HAZARDS OF COMBUSTIBLE DUST PRESENTED FOR : THE SUMMIT COUNTY SAFETY COUNCIL MEETING SEPTEMBER 21, 2011 Presented by: John L. Schmidt - Engineering Specialist, FM Global - Cleveland Operations

PRESENTATION AGENDA: History Channel video Video test demonstrations Dust explosion losses Definition (FM Global/NFPA) 5 elements of a dust explosion Recognizing dust explosion hazards Risk service testing Room/building explosion hazards Equipment/process explosion hazards Ignition source control

Imperial Sugar Mill, Port Wentworth, GA; February 2008

Some Additional Dust Explosion Pictures, with the Resulting Consequences…

“a picture is worth a thousand words”…. Dust explosion tests videos

FM Global Dust Explosion Testing: Open air fireball test Explosion bunker test Grinding process mock up test (with and without explosion suppression) Large scale dust explosion test (bituminous coal and cornstarch)

FM GLOBAL LOSS HISTORY (1983 – 2006) Woodworking – 64 Food – 26 Metals – 18 Chemical – 14 Pulp/paper – 12 Mineral - 11 Utility – 7 Plastics/Rubber – 5 each Printing/Textile – 1 each Others - 2

FM GLOBAL LOSS HISTORY (BY CAUSE): Friction – 50 Spark – 38 Chemical Action – 16 Hot Work – 13 Burner Flame – 10 Electricity/Static – 6 each Overheating – 4 Hot Surface – 2 Unknown/No data - 21

FM GLOBAL LOSS HISTORY (BY DUST TYPE): Wood – 70 Food – 25 Chemical – 17 Metal – 15 Coal – 14 Plastic/Rubber – 13 Paper – 8 Others - 4

FM GLOBAL LOSS HISTORY (BY EQUIPMENT TYPE): Dust Collector – 66 Impact Equipment – 22 Silo – 8 Processing Equipment – 7 Oven – 5 Conveyor – 4 Grain Elevator – 4 Spray Dryer – 4 Dryer – 3 Boiler - 3

What is a combustible dust? FM Global: median particle size less than 500 microns NFPA: median particle size of less than 420 microns

HOW IS DUST TYPICALLY GENERATED? Two ways : –Finished product –By-product

INTENTIONALLY MANUFACTURED DUSTS Flours; Cornstarch Pulverized Coal Carbon Black Metallic Stearates Metal Powders

BY-PRODUCT (NUISANCE TYPE) DUSTS Wood dust Plastic dust Rubber dust Coal dust Grain dust Metal dust

THE “DUST EXPLOSION PENTAGON” Fuel Oxygen Ignition Source Suspension Confinement

Questions to Ask Is a dust generated in the process? Is a dust liberated from the process? Are dust accumulations present?

Dust Hazards Testing: FM Global testing for clients Variety of dust hazard tests Various outside labs for non-FM Global clients Approximate cost for hazards test range from $600/sample (explosibility screening test) to $1700/sample (full Kst test)

Full Kst Testing Determine explosibility parameters (i.e. Kst; Pmax) for explosion protection design Two important parameter from this test: Kst/Pmax

Testing apparatus (20L Sphere – Kst Test)

Kst Classifications Kst = 0 – “Nonexplosible” 1 < Kst < 50 bar-m/s – “Very Weakly” Explosible 50 < Kst < 100 bar-m/s – “Weakly” Explosible 100 < Kst < 200 bar-m/s – “Moderately” Explosible 200 < Kst < 300 bar-m/s – “Strongly” Explosible Kst > 300 bar-m/s – “Very Strongly” Explosible

Hazard Classifications ST1 Dust: Kst = bar-m/s ST2 Dust: 201 < Kst < 300 bar-m/s ST3 Dust: Kst > 300 bar-m/s

Examples St-1 dusts: coal, coke, lampblack, etc. St-2 dusts: cornstarch; cellulose; wood flour; etc. St-3 dusts: aluminum; magnesium, etc.

Other Dust Tests Explosibility Screening Sieve Analysis “Hard-to-Ignite” Testing (internal to FM Global) Minimum Explosible Concentration (MEC) Minimum Ignition Energy

Dust Explosion Hazards Management of change most critical!

Examples New equipment Process temperatures Product formulations Process changes

Important Dust Aspects Particle size Dust chemistry Moisture

Hazard Awareness Secondary dust explosion hazards most critical! FM Standard: > 1/16”

Hazard Awareness Identify sources of liberation Eliminate fugitive dust liberations/accumulations

Preventative Measures Housekeeping: vacuuming or sweeping (air blowdown should be a last resort!) –Perform frequently –Limit to small areas –Shut down all non-hazardous rated electrical equipment –Prohibit open flames and hot work operations –Ensure no hot surfaces exist Housekeeping NOT the end all solution for fugitive dust hazards! Elimination most important!

