Fundamentals of Air Sampling – Background and Calculations · Fundamentals of Air Sampling – Background and Calculations Robert C. Adams, MS, CIH, ... during the time of sampling

© 2013 American Industrial Hygiene Association, New Jersey Section, Inc.

Fundamentals of Air Sampling – Background and Calculations

Robert C. Adams, MS, CIH, CSP ENVIRON International Corp.

[email protected] 609-243-9848 NJA

IHA

mailto:[email protected]

NJAIHA Summer Review Course: Fundamentals of Air Sampling

About the Presenter: Robert Adams, CIH, CSP

• Bachelor’s degree in Biology from Clarion University of PA and Master of Science in Safety Sciences from the Indiana University of PA.

• Exposure scientist with 30+ years’ consulting experience in industrial hygiene and occupational safety.

• Partner at ENVIRON International Corp in Princeton NJ.

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SESSION OBJECTIVES

By the end of this session, you should be able to: • define the fundamental purposes of air sampling • discuss the factors that influence the selection of air

sampling techniques • identify and differentiate the different types of air samples

and identify advantages and disadvantages of each • identify and practice calculations related to air sampling • identify limitations of interpreting air sampling data • identify basic analytical methods used for the analysis of

air samples

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AIR SAMPLING

• What is an Air Sample? – Collection of a known quantity of air – Adequate to identify potentially hazardous

components – Representative of exposure – Specific for that time, place, duration, person, task

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PURPOSE OF SAMPLING

• To identify and quantify specific contaminants present in the environment

• To determine exposures of workers in response to complaints

• To determine compliance status with respect to various occupational health standards

• To evaluate the effectiveness of engineering controls installed to minimize worker's exposures

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PURPOSE OF SAMPLING

• To identify the source of an air contaminant released into the environment

• To quantify specific contaminants to assign appropriate respiratory protection

• To establish the absence of a particular contaminant

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FACTORS INFLUENCING SAMPLING STRATEGY

• Purpose • Substance(s) or material(s) being sampled • Time of operation to be monitored • Analytical method(s) • Cost • Available sampling equipment

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FACTORS INFLUENCING SAMPLING STRATEGY

• Sensitivity of analytical method(s) and / or equipment

• Nature of operation being monitored • Explosive or non-explosive conditions in

monitoring area • Applicable standard(s) • Toxicology of substance(s) or materials(s) • Sampling interferences

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SAMPLING STRATEGY

• Minimum sample size to obtain the top 10% of exposed population at a 95% confidence limit

• Number of blanks • Sampling errors • Exposure limits - OSHA vs. NIOSH vs. ACGIH

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Size of Population (N)

1 2 3 4 5 6 7 8 9 10 11

Required no. of employees to be sampled (n)

1 2 3 4 5 6 7 8 9 10 11

Size of Population (N)

12 13-14 15-16 17-18 19-21 22-24 25-27 28-31 32-35 36-41 42-50

Required no. of employees to be samples (n)

11 12 13 14 15 16 17 18 19 20 21

Sample Size for Top 10% at the 95% Confidence Level

NUMBERS OF SAMPLES - 95% CONFIDENCE INTERVAL

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TYPES OF SAMPLING

• Personal Sample - A personal sample is one collected on a person in his / her breathing zone and moves with the person. – OSHA defines the breathing zone to be a hemisphere

forward of the shoulders with a radius of approximately 6 to 9 inches.

– A personal sample represents a person's exposure during the time of sampling without regard to the use of a respirator.

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TYPES OF SAMPLING

• Area Sample - An area sample is a fixed sample in an area that is representative of that area's contaminant level. – determine potential contamination from adjacent work

areas; – determine whether re-entry is warranted into a

contaminated area; – verify the integrity of a negative pressure enclosure

during asbestos operations; or – substitute for PS where no feasible personal sampling

method exists (e.g., cotton dust).

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TYPES OF SAMPLING

• Source Sample - A source sample is a fixed sample at the point of release or source of the contaminant, such as a vent. – It may be used to determine the quantity of a

contaminant being released. – Used to determine maximum case exposures (ceiling

or peak exposure potential). – In most cases, it does not relate directly to a

person's exposure.

