(Pty) Ltd CERTE Appointed Ex Laboratory Reg No: 1999/027771/07 Government Appointed ATL T0104 PO Box 467 Tel: +27 (11) 316 4601 Olifantsfontein Fax: +27 (11) 316 5670 1665 E- mail: info@explolabs.co.za Inspection of in-service Explosion Protected Equipment - Unsafe Conditions and Cures Presented by Johannes Auret, Explolabs and CERTE SAFA SYMPOSIUM 2011 CTICC CONSULTIING Testing and Certification Certification Mark for Explosion Protected (Ex) Equipment Area Classification / Explosion Risk Assessment Inspection of New or In-service Ex Equipment & Installations Management System for Ex Installations Consultation Presentations & Workshops Training Courses
Page 2 of 29 INDE TOPICS Page 1. Introduction... 3 2. Questions to be answered... 3 3. Definition of Inspection... 3 4. Standards / Info Basis... 3 5. GRADES of inspection... 4 6. TYPES of inspection... 5 7. Generic Inspection Sheets... 6 8. Conclusions... 25 Annex A Equipment selection... 26
1. Introduction INSPECTION OF IN-SERVICE EPLOSION PROTECTED EQUIPMENT Page 3 of 29 The inspection of Explosion Protected (Ex) Equipment, together with appropriate maintenance and repair, is critical for safety. This paper highlights the differences between electrical and Ex inspections and presents some solutions based on standards covering the subject and best practice from experience. 2. Questions to be answered 1. Q: What is the PURPOSE of an Ex inspection? 2. Q: We know we need to inspect in-service Ex equipment at least once in 2 years (periodic inspection). - What Grade of inspection must be used (V/C/D). 3. Q: When must additional inspections be done? 4. Q: Who is competent to do inspections? 3. Definition of Inspection Action comprising careful scrutiny of an item carried out either without dismantling, or with the addition of partial dismantling as required, supplemented by means such as measurement, in order to arrive at a reliable conclusion as to the (suitability and) condition of an item. 4. Standards / Info Basis Legal Compliance Standard SANS 10086-1 SANS 10086-2 Based on Old version (Edition 2) of IEC 60079-17 SANS 10086-1, adapted for underground mining Application (technically) All surface installations in hazardous areas (under both the OHS Act and the MHS Act) All underground mining installations in hazardous areas
Page 4 of 29 NOTE that information taken from SANS 60079-17 Edition 4 (IEC 60079-17 Edition 4) is used on the next pages (updated versions of the examples listed in SANS 10086-1). NOTE that this presentation is based on the above national standards. Individual companies may have stricter requirements. 5. GRADES of inspection SANS 60079-17 defines visual, close, and detailed inspections. visual inspection (V): An inspection that identifies, without the use of access equipment or tools, those defects, for example, missing bolts, which will be apparent to the unaided eye. Visual inspections do not require the enclosure to be opened, or the equipment to be de-energized. close inspection (C): An inspection that encompasses those aspects covered by a visual inspection and, in addition, identifies those defects, for example, loose bolts, which will be apparent only by the use of access equipment, for example, steps (where necessary) and tools. Close inspections do not require the enclosure to be opened, or the equipment to be de-energized. detailed inspection (D): An inspection that encompasses those aspects covered by a close inspection and, in addition, identifies those defects, for example, loose terminations, which will only be apparent by de-energizing the equipment and opening up the enclosure, or using, where necessary, tools or test equipment (or both).
