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Expeltec.presentation 1


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Expeltec.presentation 1

  1. 1. Ex Basics(An introduction to the Hazardous Area Protection ) A presentation by Asif Mirza August 2012
  2. 2. An EXPLOSION requires following three elements 1 A flammable Material 2 Oxygen from air 3 An Ignition or fire-starter
  3. 3. 1 A flammable Material 2 Oxygen from air 3 An Ignition or fire-starter…to form an explosive triangle or an ET Explosive Triangle
  4. 4. An Explosive Triangle can exist only when (a) Flammable Material & (b) Oxygen are present with-in anarrow range of quantities. The Range is Between The Upper Explosive Limit & Lower Explosive Limit Dead ETUpper Explosive Limit Quantity Of Explosive MaterialLower Explosive Limit Dead ET
  5. 5. Explosive Triangle IgnitionExplosive triangle is a way to harness the inherent energy by allowing its release throughoxidization. This energy was packed millions of years ago inside the crucibles of cosmos.This happens every time we use our motor car: ETs are deliberately created inside the internal combustion engine to get the required locomotion by TIMED and CONTROLLED explosions ET are deliberately created inside the cylinder
  6. 6. Explosive Triangle Ignition Quantifying one side of ET as to the TYPE of flammable materialFlammable material in the form of GASES or LIQUIDS belong to CLASS 1 Flammable material in the form of DUST or POWDER belong to CLASS 2 Flammable material in the form of FIBRES or FLYINGS belong to CLASS 3 The quantity of the material is quantified indirectly by the length of the time period an ET remains present in a location
  7. 7. Simple Rule of Thumb is :If an ET exists for more than 1000 Hours( >1000/ year) per year at a particular locationthen it is a HIGH RISK location and WE shall call it ZONE 0 for class 1 and ZONE 20for class 2If an ET exists for more than 10 hours but less than 1000 Hours per year ( 10<,= TIME<,= one year) at a particular location then it is a Moderate Risk location and WE shallcall it ZONE 1for class 1 and ZONE 21 for Class 2.If an ET exists for 10 Hours or less per year at a particular location then it is a Low RISKlocation and WE shall call it A ZONE 2 for Class 1 and ZONE 22 for Class2.WE refers to the STANDARDS Specifying bodies, like IEC or NEC
  8. 8. Long-life ETs create VERY HIGH RISK and short-lived ETs create LOW RISK AREA
  9. 9. Thus presence of ETs create explosion risk areas or the Hazardous AreasInternational Electro technical Commission IECInvolvement with ET: Since 1947National Electrical Code NECIndirect involvement : Since 1897Direct involvement : 1920There are many other authorized groups fully involved in research anddevelopment in this and related fields Then there is the ever present silent majority. The dedicated & self committed engineers all across the globe A constant source of valuable feed-back & innovation.
  10. 10. IEC divide the Hazardous Area in to 3 REGIONS or ZONES RISKD A N G E RZONE 2 ZONE 1 ZONE 0ZONE22 ZONE21 ZONE20
  11. 11. NEC divide the Hazardous Area in to 2 REGIONS or DIVISIONS RISKD A E RDIVISION 2 DIVISION 1
  12. 12. Let us consider flammable material of Class 1 (Vapours & Gases) The gases which form part of the ET have certain distinct and common properties which enable us to from GAS GROUPS. The Legendary Group Leader is METHANE • The explosive gas which is found in coal mines. • The nightmare of the coal miners. • The fuel of our industry. Colorless, odorless but explosive. This is the material which initiated the whole PHILOSOPHY and later the ART of explosion protection. Its’ enormous hidden energy BUT ruthless manifestation in explosions and deaths of miners inspired Humphrey Davy and his contemporaries like George Stephenson to develop the
  13. 13. That was in 1815 and later, some times after 1900 when ELECTRIC lamps & fixtureswere installed in the mines, the humanitarian side of the ELECTRICAL ENGINEERINGpractices formed the EXPLOSION PROTECTION SCIENCE. The unique parameters like • Ignition Temperature, • minimum ignition energy • and other properties are defined in the GAS GROUPS.
  14. 14. The unique parameters like Ignition Temperature, minimum ignition energy and other propertiesare defined in the GAS GROUPS. NEC A B C D Mining E F G IEC T5 100C Methane I Propane II A T2 T3 T4 300C 200C 135C Ethylene II B Carbon Acetylene Hydrogen II C T6 Disulphide T1 85C 450C
  15. 15. That was a brief analysis of the inflammable material; one side of the ET Now let us look at the remaining two sides of the ET………One of the other side is OXYGEN which manifests itself as part of AIR. Nothing remarkable about it The remaining side is THE SOURCE OF IGNITION The list is long and on top of the list is ………………………………..
  16. 16. Each time when switch is operated; spark appears at the terminals specially at the time of ‘switching-off’ Lamp ‘off’ N 220 V Switch is in ‘off position and circuit is open’ Lamp ‘on’’ N 220 V Switch is in ‘on position and circuit is closed’ This is the account of events which takes place inside an ordinary switch
  17. 17. Lamp ‘on’N 220 V Switch is in ‘on position and circuit is closed’ Lamp ‘off’’N 220 V At the time of the separation of the switch contacts small arc (spark) is initiated by the electrical inertia of the circuit . This apparently small arc can initiate an explosion In a hazardous area.
  18. 18. The strategy so far has been to know the details of the requirements for the occurrence of anexplosion .We have used the concept of The Explosive Triangle, so that we may protect ourselves andour investments from destructive powers of ET and at the same time ,utilize the vastresources of oil & gasWe can protect ourselves in two ways:FIRST OR PRIMARY PROTECTION (first defense line)BY not dealing with ETs at all-----by using substitute materials.But this is not possible all the time-- for example there is presently no substitute for oil or gas .Another way is to keep the ET handling area as ventilated as possible, so that themixture never reaches that critical concentration.SECONDARY Protection or DEFENCE LINEBasic strategy is to control the ignition sources, by-Confinement-Limiting its energy-Quenching