Marvin I. Tillery

Aerosol Sampling Efficiency of 37 mm Filter Cassettes

This research compared the sampling efficiencies of open- and closed-face 37 mm filter cassettes and an experimental cassette with a tapered inlet. The experiment involved challenging the cassettes with various aerosol sizes up to 24 micron Mass Median Aerodynamic Diameter (MMAD) in a wind tunnel operated at 100 cm/sec. Sampling efficiencies were determined by comparing cassette mass concentration measurements to paired isokinetic samples. It was found that sampling efficiencies dropped with increasing particle size and that the cassette with the tapered entry offered no improvement to sampling efficiency. Sampling efficiency appeared to be improved by placing cassettes on a manikin to simulate personal sampling.

Wind tunnel measurements of the resuspension of ideal particles

Abstract Resuspension of spherical particles was studied in a small diameter wind tunnel having a smooth resuspension surface. Resuspension was measured at wind velocities from 5 to 22 m s−1 with fully developed turbulent flow in the experimental section of the tunnel. A long inlet (L/D of 36) provided a thick boundary layer in simulation of the atmospheric boundary layer. Resuspension rates and vertical flux were determined for monolayers of

A Concentric Aerosol Spectrometer

A concentric aerosol spectrometer utilizing centrifugal sedimentation to separate the particles is described. The spectrometer utilizes a new type of inlet system that permits introduction of the sample into the deposition channel through a short inlet from an excess of dusty air. Calibration curves for several rotational speeds and deposition channel flow rates are given. The inlet losses and the resolution of the instrument are discussed.

The filtration efficiency of organic vapor sampling tubes against particulates

The particulate filtration efficiency of industrial organic vapor sampler tubes is of interest for air sampling in work environments containing toxic materials as both vapor and particulate, or where inert particles contain adsorbed toxic material. Particulate collection efficiencies, measured with dioctylphthalate and polystyrene latex aerosols ranged from 70-90%. However, only 20% of this total is deposited on the active sorbent (charcoal granules). Considerable variability in collection efficiency between tubes was observed. Recommendations are made for obtaining improved contaminant estimates using these tubes.

A LOCAL EXHAUST VENTILATION SYSTEM TO REDUCE AIRBORNE RIBAVIRIN CONCENTRATIONS

A local exhaust hood was designed and built to capture and contain aerosol emissions of ribavirin during drug administration. The newly designed over-the-head hood is similar to the single hood currently used to administer the drug. This new hood was surrounded by an exhaust plenum to form a compound hood configuration. The exhaust plenum was connected to a filtered local exhaust air system to remove the waste aerosol. The compound hood and local exhaust ventilation system were evaluated for leak rate and inside hood aerosol concentration as a function of exhaust flow rates. This hood reduced the leak rate from an average of 98% with the traditional head hood to an average of less than 1% with the compound hood with exhaust port. The compound hood did not perform quite as well when not in use (set aside during infant caretaking) with the nebulizer remaining on. The leak rate was found to increase from an average of less than 1% to an average of 12% when trials were conducted that used a doll as a simulated patient versus trials without a doll, respectively. As regards therapeutic dose inside the hood, the systems performance may lead to an 18% to 25% decrease in inside hood concentration of aerosol entering the hood. Optimum hood operating parameters were identified. An exhaust flow rate in the range from 1.0 Lpm below to 1.0 Lpm above inlet flow rate from the small particle aerosol generator (SPAG nebulizer) reduced the leak rate to an average of less than 1%.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of EPA Method 5 Probe Deposition and Filter Media Efficiency