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TYPE OF SAMPLES COLLECTED

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0 1 2 3 4 5 6 7 8

A

B A B A

B A C

B A B A

C B A

A B C D E

FULL PERIOD SINGLE SAMPLE

FULL PERIOD CONSECUTIVE

SAMPLES

PARTIAL PERIOD CONSECUTIVE

SAMPLES

RANDOM GRAB SAMPLES

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• Gas and Vapor Sampling – Adsorption methods

• Solid sorbents • Charcoal: non-polar organic

vapors • Silica gel: polar organic

solvents • Specialty sorbent tubes –

XAD-2; PUF samplers, Tenax

• Typically, no chemical reaction involved

INTEGRATED SAMPLING METHODS

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• Multiple sorbent tube sampling train

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• Gas and Vapor Sampling – Air sample bags

• Often used for sampling when the concentration is higher than the detection limits of common analytical instruments.

– Air sampling using bags usually done for short periods of time - indication of peak airborne concentrations.

– Most common is the Tedlar film bag: » inert to a wide range of chemicals. » has been shown to have the lowest sample loss in

storage and a low memory of the previous sample.

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• Bag sampling train


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• Absorption methods – Bubblers and impingers

• Detector tube methods

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DETECTOR TUBES

• Colorimetric Detector tubes – Chemical reaction between substance of interest and a

chemical indicator in the tube – Detector tubes and pumps are screening instruments which

may be used to measure more than 200 organic and inorganic gases and vapors or for leak detection

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– Many detector tubes lack specificity. • Many indicators are not highly selective

and can cross-react with other compounds.

• Consult manufacturers' data sheets for interfering contaminants. NJA

IHA


• Passive badges – Principle of collection is essentially the

same as the sorbent tube. – Major difference is that there is no

mechanical air movement. – Rely on natural air movement and

chemical diffusion across a barrier.

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GAS AND VAPOR METHOD LIMITATIONS

• Temperature • Humidity • Breakthrough • Interference from other substances

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• Filter methods – Mixed cellulose ester (MCE): for

asbestos counting, metallic fumes, acid mists

– Polyvinyl chloride (PVC): gravimetric; for total particulates, crystalline silica, mists, chromates

– Teflon: special applications (high temp)

– Silver: for total particulates, coal tar pitch volatiles, crystalline silica, PNAs

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• Size selective sampling using a cyclone – The cyclone separates the

dust particles according to size.

– The respirable particles < 10 microns collect on filter.

– Larger particles fall into the grit pot and are discarded.

– 50% collection efficiency for this type of cyclone is 4 microns.


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LIMITATIONS OF FILTER SAMPLING

• Overloading – Filter blow-by

• Static Electricity – Special cassette developed for asbestos and other

fiber sampling due to this problem • Moisture / humidity • Damage to filter • Interferences

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CALIBRATION

• Determination of airborne concentrations requires accurate knowledge of the volume of air sampled.

• The volume depends upon the constancy of the flow rate of the pump, and upon the reliability of the means of measuring that rate.

• Pump rotameters are not precision instruments and cannot be used to determine a pump's flow rate . – These devices provide only an approximation.

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• Flow rates must be measured with an instrument such as an electronic calibrator, which bases measurement on the unchanging physical dimensions of an enclosed volume.

CALIBRATION

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• Primary Devices – Direct air volume measurement based

on a fixed volume device (such as a 1000 ml burette)

• Secondary Devices – Indirect measure of air volume – must

be calibrated against a primary standard

• Precision Rotameter

CALIBRATION

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DIRECT READING INSTRUMENTS

• Advantages – Rapid estimation of concentration – Permanent record with data logging – Alarm options – Reduce manual samples – Reduce laboratory costs – Lower cost per sample – May be only method available

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DIRECT READING INSTRUMENTS

• Disadvantages – Higher initial costs – Frequent calibration

• Calibration gases – Annual factory calibrations – Some portability issues – Lack of specificity for some instruments (PIDs, CGIs) – May not be suitable for personal sampling

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PRIOR TO AIR SAMPLING

• Perform a walk-through survey of area. • Identify contaminants of concern. • Determine total number of employees exposed. • Determine employee shift times. • Determine number of employees exposed per

shift.

