HAZARDS OF COMBUSTIBLE DUST PRESENTED FOR : THE SUMMIT COUNTY SAFETY COUNCIL MEETING SEPTEMBER 21, 2011 - PowerPoint PPT Presentation

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HAZARDS OF COMBUSTIBLE DUST PRESENTED FOR : THE SUMMIT COUNTY SAFETY COUNCIL MEETING SEPTEMBER 21, 2011 PowerPoint Presentation
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HAZARDS OF COMBUSTIBLE DUST PRESENTED FOR : THE SUMMIT COUNTY SAFETY COUNCIL MEETING SEPTEMBER 21, 2011
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HAZARDS OF COMBUSTIBLE DUST PRESENTED FOR : THE SUMMIT COUNTY SAFETY COUNCIL MEETING SEPTEMBER 21, 2011

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  1. HAZARDS OF COMBUSTIBLE DUSTPRESENTED FOR:THE SUMMIT COUNTY SAFETY COUNCIL MEETINGSEPTEMBER 21, 2011 Presented by: John L. Schmidt - Engineering Specialist, FM Global - Cleveland Operations

  2. History Channel video Video test demonstrations Dust explosion losses Definition (FM Global/NFPA) 5 elements of a dust explosion Recognizing dust explosion hazards Risk service testing Room/building explosion hazards Equipment/process explosion hazards Ignition source control PRESENTATION AGENDA:

  3. Imperial Sugar Mill, Port Wentworth, GA; February 2008

  4. Some Additional Dust Explosion Pictures, with the Resulting Consequences…

  5. “a picture is worth a thousand words”…. Dust explosion tests videos

  6. FM Global Dust Explosion Testing: • Open air fireball test • Explosion bunker test • Grinding process mock up test (with and without explosion suppression) • Large scale dust explosion test (bituminous coal and cornstarch)

  7. FM GLOBAL LOSS HISTORY (1983 – 2006) • Woodworking – 64 • Food – 26 • Metals – 18 • Chemical – 14 • Pulp/paper – 12 • Mineral - 11 • Utility – 7 • Plastics/Rubber – 5 each • Printing/Textile – 1 each • Others - 2

  8. FM GLOBAL LOSS HISTORY (BY CAUSE): • Friction – 50 • Spark – 38 • Chemical Action – 16 • Hot Work – 13 • Burner Flame – 10 • Electricity/Static – 6 each • Overheating – 4 • Hot Surface – 2 • Unknown/No data - 21

  9. FM GLOBAL LOSS HISTORY (BY DUST TYPE): • Wood – 70 • Food – 25 • Chemical – 17 • Metal – 15 • Coal – 14 • Plastic/Rubber – 13 • Paper – 8 • Others - 4

  10. FM GLOBAL LOSS HISTORY (BY EQUIPMENT TYPE): • Dust Collector – 66 • Impact Equipment – 22 • Silo – 8 • Processing Equipment – 7 • Oven – 5 • Conveyor – 4 • Grain Elevator – 4 • Spray Dryer – 4 • Dryer – 3 • Boiler - 3

  11. What is a combustible dust? • FM Global: median particle size less than 500 microns • NFPA: median particle size of less than 420 microns

  12. HOW IS DUST TYPICALLY GENERATED? Two ways : • Finished product • By-product

  13. INTENTIONALLY MANUFACTURED DUSTS • Flours; Cornstarch • Pulverized Coal • Carbon Black • Metallic Stearates • Metal Powders

  14. BY-PRODUCT (NUISANCE TYPE) DUSTS • Wood dust • Plastic dust • Rubber dust • Coal dust • Grain dust • Metal dust

  15. THE “DUST EXPLOSION PENTAGON” • Fuel • Oxygen • Ignition Source • Suspension • Confinement

  16. Questions to Ask • Is a dust generated in the process? • Is a dust liberated from the process? • Are dust accumulations present?

