INDUSTRIAL HYGIENE DIRECT-READING INSTRUMENTS FOR GASES, VAPORS, AND PARTICULATES UNIVERSITY OF HOUSTON - DOWNTOWN.

INDUSTRIAL HYGIENE INDUSTRIAL HYGIENE

DIRECT-READING DIRECT-READING INSTRUMENTS FOR INSTRUMENTS FOR

GASES, VAPORS, AND GASES, VAPORS, AND PARTICULATESPARTICULATES

UNIVERSITY OF HOUSTON - UNIVERSITY OF HOUSTON - DOWNTOWNDOWNTOWN

DIRECT-READING DIRECT-READING INSTRUMENTSINSTRUMENTS

Important tool for detecting and Important tool for detecting and quantifying gases, vapors, and quantifying gases, vapors, and aerosols. The instruments permit aerosols. The instruments permit real-time or near real-time real-time or near real-time measurements of contaminant measurements of contaminant concentrations in the field. concentrations in the field.

REAL-TIME MONITORSREAL-TIME MONITORS

Generally used to obtain short-term or Generally used to obtain short-term or continuous measurements. Some have continuous measurements. Some have data-logging capabilities. data-logging capabilities.

Field monitoring instruments are usually Field monitoring instruments are usually lightweight, portable, rugged, weather lightweight, portable, rugged, weather and temperature insensitive, and are and temperature insensitive, and are simple to operate and maintain.simple to operate and maintain.

No magic black box for all No magic black box for all measurements.measurements.

DIRECT-READING UNITSDIRECT-READING UNITS

For gases and vapors, these types of For gases and vapors, these types of instruments are designed to:instruments are designed to:

1. monitor a specific single compound;1. monitor a specific single compound;

2. monitor specific multiple agents; and,2. monitor specific multiple agents; and,

3. monitor multiple gases and vapors 3. monitor multiple gases and vapors without differentiation. without differentiation.

DIRECT-READING METERSDIRECT-READING METERS

All instruments are designed to be All instruments are designed to be used within a designated detection used within a designated detection range and should be calibrated before range and should be calibrated before field use. A variety of detection field use. A variety of detection principles are used for gases and principles are used for gases and vapors including infrared (IR), vapors including infrared (IR), ultraviolet (UV), flame ionization, ultraviolet (UV), flame ionization, photoionization, colorimetric, and photoionization, colorimetric, and electrochemical reaction. electrochemical reaction.

DIRECT-READING METERSDIRECT-READING METERS

Provide immediate data that are temporally Provide immediate data that are temporally resolved into short-time intervals. Personal resolved into short-time intervals. Personal monitoring. Direct-reading monitors can monitoring. Direct-reading monitors can profile fluctuations in contaminant profile fluctuations in contaminant concentrations. concentrations.

Data can be used to estimate instantaneous Data can be used to estimate instantaneous exposures, short-term exposures, and time exposures, short-term exposures, and time integrated exposures to compare with Ceiling integrated exposures to compare with Ceiling limits, STELs, and TWAs, respectively. limits, STELs, and TWAs, respectively.

Can be used as educational/motivation tools.Can be used as educational/motivation tools.

DIRECT-READING UNIT USESDIRECT-READING UNIT USES

In conjunction with traditional integrated In conjunction with traditional integrated sampling methods, direct-reading sampling methods, direct-reading instruments can be used to develop instruments can be used to develop personal sampling strategies and for personal sampling strategies and for obtaining a comprehensive exposure obtaining a comprehensive exposure evaluation. evaluation.

Used to conduct an initial screening survey; Used to conduct an initial screening survey; document types of contaminants; and, the document types of contaminants; and, the range of concentrations in the air. range of concentrations in the air.

Estimate peak exposures in breathing zone. Estimate peak exposures in breathing zone.

Evaluate effectiveness of existing control Evaluate effectiveness of existing control measures.measures.

UNIT SELECTIONUNIT SELECTION

Selection of appropriate direct-reading Selection of appropriate direct-reading instrument depends on the application for instrument depends on the application for which it will be used. which it will be used.

