INDUSTRIAL HYGIENE -INDUSTRIAL HYGIENE - AIRBORNE PARTICULATES AIRBORNE PARTICULATES

UNIVERSITY OF HOUSTON – DOWNTOWN UNIVERSITY OF HOUSTON – DOWNTOWN

INTRODUCTIONINTRODUCTIONIntroduce the techniques available for Industrial Introduce the techniques available for Industrial Hygienists to recognize, evaluate exposures to Hygienists to recognize, evaluate exposures to particulates, and control in occupational settings. particulates, and control in occupational settings. Inhaled particles may react with or be absorbed Inhaled particles may react with or be absorbed through tissues to cause adverse health effects. through tissues to cause adverse health effects. Variables include:Variables include:-- size, shape, and density;size, shape, and density;-- chemical properties;chemical properties;-- airborne concentration and time of airborne concentration and time of exposure, and other factors, etc.; so, exposure, and other factors, etc.; so, -- health effects – irritation, illness, disease. health effects – irritation, illness, disease.

AEROSOLS AEROSOLS Aerosol – described as solid and/or liquid particles Aerosol – described as solid and/or liquid particles dispersed in a gaseous medium. Range of > 50 dispersed in a gaseous medium. Range of > 50 um to microscopic particles invisible to naked eye.um to microscopic particles invisible to naked eye.For IH, gaseous medium is usually For IH, gaseous medium is usually AIRAIR. . Occupational aerosol hazards recognized by: Occupational aerosol hazards recognized by:

-- PlinyPliny-- AgricolaAgricola-- RamazziniRamazzini-- Sir Percival PottSir Percival Pott

Least toxic as “nuisance dusts”; ACGIH – PNOC Least toxic as “nuisance dusts”; ACGIH – PNOC or OSHA with parallel term – PNOR.or OSHA with parallel term – PNOR.

PNEUMOCONIOSISPNEUMOCONIOSIS Derived from Greek; means “dust in the lungs”. Derived from Greek; means “dust in the lungs”.

Widely used to describe lung diseases. Recent Widely used to describe lung diseases. Recent universally accepted definition of “the universally accepted definition of “the accumulation of dust in the lungs and the tissue accumulation of dust in the lungs and the tissue reaction to its presence”. Assumes dust is reaction to its presence”. Assumes dust is insoluble/solid when deposited in alveoli of lung. insoluble/solid when deposited in alveoli of lung.

e.g. Asbestosis, Silicosis, Coal (black lung), dust.e.g. Asbestosis, Silicosis, Coal (black lung), dust.

Familiar with properties and techniques. Familiar with properties and techniques. Evolving ultrafine and nano-sized aerosols.Evolving ultrafine and nano-sized aerosols.Incidentally addresses bioaerosols or aerosols of Incidentally addresses bioaerosols or aerosols of biological origin. biological origin.

ASSESSMENT TECHNIQUESASSESSMENT TECHNIQUES Techniques for sampling and analysis Techniques for sampling and analysis

continue to evolve for characterization of continue to evolve for characterization of aerosols. A single technique is not aerosols. A single technique is not appropriate; IH must be familiar with appropriate; IH must be familiar with properties and assessment techniques. properties and assessment techniques.

Evolving ultrafine and nano-sized aerosols.Evolving ultrafine and nano-sized aerosols.Incidentally addresses bioaerosols or Incidentally addresses bioaerosols or aerosols of biological origin. aerosols of biological origin.

DEFINITIONSDEFINITIONSForms of Aerosols:Forms of Aerosols:

Dust (also crystalline materials)Dust (also crystalline materials) FumesFumes Mists Mists FogsFogs SmokesSmokes Fibers (length exceeds diameter)Fibers (length exceeds diameter)

DUSTSDUSTS Particulate aerosols produced by mechanical Particulate aerosols produced by mechanical

processes such as breaking, grinding, and processes such as breaking, grinding, and pulverizing. Examples: mining; material handing; pulverizing. Examples: mining; material handing; dry material prep and packaging. Chemically dry material prep and packaging. Chemically unchanged; smaller size and higher specific unchanged; smaller size and higher specific surface area may enhance ability to be airborne, surface area may enhance ability to be airborne, inhaled, penetration, toxicity, solubility or inhaled, penetration, toxicity, solubility or explosion. Less than 1 um up to 1 mm; regular in explosion. Less than 1 um up to 1 mm; regular in shape; some crystalline materials; length to width shape; some crystalline materials; length to width ratio less than 3:1 with some notable exceptions.ratio less than 3:1 with some notable exceptions.

