Lab-2 Total and Respirable Dust Sampling –

| September 11, 2019

Lab-2 Total and Respirable Dust Sampling – Questions Unit-4 Textbook pages 4-7 through 4-13 Report Print use and scan this form or copy the questions to word processing software to type answers then add to the report in pdf format Questions 1 What is the collection medium used for total dust sampling, what else do you need to sample for respirable dust? 2 Why/how particles smaller than the size of the pore of the filter are getting collected? 3 If you calibrate a pump with a standard filter, can you use it with another filter of the same batch (package)? 4 Why are filters desiccated before and after sample collection? 5 What information do we get from pre- and post-calibration of the air sampling pumps, how this affects accuracy of the sampling? 6 What is the purpose of the field and media blanks, how these are used in calculation of the concentration? 7 Does the time length of the sampling affect the calculated concentration? 8 The filter cassette is a cylinder and if it is vertically oriented with the filter on the bottom, what would be proper direction of the air flow, why? 9 Is the average weight change added to or subtracted from the weight of the field blank? 10 Why the filter collection efficiency increases as with the increase of the amount of particles accumulate on the filter (see your answer of question 2)? Lab-3 Unit 9 Organic Gas and Vapor Sampling Textbook pages 9-8 through 9-15 Overview This Lab follows Unit 9 Exercise page 9-8 with some additions described in this document. The exercise is designed to provide basic knowledge of methods for sampling for organic vapors and gases. Learning Goals Understanding area and personal sampling and the meaning of integrated sampling. Understanding the difference of whole work shift 8 hours integrated sample versus time split integration and TWA. Understanding sampling methods using separation and filtration based on sorption. Importance of flow rate for weak force of attraction such as adsorption. Calculating the time length to run a pump with assigned flow rate to reach the target total volume and how to use pre and post calibration values of the flow rate Understanding gravimetric measurements (weight) and how to use volume of total processed air to calculate gravimetric concentration. Transforming the gravimetric concentration in to ppm using the formula in the text (page 9-8) and the example (page 9-14). Understanding the meaning of molecular weight and the effect on the concentration in ppm. Understanding the difference in methods using same sorbent material but adjusting the flow rate due to specificity of targeted chemical sampled. Practicing area and personal sampling. Coding samples to track their origin and corresponding analytical lab results. Understanding that these methods not only quantify but identify the contaminants. Understanding and applying TWA’s for worker’s exposure and finding the proper REL’s or TLV’s Purpose Tasks The main purpose of this lab is evaluation of a work place (HUM312 and lab hood room) with three different areas with different levels of possible concentrations of xylene (area sampling) Also evaluating exposure of two workers spending different times in the three areas (personal sampling) and comparing 8-hour single sample TWA versus samples for each area and time spend in the corresponding area. The lab involves evaluation of area and locations with preliminary walk through to identify possible air contaminants or any materials stored in containers or bottles. Establishing strategy based on area samples and assigning personal sampling for workers possibly exposed. Developing labeling or coding nomenclature. Investigating type of contaminates and proper sorbent material for sampling tubes. Processing the data including calibration, air volumes and finally analytical data from analytical report. Evaluation of TWA exposure based on the concentrations and time periods. Search for REL’s or TLV’s of the identified contaminant to compare the TWA’s calculated for workers. Report Abstract report prepared individually and submitted individually on Blackboard. Print and answer the questions below, then attach a scanned copy to the report. The lab should describe the locations and the sampling strategy using the observations and floor plan. The results should be clearly about worker’s exposure (TWA’s) and compared with NIOSH pocket guide OEL’s., then the comparison should be used to write recommendations. The areas sampled levels should be commented in comparison with the STEL’s (IDHL’s) Lab-4 Sorbent tubes – Questions Unit-9 Textbook pages 9-1 trough 9-15 Questions 1 What are the most common solid adsorbent media used for integrated organic vapor/gas sampling? 2 What is meant by sorption? 3 What is tube adsorption efficiency directly related to (see textbook)? 4 What is the effect on humidity on adsorption tube collection efficiency? 