study guide

1

 Classes of Airborne Hazards

 Particulates

 Gases and vapors

 Oxygen-deficient atmospheres

 Size-selective sampling

 Inhalable fraction

 Thoracic fraction

 Respirable fraction

 Occupational diseases

associated with airborne

hazard exposure

EHST 3700/3701:

Industrial Hygiene

 To discuss the reasons for air sampling in the

workplace

 To explain the different types of sampling

strategies

 To describe some sampling methods for air

contaminants

 Uses of Air Sampling

 Sampling Particulates

 Sampling Gases and Vapors

 Standard Sampling and Analysis Methods

 To determine or

monitor

concentration

of airborne

contaminants

 Before design changes

 While waiting for control

implementation

 After establishment of

controls

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 Identification of contaminants in an emergency

situation or in an unknown atmosphere

 Identification of potential overexposure

situations or high-exposure activities

 Providing a historical record of employee

exposures for company and employee records

 Evaluating effectiveness of engineering controls

 Verifying adequacy of respiratory protection

 Initial determination of exposures

 Periodic sampling to meet regulatory or company

policy requirements

 Evaluation of exposure status relative to an

exposure limit

 Amount of oxygen

present

 Potential flammability

of the air

 Presence of toxic

materials at hazardous

concentration

 Selection of the sampling methods

 Type of samples taken

 Number of samples taken

 Length of the sampling interval

 Method of analysis

 Reporting of the results

Direct-reading Integrated Sampling

 Real-time sampling

 Immediate or very

fast feedback on

sampling results

Sampling medium

Tubing

Sampling pump

SAMPLING TRAIN

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High-Volume Sampling Pump Personal Sampling Pump

 Generally small

 Weigh 1-2 lbs or less

 Rates: 1 mL/min to 4 LPM

 0.001 – 200 mL/min – gases

and vapors

 1 – 4 LPM - particulates

 Larger, heavier and noisier

 Rates: > 4 LPM

 Used in a fixed location in

a work area

Area Samples Personal Samples

 Compared against

exposure limits

 Sample collecting

device attached to

the worker’s shirt

collar or lapel

(breathing zone)

Breathing Zone

 Provides info about average

levels of contamination in the

area

 Useful for evaluating overall air

quality or effectiveness of

controls

 Generally not acceptable for

evaluating worker exposure

 Applications:

 Outside of an asbestos or lead abatement area

 Clearance samples after hazard material

cleanup

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Contaminant /

Aerosol Type

Sampling Media

Commonly Used

Particulates – dust,

fibers, fumes

Filters

Dusts and mists Filters, absorbing solutions

Gases and vapors Absorbing solutions, solid

sorbent tubes, passive

samplers, evacuated

containers, and sample

bags

Filters

Filter Cassette Filter and Cassette Assembly

Open-Face Sampling Close-Face Sampling

 Impaction

 Interception

 Electrostatic attraction

 Size of the particle

 Electric charge of the particle and filter

 Type of filter

 Sample flow rate

 Mixed cellulose ester filters (MCEF)

 Polyvinyl chloride (PVC) filters

 Teflon filters

 Glass fiber filters

 Coated/ treated filters

 Pore arrangement makes very

effective collectors of

particles

 Average size of openings

controlled in manufacturing

process (0.4 – 0.8 um)

 Analysis depends on materials

collected

 Fumes – acid digestion, metal content analysis

 Fibers – removal of filter section, acetone

vapor treatment, fiber counting under

microscope

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 Good resistance to acidic and basic substances

 Do not absorb much water vapor (hydrophobic)

 Commonly used to collect dusts

 Analyzed using gravimetric analysis Desiccator Pre-sampling weight

Post-sampling weight

Dust sampling

Desiccator

24 hr

24 hr

Dust weight = post-sampling weight – pre-sampling weight

Cyclone

A ir

F lo

w

 PTFE (polytetrafluoroethylene) filters

 Chemical resistant and hydrophobic

 Use: aromatic hydrocarbon (benzo(a)pyrene)

given off from hot tar or asphalt

 Composed of layers of fibers arranged in a

haphazard pattern

 Uses: collection of particulates and some

droplets of contaminant (i.e. mercury, acid

gases)

