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Ignition Control in Dust Explosion Environments

Learn about the work procedures for controlling ignition in dust explosion environments. Identify dust explosion elements, ignition sources, and use of hot work permits and lockout/tagout procedures.

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Ignition Control in Dust Explosion Environments

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  1. Module 3 Ignition Control

  2. Terminal Objectives Upon the successful completion of this module, participants will be able to explain the work procedures for controlling ignition.

  3. Enabling Objectives • Identify the five elements present in a dust explosion. • Identify ignition sources. • Discuss hot work permits and Lockout/Tagout (LOTO). • Discuss use of separator devices. • Identify classifications applicable to combustible dust contained in the National Electric Code (NEC).

  4. 5 Elements for Dust Explosion • Combustible dust in fine particles • Oxygen • Dust dispersed into air • Energy source to ignite mixture • Confinement

  5. Triangle and Pentagon

  6. Ignition Sources • Anything that delivers enough energy for ignition • Examples • Static electricity • Hot surface • Open flame or ember • Electric arcs and sparks

  7. Ignition Sources • Examples • Industrial trucks • Powder actuated tools • Smoldering nests • Heat from accidental mechanical impact

  8. Static Electricity • Electrical charging of materials • Charging through physical contact • Properly ground to prevent discharge

  9. Hot Surfaces • Any surface that exceeds min. auto-ignition temperature • Combustible dust/liquids on hot surface • Combustible liquids • Lubricants • Oils

  10. Open Flame/Glowing Ember • Eliminate all open flames or embers • Potential sources • Candles • Smoking • Flares • Matches/lighters • Furnances

  11. Electric Arcs and Sparks • Electric Arc • Continuous discharge of a current • formed when strong current jumps gap • Spark • Random, momentary discharge

  12. Industrial Trucks • Creates spark when engine engaged • Spark can occur in • Starter • Combustion • Backfire • Diesel engine • Gases sucked in/shutoff not possible

  13. Powder Actuated Tools • Provides spark when bullet is fired • Concussion from firing can shake dust loose

  14. Smoldering Nests • Collection of material in dust environment • Material can smolder • Chemical/biological reaction

  15. Accidental Mechanical Impact • Can occur in rotating equipment • Repeated impact creates hot spots • Spark can occur if material is capable • Titanium • Some aluminums

  16. Hot Work • Obtain permit PRIOR to hot work • Combustible material • If possible remove all material • Remove outside 35-foot radius • Cover with flame retardant tarps if unmovable

  17. Electrical Lockout/Tagout • Used to prevent sparks • Eliminates accidental ignition

  18. Separator Devices • Removes foreign materials capable of igniting dust • Isolation device must be installed • When using air separation air device • Install on return air lines

  19. Intrinsically Safe Devices • Equipment/wiring incapable of releasing sufficient energy to cause ignition • Examples • Pressure, flow, and level switches • Solenoid valves • thermocouples

  20. Explosion Proof Devices • Use explosion proof devices • Light fixtures • Engine switches • Pumps/motors • Sole option when IS-rated device is unavailable

  21. National Electric Code • Standard for safe installation of electrical wiring/equipment • Part of National Fire Codes • 1st published in 1897 • Updated every 3 years

  22. National Electric Code • NEC Classification-Article 500 • Class: designates type of flammable substance • Group: designates specific substances • Division: designates likelihood of flammable substances

  23. National Electric Code-Class II Dusts • Group E: combustible metal dusts • Group F: combustible carbonaceous dusts • Group G: other combustible dusts

  24. Next Module Module 4: Support Systems

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