Low Particle Counts Research Articles

Generation of particulate matter during handling of needle and syringe packaging

Generation of airborne particulate matter during the handling and opening of various syringe and needle packages in a laminar-airflow workbench (LAFW) and in a biological safety cabinet (BSC) was measured to compare the effects on air cleanliness conditions (International Organization for Standardization [ISO] class 5 within the LAFW or BSC and ISO class 7 in buffer areas). Twenty-five to 50 packages of each of 12 needle or syringe products were opened. Probes were configured to count airborne particles during the separation of strip packages and the opening of packages by peeling back the top web or pushing the device through the packaging (for soft packages) or by twisting apart hard packages. The numbers of particles were not significantly different between the LAFW and BSC. The separation of strip packages generated visible particles and raised airborne particle counts. Peeling open plastic film packages and opening hard plastic packages generated fewer airborne particulates than did pushing devices through the packaging. For all methods of package opening, average counts downstream from the direct compounding area exceeded ISO class 5 conditions. Counts in the LAFW buffer area did not exceed ISO class 7. All methods of separating and opening the packaging of needles and syringes generated particles. The peel-and-present technique generated the lowest particulate volume. The LAFW and BSC were equally effective in maintaining low particle counts.

A multi-rate multiple model track-before-detect particle filter

Current particle filter track-before-detect (PF-TBD) algorithms assume constant velocity (CV) motion and the filter updates at a full-rate (i.e. at every measurement scan). Previous work in multi-rate processing, via a discrete wavelet transform (DWT), has shown that multi-rate tracking algorithms can provide comparable performance at a lower computational cost. To date, these multi-rate approaches have not yet been applied to low signal-to-noise ratio (SNR) targets. This paper presents a full-rate multiple model particle filter for track-before-detect (MMPF-TBD) and a multi-rate multiple model track-before-detect particle filter (MRMMPF-TBD) that extends the areas mentioned above and tracks low SNR targets which perform small maneuvers. The MRMMPF-TBD and MMPF-TBD both use a combined probabilistic data association (PDA) and maximum likelihood (ML) approach. The MRMMPF-TBD provides equivalent root-mean-square error (RMSE) performance at substantially lower particle counts than a full-rate MMPF-TBD. A performance analysis for various SNR and particle count scenarios is presented.

Impact of microparticles on UV disinfection of indigenous aerobic spores

Numerous studies have shown that the efficacy of ultraviolet (UV) disinfection can be hindered by the presence of particles that can shield microorganisms. The main objective of this study was to determine to what extent natural particulate matter can shield indigenous spores of aerobic spore-forming bacteria (ASFB) from UV rays. The extent of the protective shielding was assessed by comparing the inactivation rates in three water fractions (untreated, dispersed and filtered on an 8 μm membrane) using a collimated beam apparatus with a low-pressure lamp emitting at 254 nm. Levels of inactivation were then related to the distribution and abundance of particles as measured by microflow imaging. Disinfection assays were completed on two source waters of different quality and particle content. A protocol was developed to break down particles and disperse aggregates (addition of 100 mg/L of Zwittergent 3–12 and blending at 8000 rpm for 4 min). Particle size distribution (PSD) analysis confirmed a statistically significant decrease in the number of particles for diameter ranges above 5 μm following the dispersion protocol and 8 μm filtration. The fluence required to reach 1-log inactivation of ASFB spores was independent of particle concentration, while that required to reach 2-log inactivation or more was correlated with the concentration of particles larger than 8 μm ( R 2>0.61). Results suggest that natural particulate matter can protect indigenous organisms from UV radiation in waters with elevated particle content, while source water with low particle counts may not be subject to this interference.

