Industrial hygiene airborne particulates
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INDUSTRIAL HYGIENE - AIRBORNE PARTICULATES. UNIVERSITY OF HOUSTON – DOWNTOWN. INTRODUCTION. Introduce the techniques available for Industrial Hygienists to recognize, evaluate exposures to particulates, and control in occupational settings.

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Industrial hygiene airborne particulates

INDUSTRIAL HYGIENE -AIRBORNE PARTICULATES

UNIVERSITY OF HOUSTON – DOWNTOWN


Introduction

INTRODUCTION

Introduce the techniques available for Industrial Hygienists to recognize, evaluate exposures to particulates, and control in occupational settings.

Inhaled particles may react with or be absorbed through tissues to cause adverse health effects. Variables include:

-size, shape, and density;

-chemical properties;

-airborne concentration and time of exposure, and other factors, etc.; so,

-health effects – irritation, illness, disease.


Aerosols

AEROSOLS

Aerosol – described as solid and/or liquid particles dispersed in a gaseous medium. Range of > 50 um to microscopic particles invisible to naked eye.

For IH, gaseous medium is usually AIR.

Occupational aerosol hazards recognized by:

-Pliny

-Agricola

-Ramazzini

-Sir Percival Pott

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


Pneumoconiosis

PNEUMOCONIOSIS

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

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

Familiar with properties and techniques.

Evolving ultrafine and nano-sized aerosols.

Incidentally addresses bioaerosols or aerosols of biological origin.


Assessment techniques

ASSESSMENT TECHNIQUES

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

Evolving ultrafine and nano-sized aerosols.

Incidentally addresses bioaerosols or aerosols of biological origin.


Definitions

DEFINITIONS

Forms of Aerosols:

  • Dust (also crystalline materials)

  • Fumes

  • Mists

  • Fogs

  • Smokes

  • Fibers (length exceeds diameter)


Dusts

DUSTS

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


Fumes

FUMES

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


Mists

MISTS

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


Industrial hygiene airborne particulates

FOGS

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


Smokes

SMOKES

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


Fibers

FIBERS

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


Aerosols1

AEROSOLS

Aerosol concentrations in air are often assessed by mass per unit volume (mg/M3); when using mass, large particles have the most significant impact on total mass.

Mass = Volume x Density

Other methods to assess aerosols include particle counting (mppcf) and total surface area. Can account for contribution of reactive surfaces and give consideration to smaller particles; good evaluation tools to assess risk of ultrafine and nano-materials.


Character morpholopy

CHARACTER/MORPHOLOPY

  • Aerosol distribution – Figure 8-1

  • Monodisperse vs. Polydisperse; modal

  • Particle size distribution: log normal !!!

  • Isometric – length dimension independent of particle orientation (e.g. dusts)

  • Spherical – based on diameter

  • Singlet – single discrete particles and remain

  • Aggregate – coagulate or flocculate (i.e. soot); large surface are per unit mass

  • Morphology – optical or electron microscopy


Deposition

DEPOSITION

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

-Physical and chemical nature;

-Exposure conditions;

-Individual characteristics.


Deposition mechanisms

DEPOSITION MECHANISMS

-Inertial impaction

-Interception

-Sedimentation

-Electrostatic attraction

-Diffusion (i.e. Brownian movement)


Inertial motion deposition

INERTIAL MOTION/DEPOSITION

Inertia - defined as tendency to resist a change in motion; important for human inhalation/deposition as well as aerosol sampling.

Impaction on surface within distance traveled; likelihood increased with the mass and velocity of particle and the sharpness of change in direction.

Stokes Number = St.; inefficiency of impaction increases with increasing St.

AED


Interception

INTERCEPTION

Interception – flow of an aerosol past a surface may produce particle deposition.

Deposition process does not depend on particle motion across fluid stream lines, as for inertial impaction. Depends on particle coming close enough to a flow boundary (by any means) that it may be collected by virtue of its own physical size.