Preventative Measures Boxing in structural members Sloping of horizontal structural members If above not practical, then mitigation controls using Damage Limiting Construction (DLC)

Equipment Hazards Processing equipment Storage equipment Material handling equipment

Equipment Hazards Two potentially hazards: –inherent equipment explosion hazard –A more serious secondary explosion hazard (if excessive fugitive dust levels exist)

Prevention Techniques Phlegmatization Inerting

Mitigation Techniques Venting Suppression Containment Isolation

Venting Advantages: reliable passive protection approach; usually the most economical and effective form of protection Disadvantages: not usually applicable for indoor applications, unless venting to the outdoor s can be provided Can vent from the indoors to the outdoors, via a short vent duct

“ Flameless” Venting Option to standard explosion venting (when indoor venting only feasible option) Flame arrestor with rupture type membrane Retains burned/unburned dust; cool the combustion gases; and no trace of flame exits the device

( FM APPROVED FIKE EXPLOSION QUENCH PIPE)

Suppression Active protection approach –Advantages: indoor applications; no equipment damage –Disadvantages: complex design; lower and upper volume protection limitations; high associated installation/maintenance costs –Quick sensing of an incipient explosion; delivers extinguishing agent quickly to suppress explosion

Containment Explosion resistant design (no deformation) Shock resistant design (possible deformation ) Explosion isolation needed

“Pressure Piling” First vessel explosion pre-pressurizes second vessel Final explosion pressure directly proportional to initial pressure Subsequent second vessel explosion is pre-pressurized resulting in destruction of the vessel

Explosion Isolation Reduces potential for propagation between interconnected vessels Needed for interconnected vessels protected by explosion containment May also be warranted for interconnected vessels protected by explosion venting

Examples Chemical Blocking System Chemical suppressant injected into connecting pipe upon detection Prevents flame front from breaking through and propagating Used in conjunction with explosion suppression systems Active isolation system

Examples Rotary Airlocks –Explosion quenched within the gap between the vanes and the housing Chokes –Provides an accumulation of powder through which explosion is unable to propagate

Examples Rapid Action Valves (gate or butterfly type) –High pressure gas as the driving force –Closes in milliseconds –Active isolation device –Enough distance to allow valve to close before flame front arrival

(FIKE EXPLOSION ISOLATION VALVE)

Examples Flame Front Diverter –Pressure wave moves ahead of the flame front –Flame front cannot make the 180 degree turn after the explosion vent is opened –Works in both directions –Passive isolation device

(FIKE BI-DIRECTIONAL EXPLOSION DIVERTER)

Examples Backblast Damper –Check valve provided with an explosion vent –Works only in one direction –Passive isolation device

(FLAMEX BACKBLAST DAMPER)

Ignition Source Control Reduces frequency (not severity) Not a substitute for effective dust explosion hazard elimination and/or mitigation techniques!

Ignition Source Control Hazardous location electrical equipment: –Class II, Division 1 –Class II, Division 2 –Non-classified

Ignition Source Control Class II, Division 1 locations: –combustible dust in the air under normal operating conditions –explosible or ignitible mixtures Class II, Division 2 locations: –combustible dust not normally in air –ignitible mixtures, but may be as the result of infrequent malfunctioning of equipment

Ignition Source Control Non-classified locations: –a hazardous quantities of dust not foreseeably –released, as a result of malfunctioning equipment

Ignition Source Control Electrical classification on rate of dust accumulation: –> 1/8 in. (Division 1) –< 1/8 in. (Division 2) –Surface color discernible, and hazardous quantity of dust cannot be foreseeably released: Non-classified

Ignition Source Control Hot Work Management Smoking Control Magnetic Separators PM programs for conductive dust collector bags Grounding and bonding External bearings; belt alignment and zero speed switches for bucket elevators

Spark Extinguishing System –Detects and extinguishes an upstream spark or glowing ember –Processes with high frequency dust explosion hazards –Not the same as explosion suppression! –Reduces the frequency of an explosion, not the severity! Ignition Source Control

Dust Hazard Summary Dust hazards pose potentially catastrophic consequences, (both a property damage and business interruption) especially when fugitive dust is allowed to accumulate. 1/16 in. accumulation over a greater than 5% of the floor area. Fugitive dust hazard: –Usually what results in the secondary room explosion, –Secondary explosion causes the greatest amount of damage and business interruption.

Dust Hazard Summary Utilize either prevention or mitigation techniques to reduce the equipement explosion hazard. Implement an effective management of change policy, to ensure all potential dust hazards addressed during the design/conceptual stages of the project.