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Static Electricity

Static Electricity. A shamelessly stolen introduction Albert Ness September 15, 2008. Ouch!. Sensory Effects. Slide 2 Static Electricity -David Wechsler October, 2002. Visual Effects. Slide 3 Static Electricity -David Wechsler October, 2002.

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Static Electricity

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  1. Static Electricity A shamelessly stolen introduction Albert Ness September 15, 2008

  2. Ouch! Sensory Effects Slide 2 Static Electricity -David Wechsler October, 2002

  3. Visual Effects Slide 3 Static Electricity -David Wechsler October, 2002

  4. Workplace Effects? Slide 4 Static Electricity -David Wechsler October, 2002

  5. Static Electricity • 3 Steps • Generation • Accumulation • Discharge • Control & Mitigation

  6. A General Static Condition - 1) Whenever two materials are placed in contact, an exchange of charge occurs between them. 2) Unless the materials are conductive and electrically bonded together, when the surfaces are separated each acquires an equal and opposite net charge. The net charges drain away to ground at a rate that depends on the conductivity of the materials. 3) Electric charges may build up on ungrounded conductive materials (such as metals) non-conductive materials (most plastics) until The electrical breakdown field of the surroundings (usually air) is exceeded and an electrostatic discharge (such as a spark) occurs. The static discharge may be of sufficient energy to ignite vapors or dust, depending on the Minimum Ignition Energy (MIE) of the ignitable mixture. Slide 6 Static Electricity -David Wechsler October, 2002

  7. Generation - Streaming Current

  8. + + + + + + - - - - - + + + + + + + + + + + + - - - - - - - - - - - - - - - - Splash Charge +

  9. Dumping Powder

  10. Contact and Frictional Charging

  11. Induction

  12. Charge in Charge out + + + + + + Accumulation of Charge

  13. 10,000 gal 5–10,000 gal <5,000 gal Charge Out (grounded vessels) • Conductive liquid – Nearly instantaneous • Non-conductive liquid - eventually dissipates in grounded vessels. Relaxation Time 1 min 5 min 30 min

  14. Extra kicker - Examples of some nonconductive liquids that will accumulate charge and are flammable: • gasoline • propane • toluene • butadiene • benzene • mineral spirits • styrene monomer Slide 15 Static Electricity -David Wechsler October, 2002

  15. Accumulation of Charge on Equipment • Charge on fluid places opposite charge on equipment. • Conductive equipment (metal), if grounded, safely brings charge to ground. • Charge on non-conductive (or non-grounded) equipment will linger on equipment.

  16. Accumulated charges remain in non conductive and in non-grounded vessels. + + + +

  17. Conductive Sections in non-conductive Line

  18. Discharge

  19. Flammable Limits - Lower (LFL) and Upper (UFL) Flammable Limits Slide 20 Static Electricity -David Wechsler October, 2002

  20. A p p r o x i m a t e V a l u e s O f M . I . E . I n A i r * 1 . G a s e s : 0 . 1 M i l l i j o u l e H y d r o g e n = 0 . 0 2 m J 2 . L i q u i d s 1 . 0 M i l l i j o u l e 0 . 5 4 m J P e n t a n e = S t y r e n e = 0 . 3 0 m J 3 : D u s t s 1 0 M i l l i j o u l e O r M o r e * O x y g e n - E n r i c h e d F u e l s H a v e M u c h L o w e r M . I . E . ’ s Minimum Ignition Energy Slide 21 Static Electricity -David Wechsler October, 2002

  21. Spark

  22. Spark

  23. Discharge

  24. Static Electricity Control • Ground all isolated conductors • Reduce flow velocity • Install dip pipes • Move filters further upstream • Eliminate top electrodes • Antistatic additives, materials • Increase Humidity • Ionize the air

  25. Grounding & Bonding • Grounding. The process of bonding one or more conductive objects to the ground, so that all objects are at zero (0) electrical potential; also referred to as “earthing.”  • Bonding. The process of connecting two or more conductive objects together by means of a conductor so that they are at the same electrical potential, but not necessarily at the same potential as the earth.