Significant to elongated particles (i.e. fibers).


Sedimentation

SEDIMENTATION

Refers to movement of an aerosol particle through a gaseous medium under the influence of gravity. The rate of settling depends on particle size, shape, mass, and orientation (for non-spherical particles) and on the air density and viscosity.

Gravitational force opposed by gas viscosity. Stokes’ Law and Aerodynamic Equivalent Diameter (AED).

Aerodynamic equivalent diameter – “normalizes” different aerosols to common basis for comparison.


Surface particle retention

SURFACE PARTICLE RETENTION

Action of various forces:

- London-van der Waals (by molecular interactions between particle and surfaces);

-electrostatic attraction (charge differences between particle and surface);

-capillary forces (adsorption of water {or other liquid} film between the particle and the surface).

Smaller particles are more difficult to dislodge than larger ones.


Diffusion

DIFFUSION

Diffusion - aerosol particles in a gaseous medium collide with individual gas molecules that are in random Brownian motion associated with their fundamental microscopic thermal behavior.

Diffusion coefficient is inversely proportional to particle geometric size and is independent of particle density.

Favored by small particle diameter, large concentration differences, and short distances for diffusion.


Deposition by inhalation

DEPOSITION BY INHALATION

Definition of “Breathing zone”:

  • Nasopharyngeal(NP): hygroscopic; absorb water; humid; inertial impaction is most significant.

  • Tracheobronchial (TB): conducting airways distribute the inhaled air quickly and evenly to deeper portions of lung; therefore, lower velocities and higher residence times favor sedimentation and diffusion. Thoracic fraction of < 10 um.

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


Particle deposition

PARTICLE DEPOSITION

-Head/airways/nasopharyngeal region: nose, nasal turbinates, throat – 5 to 100 um by IMPACTION

-Thoracic/bronchial region: trachea, bronchi – 1 to 10 um by SEDIMENTATION, INTERCEPTION, AND IMPACTION

-Alveolar/Gas exchange region: terminal bronchioli and alveoli – 0.01 to 10 um by DIFFUSION


Critical exposure factors

CRITICAL EXPOSURE FACTORS

  • Chemical/biological composition

  • Crystalline, structural, and isotropic forms

  • Shape of particles

  • Size of particles

  • Dose: concentration of particles in the work environment and exposure duration

  • Pre-existing health or generic status of worker

  • Concurrent exposure to other toxic agents.


Stokes and aerodynamic diameter

STOKES AND AERODYNAMIC DIAMETER

Discuss particle size in terms of the diameter of a spherical particle of the same density that would exhibit the same behavior as the particle in question = Stokes diameter (dST).

Aerodynamic equivalent diameter, dae, which is the diameter of a unit density sphere (density = 1 g/cm3) that would exhibit the same settling velocity as the particle in question.

Aerodynamic equivalent diameter “normalizes” different aerosols to a common basis so that behaviors may be directly compared. Particle Stokes and aerodynamic diameters are important for inertial and gravitational deposition, collector design, and data interpretation.


Airborne particle motion

AIRBORNE PARTICLE MOTION

Dose– drives biological response; result of exposure history; deposition efficiency; target organs; depends on exposure history; pharmacokinetics of clearance process and intrinsic toxicity. Bioaccumulation.

Dose rate – rate at which substance arrives (inhaled or deposited) and exposure may be measured by IH. Influenced by physical properties of aerosol (size, shape, density, and hygroscopicity [take up water].


Biological reactions

BIOLOGICAL REACTIONS

-Acute sensory/pulmonary irritation

-Lung edema

-Allergic sensitization

-Fibrosis

-Emphysema

-Toxicity – systemic, lymphatic

-Oncogenesis

-Infection

-Metal fume fever


Aerosol sampling theory

AEROSOL SAMPLING THEORY

Sampling objective is to obtain information about aerosol properties at a given location over a specified length of time. Therefore, nature of air flow and particle motion both inside and outside of sampling device is a critical issue regarding performance.