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• Identify exposure areas and operations. • Estimate exposure levels for employees, areas,

and operations. • Select representative employees, areas, and / or

operations to be monitored. • Determine frequency and length of time for each

operation of concern. • Review toxicology, analytical methods, and

applicable standards for contaminant.

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• Identify interferences with analytical methods. • Select analytical method. • Select and obtain appropriate sampling

equipment. • Calibrate equipment. • Select appropriate sampling times for operation

and analytical sensitivity.

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• Determine the approximate number of samples to be collected.

• Begin sampling. • Maintain sampling records.

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SAMPLING CALCULATIONS

• Units • Minimum sample volumes • Minimum sample times • Calibration of flow rates • Adjustments for different air pressures

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BASICS OF AIR CONTAMINANT MONITORING

• Behavior of gases and vapors – Gas laws

• Behavior of Aerosols – Particle size – Settling velocity – Lung deposition

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DEFINITIONS

• Aerosol - A dispersion of solid or liquid particles of microscopic size in a gaseous medium; includes dust, smoke, fog, and mist.

• Dusts - Solid particles generated by mechanical processes such as handling, crushing, grinding, rapid impact, and detonation of organic or inorganic materials.

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DEFINITIONS

• Fumes - Solid particles generated by condensation from the gaseous states generally after volatilization from molten metals. – Popular usage sometimes refers to any type of air

contaminant as a fume. • Smoke - Small gas-borne particles resulting

from incomplete combustion and consisting predominantly of carbon and other combustible materials.

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DEFINITIONS

• Gases - Normally formless fluids which occupy the space or enclosure and which can be changed to the liquid or solid state only by the combined effect of increased pressure and decreased temperature.

• Vapors - The gaseous form of substances which are normally in the solid or liquid state at room temperature and pressure, and are usually formed by the process of evaporation.

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DEFINITIONS

• Mists - Suspended liquid droplets generated by condensation from the gaseous to the liquid state or by breaking up a liquid into a dispersed state, such as by splashing, foaming, or atomizing.

• Smog - A term derived from "smoke" and "fog," and applied to extensive atmospheric contamination by aerosols arising from a combination of natural and manufactured sources.

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DEFINITIONS

• Fog - A term loosely applied to visible aerosols in which the dispersed phase is liquid. – Formation by condensation is implied.

• Fiber - Particle having parallel sides and an aspect ratio of 3 to 1 or more. Fibers are generally considered to be those that are at least 5 microns long.

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ANALYSIS OF AIR SAMPLES

• Gravimetric Techniques - Determining mass of collected sample directly, or after the formation of a precipitate with the collected sample and a precipitating agent.

• Titrimetric Methods - Collecting acidic or basic samples, and determining their airborne concentrations by titrating them with known concentrations of acids or bases as appropriate.

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• Optical Methods - Using the microscope to determine particle sizes and / or concentrations. – Phase contrast microscopes are used to count fibers

for asbestos analyses. – Transmission electron microscopy (TEM) is also

commonly employed in asbestos determinations. • Colorimetric Procedures - Colorimetric

methods involve analytical reactions to produce a color in proportion to the quantity of contaminant of interest in the sample.

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• Spectrophotometric Methods - Principles of operation extend from the infrared radiation spectra, to the ultraviolet, and even to the X-ray region. – The latter can be used to provide information on

elemental composition (fluorescence) and crystal structure (diffraction).

– Samples are exposed to radiation of known characteristics and wavelengths, and the fractions transmitted, absorbed, or scattered are determined and quantified.

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• Spectrophotometric Methods – Color production, turbidity, and fluorescence are

examples of properties determined by electromagnetic radiations that are widely used for quantifying air samples.

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• Spectrographic Techniques - The spectrograph is useful for detecting trace amounts of metallic ions and elements when other techniques cannot be used. – In emission spectroscopy, solid samples are

vaporized in a carbon arc, the characteristic radiation dispersed by a grating or prism, and the resulting spectrum photographed.

• Metal or metal-like elements can be qualitatively identified from the spectra that are formed.

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• Spectrographic Techniques – With mass spectroscopy, gases, liquids, or solids are

ionized by passage through an electron beam, and the resulting ion patterns can be used to identify specific compounds.

