Protective clothing manufacturers routinely test their products for resistance to liquid and viral penetration. Several of the test methods specified by the American Society for Testing and Materials (ASTM) and the International Organization for Standardization (ISO) for penetration testing produce binary results (i.e. pass or fail), deliver imprecise pressure regulation, and do not record the location at which penetration events occur. Instead, our approach measures a continuous variable (time of penetration) during a slow and continuous increase of hydrostatic pressure and retains the location of penetration events. Using a fluorescent dye to enhance visual detection, we evaluate temporal and spatial patterns of penetration events. We then compare the time of liquid penetration with the time of penetration of two bacteriophages (Phi-X174 and MS2). For the fabric tested, the mean viral penetration occurred 0.29 minutes earlier than liquid penetration when solved by logistic regression. The breakthrough time of MS2 was not different from the Phi-X174 bacteriophage. The time of liquid penetration was a latent indicator of the time of viral penetration.

 

Test apparatus

All liquid and viral penetration tests in this study were conducted using a penetration apparatus based on the ASTM F903 standard [8]. Custom modifications include the following: two mass-flow regulators to provide pressure control within 1%, a 0.25 mm diameter orifice to maintain pressurization if adjacent cells depressurized during a test, and an upper sight glass to provide visual indication of the fluid level. An array of eight penetration cells were enclosed within a climate controlled chamber (Fig 1A). Temperature and humidity were controlled by an incubator (Model: 260plus, Memmert, Germany) enclosed within a chamber (Fig 1B) that was closed to atmosphere by vinyl strip doors (Model: H-3202, Uline, Pleasant Prairie, WI).

 

The primary mass flow control regulator (Model: MC-5SLPM-D, Alicat Scientific, Tucson, AZ) was configured to pressure regulation mode. A secondary regulator (Model: MC-50SCCM-D, Alicat Scientific, Tucson, AZ) was added to provide 4 cc/min nominal airflow through the primary regulator. Pressure was validated with a NIST traceable manometer to be within 1% from 0 to 90 kPa.

 

Fabric specimens

This paper is part of a multi-dimensional comparison of ten garment models, four test liquids, and factors of pre-wetting, apparatus screen, and elevated temperature and humidity. For clarity, this manuscript details methods and highlights only one garment model: an ANSI/AAMI Level 3, five layer, non-woven, spunbond and melt blown surgical gown (Fig 2). Top layer fibers, measuring 10–15 microns diameter appear to be heated and compressed into oval indentations (Figs ?(Figs2B,2B, 2C and 2D).

 

Twenty-six gowns were selected from the same production lot. From each gown, 24 swatches were cut from the continuous chest region with a die cutting machine (Model: Mark 3, AccuCut, Omaha, NE). Individual specimens were randomly selected among the 624 swatches (26 gowns x 24 swatches per gown). Specimens were conditioned at 23 ± 2°C and 50 ± 5% relative humidity at least 24 hours prior to testing. Two polyethylene closed-cell foam gaskets were placed between each side of the fabric to provide a liquid-proof seal (SKU 8722K87, McMaster Carr, Omaha, NE). A total of 155 specimens were evaluated for liquid or viral penetration .