Post on 14-Dec-2015
Dust Explosion Pentagon
Combustible Dust
Confinement
Turbulence (dispersed with
[C] > MEC) Oxidant
Ignition Source
(< 420 microns)
Remember Dispersion Limits?
0
2
4
6
8
10
12
0 50 100 150 200 250 300 350
Dust Concentration (g/m3)
Exp
losi
on P
ress
ure
(bar
)
Minimum Explosive Concentration (MEC)
Minimum Explosible Concentration
• Lower limit 10 – 30 g/M3– Polymethylacrylate 15 g/M3– Ground Dextrose 20 g/M3– Flour 60 g/M3
Questions
• Given a 10M x 10M x 3M room • How many grams of flour are needed
to be above the MEC? • How many 2.2 kg (~ 5 lb) bags of
flour are needed to exceed the MEC?
• How many bags of flour are needed to exceed the MEC in this room?
• Does that seem like a lot of flour on the floor?
18,000
8
What is the effect?
• Poor housekeeping, and secondary explosions, heighten the damage potential– Larger portion of facility, and more people,
potentially involved– Longer duration events greater impulse more
damage to structures and equipment
Housekeeping
• Importance stressed and guidance provided in NFPA 654– Dust layers >1/32 inch deep are a concern
– Can be hazardous if >5% of floor area covered
– Beams, ductwork, cabling, piping, walls all gather dust and should also be considered
– Construct buildings and equipment for ease of cleaning
Case Study – Mill / Cyclone / Baghouse
Organic chips ground to 10 (Kst = 150) Conveyed to cyclone and baghouse for collectionMill
Cyclone &Rotary Valve
Baghouse &Rotary Valve
FAN
P-7
Cooler
P-8
Feed
Questions
• Do the conditions exist for a dust explosion?• Where?• What are potential the ignition sources?• If yes, how would you protect the system?• If there were 10 of these units in a building, how
would you protect them?