Permeation

Diffusion of a gas, liquid or aerosol through a material on a molecular level.

Permeation is often measured using a gaschromatograph (photo below).

Gaschromatograph 

The material which is to be tested is placed in a test cell (photo below) and the challenging media (gas, liquid or aerosol) is fed into the cell on the outside of the material.

Permeation test cell

As soon as a molecule of the challenging media has diffused through the material, it will be picked up by a carrier gas (normally nitrogen) and fed into the gaschromatograph, which detects and "counts" the molecules.

The Breakthrough time is when a stipulated amount of molecules has diffused through the material in a certain amount of time. Different test methods use different breakthrough criterions:

 

Test method Used in Product standard Breakthrough criterion
EN 374-3 EN 943, EN 14605 1.0 µg/min/cm2
ASTM F739 NFPA 1991 0.1 µg/min/cm2

 

For practical reasons the normal test duration is 8 hours, which equals a working day at the laboratory, and if there has been no breakthrough at this time, the permeation time is defined as "No breakthrough".

  • Last updated 4/18/2012
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