INDUSTRIAL HYGIENE - AIRBORNE PARTICULATES

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21 Φεβ 2014 (πριν από 3 χρόνια και 7 μήνες)

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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
.



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


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


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


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

Forms

of

Aerosols
:



Dust

(also

crystalline

materials)


Fumes


Mists



Fogs


Smokes


Fibers

(length

exceeds

diameter)


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


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


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
.





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


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


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
.





AEROSOLS


Aerosol

concentrations

in

air

are

often

assessed

by

mass

per

unit

volume

(mg/M
3
)
;

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


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


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


-

Inertial

impaction


-

Interception


-

Sedimentation


-

Electrostatic

attraction


-

Diffusion

(i
.
e
.

Brownian

movement)



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



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


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


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

-

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

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


-

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


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


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

(d
ST
)
.



Aerodynamic

equivalent

diameter,

d
ae
,

which

is

the

diameter

of

a

unit

density

sphere

(density

=

1

g/cm
3
)

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


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


-

Acute

sensory/pulmonary

irritation


-

Lung

edema


-

Allergic

sensitization


-

Fibrosis


-

Emphysema


-

Toxicity



systemic,

lymphatic


-

Oncogenesis


-

Infection


-

Metal

fume

fever



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


-


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/M
3
.


-


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


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


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


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


Cyclones

use

centrifugal

forces

to

effect

particle

capture
.



Cut

size

indicates

aerodynamic

diameter

of

particle

for

which

penetration

through

the

cyclone

is

50
%

(d
50

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


Among

most

widely

used

in

aerosol

characterization

in

relation

to

particle

size
.



Impactor

performance

by

50
%

cut

point

size

as

d
50
,

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


-


Microbial



culturable

vs
.

non
-
culturable



-


Radon/radon

progeny


-


Diesel

exhaust




-

Fibers



e
.
g
.

asbestos


-

Total

vs
.

respirable

mass


SAMPLING TECHNIQUES


-


Size
-
Selective



-


Dual
-
Phase

Monitoring


-


Isokinetic

Sampling



-

Surface

Sampling


-

Dermal

Monitoring


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



-

Metals


-

Free

Crystalline

Silica


-

Asbestos


-

Radioactive

Particles


-

Gravimetric

Analysis


-

Biological

Organisms


-

Organic

Particles


-

Direct
-
Reading

Particle

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