Indoor Environmental Quality - Chapter 9 pdf

chapter nine Measurement of indoor contaminants Contaminant measurements are made in most, if not all, investigations conducted to evaluate potential causal relationships between illness or illness symptoms and residential and nonresidential building environments. Con- taminant measurements may include sampling of airborne concentrations of gas/vapor or particulate-phase substances, sampling of airborne biological contaminants, surface sampling, and bulk sampling of building materials. Contaminant measurements are made for various reasons. In the case of carbon dioxide (CO 2 ), they are used to determine the adequacy of ventilation; in other cases they may be used as a screening tool to determine whether target contaminants are within or above acceptable guideline values. The best reason to conduct contaminant measurements in problem buildings is to identify and confirm the presence of contaminants that may be causally associated with reported illness symptoms. In the case of carbon monoxide (CO), measurements of COHb in blood may be used to confirm a CO exposure and its magnitude. Contaminants that may pose long-term health exposure risks (e.g., radon) may also be measured. I. Measurement considerations It is important when conducting environmental measurements in indoor environments that investigators are familiar with principles and practices associated with such measurements and conduct these activities with specific objectives in mind. Contaminant concentrations are determined from samples that have been collected. © 2001 by CRC Press LLC A. Sampling In sampling, one attempts to identify or determine the concentration of a substance or substances in a relatively small volume of indoor air or human blood, on a limited surface area, or in a small mass of material. For purposes of contaminant identification and quantification, a sample is assumed to be representative of a larger volume of air (e.g., room), blood, or material surface or mass. This assumption, when used in conjunction with an appropriate sampling protocol, can be expected to provide reasonably reliable measurements that can be used to confidently interpret sampling results. B. Sampling objectives Environmental sampling is conducted in indoor environments for a number of reasons. It has, as a consequence, one or more stated or inferred objectives. These may include (1) general or specific measurements requested by a homeowner/building owner/client, (2) routine screening measurements to determine whether major identified contaminants are within guideline values or other acceptable limits, (3) measurements to confirm a hypothesis relative to problem contaminants and health effects that may be associated with such exposures, and (4) measurements to determine the effectiveness of mitigation measures. 1. Requests Environmental sampling is often requested by building managers/owners of both nonresidential and residential properties. These may be made in response to regulatory requirements (asbestos, and in some cases, lead); as a part of environmental site assessments; or as a condition of a real estate transaction (asbestos, lead, radon). They may also be made in response to problem building complaints in the case of nonresidential buildings and general or specific health concerns expressed by occupants of residential buildings. In the former case, environmental sampling may be requested (1) in response to occupant requests, (2) to demonstrate empathy for occupant concerns, (3) to allay occupant fears by demonstrating that an air/surface contamination problem does not exist, and (4) to identify the potential cause of occupant complaints. Investigators have different professional responsibilities as they relate to building manager/owner requests. Private consultants are obliged to provide only the services requested and any additional services that may be subsequently agreed upon. Public health and environmental agency staff have an obligation to protect public health. In theory, they have more latitude in conducting investigatory activities beyond simple requests for air or other environmental sampling. In practice, public health/environmental agency investigators acting in a nonregulatory mode generally respect the wishes of building managers/owners relative to the scope of environmental sampling and other building investigation activities. © 2001 by CRC Press LLC 2. Routine screening Routine screening is a common sampling objective. Measurements are made without any consideration of the probability that a contaminant is present or the nature of health or other concerns. Common indoor contaminants are measured using sampling instruments and techniques that are readily available, easy to use, and which