Dusts/Other Mine Aerosols Chapter 4 - Missouri S&T

1 1 Dusts/OtherMine AerosolsChapter 4 When the Scrubber Is Turned on ..What s like fter the scrubber has been onfor only a few minutes .. aerosol Types/DefinitionsAerosol any mass of solid orliquid particles suspended in a gasDust solid particulate matter is agas; most common; fromfragmentation or resuspension; 1-100 m diameter; generally 1-20 m; particles above 20 mrelatively quickly settleAerosol Types/DefinitionsFumes solid products fromcombustion, sublimation ordistillation; usually < 1 m; noteespecially diesel particulate matterSmoke particles generally m; usually visible; do not resultfrom condensation2 aerosol Types/DefinitionsFog liquid particles in a gas;condensation of liquid or dispersalof small liquid droplets.

2 Usuallydue to temperature change; few mto 100 m; also mistSmog combination of smoke andfog; < 1 m; contains photochemicalreaction products and water vaporAerosol Types/DefinitionsHaze similar to smog; < 1 m;solid particles and water vaporGenerally accepted size ranges,sampling and control methods foreach are given in Fig. on pp. 79-80 (accepted by American Societyof Heating, Refrigerating & AirConditioning Engineers)Dynamic Behavior of AerosolsBrownian Motion controllingmechanism for particles < msuspended in quiescent atmosphere;random movement of particlescaused by movement of gasmolecules that hit the particles.

3 Resulting mixing of particles andgases called diffusionStokes LawUsed to determine settling velocityof dust particles > 1 m falling in aquiescent setting with Reynoldsnumbers < 1 Settling velocity determined byequating drag force on falling(spherical) particle to force of gravity(~10% error)Stokes LawIf particles are non-spherical, thenStokes diameter can be usedinsteadStokes diameter diameter ofhypothetical spherical particlewith same density and settlingvelocity as the non-sphericalparticleStokes Law Derived EquationTerminal settling velocity: pDp2gVt = ------------ (Eq. ) 18 p - density of particle, kg/m3Dp - diameter of particle, m g - gravity constant, m/s2 - viscosity of air, x 10-5 Reynolds number ; diameter > 1 m3 Accompanying equation forReynolds number check: pVt DpNRe = ------------ (Eq.)

4 Vt relative velocity of particleNote: This is particle Reynolds number,different from Reynolds number for fluidflow (introduced later); if Reynolds number> , another equation must be used (seeHinds, 1982, p. 51)When particle < 1 m, is inaccurate (slippage atparticle surface)Particle falls faster thanpredictedMust apply Cunninghamcorrection factor, Cc, to thevelocity calculationCunningham correction factor: Cc = 1 + ------- (Eq. ) Dp mean free path of molecules of gas, m,which is the average distance a gas moleculetravels before colliding with anothermoleculeFor air, = x 10-8 m at 200C, 1 atm; allows useof Stokes law for particles as small as mInclude Cc in equation , when necessaryBehavior of Aerosols in aMoving AirstreamDust concentrations downwind of adust source function of rate ofconvection, diffusion, agglomeration,and other depositional factorsThus, dust concentrations can behard to predictSome studies done in pastClassification ofMineral Dustsand OtherRelevant AerosolsFibrogenic dusts:a.

5 Silica (quartz, cristobalite,tridymite, chert)b. silicates (asbestos, talc, mica,others)c. metal fumes (nearly all)d. beryllium, tin, iron orese. carborundumf. coal4 Carcinogenic Aerosols :a. asbestosb. radon daughters (attached toany dust )c. arsenicd. diesel particulate matter (DPM)- suspectede. silica suspectedToxic (poisonous) Aerosols :a. dusts of ores of beryllium,arsenic, lead, uranium, radium,thorium, chromium, vanadium,mercury, cadmium, antimony,selenium, manganese, tungsten,nickel, silver (principally oxidesand carbonates)b. mists and fumes of organic andother body-sensitizing chemicalsRadioactive dusts:a. ores of uranium, radium, andthorium (alpha and beta rays)b.

