INDUSTRIAL HYGIENE INDUSTRIAL HYGIENE --

AIR SAMPLING AIR SAMPLING

UNIVERSITY OF HOUSTON - UNIVERSITY OF HOUSTON - DOWNTOWNDOWNTOWN

PURPOSEPURPOSE

Introduce the techniques available for Introduce the techniques available for Industrial Hygienists to evaluate Industrial Hygienists to evaluate EXPOSURES to particulates, gases, and EXPOSURES to particulates, gases, and vapors arising in or from the workplace. vapors arising in or from the workplace. Also: Also:

-- be aware of technology available be aware of technology available for for assessment of environmentsassessment of environments

-- indoor and ambient air, and indoor and ambient air, and -- capabilities and limitations of capabilities and limitations of

methods.methods.

SAMPLING STRATEGYSAMPLING STRATEGY

When developing a particular sampling When developing a particular sampling strategy, review sampling and analytical strategy, review sampling and analytical methods available for the contaminants of methods available for the contaminants of interest. Select most suitable for the interest. Select most suitable for the specific application.specific application.

e.g. OSHA, NIOSHe.g. OSHA, NIOSHi.e. published and validated methodsi.e. published and validated methods

EPA methods used for lower level indoor air EPA methods used for lower level indoor air pollutants and toxic compounds in ambient pollutants and toxic compounds in ambient air media.air media.

SAMPLING METHODSAMPLING METHOD

Select a method that meets the sampling Select a method that meets the sampling and analytical ACCURACY and PRECISION and analytical ACCURACY and PRECISION requirements of the standard in its unique requirements of the standard in its unique field conditions. Usually stipulate field conditions. Usually stipulate measurement at the PEL within a +/- 25% of measurement at the PEL within a +/- 25% of the “true” value at a 95% confidence level. the “true” value at a 95% confidence level.

EPA – indoor air pollutants and toxic EPA – indoor air pollutants and toxic compounds associated with ambient air. compounds associated with ambient air.

ANALYTICAL LABORATORYANALYTICAL LABORATORY

Select and consult with a qualified analytical Select and consult with a qualified analytical laboratory, e.g. AIHA that participates in laboratory, e.g. AIHA that participates in Laboratory Accreditation Programs. Labs can Laboratory Accreditation Programs. Labs can assist in choosing methods that meet the assist in choosing methods that meet the sensitivity and specificity criteria for the sensitivity and specificity criteria for the environment being evaluated. Choose sampling environment being evaluated. Choose sampling media and strategy compatible with method media and strategy compatible with method selected and advise on special handling. selected and advise on special handling.

Two key factors: knowledge of occupational Two key factors: knowledge of occupational environment AND overall perspective of the environment AND overall perspective of the limitation of the chemistry of sampling/analysis. limitation of the chemistry of sampling/analysis.

SAMPLING PLANSAMPLING PLAN Designing a sampling plan involves Designing a sampling plan involves

consideration of the following: location of consideration of the following: location of samples, the number of workers to be samples, the number of workers to be sampled, and the duration of sampling. Also sampled, and the duration of sampling. Also consider other factors – noise, equipment, consider other factors – noise, equipment, size, flow rate, and security. size, flow rate, and security.

• Personal vs. Area SamplingPersonal vs. Area Sampling• Grab vs. Integrated SamplingGrab vs. Integrated Sampling• Active vs. Passive SamplingActive vs. Passive Sampling

GRAB SAMPLINGGRAB SAMPLING

This technique involves the direct This technique involves the direct collection of an air-contaminant mixture collection of an air-contaminant mixture into a device (i.e. sampling bag, into a device (i.e. sampling bag, syringe, or evacuated flask) over a syringe, or evacuated flask) over a short interval of a few seconds or short interval of a few seconds or minutes. Represents the atmospheric minutes. Represents the atmospheric concentrations at the sampling site at a concentrations at the sampling site at a given point in time. given point in time.