do not impose an undue financial cost on building owners or public health and environmental agencies. Screening measurements have been, and continue to be, widely used by homeowners/lessees and other building owners to determine radon levels. Such measurements are designed to identify buildings with high radon concentrations so that owners can implement appropriate mitigation measures to reduce exposure. Routine screening is an important infection control measure in hospitals. Of particular concern is the maintenance of low airborne levels of Aspergillus fumigatus in surgical operating and convalescent patient rooms, as well as oncology, transplant, and AIDS wards. Screening measurements for formaldehyde (HCHO) in urea–formaldehyde foam-insulated (UFFI) houses were conducted by the Canadian government and many homeowners in both Canada and the U.S. in the 1980s; such measurements are rare today. Mea- surements of HCHO, CO, CO 2 , respirable particles (RSP), airborne mold, and nitrogen dioxide (NO 2 ) are commonly conducted in epidemiological studies and problem building investigations. On a population basis, such screening has the potential to identify indoor environments that exceed guideline values and, as a consequence, are in need of mitigation measures. Because of its generic nature, routine screening has limited value in identifying specific causal factors responsible for building health complaints. 3. Identifying causal contaminants Ideally, environmental sampling is conducted to identify and quantify contaminants which, based on information gathered in an investigation, can reasonably be expected to be a potential causal factor in occupant health complaints. In some cases, the targeting of specific contaminants is facilitated by: (1) unique symptomology (CO exposure, hypersensitivity pneumonitis); (2) suggestive evidence that ventilation may be inadequate (human odor, poorly designed/operated heating, ventilation, and air conditioning [HVAC] systems); (3) odor (ammonia, solvents); (4) water-damaged materials and evident mold infestation; and (5) occupant allergy tests that indicate sensitivity to particular allergens. Nonspecific mucous membrane and general (headache, fatigue) symptoms are commonly reported in many problem building and residential investigations. They cannot easily be associated with unique contaminant exposures. As a result, environmental sampling is unlikely to identify environmental contaminants that may be causal agents. © 2001 by CRC Press LLC 4. Evaluating effectiveness of mitigation measures Environmental sampling is routinely used to test the effectiveness of radon mitigation measures. This requires that sampling be conducted prior to and after mitigation activities have been completed. Environmental sampling is also conducted to determine the effectiveness of post-abatement cleaning measures for asbestos and lead in buildings, and is increasingly being used to determine the effectiveness of clean-up activities after the abatement of toxigenic mold infestations such as Stachybotrys chartarum and Aspergillus versicolor . In asbestos abatements, aggressive sampling is conducted to meet clearance airborne asbestos fiber concentrations; it is also a desirable practice in toxigenic mold abatements. Surface sampling is conducted in lead abatements to determine whether clearance guidelines have been achieved. Environmental sampling has particular value in determining the effectiveness of measures implemented to improve ventilation. Pre- and post- measurements of CO 2 levels are commonly conducted to evaluate the performance of ventilation systems after operation and maintenance changes have been made. Environmental sampling in conjunction with occupant health and comfort surveys can be used to evaluate the effectiveness of mitigation efforts in reducing symptom prevalence and increasing occupant satisfaction with air quality. Such coordinated pre- and post-environmental sampling and occupant health and comfort surveys are rarely conducted. Those conducted in research studies have, for the most part, not demonstrated significant reductions in symptom prevalence rates and increases in occupant satisfaction with air quality. C. Sampling airborne contaminants Airborne gas and particulate-phase substances have historically been the major focus of environmental sampling in indoor environments subject to indoor air quality/indoor environment (IAQ/IE) concerns. The conduct of air sampling requires selection of appropriate sampling and analytical procedures including: (1) instrument selection and calibration; (2) sampling location, time, and duration; and (3) number of samples. It also involves sampling and analysis administration and quality assurance. There are a variety of approaches, sampling instruments, and analytical methods that can be used to conduct measurements of airborne contaminants. Selection of sampling and analytical techniques that provide acceptable performance is, of course, very important. Acceptable performance is ensured by implementing appropriate quality assurance practices. These performance considerations include accuracy, precision, sensitivity, and specificity. 