Real-time measurement of fibers using an HY-differential mobility analyzer with an optical particle counter (KOFAM)
This study investigated the applicability of an HY-differential mobility analyzer with an optical particle counter (HY-DMA/OPC), named as KOFAM, for counting fibrous matters in real time. Fibers separated from particles by the HY-DMA were counted with an OPC. To assess the KOFAM performance, the proposed method and the conventional gold standard phase contrast microscopy (PCM) method were compared in terms of variables such as recovery, relative difference, coefficient of determination, and conformity. The optimal sheath-to-aerosol (outlet) flow ratio of the internal flow in the HY-DMA was determined to be 1.6:1. In terms of recovery of the HY-DMA, the highest recovery was obtained at a voltage of 500 V regardless of which type of asbestos was tested. The recovery rate for serpentine was 45.5% and that for amphibole was 34.9%. The coefficients of determination of serpentine (R2 = 0.89) and amphibole (R2 = 0.87) were highly correlated. With respect to the coefficient of variation (CV), the KOFAM demonstrated superior performance over the M7400AD and F-1 methods and showed almost no difference from the PCM method (KOFAM: 22.5%, M7400AD: 32.4%, F-1: 88.8%, and PCM: 21.9%). There was no statistically significant difference between concentration measurements of the KOFAM and PCM analyses. Accordingly, it was concluded that the KOFAM can be used as a superior alternative to conventional fiber measurement methods. The preliminary results support the use of the KOFAM for constant measurement of airborne asbestos concentrations in real time.
Evaluation of a fluidized bed asbestos segregator preparation method for the analysis of low-levels of asbestos in soil and other solid media
The fluidized bed asbestos segregator (FBAS) is a sample preparation instrument that utilizes air elutriation to separate asbestos structures from heavier matrix particles and deposit these structures onto a filter which can then be analyzed by transmission electron microscopy (TEM) or other appropriate microscopic techniques. The performance of the FBAS preparation method was evaluated using a variety of performance evaluation (PE) standards that spanned different matrix materials (soil and vermiculite) and different types of asbestos (chrysotile and amphibole). Results for these PE standards show that there is an approximately linear relationship between the concentration of asbestos in the PE standard (as mass percent) and the mean concentration estimated by the TEM analysis following preparation by FBAS, expressed as asbestos structures captured on the filter per gram of test material (s g−1). Method detection limits achieved in these studies ranged from 0.002% to 0.005% by weight, which is approximately 100-times lower than the detection limits that are usually achieved using other analytical methods for asbestos in soil and other solid media. The FBAS unit is compact, fitting into a standard laboratory fume hood, and components of the unit are relatively easy to decontaminate or are disposable. The FBAS unit construction and operation costs are relatively low and sample throughput is high (up to 20 samples per day). Current research using the FBAS unit is ongoing and an inter-laboratory validation study is in progress.
Evolution of charge distributions of non-spherical particles undergoing unipolar charging
Abstract Computational methods for evolution of unipolar charge distribution on fibers and platelets were developed based on population balance equations. The minimum flux criteria were extended to obtain the ion acquisition rate for these nonspherical aerosols. Simulation results showed that evolution of charge distribution is independent of initial charge distribution and dependent on particle morphology and size.