For gases and vapors, consider high For gases and vapors, consider high selectivity and to detect and quantify target selectivity and to detect and quantify target chemical in a specific concentration range. chemical in a specific concentration range.

Other factors: price; portability; weight; size; Other factors: price; portability; weight; size; battery operation and life; and, requirements battery operation and life; and, requirements for personnel training.for personnel training.

OTHER CONSIDERATIONSOTHER CONSIDERATIONS

Require user to understand the limitations Require user to understand the limitations and conditions that can affect performance and conditions that can affect performance and calibration as well as maintenance and calibration as well as maintenance requirements and interpretation of results. requirements and interpretation of results.

Affected by interferences; environmental Affected by interferences; environmental conditions (e.g. temperature; humidity; conditions (e.g. temperature; humidity; altitude/elevation; barometric pressure; altitude/elevation; barometric pressure; presence of particulates; oxygen presence of particulates; oxygen concentrations; electromagnetic fields, etc.). concentrations; electromagnetic fields, etc.).

SOURCES OF ERRORSOURCES OF ERRORMinimize sources of error through Minimize sources of error through proper quality control practices. All proper quality control practices. All instruments require calibration before instruments require calibration before use for comparison to known use for comparison to known concentrations (e.g. multi-point concentrations (e.g. multi-point calibration). calibration).

Interferences can result in false-Interferences can result in false-positive or false-negative results by positive or false-negative results by impacting collection, detection, or impacting collection, detection, or quantification of contaminants. quantification of contaminants.

ELECTROCHEMICAL SENSORSELECTROCHEMICAL SENSORS

Variety of instruments are dedicated to Variety of instruments are dedicated to monitoring specific single gas and vapor monitoring specific single gas and vapor contaminants. contaminants.

Numerous different individual compounds. Numerous different individual compounds. (i.e. CO, H(i.e. CO, H22S, Oxygen, SOS, Oxygen, SO22, nitric oxide, NO, nitric oxide, NO22, , hydrogen cyanide) hydrogen cyanide)

Typical electrochemical sensor interferences Typical electrochemical sensor interferences and contamination concerns.and contamination concerns.

COMBUSTIBLE GASESCOMBUSTIBLE GASESOxygen measurements are usually taken Oxygen measurements are usually taken in conjunction with combustible gas in conjunction with combustible gas measurements for confined space entry measurements for confined space entry where air can be oxygen-deficient. where air can be oxygen-deficient. OSHA defines as: less than 19.5%.OSHA defines as: less than 19.5%.Normal air contains 20.9% oxygen.Normal air contains 20.9% oxygen.Verify oxygen levels first to insure proper Verify oxygen levels first to insure proper combustible sensor function. Calibrate combustible sensor function. Calibrate with clean air at same altitude/temp for with clean air at same altitude/temp for use.use.

OTHER CONSIDERATIONSOTHER CONSIDERATIONS

Inaccuracies due to interferences and Inaccuracies due to interferences and contamination. contamination.

Lack of specificity important when Lack of specificity important when assessing atmospheres with multiple assessing atmospheres with multiple unknown toxic chemicals. unknown toxic chemicals.

Sensors can be hazardous based on Sensors can be hazardous based on corrosive liquid electrolyte; content of corrosive liquid electrolyte; content of metals; may deteriorate over time, metals; may deteriorate over time, etc.etc.

COMBUSTIBLE GAS COMBUSTIBLE GAS INDICATORS (CGI)INDICATORS (CGI)

CGIs are currently used to measure CGIs are currently used to measure gases in confined spaces and gases in confined spaces and atmospheres containing combustible atmospheres containing combustible gases and vapors (i.e. methane and gases and vapors (i.e. methane and gasoline). Capable of measuring the gasoline). Capable of measuring the presence of flammable gases in presence of flammable gases in percentage of Lower Explosive Limit percentage of Lower Explosive Limit (LEL) and percentage of gas by (LEL) and percentage of gas by volume. volume.