1. Performance considerations a. Accuracy. Accuracy is the closeness of a value to its true or known value. It can be described by an error value expressed as a percentage. A © 2001 by CRC Press LLC sampling/analytical procedure may have an accuracy of 95%. This means that repeated measurements indicate that the measured value deviates from the true value by –5%, or 5% < true value. Another procedure may have an accuracy of 110%; i.e., on average the concentration is +10%, or 10% > true value. A good sampling/analytical procedure will have an accuracy within ±10% of the true value. b. Precision. Sampling/analytical procedures should also be relatively precise. Precision in the scientific (rather than dictionary definition) sense is the reproducibility of measured results. Precision indicates the relative variation around the mean. It is reported as a ± percentage around the mean of multiple values determined from measuring the same known concentration. It is determined by calculating the coefficient of variation (9.1) where σ = standard deviation x = mean Sampling/analytical procedures should have both high accuracy (within ±10% of the true value) and high precision. Acceptable precision values depend on the technique employed. For many instrumental techniques, ±10% is desirable. For techniques such as gas sampling tubes and passive samples, a precision of ±25% is generally acceptable. Though accuracy and precision are scientifically well-defined concepts, they are used interchangeably by the lay public as well as by technically trained individuals. As a consequence, it is often difficult to communicate their scientific meaning and relevance in environmental sampling. c. Sensitivity. In addition to acceptable accuracy and precision, it is important to use sampling/analytical procedures that are sufficiently sensi- tive to measure contaminant concentrations expected. Sensitivity is determined from reported limits of detection (LODs) for different sample sizes and durations. The LOD varies with different analytical procedures. It can often be extended (within limits) by increasing the volume of air sampled into/onto sorbing media by increasing sampling duration. This cannot be done on direct-read, real-time instruments. d. Specificity. In most, but not all cases, a procedure should be specific for the contaminant under test. This is especially true for gases and vapors. Nonspecific techniques have diminished accuracy when two or more contaminants with similar chemical characteristics are present. Measured concentrations may be higher than they actually are. Such results can be char- acterized as positive interference. In other cases they will be lower; therefore, interference is negative. Interference with measured concentrations can also CV σ x 100()= © 2001 by CRC Press LLC occur even when a sampling/analytical procedure has relatively high specificity. This is true for the DNPH–HPLC method used for HCHO and other aldehydes. It is subject to significant negative interference from ozone (O 3 ). e. Reference methods. The use of sampling/analytical procedures to conduct sampling for vapor-phase substances should be a relatively conser- vative one. It is desirable to use reference, approved, or recommended methods that have been systematically evaluated by the National Institute of Occupational Safety and Health (NIOSH), the U.S. Environmental Protection Agency (USEPA), the Occupational Safety and Health Administration (OSHA), or the American Society for Testing and Materials (ASTM). The use of approved methods provides a relative (but not absolute) degree of confidence in the accuracy, precision, and reliability of sampling/analytical procedures being employed. f. Quality assurance. Contaminant measurements conducted in problem buildings or in systematic research studies need to be quality assured to provide confidence in their accuracy and reliability. Quality assurance procedures include instrument calibration, and, when appropriate, use of field blanks, media blanks, replicate samples, and split or spiked samples. They focus on both field and analytical aspects of contaminant collection and measurement. i. Calibration. Calibration is a process whereby measured values of air flow and/or contaminant levels are compared to a standard. In the case of air flow, the standard may be primary or secondary, with