Combustible DustsCombustible DustsPresented byPresented by

Bruce L. Rottner, CSPBruce L. Rottner, CSPAtAt

AIHce 2006 in Chicago, IllinoisAIHce 2006 in Chicago, Illinois

First Documented Dust ExplosionFirst Documented Dust ExplosionMr. GiacomelliMr. Giacomelli’’s Bakerys Bakery

Turin, Italy Turin, Italy –– December 14 1785December 14 1785

Count Morozzo recounts his investigation as documented in the Count Morozzo recounts his investigation as documented in the Memoirs of the Academy of Science of TurinMemoirs of the Academy of Science of Turin

On the 14On the 14THTH of December, 1785, about six oof December, 1785, about six o’’clock in the evening, there clock in the evening, there took place in the house of Mr. Giacomelli, baker in the city, antook place in the house of Mr. Giacomelli, baker in the city, anexplosion which threw down the windows and windowexplosion which threw down the windows and window--frames of his frames of his shop which looked into the street; the noise was as loud as thatshop which looked into the street; the noise was as loud as that of a of a large cracker, and was heard at a considerable distance. At thelarge cracker, and was heard at a considerable distance. At themoment of the explosion, a very bright flame, which lasted only moment of the explosion, a very bright flame, which lasted only a a few seconds, was seen in the shop; and it was immediately few seconds, was seen in the shop; and it was immediately observed, that the inflammation proceeded from the flour observed, that the inflammation proceeded from the flour --warehouse which was situated over the back shop where a boy was warehouse which was situated over the back shop where a boy was employed in stirring some flour by the light of a lamp.employed in stirring some flour by the light of a lamp.

Data from 1898 until 1942Data from 1898 until 1942

The US Bureau of Chemistry of the The US Bureau of Chemistry of the Department of Agriculture whose work Department of Agriculture whose work became the basis for the NFPA committee became the basis for the NFPA committee on dust explosions reported:on dust explosions reported:780 total explosions780 total explosions519 fatalities519 fatalities1206 injured1206 injuredLosses in dollars Losses in dollars –– 55,728,94055,728,940

Case History Case History –– West West Pharmaceutical Services 1/29/2003Pharmaceutical Services 1/29/2003

6 fatalities6 fatalities38 injuries38 injuriesThe explosion could be The explosion could be heard 25 miles from the heard 25 miles from the plantplantShattering glass injured a Shattering glass injured a student at a school 0.5 student at a school 0.5 mile away.mile away.Flaming debris set woods Flaming debris set woods on fire as far as two miles on fire as far as two miles away.away.

West Pharmaceutical (cont.)West Pharmaceutical (cont.)

Plastic dust was deposited on top of a Plastic dust was deposited on top of a suspended ceiling. suspended ceiling. –– ¼¼ to to ½½ inch thick on horizontal surfaces inch thick on horizontal surfaces

(e.g., tops of the tiles, lighting fixtures, (e.g., tops of the tiles, lighting fixtures, beams, conduit, etc.)beams, conduit, etc.)

–– Estimation was that a ton of powder had Estimation was that a ton of powder had accumulated.accumulated.

–– Accumulated for a period of years.Accumulated for a period of years.

West Pharmaceutical (cont.)West Pharmaceutical (cont.)

Several Ignition Sources Identified by the Several Ignition Sources Identified by the U.S. Chemical Safety and Hazard U.S. Chemical Safety and Hazard Investigation BoardInvestigation Board–– Overheated batch of rubberOverheated batch of rubber–– Electrical faultElectrical fault–– Hot lighting ballastHot lighting ballast–– Spark from an electric motorSpark from an electric motor

MSDS PolyethyleneMSDS PolyethyleneFire and Explosion Hazard Information Fire and Explosion Hazard Information