FUMESFUMES Fine solid aerosol particles produced from Fine solid aerosol particles produced from

the re-condensation of vaporized material the re-condensation of vaporized material that is normally solid at standard conditions that is normally solid at standard conditions is melted and vaporized; condensation (0.01 is melted and vaporized; condensation (0.01 um) occurs during cooling of vapor – um) occurs during cooling of vapor – nucleation; coagulation – agglomerates at 1 nucleation; coagulation – agglomerates at 1 um in diameter are nearly spherical. Small um in diameter are nearly spherical. Small enough to penetrate to deep lung areas; enough to penetrate to deep lung areas; chemically quite reactive. Examples: chemically quite reactive. Examples: welding/smelting – “metal fume fever”. welding/smelting – “metal fume fever”.

MISTSMISTS Spherical droplet aerosols produced from Spherical droplet aerosols produced from

bulk liquid by mechanical processes such as bulk liquid by mechanical processes such as splashing, bubbling, or spraying. Droplets splashing, bubbling, or spraying. Droplets are chemically unchanged from the parent are chemically unchanged from the parent liquid and range in size from a few microns to liquid and range in size from a few microns to over 100 um. Mist aerosol from spray over 100 um. Mist aerosol from spray painting. Examples: mist aerosol from spray painting. Examples: mist aerosol from spray painting; crop spraying operations designed painting; crop spraying operations designed to produce mists; mist droplet aerosols by to produce mists; mist droplet aerosols by coughing or treatment of infected patients in coughing or treatment of infected patients in health care settings. health care settings.

FOGSFOGS Droplet aerosols produced by physical Droplet aerosols produced by physical

condensation from the vapor phase. Fog condensation from the vapor phase. Fog droplets are typically smaller than droplets are typically smaller than mechanically generated mist droplets, and mechanically generated mist droplets, and are of the order of 1 to 10 um. Whereas are of the order of 1 to 10 um. Whereas mists may visibly settle toward the ground, mists may visibly settle toward the ground, fogs appear to remain suspended in the air. fogs appear to remain suspended in the air.

SMOKESSMOKES Complex mixtures of solid and liquid aerosol Complex mixtures of solid and liquid aerosol

particles, gases, and vapors resulting from particles, gases, and vapors resulting from incomplete combustion of carbonaceous materials incomplete combustion of carbonaceous materials and are formed by complex combinations of and are formed by complex combinations of physical nucleation-type mechanisms and physical nucleation-type mechanisms and chemical reactions. Examples: tobacco smokes; chemical reactions. Examples: tobacco smokes; smokes from other combustion (i.e. plastics, smokes from other combustion (i.e. plastics, synthetic fabrics, and petrochemical products – synthetic fabrics, and petrochemical products – toxic). Primary smoke particles are on the order of toxic). Primary smoke particles are on the order of 0.01 to 1 um in diameters; but like fumes, 0.01 to 1 um in diameters; but like fumes, agglomerates containing many particles may be agglomerates containing many particles may be much larger. much larger.

FIBERSFIBERS Elongated particles with length much greater than Elongated particles with length much greater than

width. May be naturally occurring or synthetic. width. May be naturally occurring or synthetic. Examples: asbestos with convention to define a Examples: asbestos with convention to define a “fiber” as a particle with a ratio of length or width “fiber” as a particle with a ratio of length or width greater than 3:1; specific asbestos-related greater than 3:1; specific asbestos-related diseases; synthetic fibers, etc. Fibrous aerosols diseases; synthetic fibers, etc. Fibrous aerosols display aerodynamic and health effects behaviors display aerodynamic and health effects behaviors that differ in many respects from spherical or near-that differ in many respects from spherical or near-spherical particles of the same material and mass, spherical particles of the same material and mass, so aerosol characterization is more complex for so aerosol characterization is more complex for fibers than other aerosols. fibers than other aerosols.

AEROSOLS AEROSOLS Aerosol concentrations in air are often Aerosol concentrations in air are often assessed by mass per unit volume (mg/M3); assessed by mass per unit volume (mg/M3); when using mass, large particles have the when using mass, large particles have the most significant impact on total mass. most significant impact on total mass. Mass = Volume x DensityMass = Volume x DensityOther methods to assess aerosols include Other methods to assess aerosols include particle counting (mppcf) and total surface particle counting (mppcf) and total surface area. Can account for contribution of area. Can account for contribution of reactive surfaces and give consideration to reactive surfaces and give consideration to smaller particles; good evaluation tools to smaller particles; good evaluation tools to assess risk of ultrafine and nano-materials. assess risk of ultrafine and nano-materials.