CGI AS A SAFETY METERCGI AS A SAFETY METERCGI used to detect hazardous concentrations CGI used to detect hazardous concentrations up to 100 % of the LEL. When 100% LEL is up to 100 % of the LEL. When 100% LEL is reached, flammable or explosive reached, flammable or explosive concentrations are present. A relatively low concentrations are present. A relatively low percentage LEL corresponds to a high percentage LEL corresponds to a high concentration. concentration.

Methane: LEL of 5.3% or 53,000 ppm Methane: LEL of 5.3% or 53,000 ppm

10% LEL = 5300 ppm10% LEL = 5300 ppm

0.10+/- 5.3% = 0.53% or 5300 ppm0.10+/- 5.3% = 0.53% or 5300 ppm

Much greater than PEL/TLV and CGIs not used Much greater than PEL/TLV and CGIs not used to determine Occupational Exposure Limit to determine Occupational Exposure Limit (OEL) compliance.(OEL) compliance.

CGI OPERATIONCGI OPERATIONCGIs are based on catalytic combustion. CGIs are based on catalytic combustion. Wheatstone bridge (circuit that measures Wheatstone bridge (circuit that measures the differential resistance in an electric the differential resistance in an electric current) and two filaments (one coated with current) and two filaments (one coated with catalyst [platinum] to facilitate oxidation catalyst [platinum] to facilitate oxidation and other compensating filament). and other compensating filament).

Catalytic sensors are usually sensitive to Catalytic sensors are usually sensitive to concentrations as low as 0.5 to 1% of LEL.concentrations as low as 0.5 to 1% of LEL.

CGI OPERATION – CGI OPERATION – THERMAL CONDUCTIVITYTHERMAL CONDUCTIVITY

Another method to detect explosive Another method to detect explosive atmospheres that uses the specific heat of atmospheres that uses the specific heat of combustion of a gas or vapor as a measure combustion of a gas or vapor as a measure of the concentration in air. of the concentration in air.

Used where very high concentrations of Used where very high concentrations of flammable gases are expected (greater than flammable gases are expected (greater than 100% of the LEL), and measures percentage 100% of the LEL), and measures percentage of gas as compared with % LEL.of gas as compared with % LEL.

Not sensitive to low gas concentrations.Not sensitive to low gas concentrations.

CGI MEASUREMENTSCGI MEASUREMENTSData is relative to the gas used for calibration Data is relative to the gas used for calibration (i.e. methane, pentane, propane, or hexane). (i.e. methane, pentane, propane, or hexane). When exposed to calibrant, response is When exposed to calibrant, response is accurate. For calibration, instrument response accurate. For calibration, instrument response depends on the calibrant gas as well as the depends on the calibrant gas as well as the type of catalyst employed in the sensor. type of catalyst employed in the sensor. Understand implications of use of different Understand implications of use of different calibration gases and meter interpretations calibration gases and meter interpretations and field conditions for calibration!and field conditions for calibration!Similar heat of combustion for CGI to chemical Similar heat of combustion for CGI to chemical being monitored. Calibrate for least sensitive being monitored. Calibrate for least sensitive gas for wide margin of safety. gas for wide margin of safety. Awareness of response curves/conversion Awareness of response curves/conversion factors. Refer to Figure 17-7; pg 566 in IH factors. Refer to Figure 17-7; pg 566 in IH bookbook

CGI LIMITATIONSCGI LIMITATIONSPeriodically replace sensors. Periodically replace sensors.

Know response time of instrument. Know response time of instrument.

Be aware of minimum requirements for Be aware of minimum requirements for oxidation. oxidation.

Obtain oxygen concentration first, since CGI Obtain oxygen concentration first, since CGI performance depends on oxygen availability. performance depends on oxygen availability.

Situation of oxygen deficiency can be created Situation of oxygen deficiency can be created based on gas/vapor concentrations above UEL. based on gas/vapor concentrations above UEL.

CGIs measure a wide variety of flammable CGIs measure a wide variety of flammable gases and vapors, not all materials and can gases and vapors, not all materials and can give false+/- results. Also effects on sensors give false+/- results. Also effects on sensors within meters.within meters.

