Bearings, gears, small arms and jet engines require grinding, polishing, plating and laser cutting. The resulting metal dust cloud is explosible; Al, Mg, Ti release H2 on water contact. NFPA 484 governs combustible-metal safety.
Metal Dust Properties
- Al dust: Kst 400-600 bar.m/s (Class ST3)
- Mg dust: Kst 500-700, burns with water
- Ti dust: Pyrophoric, 250 C
- Steel dust: Kst 100-200 ST1
- MIE: 1-10 mJ (very low)
Collection Systems
- Wet collector: Required for Al/Mg (water spiral)
- Dry baghouse: OK for steel
- Spark detection: IR + water mist
- Grounding: 10 ohm duct bonding
- 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 vent: Av/V ratio
- Explosion relief: 50-100 kg/m2 panel
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
- Ortakoy Machine: Bearings Kayseri
- MKE: Defense aluminum
- TAI: Jet engine Ti dust
- Eregli Steel: Iron dust
- Incidents: Tuzla 2018 Al-dust blast
Metal Dust with MEP Calc
MEP Calc sizes metal-dust plants: 12 ACH capacity, capture velocity flow, deflagration vent area and NFPA 484 wet collector.
Download MEP Calc on the App Store
Sources & Further Reading
NFPA 484, NFPA 654, NFPA 68, OSHA 1910, VDI 2263. NFPA 484 Combustible Metals.