5 What are the two divided sections of adsorbent media in sorbent tubes called and which section retains the contaminant? 6 What is meant by “breakthrough”? 7 What is the purpose of the backup section media in the sorbent sampling tubes? 8 What factors can cause breakthrough? 9 If the sample flow rate is too high, how is collection efficiency of the sampling train affected? 10 How do you compensate for high concentrations of organic gases or vapors when preparing to perform integrated sampling with solid sorbent tubes? UNIT 4 Evaluation of Airborne Total Particulate: Integrated Personal and Area Monitoring Using an Air Sampling Pump with a Polyvinyl Chloride Filter Medium LEARNING OBJECTIVES At the completion of Unit 4,including sufficient reading and studying of this and related reference material, learners will be able to correctly: • Name, identify, and assemble the components of a common sampling train, including the specific sampling medium, used for conducting integrated sampling of airborne total nuisance dust or particulate not otherwise classified, hereafter referred to as total particulate. • Name, identify, and assemble the applicable calibration train that uses a primary standard for measuring flow rate of a multi- or high-flow air sampling pump. • Calibrate a multi- or high-flow air sampling pump,with the applicable representative sampling medium in-line, using a mechanical or electronic frictionless bubble-tube. • Summarize the principles of sample collection of airborne total particulate. • Conduct integrated sampling of airborne total particulate. • Prepare samples for analysis of collected particulate using gravimetry. • Name and identify the components of a mechanical or electrical balance. • Name, identify, and assemble the components necessary for analysis of samples for total particulates using an electrobalance. • Check the calibration of an electrobalance using standard weights. • Summarize the principles of sample analysis of filters used for collection of airborne total particulate. • Conduct analysis of a sample for total particulate using an electrobalance. • Perform applicable calculations and conversions related to pre- and post-sampling flow rate of an air sampling pump, average flow rate of an air sampling pump, pre- and post-weight of a filter medium, sampling time, sampled air volume, weight of total particulate collected, and concentra­ tion of total particulate in units of milligrams per cubic meter (mg/m3). • Record all applicable calibration, sampling, and analytical data using calibration, field sampling, and laboratory analysis data forms. OVERVIEW Occupational exposure limits, such as American Conference of Governmental Industrial Hygien­ ists threshold limit values (ACGIH-TLVs) and Occupational Safety and Health Administration permissible exposure limits (OSHA-PELs), for airborne particulates have been established for many individual elements and compounds based on their inherent toxicities. There are situations when it is important to know what the concentration of par ticulate, both hi ghly toxic and practically nontoxic, is in a given area. It is equally important to determine what an individual’s external exposure is to total particulate rather than a specific type. Situations also exist in which there are no occupational exposure limits for a specific type or mixture of particulate air contaminants. These materials may be generically classified and sampled and analyzed as total dust or particulate. In either situation, measurements of total particulate, that is, particulate mixtures of various sizes and compositions, are f requently warranted. There is an OSHA-PEL for total dust and an ACGIH-TLV for particulates not otherwise specified. Sampling and analytical methods are available for these particulates, and involve moving an airstream into and through a filter collection medium. Airborne particulates are electrostatically attracted to, intercepted by, and impacted on the filter medium, resulting in separation of the particulates from the air without regard to particle size or composition (Figure 4.1). The ACGIH also has TLVs based on size-selective sampling of three categories of particulate mass fractions’. These three categories of TLVs are for materials deemed hazardous when they deposit: • • • Anywhere in the respiratory tract (inhalable particulate mass-TLV) Anywhere within the lung airways and the gas-exchange region (thoracic particulate mass-TLV) Anywhere in the gas-exchange region (respirable particulate mass-TLV) Size-selective instrumentation and methods are needed and have been established to sample, analyze, and characterize airborne particulate relative to these categories. Some size-selective samplers are summarized in Unit 5. FILTER MEDIUM FOR TOTAL PARTICULATE The sample medium is a 37-mm diameter polyvinyl chloride (PVC) filter with a 5.0-(im pore size. The diameter (37 mm) of the filter provides cross-sectional