METALLIC OXIDE METALLIC OXIDE SEMICONDUCTOR SENSORSSEMICONDUCTOR SENSORS

Solid state sensors are used to detect ppm and Solid state sensors are used to detect ppm and combustible concentrations of gases. Metallic combustible concentrations of gases. Metallic Oxide Semiconductor (MOS) sensors (i.e. nitro, Oxide Semiconductor (MOS) sensors (i.e. nitro, amine, alcohols, halogenated hydrocarbons, etc.). amine, alcohols, halogenated hydrocarbons, etc.).

Used as general survey instruments because they Used as general survey instruments because they lack specificity and cannot distinguish between lack specificity and cannot distinguish between chemicals. Responds to interfering gases. chemicals. Responds to interfering gases.

Advantages are small size, low cost, and Advantages are small size, low cost, and simplicity of operation. Disadvantages are lack of simplicity of operation. Disadvantages are lack of specificity, low sensitivity, and low stability.specificity, low sensitivity, and low stability.

DETECTOR TUBESDETECTOR TUBESDetector tubes, or colorimetric indicator Detector tubes, or colorimetric indicator tubes, are the most widely used direct-tubes, are the most widely used direct-reading devices due to ease of use, minimum reading devices due to ease of use, minimum training requirements, fast on-site results, training requirements, fast on-site results, and wide range of chemical sensitivities. and wide range of chemical sensitivities.

Hermetically sealed glass tube containing Hermetically sealed glass tube containing inert solid/granular materials impregnated inert solid/granular materials impregnated with reagent(s) that change color based on with reagent(s) that change color based on chemical reaction(s). Filter and/or pre-layer chemical reaction(s). Filter and/or pre-layer to adsorb interferences. to adsorb interferences.

DETECTOR TUBESDETECTOR TUBES

Length of resulting color change or the Length of resulting color change or the intensity of the color change is intensity of the color change is compared with a reference to obtain compared with a reference to obtain the airborne concentration.the airborne concentration.

Three methods of use:Three methods of use:

1.1. calibration scaled marked on tube;calibration scaled marked on tube;

2. separate conversion chart;, and2. separate conversion chart;, and

3. separate comparison tube. 3. separate comparison tube.

DETECTOR TUBE USEDETECTOR TUBE USE

Break ends of tube and place in bellows/piston, Break ends of tube and place in bellows/piston, or bulb-type pump which are specially or bulb-type pump which are specially designed by each manufacturer; therefore, designed by each manufacturer; therefore, interchanging equipment between interchanging equipment between manufacturer results in significant manufacturer results in significant measurement errors. measurement errors.

Perform pump stroke to draw air through tube Perform pump stroke to draw air through tube at a flow rate and volume determined by the at a flow rate and volume determined by the manufacturer. A specified number of strokes manufacturer. A specified number of strokes are used for a given chemical and detection are used for a given chemical and detection range. Total pumps stroke time can range range. Total pumps stroke time can range from several seconds to several minutes. from several seconds to several minutes.

DETECTOR TUBE USEDETECTOR TUBE USE

Tube selection depends on the chemical(s) to be Tube selection depends on the chemical(s) to be monitored and the concentration range. Most monitored and the concentration range. Most tubes react with more than one chemical that tubes react with more than one chemical that are structurally similar. Interferences are are structurally similar. Interferences are documented by manufacturers and should be documented by manufacturers and should be understood.understood.

Variety of tubes – different ranges; qualitative Variety of tubes – different ranges; qualitative indicator tubes (not used regarding indicator tubes (not used regarding concentrations); presence/absence - poly tubes.concentrations); presence/absence - poly tubes.

Help to choose a more accurate method. Help to choose a more accurate method.

Grab samples; variable; source monitoring, not Grab samples; variable; source monitoring, not compliance. compliance.

