Permeation

Grafical display of adsorption

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Figures 1 to 4: Individual steps of permeation; 1: Adsorption, Sources: IFA

Grafical display of absorption

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2: Absorption

Grafical display of diffusion

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3: Diffusion

Grafiscal display of desorption

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4: Desorption

IR-image including temperature scale

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IR-thermographic image of a nitrile disposable glove after two minutes' wear
Source: IFA

A chemical protective glove is able to provide protection against a hazardous substance only until the substance has permeated through the glove membrane. Permeation is penetration at molecular level. It involves the following stages:

  1. Adsorption
    A concentration of the chemical builds up on the surface. This can occur from the gas phase or through direct contact with the chemical in liquid or solid form.
  2. Absorption
    The substance is taken up into the glove material.
  3. Diffusion
    Permeation (penetration at molecular level) of the material begins. The underlying mechanism is the concentration gradient from the outside of the glove to the inside.
  4. Desorption
    Once the molecules have reached the inside of the glove, they diffuse again away from the surface.

Conducting of a permeation measurement

Measurement of a substance's permeation through a glove material provides information on its resistance to the chemical concerned. For the purpose of this measurement, a piece is cut from the palm of the glove in accordance with DIN EN 374 and clamped within a test cell. The test substance is then applied to one side of the material (see illustration). On the other side of the material, a suitable detector within an encapsulated area measures the concentration of the substance over time (see video (ASF, 2.0 MB), click to run).

As soon as a flow of 1 µg ∙ cm-2 ∙ min-1 is detected, the chemical is deemed according to the standard to have broken through the material. The maximum wear duration of a glove is determined in the laboratory by measurement of the duration from the beginning of measurement to breakthrough.

In practice however, further factors may significantly reduce the wear duration. The temperature for example has a substantial influence upon permeation. In accordance with the standard, permeation is measured at a temperature of 23 ± 1 °C. Studies conducted at the IFA with a thermal imaging camera have shown however that the temperature at the surface of the glove stabilizes at 33 °C after a brief wear duration. This rise in temperature of 10 °C leads to the wear durations being reduced in practice to as little as a quarter of those determined by laboratory measurements. The thickness of the glove material is also a factor. A rule of thumb is that doubling of the material thickness leads to quadrupling of the permeation time.

To facilitate the performance of permeation measurements, the IFA has developed the "Permobil device (PDF, 105 kB)". This is suitable in particular for swift and easy measurement of breakthrough times, and can also be used by manufacturers to perform permeation measurements for quality control purposes.

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Literature

Polanz, O.; Paszkiewicz, P.: Praxisnahe Auswahl von Chemikalien-Schutzhandschuhen – ein neuer Ansatz (PDF, 456 kB). Gefahrstoffe – Reinhalt. Luft 63 (2003) No. 10, pp. 410-412 (in German)

Glossary

Glossary of terms (PDF, 22 kB) used on this page