[1] NEC article 500 describes the NEC Division classification system, while articles 505 and 506 describe the NEC Zone classification system. Class defines the general nature (or properties) of the hazardous material in the surrounding atmosphere. Zone 2: An area in which an explosive atmosphere is not likely to occur in normal operation, but if it does . The two general approaches are: Several techniques of flame-proofing exist, and they are often used in combination: Equipment has flameproof gaps (max 0.006" (150m) propane/ethylene, 0.004" (100m) acetylene/hydrogen), Equipment can be installed in ANY housing provided to IP54.A 'Zener Barrier', opto-isolator or galvanic unit may be used to assist with certification. Hazardous Environment Classifications: NEC vs IEC, IEC (International Electrotechnical Commission), Group E Metal dusts (eg. Then, the level of risk of an explosion is based on the frequency and duration of the occurrence of an explosive atmosphere. It is good to be aware of the fact that the mixture of flammable gas with oxygen has an optimum point where the combustion is most severe and leads to the highest explosion pressure. Guidance on assessment of hazards is given in NFPA497 (explosive gas) and NFPA499 (dust). August 2018 taper per foot. Comments. Zone 0: flammable atmosphere highly likely to be present - may be present for long periods or even continuously . . National Electrical Code, NFPA 70, Chapter 5, Article 500, 29 CFR 1910 Subpart S, Electrical 1910.307, NFPA 497, "Classification of Gases, Vapors, and Dusts for Electrical Equipment in Hazardous Classified Locations", NFPA Handbook, "Electrical Installations in Hazardous Locations, " by P. J. Schram and M. W. Earley, NFPA 70E, Chapter 5, "Hazardous (Classified) Locations", ANSI/UL 913, "Intrinsically Safe Apparatus", NFPA 496, "Purged and Pressurized Enclosure for Electrical Equipment in Hazardous Locations. Atmospheres containing combustible flyings. | For Gas/Vapor this would be Zone 0. gas, vapours, mists and dusts). For methane this is shown in the following figure. Zone 2 is a place in which an explosive atmosphere is not likely to occur in normal operation but, if it does occur, will persist for a short period only. Non-hazardous or ordinary locations. Class II combustible dusts are grouped into one of three (3) groups: E combustible metal dusts, F combustible carbonaceous dusts or G other combustible dusts. Ignitable concentrations of flammable gases or vapors which are not likely to occur under normal operating conditions and do so only for a short period of time. Equipment meeting one or more of the protection techniques described in paragraph (g)(3) of this section shall be marked with the following in the order shown: Class, except for intrinsically safe apparatus; Zone, except for intrinsically safe apparatus; Occupational Safety and Health Administration, Outreach Training Program (10- and 30-hour Cards), OSHA Training Institute Education Centers, Severe Storm and Flood Recovery Assistance. In this system, two bare wires were run along the length of a drift, and any miner desiring to signal the surface would momentarily touch the wires to each other or bridge the wires with a metal tool. The use of EPL and ATEX Category directly is an alternative for "s" marking. 0. Atmosphere containing a flammable gas, a flammable liquid produced vapor or a combustible liquid-produced vapor whose MESG is greater than 0.75 mm or MIC ratio is greater than 0.40 and less than 0.80 - such as carbon monoxide, ether, hydrogen sulfide, morphline, cyclopropane, ethyl, isoprene, acetaldhyde and ethylene or gases of equivalent hazard. Division defines the probability of the hazardous material being present in an ignitable concentration in the surrounding atmosphere. Atmosphere containing carbonaceous dusts, Atmosphere containing combustible dust not included in Group E & F - such as. Note to paragraph (g)(4) of this section: Low ambient conditions require special consideration. 2: This classification includes, Informational Note No. These applications will - due to browser restrictions - send data between your browser and our server. Fundamentally, for an explosion to take place, flammable or explosive gases, vapours, mists or dusts will be present. Motors, lighting, junction boxes, electronic equipment, This method, being by definition special, has no specific rules. But first, we must consider what is likely to cause an explosion in the first place. As mentioned, the first important step of achieving a safe work environment in relation to explosion safety is to identify and classify those areas, where a concentration of flammable gases or vapors within the flammable range can be present. The Zone system is based on Article 505/506 of the National Electrical Code (NEC) and follows the international method of area classification as developed by the International Electrotechnical Commission (IEC). Zone 0 - Explosive atmospheres present continuously long periods or frequently. July 2020 Under the "Zone" system, hazards are defined for gas as Zone 0, 1 or 2, with 0 as the highest hazard, and for dust as Zone 20, 21 or 22, with 20 as the . NEC 2 Divisions (Div 1 2) Division I Comprising of Area Same as Zone 0 1. This value of this LOC differs per substance and depends also on the inert gas for achieving a low oxygen concentration. One of the hazards of working with flammable substances is an explosion, mostly hand in hand with fire. The four steps involved in hazardous area classification are: Determine the type of hazard or "class" that might be presentcombustible gas (Class I), combustible dust (Class II), or fibers (Class III). Ignitable concentrations of flammable gases or vapors which are likely to occur under normal operating conditions. NFPA 70, the National Electrical Code (NEC), defines area classification and installation principles. 