Electrical Equipment in Hazardous Areas

1. Electrical Equipment in Hazardous Areas Compiled by Elstan A Fernandez for free distribution

2. Objectives At the end of this module you should be able to: • Identify “Hazardous Zones” on board a tanker or similar vessel. • Predict the possible “Electrical Sources of Ignition” considered to be “Hazardous”. • Identify Explosion Protected Equipment • State the significance of equipment with various “Ex” markings • Describe essential items to be checked on “Ex-Protected” Equipment. • Demonstrate the precautionary measures in the maintenance of explosive proof lights.

3. Hazardous Areas

4. The most prominent sign in sight … STATUTORY WARNING: SMOKING COULD TAKE YOUR LIFE … … AND THE LIVES OF OTHERS

5. The Fire Tetrahedron Fuel Gas, vapours or powder Chain Reaction Ignition Source Thermal or Electric Oxidiser Air or O2

6. The Dust Explosion Pentagon Read Details

7. The Incipient Flame Sphere The Incipient Flame Sphere must reach a critical diameter if combustion is to become a self-propagating explosion. the

8. The Incipient Flame Sphere If the initial spark is not large enough, (i.e. does not possess enough energy), the combustion zone will not have enough energy to self propagate. It will just collapse upon itself, and fizzle out. This means a small spark can occur in a potentially explosive air/gas mixture, with no danger of an explosion. The maximum amount of energy of this “safe” spark varies with the specific air/gas mixture present.

9. The Rules Extract from ABS Rules for Building and Classing Steel Vessels -2005 Part 4 Vessel Systems and Machinery Chapter 1 General Section 1 Classification of Machinery Quote 1.9.4 Hazardous Area 4-1-1/1.9.4 Areas where flammable or explosive gases, vapors, or dust are normally present or likely to be present are known as hazardous areas. Hazardous areas are however more specifically defined for certain machinery installations, storage spaces and cargo spaces that present such hazard, e.g.: helicopter refueling facilities, see 4-8-4/27.3.3; paint stores, see 4-8-4/27.3.3; cargo oil tanks and other spaces of oil carriers; see 5-1-7/31.5; ro-ro cargo spaces; see 5-10-4/3.9.2. Unquote

10. Classification of Hazardous Materials (The American System) Class 1 : Flammable gases or vapours Class 2 : Combustible dusts Class 3 : Fibres or flyings (particles normally suspended in air) Class 1: The following groups are listed in the most dangerous to the least dangerous ones: Group A : Acetylenes Group B : Hydrogen, Hydrogen mixtures Group C : Ethylene, Ethers, Some Aldehydes Group D: Alkanes (Butane, Ethane, Methane, Octane, Propane), Hydrocarbon mixtures (Diesel oil, Kerosene, Petroleum mixtures, Gasoline), Alcohol, Ketones, Esters, Amines, Alkenes, Benzoids Class 2 (Combustible Dusts): Group E : Metallic Dusts (resistivity < 100 kΩ/cm) Group F, Group G : Non-conductive dusts (agri, plastic, chemical and textile dusts – resistivity > 100 kΩ/cm).

11. Hazardous Areas Onboard Ships When a ship is involved in its normal operational functions there will be some areas and zones where flammable gases can accumulate in the atmosphere and present a hazard to the ship, its crew and other personnel who may be onboard. Such areas are defined as hazardous and classified in terms of the risks involved. For example, IEC Publication 79-10 defines three such categories: Zone 0: The flammable mixture is continuously present or present for long periods. Zone 1: The flammable mixture is not continuously present, but will be present during normal operations. Zone 2: The flammable mixture would not normally be present, but if it is, it would be present for a short period only. (Note: Zones 0 and 1 is also known as Division 1 while Zone 2 is known as Division 2) Continued…

12. Hazardous Areas Onboard Ships The terms ‘gas-dangerous area’ or ‘gas-safe area’ may also be mentioned on ships. The general ship’s operation manual, or other similar documents, must be referred to in order to determine the number and extent of the hazardous areas for any given ship. Hydrocarbon gases or vapours from crude oil form highly flammable mixtures with air when they are present in the proportion between 1% and 10% hydrocarbon with 99% down to 90% normal air. Below the lower explosive limit (LEL) the mixture is too lean to burn rapidly, although a lean mixture will burn slowly in the presence of a naked flame or a spark, as is proved by the operation of explosimeters in this range. Over-rich mixtures exist when the level of the hydrocarbon exceeds 10%. Read Details

13. Class I Certified Equipment Comparison Chart Note: All Ex Equipment will be explained in subsequent slides

14. Tanker Installations 3 metres from openings Hazardous Area Normally Safe Areas 2 . 4 metres from openings Pump Room Cargo Tanks Engine Room Regulations and practices applied to the installation of electrical equipment in tankers specify the types of safe equipment that can be fitted in the areas where flammable gas and air mixtures may be present. The degree of risk is not the same throughout the hazardous areas, which include cargo tanks and the spaces above them, pump rooms, cofferdams and closed or semi-enclosed spaces with direct access to a dangerous zone Read Details General Tanker Arrangement showing Hazardous Areas and Normally Safe Areas