  26. Example Grounding Bonding

  27. Example of a tank car dip-pipe liquid transfer system Slide 28 Static Electricity -David Wechsler October, 2002

  28. Safe Charge Discharge from Bags Conductive Bag + + + Conductive Gloves - - - - - - - Conductive Shoes Conductive Floor

  29. Reduce charge velocity Ground all isolated conductors Move filter further upstream Install dip pipe Eliminate top electrodes Prevent Static Discharge xyzx micro filter • - - - - - - • - - - - - - - • - - - - - - - • - - - - - - - • - - - - - - - • - - - - - - - • - - - - - - - • - - - - - - - • - - - - - - - • - - - - - - - -

  30. Inert Environment Vent N2 to a safe place!

  31. Important Summary Points 1- Ground and Bond prior to any transfer 2- Non conductive fluids are more likely for static generation 3- Bottom filling or top fill using dip tube less static generation 4- Slow filling will generate less static than rapid filling. Magic number slow start velocity of 3 feet per second until loading lance is submerged. 5- Spray filling- keep nozzles from extending into the container to avoid pulling in air and creating flammable vapor mixture. 6- Inerting eliminates the potential for combustion, but does not eliminate the static. Padding with nitrogen may not achieve the same full potential as inerting (5% or less oxygen). Slide 32 Static Electricity -David Wechsler October, 2002

  32. Quiz • With respect to “Static electricity” before you transfer a flammable liquid material • from a 55 gal drum to an open container, what should you do? • A. Make sure it is raining and you have rubber boots on, so static will not be generated • B. Make sure that the 55 gal. Drum and the open container are grounded and bonded • C. Make sure you fill the container very slowly with a thin stream and place the filling • nozzle close to the bottom of the container. • You have just finished unwrapping a skid of material with several layers of • saran wrap and are going to remove and add a combustible dust material into a • reactor containing a flammable solvent. What steps should you take. • A. Open the reactor, start the agitator, and dump the contents into the reactor • B. Open the reactor, ground the reactor, bond the agitator, start the agitator, • dump the contents and close the reactor. • C. Ground the reactor, bond the agitator, open the reactor, dump the contents, close the • reactor, start the agitator. Slide 33 Static Electricity -David Wechsler October, 2002

  33. Quiz - Answers • With respect to “Static electricity” before you transfer a flammable liquid material • from a 55 gal drum to an open container, what should you do? • A. Make sure it is raining and you have rubber boots on, so static will not be generated • B. Make sure that the 55 gal. Drum and the open container are grounded and bonded • C. Make sure you fill the container very slowly with a thin stream and place the filling • nozzle close to the bottom of the container. • You have just finished unwrapping a skid of material with several layers of • saran wrap and are going to remove add a combustible dust material into the • reactor containing a flammable solvent. What steps should you take. • A. Open the reactor, start the agitator, and dump the contents into the reactor • B. Open the reactor, ground the reactor, bond the agitator, start the agitator, • dump the contents and close the reactor. • C. Ground the reactor, bond the agitator, open the reactor, dump the contents, • close the reactor, start the agitator. Slide 34 Static Electricity -David Wechsler October, 2002

  34. Quiz • You are preparing to load a non conductive flammable solvent into a tank truck • via the top manway. From a static's perspective, what two things should be done? • A. Ground the tank truck and get the filling done as fast as possible • B. Ground the tank truck and fill slowly through a grounded down pipe • C. Stand way back and fill the tank quickly • You are asked to load a tank car and in checking the grounding clamp, you • notice that it is heavily corroded. What should your action be? • A. Continue on with the loading operation, but don’t use the grounding clamp. • B. Continue on with the loading operation by repairing the ground clamp yourself. • C. Get the ground clamp repair and then continue with the loading operation. Slide 35 Static Electricity -David Wechsler October, 2002

  35. Quiz - Answers • You are preparing to load a non conductive flammable solvent into a tank truck • via the top manway. From a static's perspective, what two things should be done? • A. Ground the tank truck and get the filling done as fast as possible • B. Ground the tank truck and fill slowly through a grounded down pipe • C. Stand way back and fill the tank quickly • You are asked to load a tank car and in checking the grounding clamp, you • notice that it is heavily corroded. What should your action be? • A. Continue on with the loading operation, but don’t use the grounding clamp. • B. Continue on with the loading operation by repairing the ground clamp yourself. • C. Get the ground clamp repair and then continue with the loading operation. Slide 36 Static Electricity -David Wechsler October, 2002

  36. More Info • NFPA 77 • IChemE Guides • Knovel • Avoiding Static Ignition Hazards in Chemical Operations • Electrostatic Hazards • Electrostatic Ignition of Fires and Explosions

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