DETECTOR TUBE LIMITATIONSDETECTOR TUBE LIMITATIONS

Sensitive to temperature, humidity, pressure, Sensitive to temperature, humidity, pressure, light, time, and presence of interferences. light, time, and presence of interferences.

Reagents are chemically reactive and can Reagents are chemically reactive and can degrade over time to heat/UV; limited shelf degrade over time to heat/UV; limited shelf life. life.

Recommended use in range of 0 to 40 degrees Recommended use in range of 0 to 40 degrees C. Sampling under different conditions [20 to C. Sampling under different conditions [20 to 25 degrees C; 760 mm Hg; 50%RH]. OR 25 degrees C; 760 mm Hg; 50%RH]. OR corrections or conversions. corrections or conversions.

Interferences – positive or negative.Interferences – positive or negative.

DETECTOR TUBESDETECTOR TUBES

Some tubes are designed to perform integrated Some tubes are designed to perform integrated sampling over long monitoring periods of up to 8 sampling over long monitoring periods of up to 8 hours and use low-flow pumps. Lower limits of hours and use low-flow pumps. Lower limits of detection over longer sampling times. detection over longer sampling times.

Length of stain is usually calibrated in microliters. Length of stain is usually calibrated in microliters. Measurement can be converted to a TWA Measurement can be converted to a TWA concentration. concentration.

Diffusion tube results divided by exposure time. Diffusion tube results divided by exposure time. Temp/pressure corrections. Cross-sensitivities. Temp/pressure corrections. Cross-sensitivities. Long-term tubes as screening device.Long-term tubes as screening device.

Accuracy varies +/- 25 to 35%.Accuracy varies +/- 25 to 35%.

Leak checks; volume/flow rate measurements.Leak checks; volume/flow rate measurements.

FLAME IONIZATION DETECTORS FLAME IONIZATION DETECTORS (FIDs)(FIDs)

Uses a hydrogen flame to produce ions. More Uses a hydrogen flame to produce ions. More difficult to operate than PIDs. difficult to operate than PIDs. Less sensitive to effects of humidity. Respond to Less sensitive to effects of humidity. Respond to greater number of organic chemicals (C-C or C-H greater number of organic chemicals (C-C or C-H bonds). Unit is linear over a greater range. bonds). Unit is linear over a greater range. Ionize materials with IP of 15.4 eV or less. Ionize materials with IP of 15.4 eV or less.

Vapor sensitivity dependent on energy required Vapor sensitivity dependent on energy required to break chemical bonds. Response depends on to break chemical bonds. Response depends on particular chemical and functional groups affect particular chemical and functional groups affect sensitivity. Detector response is proportional to sensitivity. Detector response is proportional to number of molecules; non-linear relationship.number of molecules; non-linear relationship.

FID ISSUESFID ISSUESInsensitivity to ambient gases makes FID Insensitivity to ambient gases makes FID extremely useful in the analysis of atmospheric extremely useful in the analysis of atmospheric samples. Measurements are relative to samples. Measurements are relative to calibrant gas, methane. FID response does not calibrant gas, methane. FID response does not represent the concentrations of specific organic represent the concentrations of specific organic compounds, but rather an estimate of the total compounds, but rather an estimate of the total concentration of volatile organic compounds. concentration of volatile organic compounds. One point calibration curve with methane is One point calibration curve with methane is usually sufficient because instruments are usually sufficient because instruments are linear up to 10,000 ppm. linear up to 10,000 ppm. Zero in field by background reading obtained Zero in field by background reading obtained without flame being lit High purity hydrogen without flame being lit High purity hydrogen flame. Higher background reading than PID, flame. Higher background reading than PID, since unit responds to more contaminants. since unit responds to more contaminants. Inlet particulate filters; GC-mode option.Inlet particulate filters; GC-mode option.

PHOTOIONIZATION DETECTORS PHOTOIONIZATION DETECTORS (PIDs)(PIDs)

General survey instruments. General survey instruments.

Non-specific and provide qualitative info on the Non-specific and provide qualitative info on the amount and class of chemicals present in air. amount and class of chemicals present in air. Immediate results obtained for unknowns, etc. Immediate results obtained for unknowns, etc.