Page 5 of 29 6. TYPES of inspection TYPES of inspection are as follows. Inspection Type Initial Periodic Explanation Purpose Inspection Grades (V/C/D) applicable Inspection of all electrical To check that selected D (full or partial). equipment, systems and type of protection and Example 1: New installations before they installation is correct. If installation. are brought into service. supplier has quality Example 2: Replacement control, only explosion motor. protection features affected by installation need to be checked, e.g. flameproof joints on Ex d terminal box. Inspection of all electrical To establish if the V or C. equipment, systems and explosion protection of A visual or close periodic installations carried out the item and installation is inspection might reveal the on routine basis. At least still intact. need for a detailed once in 2 years. inspection. Example: Equipment in service and operates Sample Inspection of a proportion of the electrical equipment, systems and installations To monitor the effect of environmental conditions, vibrations, inherent design weaknesses, etc. Interpretation: To complement Periodic inspections by detecting accelerated wear or damage that may only be detectable by a Detailed inspection. normally (fault free). V, C or D. Example 1: Check 10% of motor stop-starts for cracks on insulators, damaged seals. Example 2: Check the high-quality earth impedance for safety barriers on PT loops.
7. Generic Inspection Sheets 7.1 Introduction Using the preceding definitions, generic inspection sheets from SANS 60079-17 Edition 4 (IEC 60079-17 Edition 4) may be used for practical inspection. Page 6 of 29 (Reminder: These are updated versions of the examples listed in SANS 10086-1). Depending on the sophistication of the inspection staff, these can be used, or specific checklists (suitable for specific equipment, e.g. fluorescent luminaries of a particular make and model, or Ex na motors) can be compiled. The inspections sheets address three areas of compliance, i.e. the equipment, its installation and its environment. Equipment inspection requires the explosion protection rating and suitability to be first evaluated, then its condition. The inspection sheets make provision for the three grades of inspection, i.e. Visual (V), Close (C), Detailed (D).
Page 7 of 29 7.2 APPLICATION Ex ed indicator stop-start station (D)
Inspection schedule for Ex d, Ex e and Type n installation (D = detailed, C = close, V = visual) Equipment description Tag no Ex rating Page 8 of 29 1 2 3 4 Ex d Ex e Type n Grade of inspection Check that: D C V D C V D C V 1A EQUIPMENT 1 Equipment is appropriate to EPL/Zone requirement of the location... 2 Equipment group is correct... 3 Equipment temperature class is correct... 4 Equipment circuit identification is correct... 5 Equipment circuit identification is available... 6 Enclosure, glasses and glass-to-metal sealing gaskets and/or compounds are satisfactory 7 There are no uncertified modifications... 8 There are no visible uncertified modifications... 9 Bolts, cable entry devices (direct and indirect) and blanking elements are of the correct type and are complete and tight physical check... visual check... 10 Flange faces are clean and undamaged and gaskets, if any, are satisfactory... 11 Flange gap dimensions are within permitted maxima... 12 Lamp rating, type and position are correct... 13 Electrical connections are tight... 14 Condition of enclosure gaskets is satisfactory... 15 Enclosed-break and hermetically sealed devices are undamaged... 16 Restricted breathing enclosure is satisfactory... 17 Motor fans have sufficient clearance to enclosure or covers (or both).. 18 Breathing and draining devices are satisfactory... 1B INSTALLATION 1 Type of cable is appropriate... 2 There is no obvious damage to cables... 3 Sealing of trunking, ducts, pipes or conduits (or both) is satisfactory... 4 Stopping boxes and cable boxes are correctly filled... 5 Integrity of conduit system and interface with mixed system is maintained... 6 Earthing connections, including any supplementary earthing bonding, are of sufficient cross-section physical check... visual check... 7 Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory... 8 Insulation resistance is satisfactory... 9 Automatic electrical protective devices operate within permitted limits. 10 Automatic electrical protective devices set correctly (no auto-reset)... 11 Specific conditions of use (if applicable) are complied with... 12 Cables not in use are correctly terminated... 13 Obstructions adjacent to flameproof flanged joints are in accordance with IEC 60079-14... 14 Variable voltage/frequency installations are as per documentation... 1C ENVIRONMENT 1 Equipment is adequately protected against corrosion, weather, vibration and other adverse factors... 2 No undue accumulation of dust and dirt... 3 Electrical insulation is clean and dry... NOTE 1 General: The inspection for equipment that use types of protection "e" and "d " shall be a combination of columns 2 and 3. NOTE 2 Account shall be taken of the possibility of an explosive atmosphere in the vicinity of the equipment, when electrical test equipment is used.