================================================================================================ Extinguishing Media: WATER, CARBON ============== Extinguishing Media: WATER, CARBON DIOXIDE, DRY CHEMICAL. Fire Fighting Procedures: USE NIOSH DIOXIDE, DRY CHEMICAL. Fire Fighting Procedures: USE NIOSH APPRVD SCBA & FULL PROT EQUIP (FP N). IF PROT EQUIP IS NOT APPRVD SCBA & FULL PROT EQUIP (FP N). IF PROT EQUIP IS NOT AVAIL/NOT USED, FIGHT FIRE FROM PROTECTED LOCATION/SAFE AVAIL/NOT USED, FIGHT FIRE FROM PROTECTED LOCATION/SAFE DIST. KEEP PEOPLE AWAY. ISOLATE FIRE AREA & DENY UNNEC DIST. KEEP PEOPLE AWAY. ISOLATE FIRE AREA & DENY UNNEC ENTRY. COOL SURROUND S W/WATER TO LOCALIZE FIRE ZONE. ENTRY. COOL SURROUND S W/WATER TO LOCALIZE FIRE ZONE. HAND HELD CARBON DIOXIDE/DRY CHEM EXTINGS MAY BE USED HAND HELD CARBON DIOXIDE/DRY CHEM EXTINGS MAY BE USED FOR SM FIRES. SOAK THORO(SUPDAT) Unusual Fire/Explosion FOR SM FIRES. SOAK THORO(SUPDAT) Unusual Fire/Explosion Hazard: DENSE SMOKE IS EMITTED WHEN BURNED W/OUT Hazard: DENSE SMOKE IS EMITTED WHEN BURNED W/OUT SUFFICIENT OXYG. MECH HNDLG CAN CAUSE FORM OF DUSTS. TO SUFFICIENT OXYG. MECH HNDLG CAN CAUSE FORM OF DUSTS. TO REDUCE POTNTL FOR DUST EXPLO, DO NOT PERMIT DUST TO REDUCE POTNTL FOR DUST EXPLO, DO NOT PERMIT DUST TO ACCUM. HAZ COMBUST PRODS:UNDER FIRE CNDTNS POLYMERS ACCUM. HAZ COMBUST PRODS:UNDER FIRE CNDTNS POLYMERS DECOMPOSE. SMOKE MAY CONTAIN POLYMER FRAGMENTS OF DECOMPOSE. SMOKE MAY CONTAIN POLYMER FRAGMENTS OF VARYING COMPOSITIONS IN ADDN TO UNIDENTIFIED TOX &/OR VARYING COMPOSITIONS IN ADDN TO UNIDENTIFIED TOX &/OR IRRIT (SUPDAT) IRRIT (SUPDAT)

Industries At RiskIndustries At Risk

AgriculturalAgriculturalChemicalChemicalPharmaceuticalsPharmaceuticalsWoodWoodPlasticsPlasticsFoodFoodCoalCoal

Combustion PrinciplesCombustion PrinciplesFire is a rapid oxidation Fire is a rapid oxidation process with the evolution of process with the evolution of light and heat in varying light and heat in varying intensities.intensities.

2C + O2C + O22 2CO2CO

Deflagration is a combustion Deflagration is a combustion reaction in which the velocity reaction in which the velocity of the reaction front through of the reaction front through the unreacted fuel medium is the unreacted fuel medium is less than the speed of sound.less than the speed of sound.

One Explosion or TwoOne Explosion or Two

Factors Impacting a Dust ExplosionFactors Impacting a Dust Explosion

Particle sizeParticle size

Chemical properties of a dustChemical properties of a dust

Moisture contentMoisture content

Cloud dispersionCloud dispersion

Process Equipment at RiskProcess Equipment at Risk

DUST COLLECTORSDUST COLLECTORSStorage Enclosures (e.g., silos, bins, hoppers, Storage Enclosures (e.g., silos, bins, hoppers, etc.)etc.)Pneumatic Conveying SystemsPneumatic Conveying SystemsAirAir--Material SeparatorsMaterial SeparatorsSize Reduction (e.g., hammermills, granulators, Size Reduction (e.g., hammermills, granulators, grinders, etc.)grinders, etc.)Material Feeding Devices (bucket elevators)Material Feeding Devices (bucket elevators)Heating EquipmentHeating Equipment

Importance of Maintenance (and Importance of Maintenance (and Inspection) of EquipmentInspection) of Equipment

Identifies problems before they become Identifies problems before they become disasters.disasters.

Reduces the potential for ignition sources.Reduces the potential for ignition sources.

Reduces the amount of fugitive dust in the Reduces the amount of fugitive dust in the work environment.work environment.