Quantitative analysis based on most organic Quantitative analysis based on most organic compounds and some inorganic compounds compounds and some inorganic compounds can be ionized when bombarded by high-can be ionized when bombarded by high-energy UV light. Absorb energy and ion energy UV light. Absorb energy and ion current is directly proportional to mass and current is directly proportional to mass and concentration. concentration.

Ionization potential (IP); Ionization potential (IP);

Consideration of different lamp choices.Consideration of different lamp choices.

PID ISSUESPID ISSUESUse quantitatively if only one chemical is Use quantitatively if only one chemical is present in air, or if a mixture of chemicals is present in air, or if a mixture of chemicals is present and each chemical has the same IP. present and each chemical has the same IP. PIDs are more sensitive to complex PIDs are more sensitive to complex compounds than to simple ones. Detect a compounds than to simple ones. Detect a range of organic chemicals and some range of organic chemicals and some inorganic chemicals. inorganic chemicals.

Sensitivity is increased as carbon number Sensitivity is increased as carbon number increases and is affected by the functional increases and is affected by the functional group, structure, and type of bond. group, structure, and type of bond.

The lamp intensity also affects the sensitivity The lamp intensity also affects the sensitivity of the instrument to a given contaminant. of the instrument to a given contaminant.

Refer to charts from manufacturers. Refer to charts from manufacturers.

PID MEASUREMENTSPID MEASUREMENTSData readings are relative to factory calibrant Data readings are relative to factory calibrant gas (i.e. benzene or isobutylene) and also span gas (i.e. benzene or isobutylene) and also span setting adjustment, so PID reads directly for a setting adjustment, so PID reads directly for a defined concentration of a known chemical. defined concentration of a known chemical. Meter responses recorded as PPM-calibrant gas Meter responses recorded as PPM-calibrant gas equivalents! equivalents! Typical range of concentrations is 0.2 to 2000 Typical range of concentrations is 0.2 to 2000 ppm; linear to about 600 ppm. Can also refer ppm; linear to about 600 ppm. Can also refer to response factors.to response factors.Adversely affected by humidity, particulates, Adversely affected by humidity, particulates, and hot and corrosive atmospheres.and hot and corrosive atmospheres.Calibrate and zero procedures for normal use! Calibrate and zero procedures for normal use!

INFRARED (IR) GAS ANALYZERSINFRARED (IR) GAS ANALYZERSIR analyzers are versatile, can quantify many IR analyzers are versatile, can quantify many chemicals, and are capable of being used for chemicals, and are capable of being used for continuous monitoring, short-term sampling, continuous monitoring, short-term sampling, and bag sampling. and bag sampling.

Advantages are measurements of a wide Advantages are measurements of a wide variety of compounds at concentrations in low variety of compounds at concentrations in low ppm to ppb ranges; easy to use; set up ppm to ppb ranges; easy to use; set up quickly; relatively stable in the field. [e.g. IAQ; quickly; relatively stable in the field. [e.g. IAQ; tracer gas studies; source monitoring] tracer gas studies; source monitoring]

IR ISSUESIR ISSUESIR spectrometry for quantitative analysis is IR spectrometry for quantitative analysis is based on the principle that compounds based on the principle that compounds selectively absorb energy in the IR region of selectively absorb energy in the IR region of the electromagnetic spectrum. Characteristic the electromagnetic spectrum. Characteristic absorption spectrum produced can be used to absorption spectrum produced can be used to identify the chemical and is considered to be a identify the chemical and is considered to be a fingerprint. fingerprint. Bougher-Beer Lambert law/equation.Bougher-Beer Lambert law/equation.Two categories: dispersive (gratings/prisms; Two categories: dispersive (gratings/prisms; used in lab); and non-dispersive (not use used in lab); and non-dispersive (not use gratings/prisms; IR beam through filter; detects gratings/prisms; IR beam through filter; detects species that absorb IR in the selected range).species that absorb IR in the selected range).Multipoint calibration curve of absorbance vs. Multipoint calibration curve of absorbance vs. concentration (ppm); based on field use. concentration (ppm); based on field use.