  17. Dust Hazards Testing: • FM Global testing for clients • Variety of dust hazard tests • Various outside labs for non-FM Global clients • Approximate cost for hazards test range from $600/sample (explosibility screening test) to $1700/sample (full Kst test)

  18. Full Kst Testing • Determine explosibility parameters (i.e. Kst; Pmax) for explosion protection design • Two important parameter from this test: Kst/Pmax

  19. Testing apparatus (20L Sphere – Kst Test)

  20. Kst Classifications • Kst = 0 – “Nonexplosible” • 1 < Kst < 50 bar-m/s – “Very Weakly” Explosible • 50 < Kst < 100 bar-m/s – “Weakly” Explosible • 100 < Kst < 200 bar-m/s – “Moderately” Explosible • 200 < Kst < 300 bar-m/s – “Strongly” Explosible • Kst > 300 bar-m/s – “Very Strongly” Explosible

  21. Hazard Classifications • ST1 Dust: Kst = 1 - 200 bar-m/s • ST2 Dust: 201 < Kst < 300 bar-m/s • ST3 Dust: Kst > 300 bar-m/s

  22. Examples • St-1 dusts: coal, coke, lampblack, etc. • St-2 dusts: cornstarch; cellulose; wood flour; etc. • St-3 dusts: aluminum; magnesium, etc.

  23. Other Dust Tests • Explosibility Screening • Sieve Analysis • “Hard-to-Ignite” Testing (internal to FM Global) • Minimum Explosible Concentration (MEC) • Minimum Ignition Energy

  24. Dust Explosion Hazards Management of change most critical!

  25. Examples • New equipment • Process temperatures • Product formulations • Process changes

  26. Important Dust Aspects • Particle size • Dust chemistry • Moisture

  27. Hazard Awareness • Secondary dust explosion hazards most critical! • FM Standard: > 1/16”

  28. Hazard Awareness • Identify sources of liberation • Eliminate fugitive dust liberations/accumulations

  29. Preventative Measures • Housekeeping: vacuuming or sweeping (air blowdown should be a last resort!) • Perform frequently • Limit to small areas • Shut down all non-hazardous rated electrical equipment • Prohibit open flames and hot work operations • Ensure no hot surfaces exist • Housekeeping NOT the end all solution for fugitive dust hazards! • Elimination most important!

  30. Preventative Measures • Boxing in structural members • Sloping of horizontal structural members • If above not practical, then mitigation controls using Damage Limiting Construction (DLC)

  31. Equipment Hazards • Processing equipment • Storage equipment • Material handling equipment

  32. Equipment Hazards • Two potentially hazards: • inherent equipment explosion hazard • A more serious secondary explosion hazard (if excessive fugitive dust levels exist)

  33. Prevention Techniques • Phlegmatization • Inerting

  34. Mitigation Techniques • Venting • Suppression • Containment • Isolation

  35. Venting • Advantages: reliable passive protection approach; usually the most economical and effective form of protection • Disadvantages: not usually applicable for indoor applications, unless venting to the outdoor s can be provided • Can vent from the indoors to the outdoors, via a short vent duct

  36. “Flameless” Venting • Option to standard explosion venting (when indoor venting only feasible option) • Flame arrestor with rupture type membrane • Retains burned/unburned dust; cool the combustion gases; and no trace of flame exits the device

  37. (FM APPROVED FIKE EXPLOSION QUENCH PIPE)

  38. Suppression • Active protection approach • Advantages: indoor applications; no equipment damage • Disadvantages: complex design; lower and upper volume protection limitations; high associated installation/maintenance costs • Quick sensing of an incipient explosion; delivers extinguishing agent quickly to suppress explosion

  39. Containment • Explosion resistant design (no deformation) • Shock resistant design (possible deformation ) • Explosion isolation needed

  40. “Pressure Piling” • First vessel explosion pre-pressurizes second vessel • Final explosion pressure directly proportional to initial pressure • Subsequent second vessel explosion is pre-pressurized resulting in destruction of the vessel

  41. Explosion Isolation • Reduces potential for propagation between interconnected vessels • Needed for interconnected vessels protected by explosion containment • May also be warranted for interconnected vessels protected by explosion venting

  42. Examples • Chemical Blocking System • Chemical suppressant injected into connecting pipe upon detection • Prevents flame front from breaking through and propagating • Used in conjunction with explosion suppression systems • Active isolation system

  43. Examples • Rotary Airlocks • Explosion quenched within the gap between the vanes and the housing • Chokes • Provides an accumulation of powder through which explosion is unable to propagate

  44. Examples • Rapid Action Valves (gate or butterfly type) • High pressure gas as the driving force • Closes in milliseconds • Active isolation device • Enough distance to allow valve to close before flame front arrival

  45. (FIKE EXPLOSION ISOLATION VALVE)

  46. Examples • Flame Front Diverter • Pressure wave moves ahead of the flame front • Flame front cannot make the 180 degree turn after the explosion vent is opened • Works in both directions • Passive isolation device