Definition of a Definition of a ““dustdust””

Combustible Dust Combustible Dust –– Any finely divided solid Any finely divided solid material that is 420 microns or smaller in material that is 420 microns or smaller in diameter (material passing a U.S. No. 40 diameter (material passing a U.S. No. 40 Standard Sieve) and presents a fire or Standard Sieve) and presents a fire or explosion when dispersed or ignited in air.explosion when dispersed or ignited in air.

Sieve Analysis Sieve Analysis

7474200200

106106140140

150150100100

1801808080

4204204040

MicronsMicronsUS Standard Sieve No.US Standard Sieve No.

Surface Area to Mass RatioSurface Area to Mass Ratio

Dust explosion is a rapid oxidation of the Dust explosion is a rapid oxidation of the particle surface.particle surface.

Increasing the surface to mass ratio allows Increasing the surface to mass ratio allows less heat to dissipate into the mass.less heat to dissipate into the mass.

The less heat absorbed by the mass of the The less heat absorbed by the mass of the particle, the more that heat accelerates particle, the more that heat accelerates the reaction.the reaction.

Optimum Cloud DensityOptimum Cloud Density

An optimum cloud density allows sufficient An optimum cloud density allows sufficient distance between the particles to allow distance between the particles to allow access of oxygen around the particles; but access of oxygen around the particles; but close enough so that the heat of one close enough so that the heat of one ignited particle can initiate reactions in ignited particle can initiate reactions in nearby particles. nearby particles.

Ignition of Dust LayersIgnition of Dust Layers

Ignition of a dust layer is a function of the type Ignition of a dust layer is a function of the type of dust, its physical and chemical properties, and of dust, its physical and chemical properties, and the depth of the layer.the depth of the layer.The ignition of a dust layer usually occurs at a The ignition of a dust layer usually occurs at a lower temperature than a dust cloud.lower temperature than a dust cloud.Once the material is ignited it then can serve as Once the material is ignited it then can serve as an ignition source for a dust cloud.an ignition source for a dust cloud.The ignition temperature of a layer can decrease The ignition temperature of a layer can decrease over time when subjected to constant heating.over time when subjected to constant heating.

Ignition of Dust CloudsIgnition of Dust Clouds

Ignited dust particlesIgnited dust particlesMechanical sparksMechanical sparksStatic electricityStatic electricityElectrical sourcesElectrical sourcesHeat sourcesHeat sourcesOpen flamesOpen flames

General Parameters General Parameters

Average minimum concentration of a Average minimum concentration of a combustible dust is approximately 0.05 ozs / ftcombustible dust is approximately 0.05 ozs / ft33

or 50 g / mor 50 g / m33

Materials that ignite above 0.50 joules are not Materials that ignite above 0.50 joules are not considered sensitive to ignition by electrostatic considered sensitive to ignition by electrostatic discharge.discharge.Draft System +, Draft System +, --, and ?, and ?

Min. Ignition Temp. of a Cloud < 400Min. Ignition Temp. of a Cloud < 400°° CCMin. Ignition Temp. of a Layer 5mm < 300Min. Ignition Temp. of a Layer 5mm < 300°° CCMin. Ignition Energy of a Cloud < 15 mJMin. Ignition Energy of a Cloud < 15 mJ

Laboratory TestsLaboratory Tests

Minimum Explosive Concentration (MEC)Minimum Explosive Concentration (MEC)Minimum Ignition Temperature (MIT) Minimum Ignition Temperature (MIT) cloud or a layercloud or a layerMinimum Ignition Energy (MIE)Minimum Ignition Energy (MIE)Maximum Explosion Pressure and Rate of Maximum Explosion Pressure and Rate of Pressure RisePressure Rise

Factors Effecting Laboratory TestsFactors Effecting Laboratory Tests

Variation of apparatus *Variation of apparatus *

Ability to achieve perfect dispersion of the Ability to achieve perfect dispersion of the dust.dust.

Particle SizeParticle Size

Moisture ContentMoisture Content

Minimum Explosive ConcentrationMinimum Explosive Concentration

Hartmann Apparatus (Vertical tube Hartmann Apparatus (Vertical tube apparatus)apparatus)Positive result is the bursting of a paper Positive result is the bursting of a paper diaphragm at the top of the apparatus.diaphragm at the top of the apparatus.Quantity of dust is decreased 5 mg until Quantity of dust is decreased 5 mg until no explosions occurs in four successive no explosions occurs in four successive trials.trials.