Page 9 of 29 1A EQUIPMENT 1* Equipment is appropriate to EPL/Zone requirement of the location EPL/Zone is provided from the area classification process. EPLs are determined by explosion risk and are mostly directly related to the allocated zones. Group Zone Minimum Equipment Protection Level (EPL) I In underground mines, within 180m from working faces, return airways etc. Ma Equipment remains functioning when explosive atmosphere present Mb Equipment isolated when explosive atmosphere present II 0 Ga 1 Gb 2 Gc III 20 Da 21 Db 22 Dc If more than one EPL, all must comply.
Page 10 of 29 2* Equipment group is correct Selected to suit the explosive atmosphere group (related to spark ignition properties i.e. minimum ignition energy). Normally determined during area classification. 3* Equipment temperature class is correct Based on explosive atmosphere temperature class (related to heat ignition properties i.e. auto-ignition temperature) or minimum ignition temperature. Normally determined during area classification. 4,5 Equipment circuit identification is available (correct if detailed inspection) The purpose of this requirement is to facilitate the correct isolation of equipment whenever work is to be carried out. This can be achieved in a variety of ways, for example: a) Equipment is fitted with a permanent label which specifies the source of supply. b) Equipment is fitted with a tag number or the cable is fitted with a cable number adjacent to the equipment. 6* Enclosure, glasses and glass-to-metal sealing gaskets and/or compounds are satisfactory All enclosures must be able to handle reasonable impact, to prevent creation of ignition sources. Ex d equipment Enclosure must withstand internal explosion, including window glass/polymer parts. Ex e and Type n equipment Enclosure must provide IP54 rating if containing bare live parts.
7, 8 There are no (visible) uncertified modifications Page 11 of 29 Modifications = The explosion protection is affected! If not, the certified state of the equipment remains valid (painting). 9* Bolts, cable entry devices (direct and indirect entry) and blanking elements are of the correct type and are complete and tight physical check visual check Cable glands, adaptors and plugs must have the same explosion protection as the enclosure to which connected. The check-tightening of cable glands under close inspection can be effected by hand without the need to remove weatherproofing tape or shrouds. Detailed inspections may necessitate that the cable glands are dismantled only where the integrity of the glands cannot be ascertained by close Inspection.
10 Ex d Flange faces are clean and undamaged and gaskets, if any, are satisfactory Page 12 of 29 Faces must be rust-free and without deep pits, scratches or marks, e.g. caused by screwdriver to remove lid. A thin layer of grease (not silicone rubber) after removing loose rust is ideal protection. 11 Ex d Flange gap dimensions are within permitted maxima Generally speaking, the biggest flange gap that will be permitted is 0,4mm. A feeler gauge can be carried along. It should be possible to confirm a completely tight fit visually on smaller enclosures. NOTE 1 - It is normally considered not necessary to check the diametric clearance of spigot, shaft, spindle and threaded joints, unless there is evidence of wear, distortion, corrosion or other damage. NOTE 2 - When reassembling flameproof enclosures, all (inspected) joints shall be thoroughly cleaned and may be lightly smeared with a suitable grease to prevent corrosion and to assist weather-proofing. Blind bolt-holes shall be kept clear of grease. Only non-metallic scrapers and non-corrosive cleaning fluids shall be used to clean flanges. Fasteners on Ex d external flanges must not protrude. 12 Lamp rating, type and position are correct
Page 13 of 29 Lamps with higher power ratings or other types of lamps may get hotter than the approved lamp type. Some lamps will have a specific condition of use in terms of position/orientation, for example the lens of a highbay light fitting normally pointing downwards will get hotter if the light is pointed up. 13 Ex e, Type n Electrical connections are tight Loose connections can cause sparks or hot spots. 14* Ex e, Type n Condition of enclosure gaskets is satisfactory. IP54 rating of enclosures containing live bare parts must be ensured. 15 Type n Enclosed-break and hermetically sealed devices are undamaged Enclosed-break and hermetically sealed devices are part of Ex nc equipment and must respectively contain an internal explosion and provide a gas-tight seal. 16 Type n Restricted breathing enclosure is satisfactory Restricted breathing devices are part of Ex nc equipment and must only allow a low exchange rate between internal and external atmosphere. 17 Motor fans have sufficient clearance to enclosure or covers (or both) To prevent frictional heat.
