appropriate combination of purging flow direction and gas density (the potentially explosive atmosphere, i.e. a gas-air mixture, compared with the protective gas) ... 

Caution shall be given to avoid any mechanical damage of the tube of fluorescent lamps, not only when fitted inside the luminaire (and in operation), but also during transportation in a potentially explosive atmosphere. 

Accumulators in increased safety - e - cover traction batteries for locomotives in coal mines (see Fig. 6.4) as well as batteries for forklifts in chemical plants or other transportation vehicles running in hazardous areas powered by their own energy storage system. Much smaller accumulators are used as a mains-independent power source for handlamps and caplamps (Fig. 6.65) used in potentially explosive atmospheres. 

In addition, surface temperatures shall be limited to prevent any ignition of the potentially explosive atmosphere. All components (including the wiring)... 

Code of practice for the installation and maintenance of electrical apparatus for use in potentially explosive atmospheres (other than mining applications or explosives processing and manufacture), 8 parts. 

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