 Coated with special chemical that enhance

collection by chemically reacting with the

contaminant

 Example:

 NIOSH Method 6004  Sulfur dioxide

 Cellulose filter coated with sodium carbonate

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1. Overloading

2. Static electricity

3. Moisture or physical damage

4. Contamination with interfering substances

Impingers Sorbent tubes Passive samplers

Sample bags

Evacuated cylinders

 Small glass tubes that contain

sampling media

 Sorbent:

 Activated charcoal

 Silica gel

 Collected compounds

desorbed from sorbent

 Coconut shells activated through heating

with 800 – 900 ºC steam

 Used to collect organic solvents and

vapors

 Alcohols

 Ketones

 Aromatic compounds

 Produced from the action of sulfuric acid on

sodium silicate

 Most often used to collect polar compounds

 Amine

 Halogenated compounds

 Hydrogen chloride

 Hydrogen bromide

 Hydrogen fluoride

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 When the backup section contains amount of

contaminant equal to 20-25% of the amount

in the front section

 Sample result is an underestimate of the

actual airborne concentration

 To minimize:

 Shorter sampling interval

 Frequent changes of sorbent tubes

 Use of larger sorbent tubes

 Use of incorrect sorbent

 Effects of temperature and relative

humidity

 Presence of other compounds

 Samples without an air sampling pump

 Collection is accomplished through diffusion

(i.e. diffusive sampling)

 Small clip-on devices that contain solid

sorbent

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 Colorimetric diffusive

tubes

 Color change due to the

presence of a particular

contaminant

 Results:

 Present or not

 Range of concentration

 No pumps to calibrate

 No pump battery failures

 Less work interference in wearer

 Glass container with

a measured volume

of a particular

solution

 Use: sampling of

nonreactive and

highly soluble

airborne

contaminants

 Sodium hydroxide – ammonia sampling

 Distilled water – sampling of water-soluble

materials

Lab for

Analysis

 Loss of solution through spills or leaks

 Breakage of cylinder

 Evaporation during sampling

 Corrosive solutions

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 Represents a very brief sampling period

 Uses:

 Evaluation of compliance with a ceiling or peak

limit

 Screening and identification of possible

contaminants

 Characterization of the atmosphere

Sample Bag Evacuated Canister

 OSHA Reference Methods:

http://www.osha.gov/dts/sltc/methods/toc.

html

 NIOSH Manual of Analytical Methods:

http://www.cdc.gov/niosh/docs/2003-154/

 Sampling media to be used

 Sampling flow rate

 Volume of air to be sampled

 Sample preservation and handling

 Detailed procedures for analysis

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 Air flow passes slowly enough that

 Contaminant in air is collected

 Contaminant collected is not pulled off the

sampling medium

 Process of determining the rate at which the

pump draws air through the sampling

medium

10

Time it takes for

bubble to move

from 1 volume mark

to another (sec)

Volume travelled

by the bubble (mL) 60 sec

1 min

1 L _

1000 mL

Air flow =

(LPM)

 Air sampling may be done for many reasons.

 Purpose of sampling may affect the method

chosen for sample collection and analysis.

 The 2 basic approaches to air sampling are

direct-reading (produces immediate

feedback) and integrated sampling (sample

sent to the lab for analysis).

 Particulate sampling uses filters as media.

 Gas and vapor sampling uses different media,

such as sorbent tubes, passive samplers,

impingers, sample bags and evacuated

canisters.

 Validated sampling methods are available

from OSHA and NIOSH, which contain specific

instructions about sample collection,

shipping and analysis.

 Air flow calibration is one skill an industrial

hygienist must learn and is important in

ensuring accuracy of sampling results.

 Download a sampling method of your

interest (OSHA or NIOSH).

 Identify the following on the method by

highlighting and numbering:

1. Analyte

2. Sampling media used

3. Flow rate (range)

4. Total volume of air sample (range)

5. Analytical technique

 Bring to class on Friday and be

prepared to share.