Bearings, gears, small arms and jet engines require grinding, polishing, plating and laser cutting. The resulting metal dust cloud is combustible and explosible; aluminum, magnesium and titanium dusts release hydrogen (H₂) on contact with water, so firefighting with water can increase the explosion risk. NFPA 484 governs combustible-metal safety.

Metal Dust Properties

  • Aluminum dust: Kst 400–600 bar·m/s (Class ST3)
  • Magnesium dust: Kst 500–700; keeps burning in contact with water
  • Titanium dust: pyrophoric; can self-ignite around 250 °C
  • Steel/iron dust: Kst 100–200 (ST1)
  • Minimum ignition energy (MIE): 1–10 mJ (very low)

Collection Systems

  • Wet collector: The required choice for aluminum/magnesium (dust captured by a water curtain)
  • Dry baghouse: OK for steel
  • Spark detection: IR + water mist
  • Grounding: duct bonding resistance below 10 Ω
  • Central vacuum: All machines tied in

NFPA 484 Ventilation

  • Air change: 6-12 ACH shop floor
  • Capture velocity: 2.5 m/s grinding
  • Duct velocity: 20 m/s minimum (settling)
  • Deflagration venting: Av/V ratio calculated per NFPA 68
  • Explosion relief: 50–100 kg/m² panels

Field Practice

  • Grinder: Water tank beneath
  • Anodizing: Separate room + acid vent
  • Electrical: Zone 21 Ex tD motor
  • Cleaning: HEPA vacuum, NEVER broom
  • Fire gear: Class D metal extinguisher

Turkish Industry

  • Bearing plants: Steel grinding dust
  • Defense plants: Aluminum dust
  • Aerospace plants: Jet engine Ti dust
  • Integrated steel mills: Iron dust
  • Incidents: an aluminum-dust blast

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Sources & Further Reading

NFPA 484, NFPA 654, NFPA 68, OSHA 1910, VDI 2263. NFPA 484 Combustible Metals.