Minimum Ignition Temperature Minimum Ignition Temperature --CloudCloud

Conducted in a GodbertConducted in a Godbert--Greenwald Greenwald FurnaceFurnace–– Air dispersion of dust into the furnace.Air dispersion of dust into the furnace.–– Positive result is the observation of a flame at Positive result is the observation of a flame at

the bottom of the furnace.the bottom of the furnace.–– Standard quantity of dust 0.1 g. (0.05 and Standard quantity of dust 0.1 g. (0.05 and

1.0)1.0)–– Increments of 5Increments of 5°° C.C.–– Positive results in one or more trials in a Positive results in one or more trials in a

group of four.group of four.

Minimum Ignition TemperatureMinimum Ignition TemperatureLayerLayer

Hot Plate Hot Plate –– A metal ring is placed on a hot plate A metal ring is placed on a hot plate and filled with the dust. Thermocouples record and filled with the dust. Thermocouples record the temperature of the hot plate and the dust. the temperature of the hot plate and the dust. If the dust temperature exceeds the hot plate by If the dust temperature exceeds the hot plate by 2020°° C then an ignition is recorded.C then an ignition is recorded.US Bureau of Mines test involves a metal mesh US Bureau of Mines test involves a metal mesh basket which is filled with the dust. Air of a basket which is filled with the dust. Air of a known temperature is flowed across the powder. known temperature is flowed across the powder. An ignition is when the temperature of the An ignition is when the temperature of the powder exceeds the surrounding air.powder exceeds the surrounding air.

Minimum Ignition EnergyMinimum Ignition Energy

US Bureau of Mines conducted the test in US Bureau of Mines conducted the test in the Hartmann Apparatusthe Hartmann ApparatusMultiple trials are used to determine a Multiple trials are used to determine a minimum energy discharge for ignition.minimum energy discharge for ignition.The minimum spark ignition energy is the The minimum spark ignition energy is the lowest setting at which a positive result is lowest setting at which a positive result is obtained in one out of at least four trials.obtained in one out of at least four trials.

Maximum Pressure (PMaximum Pressure (PMAXMAX) and ) and Maximum Rate of Pressure Rise (RMaximum Rate of Pressure Rise (RMAXMAX))

Hartmann ApparatusHartmann Apparatus

2020--Liter SphereLiter Sphere

KKSTST

KKST ST is an index used to classify the explosion is an index used to classify the explosion severity of a combustible dust.severity of a combustible dust.

It is based on the maximum rate of pressure It is based on the maximum rate of pressure rise, (dP/dt)rise, (dP/dt)MAXMAX and the units are and the units are bar/second.bar/second.

KKSTST = (dP/dt)= (dP/dt)MAXMAX * V* V1/3 1/3 (V is the vessel (V is the vessel volume ~ mvolume ~ m33))

KKSTST IndexIndex

> 300> 300St St -- 33

201 201 -- 300300St St -- 22

Up to 200Up to 200St St -- 11

KKSTST

(bar(bar--m/s)m/s)Dust ClassDust Class

Explosion Severity Index Explosion Severity Index (US Bureau of Mines)(US Bureau of Mines)

>10>10>2.0>2.0>5.0>5.0SevereSevere

1.0 1.0 -- 10101.0 1.0 –– 2.02.01.0 1.0 –– 5.05.0Strong Strong

0.1 0.1 –– 1.01.00.5 0.5 –– 1.01.00.2 0.2 –– 1.01.0ModerateModerate

<0.1<0.1<0.5<0.5<0.2<0.2WeakWeak

Index of Index of explosibilityexplosibility

Explosion Explosion SeveritySeverity

Ignition Ignition sensitivitysensitivity

Relative Relative explosion explosion

hazard ratinghazard rating

Ignition SensitivityIgnition Sensitivity

Minimum Ignition Temperature X Minimum Ignition Energy Minimum Ignition Temperature X Minimum Ignition Energy X Minimum Explosible Concentration) Pittsburgh Coal X Minimum Explosible Concentration) Pittsburgh Coal dustdust