4: For further information on protection against static electricity and lightning hazards in hazardous (classified). Electrical equipment installation in atmosphere with flammable gases or vapors, flammable liquids, combustible dusts, ignitable fibers or flyings represents a risk for fire and explosion. The Zone system has wider use in the chemical and petrochemical industries. Flour, wood/sawdust, plastic dust). Zone defines the general nature - if it is a gas or dust - and the probability of hazardous material being present in an ignitable concentration in the surrounding atmosphere. A Zone 1 hazardous area is classified as a place in which an explosive atmosphere consisting of a mixture with air or flammable substances in the form of gas, vapour or mist is likely to occur in normal operation occasionally. Area ClassificationThe max surface temp. The American Petroleum Institute publishes analogous standards in RP500 andRP505. Area classification documentations are reviewed and updated to reflect process changes. Although OSHA does not provide a definition of group classifications in 29 CFR 1910.307 or 399 they do provide a note under 29 CFR 1910.307(c)(1) that states: NFPA 70, the National Electrical Code, lists or defines hazardous gases, vapors, and dusts by Groups characterized by their ignitable or combustible properties. To meet OSHAs marking requirement, the marking must include the hazardous group the equipment is approved to operate in. Equipment construction is such that it can withstand an internal explosion and provide relief of the external pressure via flamegap(s) such as the labyrinth created by threaded fittings or machined flanges. The disadvantage of standards with example installations, is that a huge safety factor is incorporated and thus relative large hazardous area are defined. Class I, Zone 0 = Area Classification, AEx = Symbol for equipment built to American specifications, ia = Type of protection designations, IIC = Gas classification group (as required), T6 = Temperature Classification, [46 FR 4056, Jan. 16, 1981; 46 FR 40185, Aug. 7, 1981; 72 FR 7210, Feb. 14, 2007], Occupational Safety & Health Administration. . Independent test housesNotified Bodiesare established in most European countries, and a certificate from any of these will be accepted across the EU. Zone defines thegeneral nature if it is a gas or dust and theprobabilityof hazardous material being present in an ignitable concentration in the surrounding atmosphere. Some manufacturers claim "suitability" or "built-to" hazardous areas in their technical literature, but in effect lack the testing agency's certification and thus unacceptable for the AHJ (Authority Having Jurisdiction) to permit operation of the electrical installation/system. For explosion hazards caused by flammable liquids or gases, the following zones are defined: So a zone 0 is the most hazardous zone and a zone 2 is a less hazardous zone. EN 16985 concerning spray cabins and powder coating cabins, EN 12779 related to extraction systems for hot sawdust and chips, EN 60079-10 series, 2020 version for gas and dust explosion hazard, NPR 7910 series for gas and dust explosion hazard based on EN 60079-10-1, 2015 version, EN 13617 for fuel dispensers at filling stations. Exception No. A Zone 0 location is a location in which one of the following . The Occupational Safety and Health Administration (OSHA) has adopted these hazardous classifications and all except Groups are defined in 29 Code of Federal Register (CFR) 1910.399. October 2021 We don't save this data. April 2022 This level of risk is represented by classifying the hazardous area as Zone 0, Zone 1 or Zone 2 (for gas, vapour and mist atmospheres) or Zone 21 or Zone 22 for dust atmospheres. Hazardous areas are defined as: " Zones " under worldwide IEC standards (and their local versions, such as ATEX in Europe) " Divisions " under North American NEC standards. To minimize the risk of these fires or explosions, electrical/electronic equipment must be designed, tested and labeled as being acceptable for use in the areas in which it is installed. Zone 0, 1, and 2 locations are those in which flammable gases or vapors are or may be present in the air in quantities sufficient to produce explosive or ignitible mixtures. Atmosphere containing flammable gas, flammable liquid produced vapor, or combustible liquid produced vapor mixed with air that may burn or explode, having either a MESG value greater than 0.75 mm or a MIC ratio greater than 0.80 - such as gasoline, acetone, ammonia, benzene, butane, ethanol, hexane, methanol, methane, vinyl chloride, natural gas, naphtha, propane or gases of equivalent hazard. Zone 1 (unless separated by a fire wall)P.G.Sreejith, Kerala. No. Informational Note No. In the US, the National Electrical Manufacturers Association (NEMA) defines standards for enclosure types for a variety of applications. These generally give rise to areas classied as Zones 0, 1, and 2 respectively. 10: For information on electrical resistance trace heating for hazardous (classified), Informational Note No. Arc-producing elements can be isolated from the atmosphere, by encapsulation in, Heat-producing elements can be designed to limit their maximum temperature below the. Upon detection, appropriate action is automatically taken, such as removing power, or providing notification. ethanol, methane or hydrogen. 3: For further information on the classification of, Informational Note No. The Zone system of hazardous area classification, defines the probability of the hazardous material, gas, or dust, being present in sufficient quantities that can generate explosive or ignitable mixtures. Zone 2 - Explosive atmospheres are unlikely to occur or present only infrequently and for a short period only. Have a think about it next time youre filling up! Such areas include a residence or office where the only risk of a release of explosive or flammable gas would be such things as the propellant in an aerosol spray. Flameproof "d" - This protection technique is permitted for equipment in the Class I, Zone 1 locations for which it is approved. Equipment approved for Class I, Division 1 or Class 1, Division 2 shall, in addition to being marked in accordance with (c)(2)(ii), be marked with the following: Class I, Zone 1 or Class I, Zone 2 (as applicable); Applicable gas classification groups; and. Electric equipment depending on the protection techniques described by paragraph (g)(3)(i) of this section may not be suitable for use at temperatures lower than -20 C (-4 F) unless they are approved for use at lower temperatures. . Note to paragraph (g)(5)(ii)(B) of this section: An example of such a required marking is "Class I, Zone 0, AEx ia IIC T6." Informational Note No. That is why the use of mobile phones on petrol forecourts are banned.
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