GRAB SAMPLINGGRAB SAMPLINGThis type of collected sample measures gas This type of collected sample measures gas and vapor concentrations AT A POINT IN and vapor concentrations AT A POINT IN TIME and are used to evaluate “PEAK” TIME and are used to evaluate “PEAK” exposures for comparison to “Ceiling” limits. exposures for comparison to “Ceiling” limits. Can be used to identify unknown Can be used to identify unknown contaminants, to evaluate contaminant contaminants, to evaluate contaminant sources, or to measure contaminant levels sources, or to measure contaminant levels from intermittent processes or other from intermittent processes or other sources. Collected using syringes, canisters, sources. Collected using syringes, canisters, or sampling bags.or sampling bags.Instantaneous (as well as integrated) Instantaneous (as well as integrated) measurements of gases/vapors also may be measurements of gases/vapors also may be performed using detector tubes or direct-performed using detector tubes or direct-reading instruments. reading instruments.

GRAB SAMPLING – ADVANTAGESGRAB SAMPLING – ADVANTAGES

-- After collection, can frequently be After collection, can frequently be analyzed immediately by GC or direct-analyzed immediately by GC or direct-reading instruments. reading instruments.

- - Therefore, quick decisions can be made Therefore, quick decisions can be made in field or at the site about source of in field or at the site about source of leaks, Confined Space Entry (CSE), leaks, Confined Space Entry (CSE),

PPE, etc. PPE, etc.

GRAB SAMPLING –GRAB SAMPLING –DISADVANTAGESDISADVANTAGES

- - For most applications, contaminants are For most applications, contaminants are collected but not integrated over time. Only collected but not integrated over time. Only some devices will allow use of a metering some devices will allow use of a metering device to collect sample(s) at or near constant device to collect sample(s) at or near constant flow over period of time for TWA. flow over period of time for TWA.

- - For low contaminant concentrations, For low contaminant concentrations, analytical analytical instrument may not be sensitive instrument may not be sensitive for detection. for detection.

-- Using multiple grab samples to assess full-Using multiple grab samples to assess full-shift shift exposures is time-consuming and exposures is time-consuming and subject to subject to error.error.

INTEGRATED SAMPLINGINTEGRATED SAMPLING

For gases and vapors, involves For gases and vapors, involves passage of a known volume of air passage of a known volume of air through an through an absorbingabsorbing or or adsorbingadsorbing medium to remove the desired medium to remove the desired contaminants from the air during a contaminants from the air during a specified period of time. specified period of time. Contaminants of interest are collected Contaminants of interest are collected and concentrated over a period of time and concentrated over a period of time to obtain the average exposure levels to obtain the average exposure levels during the entire sampling period. during the entire sampling period.

INTEGRATED SAMPLINGINTEGRATED SAMPLING

This type of sampling to cover the This type of sampling to cover the entire period of exposure is required entire period of exposure is required because airborne contaminant because airborne contaminant concentrations during a typical work concentrations during a typical work shift vary with time and activity. Grab shift vary with time and activity. Grab samples do not reflect average samples do not reflect average exposures. Most integrated sampling exposures. Most integrated sampling is done to determine the 8-hour TWA is done to determine the 8-hour TWA and/or STELs to compare with OSHA and/or STELs to compare with OSHA PELs, ACGIH TLVs and NIOSH RELs. PELs, ACGIH TLVs and NIOSH RELs.

INTEGRATED SAMPLINGINTEGRATED SAMPLINGCONSIDERATIONSCONSIDERATIONS

Appropriate sample duration and flow rate Appropriate sample duration and flow rate need to be chosen relative to the purpose of need to be chosen relative to the purpose of sampling, the sensitivity of the analytical sampling, the sensitivity of the analytical method, and the expected concentration of method, and the expected concentration of the contaminant of interest. It is also the contaminant of interest. It is also essential that the flow rate and time be essential that the flow rate and time be accurately measured. The accuracy depends accurately measured. The accuracy depends on the precise determination of the mass of on the precise determination of the mass of contaminant collected as well as the volume contaminant collected as well as the volume of air sampled. of air sampled.

