Purple Book (Guide for Controlling ACM in Buildings)_Part 11.pdf

and the plastic sheets covering doors, vents, and windows should be left in place until the air test has been passed.) If a negative air pressure ventilation system was used during abatement, it should continue operating while air monitoring is in progress. As discussed in Section 4.1, measuring air...

and the plastic sheets covering doors, vents, and windows should be left in place until the air test has been passed.) If a negative air pressure ventilation system was used during abatement, it should continue operating while air monitoring is in progress. As discussed in Section 4.1, measuring airborne asbestos fibers accurately is technically complex and usually expensive. It involves two steps: air sampling to capture fibers on a filter, and laboratory analysis to determine the quantity of asbestos. There are several approaches to air sampling and analysis, varying in technical requirements, cost, and availability. Which approach is more appropriate is a controversial subject. The information presented in the remainder of this chapter is based in part on a 1984 workshop sponsored by EPA and the National Bureau of Standards. A companion EPA guidance document on air monitoring following an abatement action discusses the subject in more detail (USEPA 1985 b). 6.4.2.1 Sampling Sampling for asbestos consists of collecting fibers by drawing air through a filter at a known rate. Usually, sampling equipment is placed at a fixed location for a certain period of time. But this approach may fail to detect the presence of fibers. For example, if sampling is conducted for a short time during a quiet period (i.e., when air movement is limited), many fibers will settle out of the air onto the floor and other surfaces and may not be captured on the filter. Under these conditions. air measurements could show little or no asbestos. Previously, EPA recommended sampling for at least eight hours to cover various air circulation conditions and thus increase the likelihood of capturing asbestos fibers if they are present. A quicker and more effective way to accomplish this, however, is to circulate the air artificially so that the fibers remain airborne during sampling. This “aggressive sampling” is recommended for the post-abatement air test. Recommended methods for conducting aggressive sampling are presented in Appendix M. They use forced-air equipment such as a leaf blower to dislodge free fibers, then slow-speed fans to keep the fibers suspended during sampling. Persons who conduct the sampling should wear a respirator. Even though the work site has been cleaned and has passed the visual test, levels of airborne asbestos still may be elevated. 6.4.2.2 Analysis of Samples Three microscopic methods are currently being used to analyze asbestos: phase contrast microscopy (PCM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The characteristics and relative merits of each method are summarized in Table 5 and are described in detail in the companion EPA guidance document (USEPA 1985 b). As indicated in Table 5, PCM is the method that is most familiar, available, and frequently used. It is also the least expensive and has a well-established analytical protocol. (As noted in Section 4.1.2, OSHA specifies PCM for monitoring worker exposure in asbestos industries.) However, the NIOSH protocol for PCM does not distinguish between asbestos and other types of fibers and counts only fibers longer than 5 micrometers. Nor is PCM sensitive enough to detect the extremely thin fibers typical of airborne asbestos in buildings. Thus, the interpretation of PCM results assumes that a low concentration of relatively large airborne fibers means that the concentration of asbestos fibers is also low, The TEM method gives the most complete information on airborne asbestos: it can distinguish asbestos from other fibers and also is able to detect very thin fibers. However, it can be expensive and time-consuming. TEM is not widely available. 6-5 TABLE 5. COMPARISON OF METHODS FOR MEASURING AIRBORNE ASBESTOS PCM SEM TEM Standard Methods NIOSH P&CAM 239 Method.1 No standard method. EPA provisional method & update.2 Quality Assurance Proficiency Analytical Testing Program; no NBS3 reference materials. No lab testing, or NBS reference materials. Limited lab testing; NBS reference materials available. cost $25-50 $50-300 $200-600 Availability Most available Less available. Least available. Time Requirements 1 hr. preparation & analysis, < 6 hrs. turnaround. 4 hrs. preparation & analysis, 6-24 hrs. turnaround. 4-24 hrs. preparation & analysis, 2-7 days turnaround. Sensitivity (Thinnest Fiber Visible) 0.15 µm at best; 0.25 µm typical. 0.05 µm at best; 0.20 µm typical, 0.0002 µm at best; 0.0025 µm typical. Specificity Not specific for asbestos. More specific than PCM but not definitive for asbestos. Definitive for asbestos. when used to its fullest capabilities. 1 NIOSH 1979. The new NIOSH 7400 method is an alternative. USEPA 1977, Yamate 1984. 3 National Bureau of Standards. 2 Source: Taken with modification from USEPA 1985b. The SEM method can be somewhat more specific for asbestos and more sensitive to thin fibers than PCM, but less so than TEM. It is also less expensive and time-consuming than TEM. At present, however, no standard measurement protocol is available for SEM. As a result, it has not been systematical y evaluated nor has the reliability of SEM measurements been established. EPA acknowledges that all three methods are used in air testing for the purpose of releasing abatement contractors. However, only PCM and TEM have standard methods and testing programs. A standard method has not yet been developed for SEM. While TEM is technically the method of choice, PCM is the only option in many localities. 