15. Electrical Sources of Ignition

16. Potential Sources of Ignition Should there be a flammable gas, vapour or dust in the atmosphere, the following are considered to be potential sources of ignition: • Sockets And Plugs, • Open Fuses, • Light Switches, • Relays, • Push Button Contacts, • Torches, • Starters, • Circuit Breakers, • Electric Bells, • Components like Capacitors, Inductors and Resistors

17. Potential Sources of Ignition When the switch is closed energy is stored in the inductor = ½LI2. When the switch is opened this energy is released as a spark. When the switch is open the capacitor charges to ½CV2 energy. On closing the switch, the energy is released as a spark. R R Switch L V Switch C V Hazardous Area Hazardous Area Safe Area Safe Area In resistive circuits when contacts are opened or closed, sparks can be produced. Voc is the open circuit voltage. The short circuit current Isc = Voc R R Switch V Hazardous Area Safe Area

18. Potential Sources of Ignition Non-Hazardous Side Hazardous Side Explosion Possible! Max 0.1 V produced by the TC Fault Occurs Ignition is possible from a fault occurring on the non-hazardous side

19. Potential Sources of Ignition There are no special measures taken in ordinary electrical equipment to encapsulate contacts, which arc as they close or open. Thus the following are more apparent as sources of ignition: • The danger from arcing contacts in a starter box or switch is not obvious because the arc is hidden. • Sparks from an electric motor, particularly of the commutator-type, • The momentary glow of a broken light bulb filament, • Arcing from a broken or damaged power cable Conventional equipment and cables are suitable for areas that are considered safe. Continued…

20. Potential Sources of Ignition • Static electricity is generated within tanks in several ways. Flammable gas remains in a tank even after it is discharged. This presents a hazard – particularly during washing – unless appropriate steps are taken. Here, the product or water mist or steam becomes charged with electricity. This can occur… • When filling with clean oil products • When washing with water jets • When steaming a tank • A static charge and spark may also be caused by carbon dioxide or steam being discharged at a high rate from a nozzle. • Keep tank openings closed as much as possible. • Do not disconnect tank cleaning hoses from their hydrants until they have been removed from the tank. Continued…

21. Potential Sources of Ignition • There are several ways in which this sufficient charge becomes a hot spark – capable of igniting a flammable mixture. This might involve the introduction of metal objects into a tank. Objects which may have caused a spark include: • Hand-held metal ullage tapes • Metal sample cans • Metal sounding rods • Ungrounded portable washing machines ! Do not introduce metal objects into the tank, other than a grounded washing machine.

22. Ex Equipment

23. Nameplate for Equipment used in Hazardous Areas BS 5501 Pt 5 d IIB T4 BASEEFA No. Ex 2833010 Group I is gas encountered in coal mining where methane and coal dust constitute the risks. Group II comprises gases such as cellulose vapour, petrol, benzene, amyl acetate. Group II may be further sub-divided into: IIA – propane, which requires higher ignition energy of 180 micro joules; IIB – ethylene, which requires ignition energy of 69 micro joules; and IIC – hydrogen, which requires ignition energy of 29 micro joules. Group III is coal and coke gas and ethylene oxide. Group IV covers excluded gases, i.e., where there is no flameproof general approval such as acetylene, carbon disulphide, etc. Read Details

24. Nameplate for Equipment used in Hazardous Areas BS 5501 Pt 5 d IIB T4 BASEEFA No. Ex 2833010 Read Details

25. Flame-proof (Ex d) Equipment Cover Flame Path Joint Inside Flame Path Inside Click on the image for animation Click on the image for animation Label sometimes found… Gap Inside Flame Path Glass

26. Flame-proof (Ex d) Equipment Advantages Explosion Containment No Electronics Low Maintenance No Moving Parts High-Powered Equipment Disadvantages No warning mechanism for containment failure Danger to Equipment After Explosions Possibility of Installation/Maintenance Errors Cost of Protection per ft3 Increases with Enclosure Size Windows are Limited Condensation build-up is common Few sizes to choose from Cumbersome, Limited Access Bulky Designs Causes Harmful Heat Build up Excessive Weight

27. Pressurised (Ex p) Equipment Zone 2 (Non Hazardous Area) Zone 1 (Hazardous area) Zone 2 (NHA) 1 2 3 2 4 2 5 6  0.5mbar  50Pa Over Pressure 0 External Pressure (1) Protective Gas Inlet (2) Ducting (3) Fan (4) Enclosure (5) Manometer (6) Solenoid Valve Pressurised (Ex p) Equipment with Leakage Compensation Enclosure without Rotating Parts