ACTIVE SAMPLINGACTIVE SAMPLING

Means of collecting an airborne substance Means of collecting an airborne substance that employs a mechanical device such as an that employs a mechanical device such as an air sampling pump to draw the air sampling pump to draw the air/contaminant mixture into or through the air/contaminant mixture into or through the sampling device. sampling device.

ExamplesExamples: sorbent tube, treated filter, or : sorbent tube, treated filter, or impinger containing a liquid media. impinger containing a liquid media.

A key element is calibration that reliably A key element is calibration that reliably measures the pump flow rate, thus allowing measures the pump flow rate, thus allowing for an accurate determination of air volume. for an accurate determination of air volume.

ACTIVE SAMPLING – ACTIVE SAMPLING – ADVANTAGESADVANTAGES

- - Select method to be used by compliance Select method to be used by compliance personnel during OSHA inspection.personnel during OSHA inspection.

- - Offers calibrated, measured airflow for Offers calibrated, measured airflow for assurance in accuracy of sample volume. assurance in accuracy of sample volume.

- - Sorbent tube samples have a secondary Sorbent tube samples have a secondary layer for back-up indicating layer for back-up indicating breakthrough.breakthrough.

- - Multiple phases can be assessed by a Multiple phases can be assessed by a series of samplers. series of samplers.

ACTIVE SAMPLING – ACTIVE SAMPLING – DISADVANTAGESDISADVANTAGES

- - Cumbersome equipment and may Cumbersome equipment and may interfere interfere with job of workers throughout with job of workers throughout

shift. shift.

- - Pump calibration is time consuming Pump calibration is time consuming and and requires technical training on tasks. requires technical training on tasks.

-- Pump may become somewhat less Pump may become somewhat less reliable at maintaining constant flow over reliable at maintaining constant flow over

the entire sampling period, and more the entire sampling period, and more frequent calibration may be necessary. frequent calibration may be necessary.

PASSIVE SAMPLERSPASSIVE SAMPLERS

Commercially available for a variety of airborne Commercially available for a variety of airborne contaminants. Some samplers are designed to contaminants. Some samplers are designed to collect a broad range of compounds, whereas collect a broad range of compounds, whereas others because of their collection media others because of their collection media preferentially collect a single chemical or preferentially collect a single chemical or family of chemicals. family of chemicals. ExamplesExamples: activated charcoal sorbent – : activated charcoal sorbent – organic vapors and GC analysis; chemical organic vapors and GC analysis; chemical treated sorbents or filter paper for preferential treated sorbents or filter paper for preferential collection for HPLC analysis.collection for HPLC analysis.Direct-reading passive samplers based on Direct-reading passive samplers based on colorimetric techniques. May not be as colorimetric techniques. May not be as accurate as lab analytical methods. Discuss accurate as lab analytical methods. Discuss examples.examples.

DIFFUSIVE SAMPLERSDIFFUSIVE SAMPLERS

Diffusive samplers rely on the movement of Diffusive samplers rely on the movement of contaminant molecules across a concentration contaminant molecules across a concentration gradient, which for steady-state conditions gradient, which for steady-state conditions can be defined by Fick’s first law of diffusion. can be defined by Fick’s first law of diffusion. Consist of diffusion gap between external air Consist of diffusion gap between external air and a sorbing medium which serves to collect and a sorbing medium which serves to collect the chemicals of interest, but also to maintain the chemicals of interest, but also to maintain the concentration as close to zero as possible the concentration as close to zero as possible at the end of the diffusion path. at the end of the diffusion path. Each Each gas/vapor sampled has a specified diffusion gas/vapor sampled has a specified diffusion coefficientcoefficient (D). Uptake rates can vary under (D). Uptake rates can vary under various field conditions. Validation!various field conditions. Validation!