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• Atomic Absorption Spectrophotometry - Monochromatic radiation from a discharge lamp containing the vapor of a specific element, such as lead, passes through a flame into which the sample is aspirated. – The high-temperature flame reduces the metals to

free atoms.

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• Atomic Absorption Spectrophotometry – The absorption of monochromatic radiation is

measured by a double-beam method, and the concentration is determined.

• In the parts per million range, the absorption obeys Beer's law; i.e., absorption is proportional to concentration.

• This technique permits rapid determination of almost all metallic elements in industrial hygiene samples, as well as in body fluids and tissues.

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• Chromatography - Chromatography involves the introduction of a sample into a mobile phase that flows through a stationary phase in a column. – The selective absorption and elution of different molecules

allows for the separation of substances into bands. • The sample molecules will distribute so that each spends

some time in each phase. • As the substances passes a detector (flame ionization or

electron capture detectors are common), they can be quantified by running standards of known concentration along with the unknowns.

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• Gas chromatography (GC) Applied to volatile organic compounds. The mobile

phase is a gas and the stationary phase is usually a liquid on a solid support or sometimes a solid adsorbent.

• Liquid chromatography (LC) Used to separate analytes in solution including metal

ions and organic compounds. The mobile phase is a solvent and the stationary phase is a liquid on a solid support, a solid, or an ion-exchange resin.

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UNITS TO EXPRESS CONCENTRATIONS

• mppcf - million particles per cubic foot • mg/m3 - milligrams per cubic meter

• µg/m3 - micrograms per cubic meter

• fibers/cc - fibers per cubic centimeter greater than 5 micrometers in length

• ppm - parts per million by volume

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INTERPRETING SAMPLE DATA

• Basic TWA calculations – Confidence limits

• OSHA approach • NIOSH approach

• Silica calculations • Mixtures

– Exposure index

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CALCULATING TIME-WEIGHTED AVERAGES

Cf = C1 T1 + C2 T2 + Cn Tn

Tf Cf = TWA Concentration Tf = Total Time (usually 8 hours) C1 = Measured concentration at interval n T1 = Time of interval n

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CALCULATING TLVS FOR MIXTURES

If substances have the similar toxicological values, the following equation can be used.

E.I. = C1

TLV1

C2

TLV2

Cn

TLVn

+ +

E.I. = Fraction of TLV (1 = TLV) C = Concentration of Component n TLV = TLV of component n

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CONFIDENCE INTERVALS

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Fundamental Formulas

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SILICA

)(2)(%2)(%2%

/10 3

respirabletridymitetecristobaliquartz

mmgPEL+++

=

)(2%

/10

2

3

respirableSiO

mmgPEL Quartz +=

)(2%

/5

2

3

respirableSiO

mmgPEL teCristobali +=

also for Tridymite

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• Limit of detection (LOD) • Limit of quantification (LOQ)

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• Novel work schedules • Statistical analysis of data

– Normal distribution • Mean - measure of central tendency • Standard deviation – data variability around the

mean – Lognormal distribution - the logs of the data points are

normally distributed • Geometric mean • Geometric standard deviation

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• Breakthrough – If the concentration of the contaminant on the back

section of the sorbent contains 20% or more of the contaminant concentration on the front section, then the sample should be considered invalid.

• Filter Blow-by

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Fundamental Formulas

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URL References

• NIOSH Manual of Analytical Methods http://www.cdc.gov/niosh/nmam/

• OSHA Index of Air Sampling Methods http://www.osha.gov/dts/sltc/methods/toc.html

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http://www.cdc.gov/niosh/nmam/

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


Reference Texts

• Fundamentals of Industrial Hygiene (5th edition), National Safety Council Chicago, IL.

• The Occupational Environment- Its Evaluation and Control (3rd edition), AIHA Press, 2011.

• Calculation Methods for Industrial Hygiene, DiNardi, SR, Van Nostrand Reinhold Publishers

• Quantitative Industrial Hygiene: A Formula Workbook, Caravanos, J. ACGIH Publication #3260

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Fundamentals of Air Sampling – Background and Calculations · Fundamentals of Air Sampling – Background and Calculations Robert C. Adams, MS, CIH, ... during the time of sampling