Study of very low airborne particle count in clean-unit system platform

Cleanliness of a clean-unit system platform consisting of multiply connectable clean boxes with feedback loop is studied and the time dependence of particle count is clarified experimentally and theoretically in order to achieve highly clean environment. Based on this analysis, we have demonstrated airborne particle counts as low as 5particles∕ft3 for the diameter of 0.1μm, 0.6 particles for 0.2μm, and 0.01 particles for 0.5μm by a reduction of particle density coming out from the in-wall in the system. The clean-unit system with feedback loop can serve as a platform for cross-disciplinary experiments and production for fields such as nanotechnologies and biotechnologies.

Analysis of measurement techniques to determine dry deposition velocities of aerosol particles with diameters less than 100 nm

Modeled aerosol dry deposition velocities to natural surfaces have not been verified against experimental data because data is not available. However due to recent instrumentation developments measuring vertical number fluxes of aerosols with sizes down to 10 nm became possible. Additional instrument modifications which are discussed here allows measuring size dependent fluxes of 10– 100 nm aerosols and would fulfill the data gap. This study analyzes uncertainties in such measurements. Low particle count is identified as a major contributor to the measurement uncertainty, limiting the accurate estimation of size-resolved dry deposition velocities in remote environment to particles with diameters less than 50 nm using current instrumentation. Even in this size range high concentrations are required. In the case of two particle counters with different detection limits dry deposition velocity estimates can be also systematically biased, depending on the aerosol size distribution. A difference in detection limits of counters about 10 nm is narrow enough to avoid bias in size-dependent dry deposition velocities in most circumstances.

Using turbidity and particle counts to monitor Cryptosporidium removals by filters

Physicochemical removal of protozoan pathogens is receiving increased attention because of the difficulty of chemically inactivating these organisms, particularly Cryptosporidium parvum. Most studies that have examined the removal of these and other pathogens by filtration have been conducted under steady-state conditions with optimized pre-treatment. The research on which this paper is based evaluated the removal of Cryptosporidium and surrogates at various points in the filter cycle and under non-optimal conditions, at several pilot plants. The focus of this paper is on the relationship between removals of Cryptosporidium, and turbidity and particle counts. Under stable or optimal operating conditions all pilot plants produced similar low filter effluent turbidity and particle counts. Average Cryptosporidium removal varied among locations, however, by more than two log units. Cryptosporidium removal was impaired under all of the non-optimal conditions. Particle and turbidity performance was also worse, but the relationship of these parameters to Cryptosporidium removal varied. Particle counts show greater promise than turbidity as a tool to monitor filter performance in real time for possible deterioration in Cryptosporidium removal capability.

Effects of Filter Operation on Cryptosporidium Removal Microbial Pathogens

Physicochemical removal of protozoan pathogens is receiving increased attention because of the difficulty of chemically inactivating these organisms, particularly Cryptosporidium parvum. Most research examining the removal of these and other pathogens by filtration has been conducted under steady-state conditions with optimized pretreatment. This study evaluated the removal of Cryptosporidium and changes in surrogate parameters at various points in the filter cycle and under nonoptimal conditions at two pilot plants with different coagulation regimes. The study found a reproducible 2-log difference in Cryptosporidium removals between the two locations under optimal conditions, with similar low effluent turbidity levels and particle counts. Either suboptimal coagulation or the early stages of breakthrough at the end of a filter run produced substantial deterioration of Cryptosporidium removal capability. Filter ripening or the imposition of a hydraulic step generally had much less effect on removals.

Removal and fate of Cryptosporidium in dissolved air drinking water treatment plants