28. Pressurised (Ex p) Equipment Zone 2 (NHA) Zone 1(Hazardous area) Zone 2 (NHA) 1 2 3 2 4 2 5 6  0.5mbar  50Pa Over Pressure 0 B External Pressure (1) Protective Gas Inlet (2) Ducting (3) Fan (4) Enclosure (5) Manometer (6) Solenoid Valve Pressurised (Ex p) Equipment with Leakage Compensation Rotating Electrical Machine with an Internal fan

29. Pressurised (Ex p) Equipment Zone 2 (NHA) Zone 1(Hazardous area) Zone 2 (NHA) 1 2 3 2 4 2 5 6  0.5mbar  50Pa Over Pressure 0 External Pressure (1) Protective Gas Inlet (2) Ducting (3) Fan (4) Enclosure (5) Manometer (6) Solenoid Valve Pressurised (Ex p) Equipment with Leakage Compensation Rotating Electrical Machine with an External Fan

30. Types of Purge

31. Intrinsic Safety • Intrinsic safety removes the ignition side from the fire triangle. • Intrinsically safe wiring and equipment shall not be capable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific atmospheric mixture in its most easily ignitable concentration. • The Barrier is always located in the safe area.

32. Requirements for Intrinsically Safe Systems • Ensure that there is positive separation between intrinsically and non intrinsically safe circuits; this prevents the ignition energy from entering the intrinsically safe circuit. • Separate trays, conduits be used for intrinsically safe wiring and be properly tagged / identified. • IS wiring is not to be mixed with other wiring. • If conduit is used it must be effectively sealed to prevent gases fro the hazardous area to reach safe area. • ensure that the entity parameters upon which the system is designed match correctly.

33. Intrinsically Safe (Ex i) Circuit Components

34. Intrinsically Safe (Ex i) Circuit Components What is a simple apparatus? • A simple apparatus does not generate or store more than the following: • - 1.2 V • - 100 mA • - 20 micro J • - 25 mW • This type of device does not require certification from a third party but still requires an intrinsically safe barrier. • Examples: • Switches – limit, pressure, temperature, float, flow. • Push buttons • Analogue sensors : Thermocouple, RTD • LEDs

35. Intrinsically Safe (Ex i) Circuit Components

36. Intrinsically Safe (Ex i) Circuit Components

37. Intrinsically Safe (Ex i) Circuit Components

38. Intrinsically Safe (Ex i) Circuit Components

39. Intrinsically Safe (Ex i) Circuit Components

40. Intrinsically Safe (Ex i) Circuit Components

41. Intrinsically Safe (Ex i) Circuit Components

42. Intrinsic Safety (Ex i) Barriers The intrinsic safety barrier is inserted in the safe area between the field device and the safe area instrument. The barrier blocks dangerous energy that can be released due to a fault in the safe area from being transmitted to the hazardous area. This energy may be from the power supply or stored in a capacitor, inductor, etc. The dangerous energy is diverted to the ground. Therefore it is important to ensure a high quality of intrinsic safe ground. As this grounding is so critical, two separate ground connections from each barrier are recommended, each with a resistance < 1.0 ohm.

43. Intrinsic Safety (Ex i) Barriers

44. Intrinsic Safety (Ex i) Barriers

45. Intrinsic Safety (Ex i) Barriers There are two types of intrinsic safety barriers : 1) Zener barrier (2) Active barrier. 1) Zener barrier: This works on the principle of diverting hazardous energy to the ground safely before it can reach the hazardous area. Zener diodes limit the fault voltage to the hazardous area. There are two such diodes for redundancy. The series resistor limits the current to the hazardous area. The zener barrier is a loop which can restrict the current by the resistor. At the same time it must allow the loop to function normally by allowing the required values of current to flow in normal operation to enable the instrument in the safe area to operate to full range.

46. Intrinsic Safety (Ex i) Barriers There are two types of intrinsic safety barriers : 1) Zener barrier (2) Active barrier. 1) Zener barrier: The series resistor limits the current to the hazardous area. The zener barrier is a loop which can restrict the current by the resistor. At the same time it must allow the loop to function normally by allowing the required values of current to flow in normal operation to enable the instrument in the safe area to operate to full range.

47. Intrinsically Safe (Ex i) Barriers

48. Intrinsic Safety (Ex i) Barriers

49. Intrinsically Safe (Ex i) Barriers Fuse Transformer Safety Barrier with up to 3 Zeners for triple redundancy NON HAZARDOUS AREA Field Device HAZARDOUS AREA

50. Intrinsic Safety (Ex i) Barriers 2) Active Barrier: The active barrier uses transformers, opto isolators and relays to provide the isolation between the safe and unsafe areas. It does not require an intrinsically safe ground connection. This is the safest barrier to use if a high quality intrinsically safe ground connection is not available. The active barrier can drive a higher power load as compared to a zener barrier.