How testing methods and real-world conditions influence protective apparel performance.

Selecting appropriate protective apparel for chemical and biohazard applications requires a clear understanding of how hazardous substances interact with materials. Two critical concepts—penetration and permeation—are often discussed together but represent fundamentally different mechanisms of exposure. These mechanisms highlight critical aspects of chemical protection in addition to other real-world factors.

Penetration refers to the movement of liquids, solids, or microorganisms through imperfections in a material system. These pathways may include pores, seams, pinholes, zipper interfaces, or other garment construction features. Penetration is typically visible or detectable as a bulk flow through gaps or defects.

Permeation, by contrast, is a molecular process. It occurs when a chemical is absorbed into a material, diffuses through it, and then desorbs on the opposite side. This process may happen even when the material appears intact and without visible defects or openings/ gaps.

• Non-hazardous liquid exposure
• Slurries – mixture of solid and non-hazardous liquid
• Particulate or solid contaminants
• Biological agents

It is important to note that even if the base fabric doesn’t have defects or inconsistencies failure modes may occur at seams and stitched areas, zippers and closures, and garment interfaces. Exposure conditions also play a role. Penetration risk increases with higher pressure, prolonged contact, and liquid pooling. Directionality like spraying versus immersion can significantly impact outcomes.

For biohazard protection, industry testing standards such as ASTM F1670 (synthetic blood penetration) and ASTM F1671 (viral penetration) are commonly used to assess barrier performance against bloodborne pathogens.

Penetration testing is therefore best suited for applications where exposure to non-hazardous liquids is intermittent or localized and where physical ingress is the primary concern, but permeation testing allows for an accurate evaluation of specific material hazard transfer through a protective barrier over time.

This article originally appeared in the October 2026 issue of Occupational Health & Safety.

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