Minimum Ignition Temperature X Minimum Ignition Energy Minimum Ignition Temperature X Minimum Ignition Energy X Minimum Explosible Concentration) Sample dustX Minimum Explosible Concentration) Sample dust

Explosion SeverityExplosion Severity

(Maximum Explosion Pressure X Maximum Rate of (Maximum Explosion Pressure X Maximum Rate of Pressure Rise) Sample dustPressure Rise) Sample dust

(Maximum Explosion Pressure X Maximum Rate of (Maximum Explosion Pressure X Maximum Rate of Pressure Rise) Pittsburgh Coal dustPressure Rise) Pittsburgh Coal dust

Index of ExplosibilityIndex of Explosibility

Ignition Sensitivity X Explosion SeverityIgnition Sensitivity X Explosion Severity

Protection MethodsProtection Methods

Deflagration Pressure ContainmentDeflagration Pressure ContainmentDeflagration VentingDeflagration VentingSuppressionSuppressionOxygen ReductionOxygen ReductionDeflagration venting through a listed dust Deflagration venting through a listed dust retention and flameretention and flame--arresting devicearresting device

Isolation (prevent propagation) Isolation (prevent propagation) –– chokes, rotary chokes, rotary valves, flame front diverters, fast acting valvesvalves, flame front diverters, fast acting valves

NEC Classifications NEC Classifications –– Article 500Article 500Class II, Division 1 and 2 locations where fire or explosion Class II, Division 1 and 2 locations where fire or explosion

hazards may exist due to combustible dust.hazards may exist due to combustible dust.

Division 1Division 1Combustible dust in air under normal operating conditions in Combustible dust in air under normal operating conditions in quantities sufficient to produce an explosive or ignitible quantities sufficient to produce an explosive or ignitible mixture.mixture.

Division 2Division 2Combustible dust due to abnormal conditions in quantities, Combustible dust due to abnormal conditions in quantities, ……Dust accumulation on, in, or in the vicinity of the electricalDust accumulation on, in, or in the vicinity of the electricalequipment could be sufficient to interfere with the safe equipment could be sufficient to interfere with the safe dissipation of heat from electrical equipment, or could be dissipation of heat from electrical equipment, or could be ignitible by abnormal operation or failure of electrical ignitible by abnormal operation or failure of electrical equipmentequipment..

Group EGroup E

Group E Group E –– Atmospheres containing combustible Atmospheres containing combustible metal dusts, including aluminum, magnesium, metal dusts, including aluminum, magnesium, and their commercial alloys, or other and their commercial alloys, or other combustible dusts whose particle size, combustible dusts whose particle size, abrasiveness, or conductivity present similar abrasiveness, or conductivity present similar hazards in the use of electrical equipment.hazards in the use of electrical equipment.

Aluminum, Chromium, Ferromanganese, Iron, Aluminum, Chromium, Ferromanganese, Iron, Manganese, and Magnesium Manganese, and Magnesium

Group FGroup F

Group F Group F –– Atmospheres containing combustible Atmospheres containing combustible carbonaceous dusts that have more than 8 carbonaceous dusts that have more than 8 percent total entrapped volatiles or that have percent total entrapped volatiles or that have been sensitized by other materials so that they been sensitized by other materials so that they present an explosion hazard.present an explosion hazard.

Coal, carbon black, charcoal, pitch, and coke dustCoal, carbon black, charcoal, pitch, and coke dust

Group GGroup G

Group G Group G –– Atmospheres containing other Atmospheres containing other combustible dusts, including flour, grain, combustible dusts, including flour, grain, wood flour, plastic, and chemicalswood flour, plastic, and chemicals

Housekeeping as it Relates to NECHousekeeping as it Relates to NEC

Assume a bulk density of 75 lbs/ftAssume a bulk density of 75 lbs/ft33 (1200 Kg / (1200 Kg / mm33) and assumed concentration of 0.35 oz /ft) and assumed concentration of 0.35 oz /ft33

(350 g/m(350 g/m33) it has been calculated that a dust ) it has been calculated that a dust layer averaging 1/32 inch is sufficient to form a layer averaging 1/32 inch is sufficient to form a combustible dust cloud.combustible dust cloud.Reference Section 5.2.2 of NFPA 499 which Reference Section 5.2.2 of NFPA 499 which states: When a dust layer is greater than 1/8 states: When a dust layer is greater than 1/8 inch thick (3mm) is present under normal inch thick (3mm) is present under normal conditions, the location should be classified as conditions, the location should be classified as Division 1.Division 1.