In the process of development of an improved extractive stack sampler, EPA Method 5 was evaluated to quantitate probe deposition and efficiency of several glass fiber filters accepted by the method. Monodisperse fluorescing dye aerosols from 0.6 to 4.4 ..mu..m geometric diameter were generated from a vibrating orifice aerosol generator. Collection efficiencies against these aerosols were measured for MSA 1106 BH, Reeve-Angel 934AH, and Whatman GF/A and GF/C glass fiber filters at operating velocities of 5.2 and 10.3 cm/s. Efficiencies of these four filters were comparable, ranging from 99.6 to 99.8 percent against the 0.6 ..mu..m aerosol, to above 99.9 percent for aerosols larger than 1.0 ..mu..m. Probe deposition of a large (13.4 ..mu..m mass median diameter) glass bead aerosol was 94 percent, with approximately half occurring in the nozzle. Probe deposition of a 2.0 ..mu..m fly ash aerosol was 10.5 percent, again with approximately half deposited in the nozzle. Only 1.5 percent of a 1.2 ..mu..m dye aerosol deposited in the probe. These measurements emphasize the importance of consistent probe washing procedures, lower gas velocity in the nozzle, fewer bends and diameter changes, and smoother transition between probe components in the design of an improved sampler.

Industrial Hygiene Study of a True In Situ Oil Shale Retorting Facility

An industrial hygiene study was conducted at a true in situ oil shale retorting facility located near Vernal, Utah. The study was conducted during operation of the first two in situ oil shale retorts of commercial size at the facility. Air samples were collected for analysis of dust and a number of selected gases and vapors, and limited monitoring was conducted for noise. Limited dust monitoring also was conducted during the drilling of blastholes for a third retort. Very low concentrations of dusts, and gases and vapors were observed in most areas above the operating oil shale retorts. Higher concentrations of some gases and vapors were observed in small cracks or leaks in the ground surface above the retorts, near a leaking fan that carried retort off gases, and in a confined area adjacent to tanks used for separation and storage of retort oil and water. Observed breathing-zone air concentrations would not exceed established occupational health standards, even if employees were to be exposed for 8 hr. L...

Effect of Humidity on the Aerodynamic Size Characteristics of Nonhygroscopic Aerosols

Size selective samplers used in estimating potential inhalation hazard to the worker collect particles according to their aerodynamic size. Calibration of these samplers are generally performed under low humidity conditions even though they may be required to operate in a high humidity atmosphere. A series of experiments using iron oxide and Polystyrene Latex (PSL) aerosols were performed to determine differences in aerodynamic size measured in dry and humid atmospheres. The LASL Spiral Centrifuge Aerosol Spectrometer and a horizontal elutriator were used to measure the differences in aerodynamic size (Dae). Under constant temperature conditions there is no change in Dae for particles as small as 0.312 μm for relative humidities as high as 97%. However, the combination of slight temperature decreases and a humid environment leads to significant changes nil Dae.

Measurement of Oxygen Transport Rate across Perfluorocarbon Liquids

Perfluorocarbon liquids present an absolute barrier to airborne particles while allowing the passage of oxygen. These characteristics suggest the use of perfluorocarbon liquids as liquid barrier filters for respiratory protection devices. This application would require sufficient transfer of oxygen at acceptable downstream concentrations. Oxygen transfer rates across barriers of several perfluorocarbon liquids have been determined by measurement over a range of concentration gradients at realistic operating temperatures. These transfer rates were used with a mathematical model of transfer to determine the transfer rate at acceptable downstream concentrations. The transfer rate at a downstream oxygen concentration of 17% was then used to determine the necessary surface areas for respirator application. The results indicated the required surface areas are much larger than surface areas of fibrous filters used in respirators.

Cyclone vibration effects

A Governmental Accounting Office review of coal mine dust sampling procedures recommended studies be performed to determine accuracy and precision of dust measurements taken with current equipment. The effects of vibration on the 10-mm Dorr-Oliver nylon cyclone run at a flow rate of 2 L/min were investigated. A total of 271 samples were taken during 95 tests. All tests lasted about 7 h each and were performed inside a 19-L capacity aerosol chamber. Coal dust concentrations of about 2 mg/m3 in air and a respirable fraction of 25–30% were used. The effects of a variety of vibration frequencies and stroke lengths were tested in two modes (horizontal and vertical). At most frequencies and stroke lengths, vibration was found to have an insignificant effect on cyclone performance. Significant increases in cyclone collection efficiency were found for the horizontal mode, and significant decreases were found for the vertical mode, at specific frequencies and stroke lengths. These variations could be due to direct...