OSHA ISSUESOSHA ISSUESResearch report in 1998 that attempted to Research report in 1998 that attempted to determine sampling rate variation of specific determine sampling rate variation of specific passive sampler designs. Concept of passive passive sampler designs. Concept of passive sampling equated to active sampling with sampling equated to active sampling with pump error of +/- 5%. Significant in that use of pump error of +/- 5%. Significant in that use of the sampling rate variation for a passive the sampling rate variation for a passive sampler along with the analytical error sampler along with the analytical error component allowed the calculation of the component allowed the calculation of the overall Sampling and Analytical Error (SAE). overall Sampling and Analytical Error (SAE). SAE must be used by OSHA inspectors along SAE must be used by OSHA inspectors along with sample results to determine if PEL with sample results to determine if PEL exceeded. Therefore, passive sampling exceeded. Therefore, passive sampling methods can be used by OSHA.methods can be used by OSHA.

PASSIVE SAMPLING – PASSIVE SAMPLING – ADVANTAGESADVANTAGES

-- Easy to use, allowing samples to be Easy to use, allowing samples to be collected by personnel with less technical collected by personnel with less technical training. training.

- - Less expensive. Less expensive.

- - Less obtrusive to wearer for monitoring. Less obtrusive to wearer for monitoring.

- For most applications, the mass of - For most applications, the mass of contaminant collected by passive contaminant collected by passive samplers samplers is not significantly affected by is not significantly affected by temperature or temperature or pressure. pressure.

PASSIVE SAMPLING – PASSIVE SAMPLING – DISADVANTAGESDISADVANTAGES

- - May not be OSHA/NIOSH methods to May not be OSHA/NIOSH methods to reference reference in order to insure reliability of data. in order to insure reliability of data. - - Sampling rate, if theoretically calculated, may Sampling rate, if theoretically calculated, may

not prove to be valid under field conditions. not prove to be valid under field conditions. -- Reverse diffusion may be a factor.Reverse diffusion may be a factor.-- Environmental parameters may influence the Environmental parameters may influence the

collection efficiency of passive samplers. collection efficiency of passive samplers. ExamplesExamples: stagnant air; high face velocities. : stagnant air; high face velocities.

-- Low uptake rates may not provide sensitivity Low uptake rates may not provide sensitivity required for low-level determinations, and required for low-level determinations, and

extended sampling times (>24 hours) may extended sampling times (>24 hours) may enhance reverse diffusion effects.enhance reverse diffusion effects.

AIR SAMPLING AIR SAMPLING INSTRUMENTSINSTRUMENTS

Five basic components of air sample Five basic components of air sample collection devices :collection devices :• Air inlet orificeAir inlet orifice• Collection deviceCollection device• Airflow meterAirflow meter• Flow rate control valveFlow rate control valve• Suction pumpSuction pump

COLLECTION DEVICES FOR COLLECTION DEVICES FOR PARTICULATESPARTICULATES

FiltersFilters ImpactorsImpactors Impingers Impingers ElutriatorsElutriators Electrostatic precipitationElectrostatic precipitation Thermal precipitationThermal precipitation CyclonesCyclones

Fundamentals of IH reference book (5Fundamentals of IH reference book (5thth Edition): Table 16-C, pg 528 Edition): Table 16-C, pg 528

AIR SAMPLING PUMPSAIR SAMPLING PUMPS

Integrated methods require a relatively Integrated methods require a relatively constant source of suction that can be constant source of suction that can be calibrated to the recommended flow rate calibrated to the recommended flow rate (within +/- 5% with collection media in-line).(within +/- 5% with collection media in-line).

Personal sampling within the worker’s breathing Personal sampling within the worker’s breathing zone zone oror can be used as area samplers. can be used as area samplers.

Features – constant flow capabilities/back Features – constant flow capabilities/back pressure; intrinsically safe; electromagnetic pressure; intrinsically safe; electromagnetic susceptibility, etc.susceptibility, etc.

Must be capable of maintaining the desired flow Must be capable of maintaining the desired flow rate over the entire sampling period with the rate over the entire sampling period with the sample collection device in-line. sample collection device in-line.