18 Breathing and draining devices are satisfactory Ex d equipment B&D devices contains at least one flameproof joint. Ex e and Type n equipment B&D devices must provide IP54 rating if enclosure contains bare live parts. Page 14 of 29 1B INSTALLATION 1 Type of cable is appropriate Cables used for fixed wiring in hazardous areas shall be appropriate for the ambient conditions in service. Cables shall be: a) sheathed with thermoplastic, thermosetting, or elastomeric material. They shall be circular, compact, have extruded bedding and fillers, if any, shall be non hygroscopic, or b) mineral insulated metal sheathed, or c) special, e.g. flat cables with appropriate cable glands. Such cables must be flame retardant. Flexible cables in hazardous areas shall be selected from the following: ordinary tough rubber sheathed; ordinary polychloroprene sheathed; heavy tough rubber sheathed; heavy polychloroprene sheathed; plastic insulated and of equally robust construction to heavy tough rubber sheathed flexible cables. Cables shall preferably be substantially compact ( round and filled). If not so for Ex d connections, then use barrier gland. 2 There is no obvious damage to cables 3 Sealing of trunking, ducts, pipes or conduits (or both) is satisfactory Openings in walls for cables and conduits between different hazardous areas and between hazardous and non-hazardous areas shall be adequately sealed, for example by means of sand seals or mortar sealing to maintain the area classification where relevant. Trunking, ducts or pipes connecting differently zoned areas must be sealed, for example by a sealing compound or sealing devices. For trenches, adequate venting or sand-filling may be used.
4 Stopping boxes and cable boxes are correctly filled Page 15 of 29 5 Integrity of conduit system and interface with mixed system is maintained 6 Earthing connections, including any supplementary earthing bonding, are of sufficient cross-section physical check visual check Bonding connections must prevent self loosening and corrosion which may reduce the effectiveness of connection. Metallic enclosures of intrinsically safe or energy-limited apparatus generally need not be connected to the equipotential bonding system. 7 Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory Intrinsically safe resistance measuring equipment may be used, or the measurement may be carried out under a hot work permit if absence of explosive atmospheres in the areas affected can be guaranteed. 8* Insulation resistance is satisfactory The insulation resistance for equipment and associated cabling up to 500 V (excluding safety extra-low voltage, SELV, electrical systems) shall be measured at 500 V d.c. The insulation resistance shall generally be at least 1,0 MΩ. 9* Automatic electrical protective devices operate within permitted limits The following electrical protection is compulsory and must therefore comply with the above: Wiring Protection against overload and from the harmful effects of short-circuits and earth faults. All electrical equipment Protection against the harmful effects of short-circuits and earth faults.
Page 16 of 29 Multi-phase electrical equipment (e.g. three-phase motors) Protection against loss of one or more phases where this can cause overheating to occur. Motors and transformers must be protected against overload. Resistance heating devices must be protected against overcurrent and earthleakage or earth-fault currents. In circumstances where automatic disconnection of the electrical equipment may introduce a safety risk which is more dangerous than that arising from the risk of ignition alone, a warning device (or devices) may be used as an alternative to automatic disconnection provided that operation of the warning device (or devices) is immediately apparent so that prompt remedial action will be taken. 10 Automatic electrical protective devices set correctly (no auto-reset) Short-circuit and earth-fault protection devices shall prevent auto-reclosing under fault conditions. 11* Specific conditions of use (if applicable) are complied with Specific conditions of use are determined by the ATL as part of explosion prevention and stipulated in the equipment certificate. They address the user as they comprise essential information for the installation, use, and maintenance of the equipment must be complied with by the user. They can either be shown in full on the equipment lable or if there is a lack of space, be referenced by including an suffix after the certificate number. 12* Cables not in use are correctly terminated If unused cable are not removed, the cores of the hazardous area end of such unused cables shall either be connected to earth or be adequately insulated by means of terminations suitable for the type of protection, for example isolating and capping both ends. Insulation by tape alone is not permitted.
