A GUIDE TO EUROPEAN (EEC) CERTIFICATION FOR ELECTRICAL EQUIPMENT IN HAZARDOUS AREAS For a print friendly page click here INTRODUCTION Hazardous areas are those in which there exists a risk of explosion because flammable atmospheres are likely to be present. These conditions can be man-made as in Petrochemical plants or Refineries, or occur naturally, as in coal mining. It is therefore necessary to insure that all electrical equipment and instrumentation installed in a hazardous area cannot form a spark, or hot surface, which would ignite the flammable atmospheres. Before electrical equipment or instrumentation can be used in a hazardous area, it must b e tested and approved by a recognized testing authority. Should the equipment pass this examination, then a Certificate of Conformity is issued which specifies the limits of use of the apparatus. ZONES Hazardous areas are classified into "Zones" according to the degree of risk. Zone 0 - where an explosive atmosphere is continuously present for long periods. Zone 1 - where an explosive atmosphere is likely to occur in normal operation. Zone 2 - where an explosive atmosphere is not likely to occur in normal operation and if it occurs it is only present for a short period. Zone 10 - where explosive dusts are present constantly or for long periods. Zone 11 - where explosive dusts are present occasionally. GASES Gases are grouped together according to their degree of hazard. This is based on the amount of energy required to light the gas/air mixture. Gas Group I (mining) IIA (Surface) IIB (Surface) IIC (Surface) Representative Gas Methane Propane Ethylene Hydrogen TEMPERATURE
A gas/air mixture can ignite when it comes into close contact with an excessively hot surface. The surface temperature at which equipment operates is therefore of crucial importance. This equipment is temperature classified as follows: Temp. Class T1 T2 T3 T4 T5 T6 Max. Surface Temp. 450 degrees C 300 degrees C 200 degrees C 135 degrees C 100 degrees C 85 degrees C TEMPERATURE/GAS CLASSIFICATION The following chart gives the minimum temperature class of equipment for use in the various gases most commonly found in hazardous areas. Gas T1 T2 T3 T4 T5 T6 Group I Methane IIA Acetone Ethyl alcohol Petrol Acetaldehyde Ethane I-Amyl acetate Diesel Ethyl-ether Ethyl acetate N-hexane Aviation fuel Ammonia N-butane Heating oil Benzol N-butyl-alcohol Acetic acid Carbon Monoxide Methanol Propane Toluene IIB Town gas Ethylene IIC Hydrogen Hydrogen Disulfide e.g. T6 rated equipment can be used in any of the above gases but for example, T4 rated equipment can only be used in T1 - T4 applications APPARATUS SELECTION WITHIN ZONES
Zone Zone 0 Zone 1 Zone 2 Suitable Apparatus Exi 'a', some Exs All types except Exn All types APPARATUS MARKING The following information should appear on "explosion protected" electrical equipment installed in hazardous locations: Information Typical Example 1. The manufacturer's name MEDC, Zellweger Analytics, Fire Sentry Corporation 2. The model designation Manual Call Point Type BG2 3. Code (Cenelec standard) EEx 4. The type of protection edm 5. Gas Group IIC 6. Temperature Classification T4 7. Serial number A005 8. Certifying Authority Certificate No. 9. Cenelec symbol 10. British standard symbol BASEEFA No. Ex92C3166 11. Electrical rating Max amps 0.2, Max. volts 254 TYPES OF EXPLOSION PROTECTION There are various methods used to prevent electrical apparatus from igniting the surrounding atmosphere when energized. Flameproof Enclosures - Ex protection type 'd'. (EN50018, BS5501 Part 5). Equipment that could ignite an explosive atmosphere is housed within a substantial enclosure. This is capable of containing an internal explosion without transmitting that explosion to the surrounding explosive atmosphere. Increased Safety - Ex protection type 'e'. (EN50019, BS5501 Part 6). Increased measures are taken to prevent the generation of arcs, sparks and excessively hot areas in equipment, thus preventing the risk of explosion inside or outside of the enclosure.