surface area for deposition and collection of particulate. The pore size (5 (im) causes particulates with diameters greater than the pore diameter to collect on the surface of the filter. Particulates with diameters less than the pore size are also collected. These particles are collected within the pores due to an electrostatic attraction between the particles and the filter. The fine particulate is collected primarily via diffusion into the filter material whereas the relatively coarser particulate is intercepted and impacted within the medium. Collection efficiency increases as particulates accumulate on the filter. The larger pore size (5(im) filter is used relative to smaller pore sizes (0.45 to 0.8 (im) to reduce clogging and overloading of the filter since total particulate is composed of diverse particle sizes. Since sample preparation and analysis involves a weighing or gravimetric procedure, filters are stored in a dcssicator until use. Standard dessicators contain a hygroscopic medium such as silica gel crystals. The purpose of dessication is to absorb any water that is present on the filter that would result in an erroneously higher weight when the filter is weighed pre- and post-sampling. PVC plastic filters are used instead of a paper cellulose type since the plastic is relatively hydrophobic. Nonetheless, dessication helps assure that the pre-weight is due only to the filter, and post­ weight is due only to a combination of the filter and collected particulate. Filters should be dessicated for approximately 24 h prior to weighing. Dessication can be accelerated and incubation time reduced to less than 30 min if a vacuum dessicator is used. The filter medium is positioned on a cellulose support pad and secured within a 37-mm threestage plastic cassette (Figure 4.2). The bottom or outlet stage holds the porous support pad and the filter. It has an orifice (hole) in the center that serves as the outlet port for sampled air to exit the cassette. The middle stage is a ring-shaped spacer or cowl that increases the depth or height of the cassette to facilitate more even deposition of the particulates from the air as it enters the cassette. The top or inlet stage contains a hole in the center that serves as the inlet port for sampled air to enter the cassette. PRECAUTIONS Filters can be overloaded with particulate if airborne concentrations and sample volumes are too high. Particulates can visibly accumulate and form a mound or inverted cone in the center of the filter directly below the inlet orifice of the cassette. The accumulated particulate can break off and be lost during sample analysis if the cassette and sample are not handled carefully. Filters can also become contaminated with particulate if a dusty cassette is not wiped off prior to disassembling for analysis. In either case, loss of particulate from the filter or contamination of the filter can result in erroneous data and an invalid sample. These precautions are applicable for samples collected for any airborne particulate, including total dust, respirable dust, fibers, and metal dust and fume. SAMPLING The sample collection medium is prepared by pre-weighing a filter for each field sample and blank that is going to be collected and ultimately submitted for laboratory analysis. Immediately prior to pre-weighing, the dessicated filter is passed across an ionization device to eliminate any static charge that may be present on the filter, and cause contamination due to an unwanted attraction of airborne particulate. The anti-static device contains a radioisotope such as poionium-210. A filter is pre-weighed using an electrobalance to determine pre-weight. The pre-weighed filter is subse­ quently positioned on a cellulose support pad in a three-stage plastic cassette. The cassette is assembled, and plugs are inserted at the inlet and outlet ports or orifices. When used for sampling, the orifice plugs are removed and the cassette is attached to an air sampling pump using a length of ‘/4 in. internal diameter (i.d.) flexible hose (Figure 4.3). Typical sampling rates range from 1.5 to 2.0 1/min. Following sampling, the cassette is removed and plugs are reinserted in the open orifices in the field. The sample is then transported to a laboratory for analysis. A brief outlined summary of sample collection follows. (i) Calibration • The air sampling pump is calibrated pre- and post-sampling to adjust or determine flow rate using a manual or electronic calibrator with representative media (i.e., an assembled three-stage cassette containing a 37-mm, 5.0-gm pore size PVC filter and support pad) in-line (Figure 4.4). • Pre- (Qpre) and post-sampling (Q^) flow rates are determined by measuring the average time (Tavg sec) based on three trials (Z T, 2 3/3) for a bubble to traverse a specific volume (V cc) of the bubbletube. Figure 4.4 Calibration train for total particulate composed of (a) high-flow pump connected with flexible