6.4.2.3 Recommended Test Specifications Regardless of the microscopic method for measuring asbestos, identifying homogeneous work sites is the first important step in the process. A site within the abatement work area is homogeneous if it contains one type of ACM and only one type of abatement was used. For sampling purposes, the air in each 6-6 homogeneous site is assumed to be relatively uniform. Guidelines for locating the samplers are included in Appendix M. Several other aspects of the air test are identical, regardless of microscopic method: ● Choose sampling locations within the homogeneous work site to assure representative samples. (See Appendix M). ● Begin sampling when the work site is dry (24 hours after cleaning). ● Conduct aggressive air sampling in all cases. ● Follow sampling and analysis specifications, including procedures for quality control. The asbestos program manager should be sure the technical advisor in charge of the air test knows the specifications listed below. The advisor should insist that recommended procedures be followed for both air sampling and laboratory analysis. Testing with the TEM Method Sampling: ● Draw at least 3000 liters of air through each filter at a rate of 2 to 12 liters per minute. ● Collect at least five samples in each homogeneous work site. ● At the same time, collect at least five samples just outside the work site but within the building. These samples will be compared with those collected inside the work site to ensure that the work site is at least as clean as the incoming air (see Appendix M for details). 1 Analysis: ● Measure the asbestos on each filter with TEM using the EPA provisional procedures and updates (USEPA 1977 and Yamate 1984). ● Use a direct transfer method of sample preparation if possible (see Appendix M). ● Express the results as f/cc, or as ng/m3 if an indirect sample preparation is used. ● Include at least one field blank 2and one laboratory blank per abatement job for quality control purposes (see Section 6.4.3). Also, split one work site sample and conduct duplicate analyses. Release Criterion: ● Release the contractor if the average fiber concentration of the work site samples is not statistically larger than the average of the outside samples. Each homogeneous site must pass the test before the contractor is released. (Appendix M contains information to determine statistical differences.) ● If the average of the work site samples is statistically larger than the average of the outside samples, clean the entire work site again and repeat the test (collect new work site samples and follow the procedures described above). 1 2 If a negative pressure system has not been used, collect the “outside” samples outdoors. A blank is a filter that is not used for sampling but is otherwise treated in the same way as other filters. 6-7 Testing with the PCM Method Sampling: ● ● Draw at least 3000 liters of air through each filter at a rate of 2 to 12 liters per minute. Collect at least five samples per homogeneous work site, or one per room, whichever is greater. Analysis: ● Measure the asbestos on each filter with PCM using the NIOSH P&CAM 239 procedures. (The newer NIOSH 7400 procedures can also be used. See Appendix M.) ● Include at least one field blank and one laboratory blank per abatement project, for quality control purposes. Also, split one work site sample for duplicate analysis. Release Criterion: ● Release the contractor if every sample value IS below the limit of reliable quantification (approximately 0.01 f/cc when 3000 liters of air are sampled; see Appendix M). ● If any of the sample values is above the prescribed level, clean the entire work site again, collect new samples, and evaluate the samples as described above. For each method, the recommended number of samples and the prescribed use of the data defining the release criteria are based on a compromise involving practical considerations of cost, time required for the tests, performance characteristics of the methods, and statistical criteria. Details of the sampling and analysis specifications are provided in Appendix M. 6.4.3 Quality Assurance Notwithstanding the advantages of one microscopic method over another, no method will produce reliable results unless both the field sampling and Iaborabory analysis are properly conducted. To obtain reliable results, a quality assurance (QA) program for the collection and analysis of data is essential. The objective is to produce measurements with sufficient and documented quality for their intended purpose. In this case, the purpose is to determine satisfactory completion of an abatement project. The components of a QA program range from clerical activities such as labeling samples and documenting results, to performing technically complex tasks in the laboratory. When establishing the quality of data, however, all activities are equally important. Preparing and implementing a QA program requires the assistance of a technical advisor on asbestos measurement. EPA and OSHA have published guidelines on quality assurance for TEM and PCM (Yamate 1984, and NIOSH 1979). The QA Program Checklist below can be used by the asbestos program manager in reviewing a proposed QA program. QA Program Checklist ● Training and Experience: Be sure that all persons producing the measurement understand their roles and are trained. Select a laboratory with demonstrated proficiency in asbestos analysis. Request details of the laboratory’s quality control program, and get documentation of the lowest level of fibers routinely reported. 6-8 ● Quality Control Checks: Use field and laboratory blanks to check for fiber contamination, coded sample labels to avoid analyst bias, duplicate analyses to confirm precision. and a second laboratory to spot-check the accuracy of results. ● Chain-of-Custody: Assign responsibility for security of the samples to specific persons at each stage of the analysis. Document each step in the passage of the sample from the field to the laboratory. ● Documentation: Check and document laboratory results as well as their labeling. The building owner should retain all test results and records documenting the testing process. 6-9