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:

Physical and chemical properties of the fabric: Includes factors such as thickness pore size, and repellency
Shape, size, and other characteristics of the microorganisms: Includes factors such as morphology, motility, and adaptation to environmental extremes
Characteristics of the carriers: Includes factors such as surface tension, volume, and viscosity
External 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.

Terminology

One challenge that employers such as hospitals and pre-hospital emergency care organizations face is selecting the most appropriate protective clothing for healthcare workers based on the recommendations, practices, and regulations. This challenge is complex because there are several terms (e.g., fluid-resistant, fluid-proof, impermeable, and impervious) used in the industry to define barrier resistance properties of garments. The term “fluid-resistant” usually refers to fabrics that resist liquid penetration, but may allow penetration with pressure. According to Taber’s Cyclopedic Medical Dictionary, “impermeable” means not allowing passage, as of fluids; impenetrable [Thomas 1997]. Calling a fabric “impermeable” or “impervious” usually means that the fabric prevents liquids or microorganisms from penetrating. Impermeable could be in reference to water, to blood, to viruses, or to all. The terms “impervious” and “impermeable” are often used interchangeably. Unfortunately, there is no industry consensus for using these terms. Therefore, manufacturers usually provide fabric or garment specifications associated with the standard test methods or standard classifications. In addition, due to the misleading use of these terms, the FDA does not approve marketing surgical gowns or drapes with “impervious,” “impermeable,” “fluid repellant,” or “fluid-resistant” labeling claims.

Evidence-based guidance is needed in order to define these terms to improve communication among employers/purchasers and gown and coverall manufacturers/suppliers. In this document, we use the term “fluid-resistant” to apply to protective clothing tested against water as the liquid challenge and reserve the use of the term “impermeable” to materials that have demonstrated blockage of microorganisms using a recognized standard test method .

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