Page 17 of 29 13 Obstructions adjacent to flameproof flanged joints are in accordance with SANS 60079-14 Minimum distance are as follows: Gas group IIA 10 IIB 30 IIC 40 Minimum distance (mm) 14 Variable voltage/frequency installations are as per documentation Ex motors must be type-tested together with the VSD. Ex d, Ex p, Type n and Ex td motors can alternatively be installed with a temperature sensing system. The maximum temperature of Type n motors operating with VSDs can alternatively be calculated. 1C ENVIRONMENT 1* Equipment is adequately protected against corrosion, weather, vibration and other adverse factors 2 No undue accumulation of dust and dirt 3 Electrical insulation is clean and dry
Page 18 of 29 7.3 APPLICATION Ex i level gauge (D)
Inspection schedule for Ex i, Ex id and Ex nl installations Page 19 of 29 Equipment description Tag no Ex rating 1 2 3 4 Grade of inspection Check that: Detailed Close Visual 2A EQUIPMENT 1 Circuit or equipment (or both) documentation is appropriate to area classification 2 Equipment installed is that specified in the documentation Fixed equipment only 3 Circuit or equipment (or both) category and group are correct... 4 Equipment temperature class is correct... 5 Installation is clearly labelled... 6 Enclosures, glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory 7 There are no unauthorized modifications... 8 There are no visible unauthorized modifications... 9 Safety barrier units, relays and other energy limiting devices are of the approved type, installed in accordance with the certification requirements and securely earthed, where required 10 Electrical connections are tight... 11 Visible printed circuit boards are clean and undamaged... 2B INSTALLATION 1 Cables are installed in accordance with the documentation... 2 Cable screens are earthed in accordance with the documentation... 3 There is no obvious damage to cables... 4 Sealing of trunking, ducts, pipes or conduits (or both) is satisfactory... 5 Point-to-point connections are all correct... 6 Earth continuity is satisfactory (for example, connections are tight and conductors are of sufficient cross-sectional area)... 7 Earth connections maintain the integrity of the type of protection... 8 The intrinsically safe circuit is isolated from earth or earthed at one point (see the documentation)... 9 Separation is maintained between intrinsically safe and non-intrinsically safe circuits in common distribution boxes or relay cubicles... 10 As applicable, short-circuit protection of the power supply is in accordance with the documentation... 11 Special conditions of use (if applicable ) are complied with... 12 Cables not in use are correctly terminated... 2C ENVIRONMENT 1 Equipment is adequately protected against corrosion, weather, vibration and other adverse factors... 2 There is no undue accumulation of dust and dirt...
