study guide

EHST 3700 1

 Basic air sampling approaches

 Integrated sampling

 Direct-reading method

 Types of sampling

 Personal sampling

 Area sampling

 Particulate sampling

 Filters

 Size-selective sampling

 Gas/vapor sampling

 Sorbent tube

 Passive sampling

 Impingers

 Grab sampling

 Validated sampling methods

 OSHA Reference Methods

 NIOSH Manual of Analytical Methods

 Pump calibration

 Liters/minute

 Inverted buret, electronic calibrators

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

 To describe analytical instruments and methods

in laboratories to evaluate air samples

 To interpret and evaluate air sampling results

 To discuss documentation of sampling events

 To discuss about sources of errors in sampling

 To discuss problems or limitations associated

with air samples

 Uses of Air Sampling

 Sampling Particulates

 Sampling Gases and Vapors

 Standard Sampling and Analysis Methods

 Laboratory Analytical Techniques

 Direct-Reading Methods

 Air Sampling Strategies

Sampling train

Sampling media

Laboratory analysis

EHST 3700 2

 Dusts and fibers

 Gravimetric analysis

 Graticule or reticule

 Metal dust and

fumes

 Similar to gas and

vapor analysis

 Gas and vapor analysis

 Spectrophotometer

 Gas chromatography

 Mass spectrometry

 Absorption spectroscopy

 Inductively coupled plasma

 Fluorescence spectrometry

Gravimetric analysis Graticule or Reticule

Walton-Beckett Graticule

Porton Counting Reticule

Desiccator Pre-sampling weight

Post-sampling weight

Dust sampling

Desiccator

24 hr

24 hr

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

 Spectrophotometer

 Gas chromatography (GC)

 Mass spectrometry (MS)

 Absorption spectroscopy

 Inductively coupled plasma (ICP)

 Fluorescence spectrometry

 For gases and vapors collected by dissolution

or absorption in a solution

 Measures the intensity of the solution color

(proportional to the analyte concentration)

 Measures the degree of light scattering that

is proportional to the amount of precipitate

in the solution

 Used for detection of dusts and other

airborne particulates

 Technique used in direct-reading instruments

EHST 3700 3

Lab Analysis

Sorbent Tube

Desorbed

Analyte Desorbing

Solution

 Used for organic compounds

 Identity of compound is determined by the

amount of time needed for it to pass through

the column (retention time)

 Sample output from a

GC analysis used to

identify an unknown

 Sample bombarded with a beam of electrons to become ionized

 Each ion produced has specific mass

 Relationship between mass of an ion and its charge (m/e) is unique

 Unique to a compound (fingerprint)

n-octane

2,2,4-trimethylpentane

 Involves the measurement of the amount of

energy that is absorbed by a compound

 The particular wavelength where energy is

absorbed indicates the identity of the

compound

 Techniques

 Ultraviolet spectrometry

 Infrared spectrometry

 Atomic absorption

EHST 3700 4

Benzene

Toluene

 Also relies on specific spectrum of energy

absorption to identify the analyte compound

 Used most commonly to detect metals

 An example of emission spectroscopy

 Utilizes the ability of electrons to absorb

energy but measures the energy loss of

excited electrons as they return to the

ground state

 Spectrum emission is specific to the analyte

 Intensity of emissions is proportional to the

amount that is present

 Useful in metal scans (a number of elements

analyzed from the same sample)

 Determines intensity and wavelength of

energy emitted by excited electrons

 Used in the analysis of organic compounds,

particularly those with aromatic rings (i.e.

benzene)

 Lamp used as a source of energy to excite

the sample

 Lamp selection depends on the analytes of

interest (i.e. xenon-arc, tungsten, mercury

lamps)

EHST 3700 5

 Gas meters

 Photoionization and flame ionization

detectors

 Detector or length-of-stain tubes

 Portable units containing a

small pump that draws air

into the instrument

 Passes into sampling

chamber (sensor unit)

 Connected to a readout

device

 Can be specific to a gas or

multi-gas

 Oxygen

 Combustibles

 Toxics: total hydrocarbons

(non-specific)

1. Wheatstone bridge circuit

 Catalytic combustion sensors

 Heat of combustion  Change in electrical

resistance  imbalance in the circuit

2. Metal-oxide semiconductor (MOS)

 Adsorption onto an MOS

 Change in electrical conductivity

3. Thermal conductor

 Thermal conductivity

 Change in temperature

Sensors can become

less sensitive over

time.

Sensors can become

contaminated by

interfering compounds.

 Instrument most often used to

detect organic vapors (i.e.

alcohols, ketones, ethers)

 UV lamp  light energy 

absorbed by contaminants 

become charged  collected by an

electrode  current proportional

to the concentration of

contaminant ions

 Limitation: non-specific

 Use: Screening of atmosphere for

set of contaminants

EHST 3700 6

 Ionizes contaminant molecules using energy

from hydrogen flame

 Commonly used to detect hydrocarbons and

organic compounds

 Limitation: non-specific

 Use: Screening of atmosphere for set of

contaminants

 Length-of-stain tubes

 Contain a solid sorbent coated

with a reagent that reacts with

a contaminant and causes a

color change

1. Determine agents to be sampled.

2. Select the sampling method.

3. Obtain and review a copy of the sampling

method.

4. Obtain adequate sampling media and

equipment.

5. Calibrate sampling pumps or instruments.

6. Perform sampling.

7. Ship samples to laboratory for analysis.

8. Interpret analytical results.

9. Prepare a report to employee and

management.

 Laboratory techniques for particulates

include gravimetric analysis, counting

tecniques and microscopy.

 Laboratory techniques for gases and vapors

include GC, MS, AA, ICP, FS, etc.

 Direct-reading methods involve the use of

portable instruments that provide results at

the site, including gas meters, PID, FID and

detector tubes.