We have recently described a new, systematic method for assessing the barrier performance characteristics of various protective clothing fabrics to aerosols of chrysotile asbestos fibers. This morphometric technique is rather labor intensive, requiring significant efforts for filter preparation, subsequent scanning electron microscopy identification of fibers and computerized morphometric analysis for assessing penetration of fibers through fabrics. In the current study, we are developing an online instantaneous method for assessing barrier protection by measuring particle penetration among various fabric samples. Assessments of particle penetration for each fabric type were made using particle counters to quantify the particle concentrations in the airstream both before and after exposure to the commercial fabric samples. Crystalline silica particles (Min-U-Sil 5, particle size < 1 μm) were generated with a microdust feeder and dispersion nozzle. Assessments for each fabric-type were made by measuring the penetration of crystalline silica particles (particle counter size range = 0.5 μm – 10.0 μm) through the fabric materials by an online particle counter measuring system as described above. Five, one-minute measurements in front of the fabric and five, one-minute measurements behind the fabric were performed using this technique. In preliminary studies, our results showed that flashspun polyethylene fabrics were exposed to a mean particle concentration of 23,600 particles/minute and that an average of 95 particles/minute penetrated through the flashspun polyethylene fabrics. In contrast, a spunbonded polypropylene composite fabric was subjected to 24,500 particles/minute and 1840 particles/minute penetrated through the fabric. In subsequent experiments, following a sampling period of 3 minutes, the % particle penetration values for flashspun polyethylene fabrics were 0.0017%, 0.0010%, and 0.0008%, respectively. In contrast, the penetration values for the spunbonded polypropylene composite fabrics were 0.53%, 0.53%, and 0.49%, respectively. When the barrier penetration effects were monitored over a 6-minute period, the % penetration value for the flashspun polyethylene fabric was determined to be 0.0068%, while the penetration value for the spunbonded polypropylene composite fabric was 1.18 %. Studies are ongoing to standardize these methods for assessing online particle penetration through commercial fabric samples.