Page 20 of 29 2A EQUIPMENT 1* Circuit and/or equipment documentation is appropriate to the EPL/zone requirements of the location The essential documents are the ATL-certified installation (loop) drawing and the ATL certificates for individual equipment used in the loop. EPL/Zone is provided from the area classification process. EPLs are determined by risk and are mostly directly related to the allocated zones 2* Equipment installed is that specified in the documentation Fixed equipment only 3* Circuit or equipment (or both) category and group are correct Levels of protection (EPLs) available for intrinsic safety equipment are ia, ib and ic. EPL/Zone is provided from the area classification process. EPLs are determined by risk and are mostly directly related to the allocated zones. Equipment group is selected to suit the explosive atmosphere group (related to spark ignition properties i.e. minimum ignition energy). Normally determined during area classification. 4* Equipment temperature class is correct Only the instrument (equipment exposed to explosive atmosphere) has a temperature rating. 5 Installation is clearly labelled The compulsory labeling of equipment must be checked to ensure that the equipment actually fitted is that specified. Further, the tag numbers must correspond with the tag numbers used in the control room basement,
Page 21 of 29 6* Enclosures, glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory IP ratings are sometimes essential. 7, 8 There are no (visible) unauthorized modifications This includes exchanging one type of device with a similar (but not identical) unit, e.g. a new series. 9 Safety barrier units, relays and other energy limiting devices are of the approved type, installed in accordance with the certification requirements and securely earthed, where required (Shunt-diode safety) barriers require a high-quality earth connection in order to provide protection. 10 Electrical connections are tight Loose connections can cause loss of protection, e.g. earth connection on barrier, earthing of screens and redundant cores. 11* Visible printed circuit boards are clean and undamaged
Page 22 of 29 2B INSTALLATION 1* Cables are installed in accordance with the documentation The insulation properties and inductance and capacitance values of the specified cable are critical for safety. 2* Cable screens are earthed in accordance with the documentation Generally, screens are earthed at one point i.e. in the safe area. They must however not be cut off. 3 There is no obvious damage to cables 4 Sealing of trunking, ducts, pipes or conduits (or both) is satisfactory Openings in walls for cables and conduits between different hazardous areas and between hazardous and non-hazardous areas shall be adequately sealed, for example by means of sand seals or mortar sealing to maintain the area classification where relevant. Trunking, ducts or pipes connecting differently zoned areas must be sealed, for example by a sealing compound (e.g. expansion foam) or sealing devices. For trenches, adequate venting or sandfilling may be used. 5 Point-to-point connections are all correct This check only needs to be done during the initial inspection.
Page 23 of 29 Point-to-point generally refers to a connection restricted to two endpoints. In this case, the termination points of conductors. The reliability of a termination is influenced by the termination method. For example, soldered, bolted or screwed connections may have infallibility status. 6* Earth continuity is satisfactory (for example, connections are tight and conductors are of sufficient cross-sectional area) For an earthed (shunt-diode safety) barrier, earthing conductor must be at least x2 1.5mm 2 or x1 4mm 2. 7 Earth connections maintain the integrity of the type of protection Check continuity of essential earth connections, e.g. transformer screen earth, barrier relay frame earth. 8* The intrinsically safe circuit is isolated from earth or earthed at one point (see the documentation) This check is only needed on a sampling basis. Insulation from or connection to earth, as required by the loop design, to be verified. Not necessary to test if a fault is self-revealing. If shunt-diode safety barrier (Zener barrier) earths have to be disconnected for such a test, ensure that loops are first de-energized. 9 Separation is maintained between intrinsically safe and non-intrinsically safe circuits in common distribution boxes or relay cubicles Clearance of at least 50mm is required, or insulating or earthed barriers.