Housekeeping as it Relates to NEC Housekeeping as it Relates to NEC (continued)(continued)

Table A.5.2.2(a) Division Determination Guidelines Table A.5.2.2(a) Division Determination Guidelines Based on Dust Layer ThicknessBased on Dust Layer Thickness

Greater than 1/8 inch (3.0mm) Division 1Greater than 1/8 inch (3.0mm) Division 1

Less than 1/8 inch, but surfaceLess than 1/8 inch, but surfacecolor not discernable Division 2color not discernable Division 2

Surface color discernable underSurface color discernable underthe dust layer Unclassifiedthe dust layer Unclassified

Temporary Equipment that Defeats Temporary Equipment that Defeats Electrical Area ClassificationElectrical Area Classification

ForkliftsForklifts

Vacuum CleanersVacuum Cleaners

Power ToolsPower Tools

Fire Brigades and Emergency Fire Brigades and Emergency ResponseResponse

A dust explosion can be initiated by an A dust explosion can be initiated by an incipient fire.incipient fire.Incipient Fire Brigades:Incipient Fire Brigades:–– Have limited training.Have limited training.–– Can use hose streams to fight fires.Can use hose streams to fight fires.–– Have little or no Personal Protective Have little or no Personal Protective

Equipment (PPE).Equipment (PPE).A dust explosion can be initiated by A dust explosion can be initiated by an incipient fire.an incipient fire.

Emergency Response PlanningEmergency Response Planning

PrePre--ExplosionExplosion

Dust ExplosionDust Explosion

PostPost--ExplosionExplosion

Determining the CauseDetermining the Cause

Ignited materials can travel through Ignited materials can travel through process equipment far from its ignition process equipment far from its ignition source until it reaches a combustible source until it reaches a combustible cloud.cloud.Fire and explosions destroy some of the Fire and explosions destroy some of the evidence necessary to make a evidence necessary to make a determination.determination.For the most part, determining cause is For the most part, determining cause is only achieved in about 50% of the cases.only achieved in about 50% of the cases.

Post Event Working EnvironmentPost Event Working Environment

Community and regulatory industries have Community and regulatory industries have a renewed interest in your facility.a renewed interest in your facility.Facility personnel have a perceived risk of Facility personnel have a perceived risk of an elevated hazard.an elevated hazard.Strong push to rebuild and resume Strong push to rebuild and resume operations.operations.EHS personnel along with facility EHS personnel along with facility management must decide when to resume management must decide when to resume normal operations.normal operations.

Resuming Normal OperationsResuming Normal Operations

Rebuilding equipment and facilities once Rebuilding equipment and facilities once thought to be safe but led to a dust thought to be safe but led to a dust explosion.explosion.The exact ignition source of a dust The exact ignition source of a dust explosion is only identified approximately explosion is only identified approximately 50% of the time.50% of the time.Theories and solutions are numerous and Theories and solutions are numerous and varied.varied.

StandardsStandardsNFPA 61, Standard for the Prevention of Fires and Dust NFPA 61, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Product FacilitiesExplosions in Agricultural and Food Product Facilities

NFPA 70, National Electrical Code (2005)NFPA 70, National Electrical Code (2005)

NFPA 499, Recommended practice for the Classification NFPA 499, Recommended practice for the Classification of Combustible Dusts and of Hazardous (classified) of Combustible Dusts and of Hazardous (classified) Locations for Electrical Installations in Chemical Process Locations for Electrical Installations in Chemical Process Areas (2004)Areas (2004)

NFPA 654, Standard for the Prevention of Fire and Dust NFPA 654, Standard for the Prevention of Fire and Dust explosions from the Manufacturing, Processing, and explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids (2006)Handling of Combustible Particulate Solids (2006)

NFPA 664, Standard for the Prevention of Fires and NFPA 664, Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Explosions in Wood Processing and Woodworking FacilitiesFacilities