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Hazardous Area
Information :- Intrinsic Safety (ia) Increased safety (e) Flameproof Enclosure (d) Non - incendive (N)
General Description :- Jagian produces a range of certified equipment to conform with most of the popular methods of Explosion Protection. This guide is intended to enable customers to select the best combination of equipment to meet their needs. Area Classification :- Potentially hazardous areas are divided into Zones which are graduated according to the degree of risk. Zone 0 :- Where an explosive gas - air mixture is continuously present, or present for long periods. Zone 1 :- Where an explosive gas - air mixture is likely to occur in normal operation. Zone 2 :- Where an explosive gas - air mixture is NOT likely to occur and , if it occurs, it will not exist for long periods. Zone 20 :- Where an explosive atmosphere in the form of a cloud of dust in air is continuously present, for long periods, or frequently. Zone 21 :- Where an explosive atmosphere in the form of a cloud of dust in air is likely to occur in normal operation. Zone 22 :- Where an explosive atmosphere in the form of a cloud of dust in air is NOT likely to occur in normal operation but, if it does occur it will not exist for long periods. Gas Groups :- Flammable gasses, vapours and mists are classified in order of the ease with which they can be ignited in a mixture with air. Apparatus is grouped according to the gases it may be used in. Surface Industries :- Group
IIC : Acetylene Most easily ignited Underground :- Group 1 : Methane (Firedamp) Temperature Classifications :- Hazardous area apparatus is classified according to the maximum surface temperature it might attain under fault conditions at an ambient temperature of 40 oC, or at some other specified temperature. Maximum temperatures for each "T" rating are as shown in the table below.
Apparatus intended for operation at ambient temperatures higher than 40oC is often given a dual "T" rating e.g. T4/T5. This means that it is rated T5 in the normal ambient of 40 oC, but if the ambient temperature is raised to 85oC the potential temperature rise in fault conditions will take it above the 100oC limit for T5 rating. Labelling :- A typical label for an approved product will show details of the protection system, gas group and temperature rating. Example : EExia IIC T5
Intrinsic Safety- Exia :- Intrinsic Safety is the ONLY completely safe Hazardous Area Protection system, as it relies on limiting the power available to cause a spark in the hazardous area. This is achieved by using Zener Barriers or Isolating Repeaters, which prevent dangerous levels of voltage or current, even in the worst case such as a short circuit across the supply terminals of a transmitter. The other vital factor is that the equipment situated in the hazardous Area, such as our range of transmitters and their connecting cables do not store up sufficient energy to cause a spark, this is controlled at the design stage and certified by Cenelec. The result is that a correctly installed I.S. system, using the approved barriers and cable parameters cannot cause a spark even in the event of gross negligence, for this reason it is the ONLY protection allowed in Zone O areas where explosive gasses are continuously present. Because of this the enclosure requirements for I.S. equipment are not stringent, in fact all that is required is a housing with a degree of protection of IP20, which simply ensures that any electrical terminals etc., cannot be touched by fingers.
Thermocouples and RTDs :-
Exia and Exib :- EExia is the highest grade of intrinsically safe approval, where the apparatus is INCAPABLE of causing ignition with any combination of TWO FAULTS applied, such apparatus has the highest level of protection and can be located in Zones0, 1 and 2. EExib is a lower category, which is INCAPABLE of causing ignition to Zones 1 and 2. Both EExia and EExib categories maintain a safety factor of 1.5 in normal operation with one fault , and are suitable for any gas group. Non Incendive -ExN :- ExN is the least satisfactory protection concept. It specdifies that the apparatus is not capable in normal Operating Conditions of igniting a surrounding explosive mixture, therefore it must not produce sparks or generate excessive surface temperatures in normal use. its use is limited to Zone 2 only where explosive mixtures are not expected, and will not exist for long periods. ExN relies heavily on correct installation and maintenance, as any error such as leaving a screw loose or not fitting a cover correctly will create a potentially explosive situation. ExN Equipment :- Connection Heads :- Models TDMC, NHD and SMSS are certified ExN II T1-T6. The T rating depends upon the maximum process temperature to be measured . Conventional head / thermowell assemblies are given the variable T1-T6 rating because, in the event of thermowell failure, it is considered that the hot liquids or gases can enter directly into the certified connection head. The "T" rating therefore depends on the maximum potential temperature rise caused by the temperature of the medium measured, for this reason unsealed assemblies cannot be used to monitor temperatures above 450oC. Jagan also produces a sealed model. This features a double "O ring" seal to prevent ingress in the event of thermowell failure. This option can be sued without a thermowell and is NOT restricted by the process temperature.
Increased Safety - Exe :- Exe is a concept in which additional measures are taken to ensure that excessive temperatures or sparks do not occur in service, this is achieved by paying particular attention to the quality and reliability of materials and careful design of terminals etc., to prevent the possibility of sparks. Analog transmitters may not be fitted in Exe assembiles because the "wipers" of the adjustment potentiometers are considered to be potentially sparking Exe assemblies can be used in Zones 1 & 2, but as above particular attention must be paid to correct installation, especially in Zone 1 areas where explosive mixtures are commonly present. Exe certified thermocouple & RTD assemblies use special materials and construction methods; standard probes MUST NOT be used. Flameproof - Exd :- Flameproof protection depends on the enclosure being able to contain any explosion, preventing transmission of flames to the hazardous atmosphere surrounding the device. The concept provides a good level of protection, if correctly installed and maintained, but its use is limited to Zones 1 and 2 areas where explosive mixtures are likely to occur in normal operation, but are not continuously present. To achieve thisthe enclosure must be very stong and all entries, lids, covers and especially flame - path collars, must be made to a very high standard of quality and fit to prevent leakage and flame transmission. Connection Heads :- Certified heads can be provided. |