CHARACTER/MORPHOLOPYCHARACTER/MORPHOLOPY Aerosol distribution – Figure 8-1Aerosol distribution – Figure 8-1 Monodisperse vs. Polydisperse; modalMonodisperse vs. Polydisperse; modal Particle size distribution: Particle size distribution: log normal log normal !!!!!! Isometric – length dimension independent of Isometric – length dimension independent of

particle orientation (e.g. dusts)particle orientation (e.g. dusts) Spherical – based on diameterSpherical – based on diameter Singlet – single discrete particles and remainSinglet – single discrete particles and remain Aggregate – coagulate or flocculate (i.e. Aggregate – coagulate or flocculate (i.e.

soot); large surface are per unit masssoot); large surface are per unit mass Morphology – optical or electron microscopy Morphology – optical or electron microscopy

DEPOSITIONDEPOSITIONFor a given exposure situation, the amount For a given exposure situation, the amount of aerosolized material actually inhaled; the of aerosolized material actually inhaled; the fraction of inhaled aerosol depositing in the fraction of inhaled aerosol depositing in the different regions of the respiratory tract, and different regions of the respiratory tract, and the fate of the deposited material are the fate of the deposited material are functions of: functions of:

-- Physical and chemical nature; Physical and chemical nature; -- Exposure conditions;Exposure conditions;-- Individual characteristics.Individual characteristics.

DEPOSITION MECHANISMSDEPOSITION MECHANISMS-- Inertial impactionInertial impaction-- InterceptionInterception-- SedimentationSedimentation-- Electrostatic attractionElectrostatic attraction-- Diffusion (i.e. Brownian movement)Diffusion (i.e. Brownian movement)

INERTIAL MOTION/DEPOSITIONINERTIAL MOTION/DEPOSITIONInertia - defined as tendency to resist a Inertia - defined as tendency to resist a change in motion; important for human change in motion; important for human inhalation/deposition as well as aerosol inhalation/deposition as well as aerosol sampling. sampling. Impaction on surface within distance Impaction on surface within distance traveled; likelihood increased with the mass traveled; likelihood increased with the mass and velocity of particle and the sharpness of and velocity of particle and the sharpness of change in direction. change in direction. Stokes Number = St.; inefficiency of Stokes Number = St.; inefficiency of impaction increases with increasing St.impaction increases with increasing St.AEDAED

INTERCEPTIONINTERCEPTIONInterception – flow of an aerosol past a Interception – flow of an aerosol past a surface may produce particle deposition. surface may produce particle deposition. Deposition process does not depend on Deposition process does not depend on particle motion across fluid stream lines, as particle motion across fluid stream lines, as for inertial impaction. Depends on particle for inertial impaction. Depends on particle coming close enough to a flow boundary (by coming close enough to a flow boundary (by any means) that it may be collected by any means) that it may be collected by virtue of its own physical size. virtue of its own physical size. Significant to elongated particles (i.e. fibers). Significant to elongated particles (i.e. fibers).

SEDIMENTATIONSEDIMENTATIONRefers to movement of an aerosol particle through Refers to movement of an aerosol particle through a gaseous medium under the influence of gravity. a gaseous medium under the influence of gravity. The rate of settling depends on particle size, The rate of settling depends on particle size, shape, mass, and orientation (for non-spherical shape, mass, and orientation (for non-spherical particles) and on the air density and viscosity. particles) and on the air density and viscosity. Gravitational force opposed by gas viscosity. Gravitational force opposed by gas viscosity. Stokes’ Law and Aerodynamic Equivalent Stokes’ Law and Aerodynamic Equivalent Diameter (AED).Diameter (AED).Aerodynamic equivalent diameter – “normalizes” Aerodynamic equivalent diameter – “normalizes” different aerosols to common basis for different aerosols to common basis for comparison. comparison.

