Showing papers by "Lidia Morawska published in 1997"

Investigation of the Filtration Efficiency of HEPA and ULPA Filters in Submicron Particle Size Range

Abstract: High efficiency particulate (HEPA) and ultra low penetration air filters (ULPA) have been used as filtration devices for more than fifty years. Their high efficiency makes them suitable for application in areas where clean room conditions or contamination control is required. This paper presents the results of a performance evaluation of HEPA and ULPA filters used at the Australian Animal Health Laboratory, Geelong, Victoria. A detailed description of the experimental system, test procedure, and measuring techniques is provided. HEPA and ULPA filter efficiencies were measured for both types of filters in single and tandem configurations, and for different airflow conditions. Particle counting technique and sodium flame method were applied, and the sensitivity of both techniques compared. The performance of a damaged HEPA filter was also investigated. The integrated efficiency of a HEPA filter, challenged with dry polydisperse NaCl aerosols of count median diameter 60 nm, at a flow rate of 472 L s-1 was approximately 99.999957%. For an ULPA filter, tested under the same conditions, the efficiency was two orders of magnitude higher at 99.9999990%. The penetration through a HEPA and ULPA filter in tandem was one quarter that of an ULPA filter and less than one two hundredth that of a HEPA filter.

Investigation of the Source of Blank Problems in the Measurement ofLead in Sub-micrometre Airborne Particulates by Inductively Coupled PlasmaMass Spectrometry

Abstract: The development of a method for the determination of trace amounts of lead in airborne fine particulates using ICP-MS for sample analysis is described. A systematic approach to the reduction of blank readings and to the identification of sources of contamination was applied, using the techniques of factorial experimental design and multi-way analysis of variance (ANOVA). The former provides an economical method for indicating significant sources of contamination to the blank readings. The latter is a statistical method for the study of the effects of these sources and their interactions. It was found that a significant contribution of the high blank readings is attributable to the ‘memory effect’ exhibited by the laboratory PTFE-ware. As a result of this study, the detection limit of the method, in terms of the mass of lead on the filter, was reduced from 20 to 1 ng.

Determination of the Activity Size Distribution of Radon Progeny

Abstract: There has been significant progress in techniques for the determination of the activity size distribution of radon progeny. Despite this progress, many inconsistencies still exist with respect to the activity distribution, especially in the smaller particle size range. The aim of this work is to evaluate a measurement technique for determination of the activity size distribution of radon progeny, and to investigate the effect of different screen configurations and different deconvolution procedures. The measurements were performed in a large experimental chamber, using three different sets of Wire Screen Diffusion Batteries (WSDB) constructed for these studies. Aerosol concentration and size distribution in the chamber were monitored by a scanning mobility particle sizer. The Twomey and Reconstruct deconvolution methods were used to derive the activity particle size distribution from the diffusion battery data. Investigations of activity size distribution using three WSDB sets of different sensit...