hose to (b) a 37-mm PVC filter in three-stage cassette in-line with (c) a frictionless bubble-tube. • Average flow rate (Qavg) is based on the average of pre- (Qpre) and post-sampling flow rates. • Typical flow rates for sampling total particulate are 1.5 to 2 I/min. (ii) Preparation for Sampling • • A weighed PVC filter plus unweighed support pad are inserted into a plastic cassette which is then assembled and labeled. The sampling train is assembled and consists of a multi- or high-flow pump; 74 in. i.d. flexible hose with clips; and a 37-mm three-stage plastic cassette containing a weighed 37-mm, 5.0-gm pore size filter on an unweighed cellulose support pad. (iii) Conducting Sampling • • • • A labeled plastic cassette is positioned with the inlet port facing downward and attached within the breathing zone. An air sampling pump connected to the cassette is clipped to the belt of the worker for personal sampling. The sampling train is positioned and secured in a specific location for area sampling. The pump is turned “ON” and start time is recorded. After a specified time, the pump is turned “OFF’ and stop time is recorded. The orifice plugs arc inserted into the inlet and outlet ports of the plastic cassette and the sample is transported to laboratory for analysis. ANALYSIS The sampling method for total particulate is similar to those methods used to detect and measure specific particulate air contaminants. The most significant difference is the method of analysis. Whereas specific particulate air contaminants require an analytical method that will both identify the specific analyte and measure the amount collected, analysis of total particulate only involves measurement of the amount (weight) collected via a simple gravimetric procedure. Accordingly, the identification of the specific components or composition of the collected particulate matter is not determined. Analysis of the sample involves a gravimetric method using a mechanical or electrical balance (Figure 4.5). The gravimetric procedure involves comparison of post- and pre­ weight of filter. Theoretically, the pre-weight is the weight of only the filter and the post-weight is the weight of only the filter plus the collected particulate. The difference in weights (post-sample minus pre-sample filter weight) represents the total particulate collected. Gravimetric analysis is the most simplistic of the major analytical methods. A brief outlined summary of the components and the principles follows. (i) Components • • • • Sample/weighing chamber: transparent glass enclosure with sliding door/sash where filter is placed and shielded from moving airstreams and related turbulence during weighing Weighing pan: stage on which filter is placed for weighing Mechanical or electrical balance mechanism: mechanical or electrical device that responds to weight of filter Readout: responds to mechanical or electrical signal from balance mechanism and provides weight of filter (ii) Principle of Analysis • • • Following sampling and prior to analysis, the orifice plugs are removed from the cassette that is placed in a dessicator to allow time for absorption of water that may have sorbed to the particulate and filter during sampling. Following dessication, the cassette is disassembled and the filter is removed and weighed to determine the post-weight to the nearest 0.001 mg. To minimize the attraction and contamination of the filter and sample, they are passed through an ionization device to eliminate static charge during pre- and post-sampling weighing. (iii) Determination of Concentration of Total Dust • Determine the amount of total particulate collected by subtracting filter pre-weight from filter post-weight and express amount as weight in milligrams (mg). Total Particulate (mg) = Filter Post-weight (mg) – Filter Pre-weight (mg) (4.3) • Determine the sampled volume of air by multiplying sampling time (T [min]) by average sampling flow rate (Q [1/min]) and convert liters (I) to cubic meters (m3). i Air Volume (m3) = T (min) x Qavg (1 / min) X – (4.4) • Determine the concentration of total particulate by dividing the weight (mg) by sampled volume of air (m3) and express concentration in units of milligrams of total particulate per cubic meter of air (mg/m3). Total Particulate (mg/m3) = Zgtal_Particulate_(mg) Air Volume (m ) (4 5) • Note: The adjusted concentration (C) can be calculated by subtracting the weight of particulate measured on a blank PVC filter (B) from the sample PVC filter (S); dividing by air volume sampled (V); and correcting for sampling efficiency (E), which is equal to < 1 depending if 100% or less efficiency is attained. (4.6) UNIT 4 EXERCISE OVERVIEW The exercise will provide the fundamental concepts for conducting integrated sampling for total particulate using a filter medium. In addition, a common and related analytical method using an electrobalance is int …
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