Chapter 4 by yantingting


    Mine Aerosols
         Chapter 4

   When the Scrubber Is Turned on . . .   What’s like fter the scrubber has been on
                                                 for only a few minutes . . .

    Aerosol Types/Definitions                  Aerosol Types/Definitions

Aerosol – any mass of solid or            Fumes – solid products from
liquid particles suspended in a gas       combustion, sublimation or
                                          distillation; usually < 1 µm; note
Dust – solid particulate matter is a
                                          especially diesel particulate matter
gas; most common; from
fragmentation or resuspension; 1-         Smoke – particles generally 0.01-1
100 µm diameter; generally 1-20           µm; usually visible; do not result
µm; particles above 20 µm                 from condensation
relatively quickly settle

     Aerosol Types/Definitions              Aerosol Types/Definitions

Fog – liquid particles in a gas;       Haze – similar to smog; < 1 µm;
condensation of liquid or dispersal    solid particles and water vapor
of small liquid droplets; usually
                                       Generally accepted size ranges,
due to temperature change; few µm
to 100 µm; also mist                   sampling and control methods for
                                       each are given in Fig. 4.1 on pp. 79-
Smog – combination of smoke and        80 (accepted by American Society
fog; < 1 µm; contains photochemical    of Heating, Refrigerating & Air
reaction products and water vapor      Conditioning Engineers)

  Dynamic Behavior of Aerosols                       Stokes’ Law

Brownian Motion – controlling          Used to determine settling velocity
mechanism for particles < 0.1 µm       of dust particles > 1 µm falling in a
suspended in quiescent atmosphere;     quiescent setting with Reynolds
random movement of particles           numbers < 1
caused by movement of gas              Settling velocity determined by
molecules that “hit” the particles;    equating drag force on falling
resulting mixing of particles and      (spherical) particle to force of gravity
gases called diffusion                 (~10% error)

                                        Stokes’ Law – Derived Equation
            Stokes’ Law
                                       Terminal settling velocity:
If particles are non-spherical, then               ρpDp2g
Stokes’ diameter can be used                Vt = ------------           (Eq. 4.1)
instead                                             18 µ

Stokes’ diameter – diameter of         ρp - density of particle, kg/m3
hypothetical spherical particle        Dp - diameter of particle, m
                                       g - gravity constant, 9.807 m/s2
with same density and settling         µ - viscosity of air, 1.81 x 10-5 Pa.s
velocity as the non-spherical
particle                               For Reynolds number ≤ 1.0; diameter > 1 µ m

Accompanying equation for
Reynolds number check:                                 When particle < 1 µm, equation
                                                       4.1 is inaccurate (slippage at
             ρpVt Dp
      NRe = ------------               (Eq. 4.2)       particle surface)
                                                       Particle falls faster than
Vt – relative velocity of particle                     predicted
Note: This is particle Reynolds number,                Must apply Cunningham
different from Reynolds number for fluid
flow (introduced later); if Reynolds number            correction factor, Cc, to the
> 1.0, another equation must be used (see
Hinds, 1982, p. 51)                                    velocity calculation

Cunningham correction factor:                             Behavior of Aerosols in a
               2.52λ λ                                       Moving Airstream
      Cc = 1 + -------                 (Eq. 4.3)         Dust concentrations downwind of a
                                                         dust source function of rate of
λ– mean free path of molecules of gas, m,                convection, diffusion, agglomeration,
which is the average distance a gas molecule             and other depositional factors
travels before colliding with another
molecule                                                 Thus, dust concentrations can be
For air, λ = 6.6 x
                 10-8 m at 200C,  1 atm; allows use      hard to predict
of Stokes’ law for particles as small as 0.1 µm
                                                         Some studies done in past
Include Cc in equation 4.1, when necessary

                                                      Fibrogenic dusts:
                                                        a. silica (quartz, cristobalite,
    Classification of                                      tridymite, chert)
                                                        b. silicates (asbestos, talc, mica,
     Mineral Dusts                                        others)

      and Other                                         c. metal fumes (nearly all)
                                                        d. beryllium, tin, iron ores
   Relevant Aerosols                                    e. carborundum
                                                        f. coal

Carcinogenic aerosols:                 Toxic (poisonous) aerosols:
  a. asbestos                            a. dusts of ores of beryllium,
                                           arsenic, lead, uranium, radium,
  b. radon daughters (attached to          thorium, chromium, vanadium,
    any dust)                              mercury, cadmium, antimony,
  c. arsenic                               selenium, manganese, tungsten,
                                           nickel, silver (principally oxides
  d. diesel particulate matter (DPM)       and carbonates)
    - suspected
                                         b. mists and fumes of organic and
  e. silica – suspected                    other body-sensitizing chemicals

