Barrier Properties of Protective Clothing

Once the hazard and the risks of exposure are identified, gown and coverall selection can be guided by current scientific understanding of how protective clothing materials provide protection against microorganisms in blood and body fluids. A microorganism's movement through protective clothing materials depends upon several factors, including the following:

ㆍPhysical and chemical properties of the fabric: Includes factors such as thickness pore size, and repellency

ㆍShape, size, and other characteristics of the microorganisms: Includes factors such as morphology, motility, and adaptation to environmental extremes

ㆍCharacteristics of the carriers: Includes factors such as surface tension, volume, and viscosity

ㆍExternal factors: Includes factors such as physical, chemical, and thermal stresses

Several different microorganisms have been found in healthcare settings, including bacteria, viruses, and some fungi. The shape and size of microorganisms varies, and this will affect their ability to move through a fabric structure. In general, fungi are larger than bacteria, and bacteria are larger than viruses. For instance, HIV virus is spherical and 100–120 nanometers (nm) in diameter. The Ebola virus is a single-stranded RNA virus with a filamentous shape, a median particle length ranging from 974 nm to 1,086 nm, and average 80 nm in diameter.

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Microorganisms are transported by carriers such as body fluids, sloughed skin cells, lint, dust, and respiratory droplets. A significant number of microorganisms can be carried in a very minute volume of blood or body fluids, which may not be visible to the naked eye. For example, the number of infectious units of Hepatitis B in a 0.1-microliter (µL) droplet is 10,000, which is why it is highly infectious and easily transferrable. Ebola virus RNA levels in blood also increase rapidly during the acute phase of the illness. One study reported an average peak titer of 3.4 x 105 RNA copies per 0.1 µL (i.e., 34 times higher than the concentration of Hepatitis B) for cases associated with a fatal outcome. Several studies have also reported that when liquid containing microorganisms penetrate a material, microorganisms are carried with it, and penetration is possible without liquid being visible. Because of this, standardized test methods must be sensitive enough to detect microorganism penetration, since this is the only way to determine if microorganism penetration has occurred in any part of the garment, including the seams.

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