In the first part of the paper, data from pilot plant studies are used to evaluate Cryptosporidium removal by dissolved air flotation (DAF) clarification and dual media filters under challenge conditions. Oocyst removals were investigated for design detention times and hydraulic loadings for winter and spring seasons. Coagulation was optimized for turbidity and removal of natural organic matter. DAF performance was better for spring water temperatures achieving 2.5 +/- 0.3 log removal of oocysts compared to 1.7 +/- 0.3 log removal in the winter. Cumulative log removal across DAF and filtration exceeded 5.4, and was not affected by water temperature. Low turbidities and particle counts are indicators of good treatment and good removals of Cryptosporidium. The second part of the paper uses a mathematical model to predict the fate of Cryptosporidium through a DAF plant and the impact of filter backwash recycle on oocyst build-up in the plant influent. Model predictions show that the fate of Cryptosporidium and the build-up of oocysts in the plant influent depend on: DAF performance, the percent of filtered water production used for backwashing, and the percent of filter backwash recycle flow. A DAF plant with 2.5% filtered water production for backwashing and that achieves 1.6 log removal or greater of oocysts by DAF clarification will not have a build-up of oocysts in the plant influent regardless of the recycle rate. This is because the oocysts are concentrated in the DAF floated sludge and not within granular filters.

Enhanced Coagulation: US Requirements and a Broader View

Enhanced Coagulation is a new regulatory requirement in the United States aimed at removing TOC by coagulation thereby controlling formation of disinfection byproducts. Coagulation principles are summarized for alum coagulation of natural organic matter (NOM). Negatively charged NOM creates a coagulant demand for positively charged Al species resulting in a stoichiometric relationship between the alum dosage and the raw water DOC that is pH dependent. The paper addresses coagulation with a broader view than Enhanced Coagulation, termed multiple objective coagulation. In general the objectives include: 1) to maximize particle and turbidity removals by downstream solid-liquid separation, 2) to maximize TOC and DBP precursor removals, 3) to minimize residual coagulant, 4) to minimize sludge production, and 5) to minimize operating costs. Optimum coagulation conditions are those that maximize pathogen removals, produce low turbidities and particle counts, and minimize residual Al. It is shown, for treatment of waters of low alkalinity, that the optimum alum dosage selected to minimize UV absorbance with strict pH control produced excellent treatment for turbidity, pathogens, and NOM. Full scale plant data are used to demonstrate a dual coagulation strategy of alum and cationic polymer that reduces sludge production and overall operating costs compared to alum alone.

Enhanced coagulation: Us requirements and a broader view

Enhanced Coagulation is a new regulatory requirement in the United States aimed at removing TOC by coagulation thereby controlling formation of disinfection byproducts. Coagulation principles are summarized for alum coagulation of natural organic matter (NOM). Negatively charged NOM creates a coagulant demand for positively charged Al species resulting in a stoichiometric relationship between the alum dosage and the raw water DOC that is pH dependent. The paper addresses coagulation with a broader view than Enhanced Coagulation, termed multiple objective coagulation. In general the objectives include: 1) to maximize particle and turbidity removals by downstream solid-liquid separation, 2) to maximize TOC and DBP precursor removals, 3) to minimize residual coagulant, 4) to minimize sludge production, and 5) to minimize operating costs. Optimum coagulation conditions are those that maximize pathogen removals, produce low turbidities and particle counts, and minimize residual Al. It is shown, for treatment of waters of low alkalinity, that the optimum alum dosage selected to minimize UV absorbance with strict pH control produced excellent treatment for turbidity, pathogens, and NOM. Full scale plant data are used to demonstrate a dual coagulation strategy of alum and cationic polymer that reduces sludge production and overall operating costs compared to alum alone.

Accretion rate of cosmic spherules measured at the South Pole.

Micrometeorites are terrestrially collected, extraterrestrial particles smaller than about 1 mm, which account for most of the mass being accreted to the Earth. Compared with meteorites, micrometeorites more completely represent the Earth-crossing meteoroid complex and should include fragments of asteroids, comets, Mars and our Moon, as well as pre-solar and interstellar grains. Previous measurements of the flux of micrometeoroids that survive to the Earth's surface have large uncertainties owing to the destruction of particles by weathering, inefficiencies in magnetic collection or separation techniques, low particle counts, poor age constraint or highly variable concentrating processes. Here we describe an attempt to circumvent these problems through the collection of thousands of well preserved and dated micrometeorites from the bottom of the South Pole water well, which supplies drinking water for the Scott-Amundsen station. Using this collection, we have determined precise estimates of the flux and mass distribution for 50-700-microm cosmic spherules (melted micrometeorites). Allowing for the expected abundance of unmelted micrometeorites in the samples, our results indicate that about 90% of the incoming mass of submillimetre particles evaporates during atmospheric entry. Our data indicate the loss of glass-rich and small stony spherules from deep-sea deposits, and they provide constraints for models describing the survival probability of micrometeoroids.