the latter trace- able to the former. Primary standards can be traced directly to those at the National Institute of Standards and Technology (NIST). A gas burette serving as an airflow measuring device is a primary standard; a rotometer (which must be calibrated) is a secondary standard. All dynamic sampling instruments, particularly gas sampling pumps and tube systems, should be calibrated frequently. In common practice, calibration of real-time, direct-read instruments is conducted by using calibration gases that have been prepared to provide sample concentrations within the measuring range of the instrument. Single- and multiple-point calibrations are conducted depending on the user; multipoint calibrations are preferred. ii. Blank/replicate samples, etc. In collecting samples onto a medium, it is essential that field or media blanks be used. A field blank is a media sample taken to the field, opened, then closed and returned to the laboratory where it is analyzed. Media blanks are samples of liquid media prepared at the same time as samples used in the field or the same lot of solid media. Both are used to adjust environmental sample concentrations for contaminant levels present in unexposed media. Field blanks are used to determine whether contamination occurred as a consequence of sample © 2001 by CRC Press LLC media being taken into the field. Two field blanks for each of 10 environmental samples are generally recommended. Replicate samples are often collected to assess the accuracy and precision of analytical results, split samples to compare the performance of different analysts, and spiked samples to assess analytical performance relative to a known sample concentration. 2. Resource limitations In addition to performance characteristics described above, selection of a sampling/analytical procedure will often be determined by the availability of resources. Despite significant performance limitations, sampling/analytical procedures are often chosen because of their relatively low cost. This is particularly true for gas sampling tubes and, in some cases, passive samplers. Other factors affecting the selection of sampling/analytical procedures include equipment availability, portability, and degree of obtrusiveness. 3. Sampling procedures Samples of airborne contaminants can be collected and analyzed by utilizing both dynamic and passive sampling procedures. a. Dynamic sampling. In dynamic sampling, vapor-phase substances are drawn (by means of a pump) at a controlled rate through a liquid or solid sorbent medium or into a sensing chamber. In sampling for particulate- phase substances, air is drawn through a filter, impacted on an adhesive- coated surface, attracted to collecting surfaces by electrostatic or thermostatic processes, or brought into a sensing chamber. The sample volume is determined from the known flow rate and sampling duration. Concentrations can be calculated or read directly from electronic real-time instruments. Dynamic sampling is conducted using two approaches. In the first, sampling and analysis are discrete events. Sampling is conducted with pumps that collect vapor-phase substances in a liquid medium (absorption) or onto one or more solid sorbents (adsorption) such as charcoal, tenax, silica gel, etc. Exposed sorbent media must be analyzed by a laboratory. Depending on laboratory schedules, results may be available in a matter of days or up to several weeks. In the case of particulate matter samples, gravimetric analysis may be conducted within a day or so after samples have been sent to a laboratory. The relatively long period between sample collection and availability of results is an obvious disadvantage of this type of sampling. For many contaminants, alternatives may not yield acceptable results or may be too expensive. Dynamic sampling (and analysis) can also be conducted using direct- read, real-time (instantaneous) or quasi-real-time instruments. Such instruments are available for a limited number of common indoor contaminants. Sampling and analysis are combined so that results are immediately available to individuals conducting investigations and testing (providing an obvious advantage). © 2001 by CRC Press LLC Real-time sampling/analysis is conducted with electronic direct-read instruments or by gas sampling tubes. A variety of electronic direct-read instruments are commercially available for determining concentrations of gases, vapors, or particulate matter. They are usually pump-driven devices which draw air at a known, low, constant rate into a small chamber where sensors measure specific chemical or physical properties of contaminants under test. Commonly used principles for gas/vapor substances include electrochemistry, photometry, infrared absorption, and