Conditions for Dust Explosions

Albert NessSAChE 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?

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

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

2008 - Imperial Sugar, GA

Want Proof?

13 Dead, > 40 injured

Q; Are these layers > 1/32 in?

West Pharmaceuticals, NC6 Dead

37 Injured

2003 - West Pharmaceutical, NC

CTA Acoustics, KY7 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 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?

Our Answer