Observations of the nitrate radical in the free troposphere at Izaña de Tenerife

This paper reports direct measurements of the nitrate radical (NO3) in the lower free troposphere. The measurements were carried out at Izaña de Tenerife (2300 m altitude) in the Canary Islands during May 1994, using the technique of differential optical absorption spectroscopy (DOAS). The average nighttime NO3 concentration in very clean air from the mid‐Atlantic was found to be 8 ppt, with a maximum observed concentration of about 20 ppt. Combining the NO3 data with ancillary measurements of NO2 and O3 in a model shows that there are no important NO3 scavengers in a part of the troposphere that is characterized by a very low relative humidity and aerosol particle count, and where the concentration of NO2 is too small for significant quantities of N2O5 to form. On occasion, the presence of a trace concentration of NO or an organic species such as α‐pinene is required to explain the observations. The lifetime of NO3 at night was in excess of 2 hours, much longer than measured hitherto in the tropospheric boundary layer.

Dynamic particulate characterization of a vacuum load-lock system

Particle contamination is an important issue for the development of vacuum interface technology. In this work the relative particle levels between a clean room and a vacuum chamber are compared; once vacuum conditions are reached no particles are detected implying that vacuum environments are intrinsically cleaner than clean rooms. Then the dynamics of particles are systematically studied in a vacuum load-lock chamber during pump down. The relationship between particle count and turbulence is developed through the Reynolds number. Higher particle counts are observed under turbulent conditions and lower particle counts are obtained by reducing the pumping and venting speed. The nature of the chamber ambient is also shown to be a critical parameter. A large reduction in particle density is obtained by preparing the chamber by backfilling with dry nitrogen as compared with (moist) clean room air, even if pumped under turbulent conditions. This and other data suggests a correlative effect between moisture and pumping rate. Particular methodologies of alternate pumping and venting cycles are used to demonstrate lower particle densities. Recommendations are discussed.

Ultrastructural localization of the 9-kilodalton vitamin D-dependent calcium-binding protein in the murine intraplacental yolk sac.

The calcium-binding protein (CaBP) calbindin has been implicated in the molecular mechanism of placental calcium transfer. Previous light microscopic studies have identified CaBP in visceral (but not parietal) endodermal cells of the yolk sac with the most intense immunocytochemical signal observed in the intraplacental yolk sac. In the present studies, electron microscopy was used to study the localization of CaBP in placenta. Placentas of 17-day pregnant mice were fixed by perfusion in 0.5% glutaraldehyde, embedded in low-temperature Lowicryl K4M, and examined in thin section for specific labeling with a polyclonal antiserum. Antibody to CaBP was localized by using protein A-gold particles which were quantified for subcellular compartmentation by using a Videoplan computer system. A high signal for CaBP was found in the visceral endodermal cells of the intraplacental yolk sac. In these cells, gold particles indicating the location of CaBP were observed over 1) the cytoplasmic matrix where the average number of gold particles per micron 2 was 33; 2) the microvilli (17/micron 2); 3) the mitochondria (17/micron 2); and 4) the nucleus (43/micron 2). Sections from antigen-absorbed controls, by contrast, showed few gold particles: cytosol, 2/micron 2; microvilli, 5/micron 2; mitochondria, 5/micron 2; and nucleus, 4/micron 2. Electron-lucent profiles of the Golgi and endoplasmic reticulum contained no particles in the controls and a low particle count (4/micron 2) in the stained sections. Parietal endodermal cells of the intraplacental yolk sac showed a relatively low signal for CaBP compared with the visceral endodermal cells (5 particles/micron 2 vs. 39).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of Floe Size Distribution on Clarification