chemiluminescence. Commonly used principles for airborne particles include optical techniques that measure light scattering or absorption and piezoelectric resonance. Por- table, direct-read, real-time instruments are widely used to measure CO 2 , CO, and RSP in indoor air. Electronic instruments have a continuous output of concentration readings, and as a consequence, concentration values can be continuously recorded. An electronic direct-read sampling instrument for CO 2 is illustrated in Figure 9.1. Gas sampling tube systems are used to measure a variety of contaminants in industrial workplaces and, less commonly, IAQ/IE investigations. They consist of a gas syringe or bellows into which a gas sampling tube designed to detect and quantify a specific gas or gases is inserted. The syringe/bellows is designed to draw a minimum sample volume of 0.1 L. Larger volumes can be utilized by employing multiple pumping actions. Gas sampling tubes are hermetically sealed prior to use. They contain a granular sorbent such as silica gel, alumina, or pumice, impregnated with one or more chemicals that react on contact with a specific contaminant or contaminant group, producing a colored or stained substrate medium. The length of the stain or colored sorbent is proportional to the concentration of contaminants in the air volume sampled. The concentration is typically read from a calibrated scale printed on the side of the tube. A gas sampling tube system is illustrated in Figure 9.2. Figure 9.1 Real-time electronic CO 2 monitor. © 2001 by CRC Press LLC Gas sampling tubes are commercially available for a large number (100+) of gases and concentration ranges. Their accuracy and precision varies. They are designed in most cases to provide an accuracy within ±25% of the true value with similar precision. Gas sampling tube systems are attractive for conducting sampling in indoor and other environments. They are relatively inexpensive, simple to use, and provide quasi-real-time sampling results. Unfortunately, they have significant limitations. These include, in many cases, relatively poor accuracy and precision, lack of specificity, high LODs, and limited shelf-life (1+ year). In addition the length of the color-stained substrate tends to be indeterminate (no sharp demarcation) and concentrations may be difficult to read. These limitations vary for the contaminants being sampled. Despite these limitations, gas sampling tube use is common in IAQ investigations. Best results have been reported for measurements of CO and CO 2 . b. Passive sampling. Passive sampling techniques are widely used in measuring indoor contaminants. They are particularly useful for determining concentrations integrated or averaged over a period of hours, a week, or even months. In most cases, they are based on the principle of collecting contaminants by diffusion onto or into a sorbent medium. In passive samplers used for gas-phase substances, the sampling rate, and therefore volume of air that comes into contact with the collecting medium, can be determined from the cross-sectional area of the sampling face, the length/depth through the sampler that gases must travel to be collected on absorbing surfaces, and the diffusion constant of the gas being collected. The Palmes diffusion tube (Figure 9.3) was the first passive device to be developed and used. Palmes tubes are still commonly used to measure NO 2 levels in buildings. They have a sampling rate of 55 ml/hr, and concentrations are usually integrated over a period of 7 days. Since the development of passive samplers in the 1970s, a number of new devices using the same sampling principles have been developed. These Figure 9.2 Gas sampling tube system. © 2001 by CRC Press LLC include small badges that provide relatively high sampling rates over a period of 8 hours (Figure 9.4), and charcoal canisters used for radon measurements over a period of 2 to 7 days. Track-etch detectors are passive samplers that record alpha particle tracks on plastic film over a period of months. Unlike most passive samplers, track-etch detectors do not use the principle of diffusion directly. Passive samplers have the advantage of low cost, simplicity of use, and reliability. They are designed to have an acceptable accuracy/precision (e.g., ±25%). Their accuracy/precision is diminished by changes in face velocity (due to changes in room airflow), which may occur during sampling. Passive samplers are not particularly useful in conducting problem building investigations because of the long sampling times required (generally 8 hours or more). They have, however, been widely used in screening measurements of HCHO, NO 2 , and radon in indoor environments. Figure 9.3 Palmes diffusion tube. (From Palmes, E.P. et al., AIHAJ , 37, 570, 1976. With permission.) Figure 9.4 Badge-type passive samplers. © 2001 by CRC Press LLC [...]