FOURIER TRANSFORM IR (FTIR)FOURIER TRANSFORM IR (FTIR)

Forefront of monitoring technology. Potential to Forefront of monitoring technology. Potential to monitor a wide range of compounds monitor a wide range of compounds simultaneously at very low limits of detection simultaneously at very low limits of detection (ppb). More efficient collection and radiation (ppb). More efficient collection and radiation analysis; higher spectral resolution; greater analysis; higher spectral resolution; greater specificity; higher signal to noise ratio; lower specificity; higher signal to noise ratio; lower limits of detection.limits of detection.Can be used to identify unknown as well as Can be used to identify unknown as well as known contaminants and can quantify chemicals known contaminants and can quantify chemicals in mixtures. Fingerprint as pattern of absorption.in mixtures. Fingerprint as pattern of absorption.Modes: extractive or open-path (i.e. real-time Modes: extractive or open-path (i.e. real-time monitoring; STELs, TWAs of complex mixtures)monitoring; STELs, TWAs of complex mixtures)Challenging calibration problems; background Challenging calibration problems; background spectrum. spectrum. Other: computed tomography applications.Other: computed tomography applications.

PHOTOACOUSTIC ANALYZERS PHOTOACOUSTIC ANALYZERS (PAS)(PAS)

Involves use of sound and UV or IR radiation to Involves use of sound and UV or IR radiation to quantify air contaminants. Spectroscopy uses quantify air contaminants. Spectroscopy uses fact that molecules vibrate at a particular fact that molecules vibrate at a particular frequency called the resonance frequency. frequency called the resonance frequency. Number and types of atoms determine a Number and types of atoms determine a chemical’s unique resonance frequency (i.e. chemical’s unique resonance frequency (i.e. 1013 Hz or 1013 vibrations per second). 1013 Hz or 1013 vibrations per second). Measures sound energy.Measures sound energy.Pattern of energy absorption at specific Pattern of energy absorption at specific wavelengths (i.e. fingerprint) can be used to wavelengths (i.e. fingerprint) can be used to identify chemical. Intensity of absorption is identify chemical. Intensity of absorption is proportional to the contaminant concentration. proportional to the contaminant concentration. Interferences – COInterferences – CO22, water vapor limit detection , water vapor limit detection and accuracy of measurement. and accuracy of measurement.

GAS CHROMATOGRAPHY (GC)GAS CHROMATOGRAPHY (GC)

Portable GCs are particularly good for Portable GCs are particularly good for identification of specific chemicals in mixtures identification of specific chemicals in mixtures and unknown chemicals; also best for and unknown chemicals; also best for monitoring volatile compounds. monitoring volatile compounds. In general, consists of an injection system, a In general, consists of an injection system, a GC column, and a detector. GC column, and a detector. Columns: packed and capillary. Choice is Columns: packed and capillary. Choice is essential to adequate resolution of the essential to adequate resolution of the contaminants. Column temp is 5 degrees contaminants. Column temp is 5 degrees above ambient as a rule of thumb. above ambient as a rule of thumb. Thermal drift. Back-flushing technique.Thermal drift. Back-flushing technique.

GC DETECTORSGC DETECTORSDetectors vary in sensitivity, selectively, and Detectors vary in sensitivity, selectively, and linearity. linearity.

Choice depends on the chemicals investigated, Choice depends on the chemicals investigated,

the presence of other contaminants, and required the presence of other contaminants, and required sensitivity. sensitivity. Peaks of separated components; concentration Peaks of separated components; concentration determined by area under peaks; compare with determined by area under peaks; compare with calibration. calibration. Field operation of GC requires calibration with the Field operation of GC requires calibration with the chemical of interest under the same conditions as chemical of interest under the same conditions as the chemical to be measured in field. the chemical to be measured in field. Limitation is requirement of high degree of skill. Limitation is requirement of high degree of skill. Not unique retention times. Not unique retention times. QA/QC – repeatability and reproducibility.QA/QC – repeatability and reproducibility.