The purpose of this study was to examine the relationship between optimum coagulant dose and optimum clarification rate in order to design a smaller, more efficient clarifier. The optimum coagulant dose produced a flocculant suspension containing a low total particle count, a floc with a large mean size, and a supernatant with a low count of small particles. The use of an electronic particle counter resulted in size distribution data that were an order of magnitude smaller than the actual size. This was attributed to floc breakup produced by the high fluid shear in the measuring aperture.

Process and film characterization of low pressure tetraethylorthosilicate–borophosphosilicate glass

The pyrolytic decomposition of tetraethylorthosilicate (TEOS) has been used to deposit highly doped borophosphosilicate glass (BPSG) films. The experiments were carried out in a modified low pressure chemical vapor deposition furnace in the 620–680 °C range at a deposition pressure of 0.5 Torr. Trimethylborate and phosphine together with oxygen were found to be the best dopant source combination. The deposited layers adhere strongly to the quartzware and low particle counts of typically less than 0.2 per cm2 were measured. The thickness uniformity was below ±6%, the dopant uniformity was ±0.1 wt. % over a wafer. If compared to low pressure SiH4–BPSG films, the TEOS–BPSG shows superior step coverage and much higher chemical stability up to dopant levels of about 5 wt. % B, 5 wt. % P. The etch rate behavior in buffered HF corresponds to the trends reported for SiH4–BPSG. The electrical characterization of thin TEOS–BPSG and TEOS–SiO2 layers yielded an electrical breakdown strength in the 7–8 MV/cm range. The glass flow properties (wet and dry ambient) were investigated and found to be very good in the 800–850 °C region. By using a rapid optical anneal system, the required step tapering could be achieved at time/temperature combinations of 40 s/900 °C or 10 s/1000 °C. Detailed infrared studies showed strong interaction among the different oxide absorption bands of the TEOS–BPSG layers.

Evaluation of dust exposure in asbestos cement manufacturing operations.

Previous investigations of the health of workers of the asbestos cement industry have demonstrated dose-response relationships for the diffuse radiographic changes of asbestosis and pulmonary function impairment. Studies of the mortality experience of past employees have also identified levels of cumulative exposure above which an excess of respiratory cancer could be detected. These epidemiologic studies were based on particulate concentrations determined by the midget impinger. We attempted to develop information that might lead to conversion of particulate to fiber concentrations in the industry in order that the risk assessment could be related to the current membrane filter methods. Pairs of impinger and membrane filter samples were taken in the various areas of the plant. Personal samples were also taken to determine the current exposure of workers. The ratio of fiber concentration to particle count varied from 0.63 to 2.5. Por correlation (0.18) was obtained at low fiber and particle counts and good correlation (0.91) was demonstrated in dustry areas where asbestos and silica were handled in a dry form. The concentration of fibers in 80% of the personal samples was less than 2 fibers/cc, and 60% were less than 0.5 fibers/cc. The results also show that no one conversion factor can be used for all areas of this type of operation.

The role of particulate matter in the productivity of surface waters

Except for the special cases of upwelled water and the spring blooms in temperate and boreal waters, the productivity of the oceans is largely governed by the rate of nutrient regeneration in surface waters. This rate of regeneration is a function of the number of actively metabolizing bacteria present, which in turn appears to be a function of the particle content of the water. Thus, particle content may be the basic control on the productivity of the open oceans. The possibility of increasing productivity by artificially increasing the particle content of the water should be considered for regions characterized by low particle count, such as the Sargasso Sea. Since silicate can only be resupplied by re-solution of diatom tests, a process taking place at depth, plankton blooms following regeneration kinetics will typically be dinoflagellate rather than diatom blooms.