... indoor air, Indoor Air, 5, 247, 199 5 Maroni, M., Siefert, B., and Lindvall, T., Indoor Air Quality: A Comprehensive Reference Book, Elsevier, Amsterdam, 199 5, chaps 23, 24, 26, 27 McCarthy, J.E., Bearg, D.W., and Spengler, J.D., Assessment of indoor air quality, in Indoor Air Pollution — A Public Health Perspective, Samet, J.M and Spengler, J.D., Eds., Johns Hopkins University Press, Baltimore, 199 1,... CRC Press LLC Table 9. 2 Selected Positive Hole Correction Values Measured concentration (count/plate) Corrected concentration (count/plate) 40 50 60 70 80 90 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 42 53 65 77 89 102 115 143 172 204 2 39 277 3 19 367 420 422 555 644 7 59 921 1 198 2628 Source: Data extracted from Macher, J., Am Ind Hyg Assoc J., 50, 561, 198 9 iii Enumeration Enumeration... Single-stage, portable impactor Single-stage (N-6) impactor Two-stage impactor Multiple-stage impactor Centrifugal Impingers All glass/AGI-30 All glass/AGI-4 Filters Cassette 1-6 0, Depending on model and sampling circumstances a Contemporary practice is 1 to 5 minutes Source: From Chatigny, M.A et al., Air Sampling Instruments for Evaluation of Atmospheric Contaminants, ACGIH, Cincinnati, 198 9, 10... Monitoring Indoor Air Quality, ASTM STP, American Society for Testing and Materials, Philadelphia, 198 9 Spengler, J.D., Samet, J.M., and McCarthy, J.F., Eds., Indoor Air Quality Handbook, McGraw-Hill Publishers, New York, 2000, chaps 51, 52, 56, 58 Thorsen, M.A and Molhave, L., Elements of a standard protocol for measurements in the indoor atmospheric environment, Atmos Environ., 21, 1411, 198 7 Tichenor,... board predicted by first order decay and double-exponential models (From Brown, S.K., Indoor Air, 9, 2 09, 199 9 With permission.) © 2001 by CRC Press LLC Source emission models have also been developed that are based on mass transfer processes Emission rates for wet sources (paint coatings, etc.) can be described by the simplified equation: ER = Kg (Cs – C) (9. 7) where Kg = mass transfer coefficient (m/hr)... Determination of VOC Emissions in Environmental Chambers from Materials and Products, ASTM, Philadelphia, 199 0 Cox, C.S and Wathes, C.M., Bioaerosols Handbook, CRC Press, Boca Raton, 199 5 Dillon, H.K., Heinsohn, P.A., and Miller, J.D., Eds., Field Guide for the Determination of Biological Contaminants in Environmental Samples, American Industrial Hygiene Association, Fairfax, VA., 199 6 Hodgson, A.T., A review... to the CO concentration in the sampled air stream Both pump-driven and passive, hand-held sampling devices are available The former produces instantaneous real-time values, whereas the latter is somewhat slower, requiring a minute or more to respond Real-time or quasi-real-time CO monitors have advantages similar to those used for CO2 Pump-driven devices can be easily calibrated with standard gas mixtures,... of gamma ray energy Electret devices can also be used for longer-term sampling (up to 3 months) As indicated in Chapter 3, short-term measurements are not adequate to determine long-term exposures which may pose a cancer risk For such determinations it is common to measure radon using a track-etch detector (Figure 9. 7, center) The track-etch detector is a simple device that consists of a plastic strip... composition/rate data for controlled environmental conditions Chamber size limits use to small samples Large Chambers Provides emission composition/rate data under controlled environmental conditions; used to evaluate emissions from large products Used to simulate real-world conditions Full-Scale Studies Test Houses Provides emission composition/rate data under semi-controlled real-world conditions; useful for... Sources of Indoor Air Pollution and Related Sink Effects, ASTM STP 1287, American Society of Testing Materials, West Conshohocken, PA, 199 6, 10 With permission II Source emissions characterization A variety of techniques and systems are used to characterize emissions from indoor sources, emission rates, changes in emissions over time, and potential indoor concentrations These are summarized in Table 9. 3 A . measured indoor air contaminant. Carbon dioxide measurements are made using direct-read, real-, or quasi-real-time instruments. These include electronic instruments that can provide instantaneous. also be conducted using direct- read, real-time (instantaneous) or quasi-real-time instruments. Such instruments are available for a limited number of common indoor contaminants. Sampling and. satisfaction with air quality. C. Sampling airborne contaminants Airborne gas and particulate-phase substances have historically been the major focus of environmental sampling in indoor