6 Dusts with radon daughtersattached (alpha radiation)Explosive dusts (airborne):a. metallic dusts (magnesium,aluminum, zinc, tin, iron)b. coal (bituminous, lignite)c. sulfide oresd. organic dustsNuisance dusts:a. gypsumb. kaolinc. limestoneNote: can overload lung clearance mechanism, causing some respiratory effectPhysiological Effects of Mineral Dusts5 Respiratory system s clearancemechanisms:Nose hair, mucousMouth mucousTrachea, bronci, bronchioles mucous,ciliaAlveoli surfactant, macrophages(phagocytes), lymphatic systemTerminology on inhaled particles:Inspirable capable of being inhaledinto the nose or mouth; < 100 mThoracic reach past mouth andnasal region; < 25 mTracheobronchial 5-25 mRespirable dust enter aveolar region;generally < 5 m.

7 Some up to 10 mRespirable dust Penetration CurvesRespirable dust Penetration CurvesBased on aerodynamic diameter diameter of particle with a density of 1g/cm3 that has the same aerodynamicproperties as a given particle ofarbitrary shapeNot all particles inhaled to the lungsare deposited; the maximumdeposition rate occurs at 3 mRespirable dust Deposition CurvesHistorical Background of Health EffectsPliny the Younger diseases first reportedin first centuryAgricola described health effects in 1500sFor centuries, diseases recognized but notwell understood1896 Roentgen invented x-ray machine,which would be used later to diagnosedisease6 Historical Background of Health EffectsGauley Bridge, WV galvanizing event (1930s); protection laws vs.

8 SilicosisExtensive research on coal workers pneumoconiosis just before WW II, thenaccelerated afterwardsAsbestos link to cancer proved in the 1970sResearch results from animal studies linkDPM to cancer in 1980sRespiratory Ailments and DiseasesSilicosisSilicate pneumoconiosisAsbestosisCoal workers pneumoconiosisBeryllium diseaseSiderosisDust Harmfulness FactorsCompositionConcentrationParticle sizeExposure timeIndividual susceptibilityExplosive DustsWhen suspended in air in highconcentrationLarge surface area of particlesPowerful chemical reaction uponoxidationIgnite from open flame, electric arc,blast, methane ignition,autoignition at critical temperatureExplosive DustsExplosions in air-methane mixturespropagate at speed of sound (1117fps); called detonating explosionsAir- dust mixtures propagate slower;flame speed ~ 30-35 fps; calleddeflagrating explosions.

9 Self-feedsince shock wave travels faster,stirring up dustExtensive research on explosionsCoal dust Explosions Explosibility VariablesCompositionParticle sizeConcentrationFlammable gasMoisture effectsPresence of incombustible materialOther dusts7 Lean flammability limit for mixturesof methane and coal dustExplosibility data for mixtures of coaldust and limestone dust for varyingamounts of rock dustExplosibilities of mineral-relateddustsTable aerosol Sampling Instruments (Continued)8 Measures of aerosol Exposure nDose = EiTi (integral form, too) i = 1Ei exposureTi time periodMeasures of aerosol Exposure nDeposited dose = IPpPd EiTi i = 1I inhalation rate, m3/hPp probability that measured dust will penetrate to alveoliPd probability that dust penetrating alveoli will be depositedMeasures of aerosol ExposureLastly,ETWA = dose/total exposure timeDiesel Particulate Matter (DPM)Fumes and soot from incompletecombustionSpherical carbon core < 1 mPolycyclic aromatic hydrocarbons(PAHs)

10 And other chemicalcompounds are absorbed on carboncoreParticles agglomerate and formclustersMeasurement of DPMMany studies using 10-stageimpactors, MOUDI (gravimetric)Complications in analysis (see figure,next slide)Dichotomous sampler developedRespirable Combustible dust methodNIOSH Method 5040 carbonanalysis => elemental carbonIn-mineDPMsamples9 Sources of Dustsin MinesDiscussionNext LectureAerosol ControlTechnology andPersonal ProtectiveEquipment