Pressure drop; constant flow vs. constant Pressure drop; constant flow vs. constant pressurepressure

FLOW RATE METERSFLOW RATE METERS

Pressure compensating devicesPressure compensating devices Critical flow orifice Critical flow orifice

SAMPLE COLLECTION SAMPLE COLLECTION MEDIAMEDIA

Consult published air sampling methods to Consult published air sampling methods to determine the appropriate collection media determine the appropriate collection media for a specific chemical contaminant. for a specific chemical contaminant.

Review methods to determine applicability Review methods to determine applicability relative to field conditions. Such as: vp, bp, relative to field conditions. Such as: vp, bp, reactivity; interferences as well as also reactivity; interferences as well as also humidity/temperature effects, proper humidity/temperature effects, proper measuring range; physical state of the measuring range; physical state of the contaminant being sampled; multiple contaminant being sampled; multiple phases (i.e. particulate and vapor phase). phases (i.e. particulate and vapor phase).

SOLID SORBENT MEDIASOLID SORBENT MEDIAAdsorb onto surface; Effectiveness determined Adsorb onto surface; Effectiveness determined byby:: Trap and retain nearly all contaminant from airTrap and retain nearly all contaminant from air Amenable to desorption from sorbent Amenable to desorption from sorbent Sufficient capacity to retain quantity of Sufficient capacity to retain quantity of

contaminant to facilitate analysis without contaminant to facilitate analysis without creating large pressure drop across sample creating large pressure drop across sample mediamedia

Not cause chemical change of contaminant Not cause chemical change of contaminant except by analytical method as neededexcept by analytical method as needed

Collect contaminant of interest in presence of Collect contaminant of interest in presence of other contaminants, possibly in higher other contaminants, possibly in higher concentrations than the contaminant of interest.concentrations than the contaminant of interest.

COLLECTION EFFICIENCY OF COLLECTION EFFICIENCY OF SOLID SORBENTSSOLID SORBENTS

Various Factors:Various Factors: TemperatureTemperature Humidity Humidity Sampling RateSampling Rate Other ContaminantsOther Contaminants Sample Breakthrough Sample Breakthrough

-- 25%25%

-- MigrationMigration

TYPES OF SORBENT MATERIALSTYPES OF SORBENT MATERIALS

Inorganic Sorbents – silica gel (polar;%RH); Inorganic Sorbents – silica gel (polar;%RH); less reactive than charcoalless reactive than charcoal

Elemental Carbon – charcoal types; Elemental Carbon – charcoal types; organics; high adsorptive capacity; stable organics; high adsorptive capacity; stable compounds; high humidity parameterscompounds; high humidity parameters

Carbonized or Graphitized Sorbents – low to Carbonized or Graphitized Sorbents – low to moderate surface area; intermediate to high moderate surface area; intermediate to high volatility; stable compounds for thermal volatility; stable compounds for thermal desorptiondesorption

Fundamentals of IH reference book (5Fundamentals of IH reference book (5thth Edition): Table 16-B, pg 527 Edition): Table 16-B, pg 527

OTHER MEDIAOTHER MEDIA Chemically treated filters – derivatize/desorbChemically treated filters – derivatize/desorb Liquid absorbersLiquid absorbers

• Gas washing bottles – e.g. impingersGas washing bottles – e.g. impingers• Fritted glass bubblers Fritted glass bubblers

Sampling bags/partially evacuated rigid Sampling bags/partially evacuated rigid containers (canisters) containers (canisters) • SituationsSituations: use of direct-reading : use of direct-reading

instruments; leaks/emergencies; peak instruments; leaks/emergencies; peak concentrations; highly volatile compoundsconcentrations; highly volatile compounds

- Precautions – storage time; reaction; Precautions – storage time; reaction; diffusiondiffusion

CALIBRATIONCALIBRATIONPump flow must be calibrated with the Pump flow must be calibrated with the entire sampling train assembled as it entire sampling train assembled as it will be used in the field. Good IH will be used in the field. Good IH practice requires both pre- and post-practice requires both pre- and post-pump calibration on the same day pump calibration on the same day under pressure and temperature under pressure and temperature conditions similar to those at site. conditions similar to those at site. Should not be done with built-in Should not be done with built-in rotameters (not precision devices and rotameters (not precision devices and will not give a quantitative measure of will not give a quantitative measure of the rate of airflow). the rate of airflow).