SURFACE PARTICLE RETENTION SURFACE PARTICLE RETENTION

Action of various forces: Action of various forces: - - London-van der Waals (by molecular London-van der Waals (by molecular

interactions between particle and interactions between particle and surfaces); surfaces);

-- electrostatic attraction (charge electrostatic attraction (charge differences between particle and differences between particle and

surface);surface);-- capillary forces (adsorption of water capillary forces (adsorption of water

{or other liquid} film between the {or other liquid} film between the particle particle and the surface). and the surface). Smaller particles are more difficult to dislodge than Smaller particles are more difficult to dislodge than larger ones. larger ones.

DIFFUSIONDIFFUSIONDiffusion - aerosol particles in a gaseous Diffusion - aerosol particles in a gaseous medium collide with individual gas medium collide with individual gas molecules that are in random Brownian molecules that are in random Brownian motion associated with their fundamental motion associated with their fundamental microscopic thermal behavior. microscopic thermal behavior. Diffusion coefficient is inversely proportional Diffusion coefficient is inversely proportional to particle geometric size and is to particle geometric size and is independent of particle density. independent of particle density. Favored by small particle diameter, large Favored by small particle diameter, large concentration differences, and short concentration differences, and short distances for diffusion. distances for diffusion.

DEPOSITION BY INHALATIONDEPOSITION BY INHALATIONDefinition of “Breathing zone”:Definition of “Breathing zone”: NasopharyngealNasopharyngeal (NP):(NP): hygroscopic; absorb water; hygroscopic; absorb water;

humid; inertial impaction is most significant. humid; inertial impaction is most significant. TracheobronchialTracheobronchial (TB): (TB): conducting airways conducting airways

distribute the inhaled air quickly and evenly to distribute the inhaled air quickly and evenly to deeper portions of lung; therefore, lower velocities deeper portions of lung; therefore, lower velocities and higher residence times favor sedimentation and higher residence times favor sedimentation and diffusion. Thoracic fraction of < 10 um.and diffusion. Thoracic fraction of < 10 um.

PulmonaryPulmonary (P): (P): depending on particle size, either depending on particle size, either sedimentation or diffusion is the dominant sedimentation or diffusion is the dominant deposition mechanism. Respirable fraction. deposition mechanism. Respirable fraction.

PARTICLE DEPOSITIONPARTICLE DEPOSITION-- Head/airways/nasopharyngeal region: Head/airways/nasopharyngeal region:

nose, nose, nasal turbinates, throat – 5 to nasal turbinates, throat – 5 to 100 100 um by um by IMPACTIONIMPACTION

-- Thoracic/bronchial region: trachea, Thoracic/bronchial region: trachea, bronchi – 1 to 10 um by bronchi – 1 to 10 um by SEDIMENTATION, SEDIMENTATION, INTERCEPTION, INTERCEPTION, AND IMPACTIONAND IMPACTION-- Alveolar/Gas exchange region: Alveolar/Gas exchange region: terminal terminal bronchioli and alveoli – 0.01 to 10 bronchioli and alveoli – 0.01 to 10 um by um by DIFFUSIONDIFFUSION

CRITICAL EXPOSURE FACTORSCRITICAL EXPOSURE FACTORS Chemical/biological composition Chemical/biological composition Crystalline, structural, and isotropic formsCrystalline, structural, and isotropic forms Shape of particlesShape of particles Size of particlesSize of particles Dose: concentration of particles in the work Dose: concentration of particles in the work

environment and exposure durationenvironment and exposure duration Pre-existing health or generic status of Pre-existing health or generic status of

workerworker Concurrent exposure to other toxic agents. Concurrent exposure to other toxic agents.

STOKES AND AERODYNAMIC STOKES AND AERODYNAMIC DIAMETERDIAMETER

Discuss particle size in terms of the diameter of a Discuss particle size in terms of the diameter of a spherical particle of the same density that would spherical particle of the same density that would exhibit the same behavior as the particle in exhibit the same behavior as the particle in question = Stokes diameter (dquestion = Stokes diameter (dSTST). ). Aerodynamic equivalent diameter, dAerodynamic equivalent diameter, daeae, which is the , which is the diameter of a unit density sphere (density = 1 diameter of a unit density sphere (density = 1 g/cmg/cm33) that would exhibit the same settling velocity ) that would exhibit the same settling velocity as the particle in question. as the particle in question. Aerodynamic equivalent diameter “normalizes” Aerodynamic equivalent diameter “normalizes” different aerosols to a common basis so that different aerosols to a common basis so that behaviors may be directly compared. Particle behaviors may be directly compared. Particle Stokes and aerodynamic diameters are important Stokes and aerodynamic diameters are important for inertial and gravitational deposition, collector for inertial and gravitational deposition, collector design, and data interpretation. design, and data interpretation.