Aerosol mass per unit air volume (mass concentration) based on size fractions and respiratory system penetration by inhalation.

Breathing zone definition.


Filtration techniques

FILTRATION TECHNIQUES

- Study aerosol mass concentration; number concentration; particle morphology; radioactivity; chemical content; and biohazard potential.

- Choice of media depends on the aerosol characteristics and the analytical technique to be used. Various types of filter media. Table 8-E.

- Gravimetric analysis: mass/volume; mg/M3.

- Open–face vs. Closed-face filter cassettes.

-“Total” particulates; under-sample inhalable fraction of larger particle sizes.

-Best is IOM sampler for inhalable fraction.


Particle size selection

PARTICLE SIZE SELECTION

  • Size selective aerosol sampling.

  • External and internal sampling losses.

  • Sampler efficiency is a complex function of: sampler geometry; sampling rate; flow external to sampler; and sampler orientation with respect to direction of air flow.

  • Personal vs. area sampling.

  • Clearance vs. aggressive techniques depending on specific application.


Sampling theory

SAMPLING THEORY

The intention of “total dust” sampling is that all particles in the air should be collected with equal efficiency without respect to any particular particle size fraction. By contrast, particle size-selective sampling is intended to separate the aerosol into size fractions based on health rationale.

Exercise caution regarding sampler choice and insure that the particle size fraction of interest is properly collected.


Particle size selective sampling

PARTICLE SIZE-SELECTIVE SAMPLING

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

-inhalable,

-thoracic, or

-respirable fractions.


Sedimentation techniques

SEDIMENTATION TECHNIQUES

Cyclones use centrifugal forces to effect particle capture.

Cut size indicates aerodynamic diameter of particle for which penetration through the cyclone is 50% (d50 at 4 um for respirable fraction).

Efficient for large particle sizes and IH use as pre-separators in respirable aerosol samplers:

-Dorr-Oliver nylon – 1.7 lpm

-Casella and SKC cyclones – 1.9 lpm.

Others: electrostatic or thermal precipitators.


Impaction techniques

IMPACTION TECHNIQUES

Among most widely used in aerosol characterization in relation to particle size.

Impactor performance by 50% cut point size as d50, which is the particle size captured by the impactor with 50% efficiency.

Single stage – DPM or PEM.

Multi-stage – used in cascade configuration – cumulative mass distribution; Andersen or Marple.

Different analysis – gravimetric; chemical, etc..

Airborne Particulate Matter fractions – PM 2.5 / 10.

Liquid impingers for mists; particle counting.


Airborne particulates

AIRBORNE PARTICULATES

- Microbial – culturable vs. non-culturable

- Radon/radon progeny

- Diesel exhaust

-Fibers – e.g. asbestos

-Total vs. respirable mass


Sampling techniques

SAMPLING TECHNIQUES

- Size-Selective

- Dual-Phase Monitoring

- Isokinetic Sampling

-Surface Sampling

-Dermal Monitoring


Aerosol size distribution analysis

AEROSOL SIZE DISTRIBUTION ANALYSIS

Particle sizes in an aerosol are often approximately lognormally distributed; that is , the logarithms of the particles sizes follow a Gaussian, or normal, frequency distribution.

Therefore, “statistics” include geometric mean (or median) size and geometric standard deviation (GSD). Distribution expressed using either the count median diameter (CMD) and GSD or the mass median aerodynamic diameter (MMAD) and GSD, depending on how the measurement data were obtained.


Particle sample analysis

PARTICLE SAMPLE ANALYSIS

-Metals

-Free Crystalline Silica

-Asbestos

-Radioactive Particles

-Gravimetric Analysis

-Biological Organisms

-Organic Particles

-Direct-Reading Particle Detectors


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