PARTICULATE PARTICULATE MEASUREMENTSMEASUREMENTS

Complications to be considered. Complications to be considered. Measurement affected by various factors: Measurement affected by various factors: particle size and shape; particle settling particle size and shape; particle settling velocity; wind currents, and sampling flow velocity; wind currents, and sampling flow rates. Careful calibration necessary. rates. Careful calibration necessary.

For potentially explosive atmospheres, For potentially explosive atmospheres, direct-reading instruments need to be direct-reading instruments need to be intrinsically safe (not release thermal or intrinsically safe (not release thermal or electrical energy that may cause ignition of electrical energy that may cause ignition of hazardous chemicals) or explosion-proof hazardous chemicals) or explosion-proof (contains chamber to withstand explosion). (contains chamber to withstand explosion).

OPTICAL PARTICLE COUNTEROPTICAL PARTICLE COUNTER

Most popular direct-reading aerosol Most popular direct-reading aerosol monitors are light-scattering devices monitors are light-scattering devices (aerosol photometers). (aerosol photometers). As number of particles increase, the light As number of particles increase, the light reaching the detector increases. Scattering reaching the detector increases. Scattering angle has a great influence on aerosol angle has a great influence on aerosol measurements. measurements. Factory and field calibrated. Factory and field calibrated. Single particle, direct-reading OPC illuminate Single particle, direct-reading OPC illuminate aerosols. Number/concentration and size of aerosols. Number/concentration and size of particles can be determined. particles can be determined.

CONDENSATION NUCLEUS CONDENSATION NUCLEUS COUNTERCOUNTER

Can measure very small particles (less than Can measure very small particles (less than 1.0 um); e.g. atmospheric aerosols. 1.0 um); e.g. atmospheric aerosols.

Testing HEPA filters in clean room and Testing HEPA filters in clean room and quantitative fit-testing respirators.quantitative fit-testing respirators.

Fast response time, is lightweight, and Fast response time, is lightweight, and portable, and can be used for real-time portable, and can be used for real-time measurement. measurement.

MULTIPLE PARTICLE MONITORSMULTIPLE PARTICLE MONITORS

Real-time dust monitors used for aerosol concentrations. Real-time dust monitors used for aerosol concentrations. Intensity of light scattered into the detector can be used to Intensity of light scattered into the detector can be used to estimate concentration. As number of particles increases, estimate concentration. As number of particles increases, the light reaching the detector increases. Depends on the the light reaching the detector increases. Depends on the size, shape, and refractive index of the particle. size, shape, and refractive index of the particle. Advantage is linear response over a large concentration Advantage is linear response over a large concentration range; sampling rate influences unit response rate; and, range; sampling rate influences unit response rate; and, measures particle count and not mass. measures particle count and not mass. Calibration with similar aerosol based on refractive index Calibration with similar aerosol based on refractive index and particle size for measurement; operated in linear and particle size for measurement; operated in linear range. range. Electrical techniques for aerodynamic diameters of Electrical techniques for aerodynamic diameters of particles.particles.

FIBROUS AEROSOL MONITORS FIBROUS AEROSOL MONITORS (FAMs) (FAMs)

FAMs are modified light-scattering monitors that FAMs are modified light-scattering monitors that are direct-reading devices designed to measure are direct-reading devices designed to measure airborne concentrations of fibrous materials with airborne concentrations of fibrous materials with a length-to-diameter aspect ratio greater than 3 a length-to-diameter aspect ratio greater than 3

(e.g. asbestos, fiber glass). Results reported as (e.g. asbestos, fiber glass). Results reported as fiber counts rather than mass concentrations. fiber counts rather than mass concentrations. Real-time measurements. Real-time measurements.

Limitation is that measurements assume that Limitation is that measurements assume that ideal cylindrical fibers are being detected. ideal cylindrical fibers are being detected. Calibrated by side-by-side comparison to NIOSH Calibrated by side-by-side comparison to NIOSH Method 7400.Method 7400.