Radioactive dusts:                     Explosive dusts (airborne):
  a. ores of uranium, radium, and        a. metallic dusts (magnesium,
     thorium (alpha and beta rays)         aluminum, zinc, tin, iron)
  b. dusts with radon daughters          b. coal (bituminous, lignite)
    attached (alpha radiation)
                                         c. sulfide ores
                                         d. organic dusts

                                       Physiological Effects of Mineral Dusts
Nuisance dusts:
  a. gypsum
  b. kaolin
  c. limestone

Note: can overload lung clearance
      mechanism, causing some
      respiratory effect

Respiratory system’s clearance           Terminology on inhaled particles:
mechanisms:                              Inspirable – capable of being inhaled
                                         into the nose or mouth; < 100 µm
Nose – hair, mucous
                                         Thoracic – reach past mouth and
Mouth – mucous                           nasal region; < 25 µm
Trachea, bronci, bronchioles – mucous,   Tracheobronchial – 5-25 µm
                                         Respirable dust – enter aveolar region;
Alveoli – surfactant, macrophages        generally < 5 µm ; some up to 10 µm
(phagocytes), lymphatic system

 Respirable Dust Penetration Curves
                                           Respirable Dust Penetration Curves

                                         Based on aerodynamic diameter –
                                         diameter of particle with a density of 1
                                         g/cm3 that has the same aerodynamic
                                         properties as a given particle of
                                         arbitrary shape
                                         Not all particles inhaled to the lungs
                                         are deposited; the maximum
                                         deposition rate occurs at 3 µm

  Respirable Dust Deposition Curves
                                         Historical Background of Health Effects
                                           Pliny the Younger – diseases first reported
                                           in first century
                                           Agricola – described health effects in 1500s
                                           For centuries, diseases recognized but not
                                           well understood
                                           1896 Roentgen invented x-ray machine,
                                           which would be used later to diagnose

Historical Background of Health Effects         Respiratory Ailments and Diseases
  Gauley Bridge, WV – galvanizing event in          Silicosis
  U.S. (1930s); protection laws vs. silicosis
                                                    Silicate pneumoconiosis
  Extensive research on coal workers’
  pneumoconiosis just before WW II, then            Asbestosis
  accelerated afterwards
                                                    Coal workers’ pneumoconiosis
  Asbestos link to cancer proved in the 1970s
                                                    Beryllium disease
  Research results from animal studies link
  DPM to cancer in 1980s                            Siderosis

                                                       Explosive Dusts
   Dust Harmfulness Factors
                                                 When suspended in air in high
          Composition                            concentration

          Concentration                          Large surface area of particles

          Particle size                          Powerful chemical reaction upon
          Exposure time
                                                 Ignite from open flame, electric arc,
          Individual susceptibility              blast, methane ignition,
                                                 autoignition at critical temperature

          Explosive Dusts                          Coal Dust Explosions –
                                                   Explosibility Variables
    Explosions in air-methane mixtures
    propagate at speed of sound (1117                   Composition
    fps); called detonating explosions                  Particle size
    Air-dust mixtures propagate slower;                 Concentration
    flame speed ~ 30-35 fps; called                     Flammable gas
    deflagrating explosions; self-feed
    since shock wave travels faster,                    Moisture effects
    stirring up dust                                    Presence of incombustible material
    Extensive research on explosions                    Other dusts

Lean flammability limit for mixtures      Explosibility data for mixtures of coal
     of methane and coal dust              dust and limestone dust for varying
                                                  amounts of rock dust

 Explosibilities of mineral-related

                                       Table 4.3 Aerosol Sampling Instruments (Continued)

                                              Measures of Aerosol Exposure
  Measures of Aerosol Exposure
                                             Deposited dose = IPpPd Σ EiTi
Dose = Σ EiTi      (integral form, too)

                                             I – inhalation rate, m3/h
Ei – exposure                                Pp – probability that measured dust
                                                 will penetrate to alveoli
Ti – time period
                                             Pd – probability that dust
                                                  penetrating alveoli will be

                                            Diesel Particulate Matter (DPM)
Measures of Aerosol Exposure                   Fumes and soot from incomplete

 Lastly,                                       Spherical carbon core < 1 µm
                                               Polycyclic aromatic hydrocarbons
 ETWA = dose/total exposure time               (PAHs) and other chemical
                                               compounds are absorbed on carbon
                                               Particles agglomerate and form

     Measurement of DPM
  Many studies using 10-stage              In-mine
  impactors, MOUDI (gravimetric)
  Complications in analysis (see figure,
  next slide)                              samples

  Dichotomous sampler developed
  Respirable Combustible Dust method
  NIOSH Method 5040 – carbon
  analysis => elemental carbon

                    Next Lecture
Sources of Dusts
   in Mines         Aerosol Control
                    Technology and
  Discussion       Personal Protective


To top