Page 24 of 29 10 As applicable, short-circuit protection of the power supply is in accordance with the documentation Output voltage restricted to Um shown on the label of the associated apparatus; normally 250V. The prospective short-circuit current of the supply shall not be greater than 1500A. 11* Specific conditions of use (if applicable) are complied with Specific conditions of use are determined by the ATL as part of explosion prevention and stipulated in the equipment certificate. They address the user as they comprise essential information for the installation, use, and maintenance of the equipment must be complied with by the user. They can either be shown in full on the equipment lable or if there is a lack of space, be referenced by including an suffix after the certificate number. 12 Cables not in use are correctly terminated All screens, armour and conductors of redundant cables must be earthed inside the hazardous area using an explosion protected junction box. In the safe area, follow standard isolation protocol. 2C ENVIRONMENT 1 Equipment is adequately protected against corrosion, weather, vibration and other adverse factors 2 There is no undue accumulation of dust and dirt
8. Conclusions INSPECTION OF IN-SERVICE EPLOSION PROTECTED EQUIPMENT 1. Q: What is the PURPOSE of an Ex inspection? A: To preserve the explosion protection features (and certification). Page 25 of 29 2. Q: We know we need to inspect in-service Ex equipment at least once in 2 years (periodic inspection). - What Grade of inspection must be used (V/C/D). A: V and C are prescribed. 3. Q: When must additional inspections be done? A: Firstly, Initial inspection before putting replacement equipment or equipment that has been opened for calibration or routine servicing back in operation. Partial or comprehensive, for example only the terminal box of a repaired motor. Secondly, sample inspections must complement periodic inspections to reveal hidden damage due to equipment design weaknesses and environmental conditions. Premature failure can generate ignition sources. 4. Q: Who is competent to do inspections? A: The OHS Act requires inspectors to have appropriate competence. Operatives shall possess, to the extent necessary to perform their tasks, the following competencies according to SANS 60079-17: a) understanding of the general principles of explosion protection; b) understanding of the general principles of types of protection and marking; c) understanding of those aspects of equipment design which affect the protection concept; d) understanding of certification of Ex equipment and installations; e) understanding of the additional importance of Permit to Work systems and safe isolation in relation to Explosion Protection; f) familiarity with the particular techniques to be employed in the inspection and maintenance of Ex equipment; g) comprehensive understanding of the selection and erection requirements of Ex equipment and installations; h) general understanding of the repair and reclamation requirements of SANS 10086-3; i) use and availability of certification documentation; j) practical skills necessary for the inspection and maintenance of relevant concepts of Ex protection. THANK YOU QUESTIONS?
Page 26 of 29 Annex A Equipment selection A.1 Information required In order to select the appropriate electrical equipment for hazardous area caused by gases, vapours or dusts, the following information is required: Classification of the hazardous area including the equipment explosion protection level (EPL) requirements where applicable; Where applicable, gas, vapour or dust classification in relation to the group or subgroup of the electrical equipment; Temperature class or ignition temperature of the gas or vapour involved; Minimum ignition temperature of the combustible dust cloud, minimum ignition temperature of the combustible dust layer and minimum ignition energy of the combustible dust cloud; External influences and ambient temperature. A.2 Selection according to EPL Statistical approach and Zones In the past, a statistical approach to equipment selection was followed: probability of a fire or explosion occurring can be expressed as: The Where - p e is the probability of a fire or explosion occurring; - p g is the probability that an explosive atmosphere will be present in a particular place at a particular time (given by the zone); and - p i is the probability that the above explosive atmosphere can be ignited. p e and consequently the product p g x p i must be acceptably low. (A probability of 10-5 is considered acceptable, refer to Hickes and Brown). This means that if the probability of an explosive atmosphere being present increases, the probability that it can be ignited must decrease and vice versa. Equipment protection is selected in accordance with the zone in this approach. Risk-based approach p e = p g x p i The equipment selection standard now also allows for a risk-based approach. In a risk-based approach, the consequence of an explosion is also taken into account, together with the probability of an explosion. This means quite simply that under certain circumstances, the occurrence of an explosion is more tolerable (or less tolerable) than normal.