CALIBRATION STANDARDSCALIBRATION STANDARDSTwo terms:Two terms: Primary – direct and measurable linear Primary – direct and measurable linear

dimensions (length and diameter of dimensions (length and diameter of cylinder)cylinder)• Examples: spirometers and bubble Examples: spirometers and bubble

metersmeters Secondary – flowmeters that trace Secondary – flowmeters that trace

calibration to primary standards and calibration to primary standards and maintain accuracy with reasonable care and maintain accuracy with reasonable care and handling in operation. handling in operation. • Examples: precision rotameters, wet test Examples: precision rotameters, wet test

meters, and dry gas meters.meters, and dry gas meters.Refer to instructions from manufacturers.Refer to instructions from manufacturers.

OPERATIONAL LIMITS OF OPERATIONAL LIMITS OF SAMPLING AND ANALYSISSAMPLING AND ANALYSIS

Inherent limitations of method:Inherent limitations of method:- Sampler capacitySampler capacity- Limit of Detection (LOD)Limit of Detection (LOD)- Limit of Quantification (LOQ)Limit of Quantification (LOQ)- Upper measurement limits which define the Upper measurement limits which define the

useful range of the method. useful range of the method. These factors determine the minimum, These factors determine the minimum,

maximum, or optimum volume of air to be maximum, or optimum volume of air to be sampled and may determine the confidence sampled and may determine the confidence that can be placed in the results.that can be placed in the results.

Discuss with lab before sampling!Discuss with lab before sampling!

SAMPLER CAPACITYSAMPLER CAPACITYPredetermined conservative estimate of the Predetermined conservative estimate of the total mass of contaminant that can be total mass of contaminant that can be collected on the sampling medium without collected on the sampling medium without loss of overloading.loss of overloading.NIOSH definition of 2/3 of the experimental NIOSH definition of 2/3 of the experimental breakthrough capacity of the solid sorbent, breakthrough capacity of the solid sorbent, that is 67% of the mass of contaminant on the that is 67% of the mass of contaminant on the sorbent at the breakthrough volume. sorbent at the breakthrough volume. Breakthrough volume is defined as that Breakthrough volume is defined as that volume of an atmosphere containing two volume of an atmosphere containing two times the PEL for the contaminant that can be times the PEL for the contaminant that can be sampled at the recommended flow rate before sampled at the recommended flow rate before the efficiency of the sampler degrades to 95%.the efficiency of the sampler degrades to 95%.

CALCULATIONSCALCULATIONS

Total Mass of ContaminantTotal Mass of Contaminant Airborne Concentration by sample Airborne Concentration by sample

volume (mass over volume)volume (mass over volume) Air Volume (flow rate x sample time)Air Volume (flow rate x sample time) Unit Conversions – mg/M3 to/from ppmUnit Conversions – mg/M3 to/from ppm Temperature/Pressure CorrectionsTemperature/Pressure Corrections Time-Weighted Averages Time-Weighted Averages Potential Work Shift Adjustments Potential Work Shift Adjustments

REMEMBERREMEMBERCALCULATIONSCALCULATIONS

A range of temperature and pressure changes A range of temperature and pressure changes can be tolerated before corrections are applied can be tolerated before corrections are applied to the to the volumevolume or or air sampledair sampled during an during an exposure assessment. exposure assessment.

All OELs and environmental exposure standards All OELs and environmental exposure standards and limits are expressed at 25 degrees C and 1 and limits are expressed at 25 degrees C and 1 atmosphere (760 mm Hg), defined as normal atmosphere (760 mm Hg), defined as normal temperature and pressure (NTP). temperature and pressure (NTP).

Therefore, corrections needed for meaningful Therefore, corrections needed for meaningful comparisons related to published exposure comparisons related to published exposure limits.limits.