AIRBORNE PARTICLE MOTIONAIRBORNE PARTICLE MOTIONDoseDose – drives biological response; result of – drives biological response; result of exposure history; deposition efficiency; exposure history; deposition efficiency; target organs; depends on exposure history; target organs; depends on exposure history; pharmacokinetics of clearance process and pharmacokinetics of clearance process and intrinsic toxicity. Bioaccumulation.intrinsic toxicity. Bioaccumulation.Dose rateDose rate – rate at which substance arrives – rate at which substance arrives (inhaled or deposited) and exposure may be (inhaled or deposited) and exposure may be measured by IH. Influenced by physical measured by IH. Influenced by physical properties of aerosol (size, shape, density, properties of aerosol (size, shape, density, and hygroscopicity [take up water].and hygroscopicity [take up water].

BIOLOGICAL REACTIONSBIOLOGICAL REACTIONS-- Acute sensory/pulmonary irritationAcute sensory/pulmonary irritation-- Lung edemaLung edema-- Allergic sensitizationAllergic sensitization-- FibrosisFibrosis-- EmphysemaEmphysema-- Toxicity – systemic, lymphaticToxicity – systemic, lymphatic-- OncogenesisOncogenesis-- InfectionInfection-- Metal fume feverMetal fume fever

AEROSOL SAMPLING THEORYAEROSOL SAMPLING THEORYSampling objective is to obtain information Sampling objective is to obtain information about aerosol properties at a given location about aerosol properties at a given location over a specified length of time. Therefore, over a specified length of time. Therefore, nature of air flow and particle motion both nature of air flow and particle motion both inside and outside of sampling device is a inside and outside of sampling device is a critical issue regarding performance. critical issue regarding performance. Aerosol mass per unit air volume (mass Aerosol mass per unit air volume (mass concentration) based on size fractions and concentration) based on size fractions and respiratory system penetration by inhalation. respiratory system penetration by inhalation. Breathing zone definition. Breathing zone definition.

FILTRATION TECHNIQUESFILTRATION TECHNIQUES- - Study aerosol mass concentration; number Study aerosol mass concentration; number concentration; particle morphology; concentration; particle morphology; radioactivity; radioactivity; chemical content; and biohazard chemical content; and biohazard potential. potential. - - Choice of media depends on the aerosol Choice of media depends on the aerosol characteristics and the analytical technique to characteristics and the analytical technique to be be used. Various types of filter media. Table 8-E.used. Various types of filter media. Table 8-E.- - Gravimetric analysis: mass/volume; mg/M3.Gravimetric analysis: mass/volume; mg/M3.- - Open–face vs. Closed-face filter cassettes. Open–face vs. Closed-face filter cassettes. -- “Total” particulates; under-sample inhalable “Total” particulates; under-sample inhalable fraction of larger particle sizes. fraction of larger particle sizes. -- Best is IOM sampler for inhalable fraction. Best is IOM sampler for inhalable fraction.

PARTICLE SIZE SELECTIONPARTICLE SIZE SELECTION Size selective aerosol sampling. Size selective aerosol sampling. External and internal sampling losses. External and internal sampling losses. Sampler efficiency is a complex function of: Sampler efficiency is a complex function of:

sampler geometry; sampling rate; flow sampler geometry; sampling rate; flow external to sampler; and sampler orientation external to sampler; and sampler orientation with respect to direction of air flow.with respect to direction of air flow.

Personal vs. area sampling.Personal vs. area sampling. Clearance vs. aggressive techniques Clearance vs. aggressive techniques

depending on specific application. depending on specific application.

SAMPLING THEORYSAMPLING THEORYThe intention of “total dust” sampling is that The intention of “total dust” sampling is that all particles in the air should be collected all particles in the air should be collected with equal efficiency without respect to any with equal efficiency without respect to any particular particle size fraction. By contrast, particular particle size fraction. By contrast, particle size-selective sampling is intended particle size-selective sampling is intended to separate the aerosol into size fractions to separate the aerosol into size fractions based on health rationale. based on health rationale. Exercise caution regarding sampler choice Exercise caution regarding sampler choice and insure that the particle size fraction of and insure that the particle size fraction of interest is properly collected. interest is properly collected.