Page 27 of 29 Example: A typical example is of two neighbouring plants of similar design, but due to differences in the materials being handled, the one is Zone 1 and the other Zone 2. Some engineers will decree that Zone 1 equipment is used even in the Zone 2 plant, because the danger exists that the wrong replacement equipment will be selected from stores during a breakdown. Equipment Protection Level (EPL) To facilitate the risk-based approach, the concept of Equipment Protection Level (EPL) was introduced. The EPL for each explosion protection technique has been determined, based on its likelihood of becoming a source of ignition. The EPL ranges from a Very High to b High to c Normal and distinguishes between explosive gas (G), dust (D) and mine (M) atmospheres. The table below shows the relationship between types of protection and EPLs. Protection afforded EPL Type of protection Code According to standard Conditions of operation Group I Group II Group III Very High Ma Same as Ga Equipment remains functioning when explosive atmosphere present Very High Ga Intrinsically safe ia SANS 60079-11 Equipment remains Encapsulation ma SANS 60079-18 Two independent type of protection each meeting EPL Gb Protection of equipment and transmission systems using optical radiation SANS 60079-26 SANS 60079-28 functioning in Zones 0, 1 and 2 Very High Da Intrinsically safe id SANS 60079-11 Equipment remains Encapsulation md SANS 60079-18 functioning in Zones 20, 21 and 22 Protection by enclosure td SANS 60079-31 High Mb Same as Gb Equipment deenergised when explosive atmosphere present High Gb Flameproof enclosures d SANS 60079-1 Equipment remains Increased safety e SANS 60079-7 Intrinsically safe ib SANS 60079-11 Encapsulation m mb SANS 60079-18 Oil immersion o SANS 60079-6 Pressurized enclosures p, px SANS 60079-2 or py Powder filling q SANS 60079-5 Fieldbus intrinsically safe concept (FISCO) SANS 60079-27 functioning in Zones 1 and 2 Protection of SANS 60079-28 equipment and transmission systems using optical radiation High Db Intrinsically safe id SANS 60079-11 Equipment remains
Protection afforded INSPECTION OF IN-SERVICE EPLOSION PROTECTED EQUIPMENT EPL Type of protection Code According to standard Group Group Group I II III Page 28 of 29 Conditions of operation Encapsulation md SANS 60079-18 functioning in Zones Protection by td SANS 60079-31 21 and 22 enclosure Pressurized enclosures pd SANS 61241-4 Normal Gc Intrinsically safe ic SANS 60079-11 Equipment remains Encapsulation mc SANS 60079-18 functioning in Zone Non-sparking n or SANS 60079-15 2 na Restricted breathing nr SANS 60079-15 Energy limitation nl SANS 60079-15 Sparking equipment nc SANS 60079-15 Pressurized enclosures pz SANS 60079-2 Fieldbus non-incendive SANS 60079-27 concept (FNICO) Protection of SANS 60079-28 equipment and transmission system using optical radiation Normal Dc Intrinsically safe id SANS 60079-11 Equipment remains Encapsulation md SANS 60079-18 functioning in Zone Protection by td SANS 60079-31 22 enclosures Pressurized enclosures pd SANS 61241-4 Selection If risk is normal, which is mostly the case, the probability of an explosion is the only controlling factor and a direct relationship between EPL and Zone exists that is used to select equipment: Table A.1 Equipment protection level (EPLs) where only zones are assigned Zone Minimum Equipment Protection Level (EPL) 0 Ga 1 Gb 2 Gc 20 Da 21 Db 22 Dc Where in exceptional circumstances, the risk is not normal, a higher or lower EPL than that defined in the table may be required. It is recommended that the required explosion protection levels (EPLs) are recorded on the area classification drawing, even if the risk-based approach has not been followed.
Page 29 of 29 A.3 Selection according to equipment grouping Relationship between gas/vapour subdivision and equipment subgroup Environment Underground mines Gas and vapour, Surface Dust, Surface Gas, vapour or dust (sub)division I IIA IIB IIC IIIA IIIB IIIC Permitted equipment group I II, IIA, IIB or IIC II, IIB or IIC II or IIC IIIA, IIIB or IIIC IIIB or IIIC IIIC A.4 Selection according to the ignition temperature of the gas or vapour The electrical equipment shall be so selected that its maximum surface temperature will not reach the ignition temperature of any gas or vapour which may be present. Relationship between the equipment temperature classes and surface temperatures and ignition temperature Temperature class required by the area classification Ignition temperature of gas or vapour ( C) Maximum surface temperature of equipment ( C) Suitable equipment temperature class T1 >450 450 T1 - T6 T2 >300 300 T2 - T6 T3 >200 200 T3 - T6 T4 >135 135 T4 - T6 T5 >100 100 T5 - T6 T6 >85 85 T6