Intrinsic Safety - Ex protection type 'i'. (EN50020, BS5501 Part 7). Power is limited to this equipment in such a way that a spark or a hot surface would not be hot enough to ignite the explosive atmosphere. Pressurized or Purged - Ex protection type 'p'. (EN50016, BS5501 Part. 3). Here the concept used is to house the equipment in an enclosure, which is pressurized or purged by inert gas, thus preventing an explosive atmosphere from reaching the equipment. Oil Immersion - Ex protection type 'o'. (EN50015, BS5501 Part 2). All equipment is totally immersed in oil, thus preventing an explosive atmosphere from reaching the equipment. Powder Filled - Ex protection type 'q'. (EN50017, BS5501 Part 4). All equipment is totally immersed in powder, thus preventing an explosive atmosphere from reaching the equipment. Non-Sparking and Restricted Breathing - Ex protection type 'n' or 'N'. (BS4683 Part 3). This gives a level of protection by housing electrical equipment in substantial enclosures that inhibit mechanical damage and give some degree of ingress protection. Special Protection - Ex protection type 'S'. This applies to items of equipment not entirely covered by any of the foregoing concepts but one that can clearly be demonstrated to be explosion protected. Moulded/Encapsulated - Ex protection type 'm'. EN50028, BS5501 Part 8). The apparatus is totally encapsulated by a non-porous compound. Electrical connection is by flying leads. CODES AND PRACTICES FOR SELECTION, INSTALLATION & MAINTENANCE OF EXPLOSION PROTECTED EQUIPMENT The correct selection, safe installation and maintenance of explosion protected equipment is of the utmost importance. Always follow the relevant standards of the country where electrical equipment is to be installed, as local requirements vary from country to country. The selection of the correct type of cable gland is critical. Please refer to the local codes and standards for the types that may be used. Corrosion can attack flamepaths and render an enclosure unsafe. Care must be taken to prevent or reduce corrosion where possible. Spares for, and repairs to explosion protected equipment should be obtained from the original equipment manufacturer to ensure compliance with explosion protection area certification of that equipment.
TESTING AUTHORITIES Region Testing Authority Country Marks Used EEC All All BASEEFA UK SIRA UK SCS PTB BVS Germany Germany Cherchar France MS AE LCIE France CESI Italy AD-PE INIEX Belgium Ex DEMKO Denmark Ex Laboratorio Oficial Spain - N. America Underwriters Laboratories USA Factory Mutual USA CSA Canada CENELEC/NORTH AMERICAN STANDARDS COMPARISON (For general guidance only) CENELEC N. America Zone 0 Class 1, Division 1 Zone 1 Class 1, Division 1 Zone 2 Class 1, Division 2 INGRESS PROTECTION 2 digits are used to denote the level of ingress protection ("IP rating") that a piece of electrical equipment meets. Solids 0 No protection. 0 No protection. Liquids
1 Protected against solid objects up to 50mm, e.g. hands. 1 Protected against vertically falling drops of water. 2 Protected against solid objects up to 12mm, e.g. fingers. 2 Protected against water spray up to 15 degrees from vertical. 3 Protected against solid objects up to 2.5mm, e.g. tools. 3 Protected against water spray up to 60 degrees from vertical. 4 Protected against solid objects up to 1mm, e.g. wires. 4 Protected against water sprays from all directions. 5 Protected against dusts. (No harmful deposits). 5 Protected against water jets from all directions. 6 Totally protected against dust. 6 Protected against strong water jets from all directions, e.g. Offshore. 7 Protected against immersion between 15cm and 1meter in depth. 8 Protected against long immersion under pressure For example, an IP67 rating would mean that the equipment is "totally protected against dust" (Solid rating of 6), and is "protected against immersion between 15cm and 1 meter in depth" (Liquids rating of 7). For a print friendly page click here