Chemical Permeation Testing

What is Chemical Permeation?

Permeation is the process by which a chemical moves through a protective clothing material on a molecular level.

Permeation involves

  • Sorption of molecules of the chemical into the contacted (outside) surface of a material
  • Diffusion of the sorbed molecules in the material
  • Desorption of the molecules from the opposite (inside) surface of the material

How is Permeation measured?

The resistance of a protective clothing material to permeation by hazardous liquid and gaseous chemicals is defined by the permeation rate of the chemical through the material and the breakthrough time. Permeation test methods include ASTM F739, EN374-3 and ISO 6529; exposure of the material to the chemical is total and constant, and emulates total immersion conditions. There are no permeation test methods at this time for chemicals which are solids; generally it is considered that solids do not permeate.


The Permeation Test Cell

The protective clothing material specimen acts as a partition between one chamber of a permeation test cell, which contains the test chemical, and another chamber, which contains the collection medium. The outer surface of the material is exposed to the test chemical. The inner surface of the material is monitored analytically to determine the amount of chemical (if any) permeating the material.

Normalised breakthrough time (according to EN374-3:2003)

The elapsed time measured from the start of the test to the time at which the test chemical reaches a permeation rate of 1.0 μg/(min.cm2).

Interpreting permeation test results

All permeation tests were conducted with pure chemicals under laboratory controlled conditions on materials only and are not intended to indicate the duration of “safe wear time” for a garment.

A normalised breakthrough time of >480 minutes indicates that the permeation rate did not reach the defined rate of 1.0μg/(min.cm2) (EN374-3:2003). Permeation however may still have occurred at lower rates; and depending on the chemical toxicity, it is possible that a chemical may be permeating the material and a level of toxicity reached within a protective clothing garment long before the reportable breakthrough of 480 minutes. Breakthrough time alone therefore is only a means of comparing different material performances and does not indicate safe protection for up to the number of minutes reported.

The “safe wear time” of a protective clothing garment depends on a number of factors such as:

  • Temperature
  • Type of exposure
  • Toxicity of chemical

The determination of suitability of a garment for an application should be based on end user risk assessment.

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