PARTICLE SIZE-SELECTIVE PARTICLE SIZE-SELECTIVE SAMPLINGSAMPLING

Aerosol particle size greatly influences where Aerosol particle size greatly influences where deposition occurs in the respiratory tract, and the deposition occurs in the respiratory tract, and the site of deposition often determines the degree of site of deposition often determines the degree of hazard represented by the exposure. Sampling hazard represented by the exposure. Sampling techniques to measure aerosol as:techniques to measure aerosol as:

-- inhalable,inhalable,-- thoracic, or thoracic, or -- respirable fractions. respirable fractions.

SEDIMENTATION TECHNIQUESSEDIMENTATION TECHNIQUESCyclones use centrifugal forces to effect particle Cyclones use centrifugal forces to effect particle capture. capture. Cut size indicates aerodynamic diameter of Cut size indicates aerodynamic diameter of particle for which penetration through the cyclone particle for which penetration through the cyclone is 50% (d50 at 4 um for respirable fraction). is 50% (d50 at 4 um for respirable fraction). Efficient for large particle sizes and IH use as pre-Efficient for large particle sizes and IH use as pre-separators in respirable aerosol samplers: separators in respirable aerosol samplers:

-- Dorr-Oliver nylon – 1.7 lpmDorr-Oliver nylon – 1.7 lpm-- Casella and SKC cyclones – 1.9 lpm.Casella and SKC cyclones – 1.9 lpm.

Others: electrostatic or thermal precipitators.Others: electrostatic or thermal precipitators.

IMPACTION TECHNIQUESIMPACTION TECHNIQUESAmong most widely used in aerosol Among most widely used in aerosol characterization in relation to particle size. characterization in relation to particle size. Impactor performance by 50% cut point size as Impactor performance by 50% cut point size as d50, which is the particle size captured by the d50, which is the particle size captured by the impactor with 50% efficiency. impactor with 50% efficiency. Single stage – DPM or PEM.Single stage – DPM or PEM.Multi-stage – used in cascade configuration – Multi-stage – used in cascade configuration – cumulative mass distribution; Andersen or Marple. cumulative mass distribution; Andersen or Marple. Different analysis – gravimetric; chemical, etc..Different analysis – gravimetric; chemical, etc..Airborne Particulate Matter fractions – PM 2.5 / 10.Airborne Particulate Matter fractions – PM 2.5 / 10.Liquid impingers for mists; particle counting. Liquid impingers for mists; particle counting.

AIRBORNE PARTICULATESAIRBORNE PARTICULATES- - Microbial – culturable vs. non-Microbial – culturable vs. non-culturable culturable - - Radon/radon progenyRadon/radon progeny- - Diesel exhaust Diesel exhaust -- Fibers – e.g. asbestosFibers – e.g. asbestos-- Total vs. respirable mass Total vs. respirable mass

SAMPLING TECHNIQUESSAMPLING TECHNIQUES- - Size-Selective Size-Selective - - Dual-Phase MonitoringDual-Phase Monitoring- - Isokinetic Sampling Isokinetic Sampling -- Surface SamplingSurface Sampling-- Dermal Monitoring Dermal Monitoring

AEROSOL SIZE DISTRIBUTION AEROSOL SIZE DISTRIBUTION ANALYSIS ANALYSIS

Particle sizes in an aerosol are often Particle sizes in an aerosol are often approximately lognormally distributed; that is , the approximately lognormally distributed; that is , the logarithms of the particles sizes follow a Gaussian, logarithms of the particles sizes follow a Gaussian, or normal, frequency distribution. or normal, frequency distribution. Therefore, “statistics” include geometric mean (or Therefore, “statistics” include geometric mean (or median) size and geometric standard deviation median) size and geometric standard deviation (GSD). Distribution expressed using either the (GSD). Distribution expressed using either the count median diameter (CMD) and GSD or the count median diameter (CMD) and GSD or the mass median aerodynamic diameter (MMAD) and mass median aerodynamic diameter (MMAD) and GSD, depending on how the measurement data GSD, depending on how the measurement data were obtained.were obtained.

PARTICLE SAMPLE ANALYSIS PARTICLE SAMPLE ANALYSIS -- MetalsMetals-- Free Crystalline SilicaFree Crystalline Silica-- AsbestosAsbestos-- Radioactive ParticlesRadioactive Particles-- Gravimetric AnalysisGravimetric Analysis-- Biological OrganismsBiological Organisms-- Organic ParticlesOrganic Particles-- Direct-Reading Particle Detectors Direct-Reading Particle Detectors