Conditions for Dust Explosions Albert Ness SAChE Workshop Sept. 15, 2008

Dust Explosion Pentagon Combustible Dust Confinement Turbulence (dispersed with [C] > MEC) Oxidant Ignition Source (< 420 microns)

Questions Is this a dust explosion? Why or why not?

Venting

Mental / Visual Exercise

Remember Dispersion Limits?

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

Secondary Explosions Why do we care?

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

Imperial Sugar, GA Want Proof? 13 Dead, > 40 injured

Q; Are these layers > 1/32 in?

West Pharmaceuticals, NC 6 Dead 37 Injured West Pharmaceutical, NC

CTA Acoustics, KY 7 Dead 37 Injured 2003 – CTA Acoustics, KY

Case Study – Mill / Cyclone / Baghouse Organic chips ground to 10  (Kst = 150) Conveyed to cyclone and baghouse for collection

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?

Our Answer