ASTM F739 - CHEMICAL PERMEATION

"Standard Test Method for Resistance of Protective Clothing Materials to Permeation by Liquids or Gases Under Conditions of Continuous Contact:"

Explanation of Test Method:

Material is clamped between two chambers. One is filled with chemical and the other is checked for the presence of chemical. Once chemical is detected, rate of permeation through the material is measured over time.

Permeation Defined:

The process by which a chemical moves through a material on a molecular level. The three step process includes:

Absorption: Chemical is absorbed into the outer surface of a material.

Diffusion: Chemical then diffuses through the material on a molecular level.

Desorption: Chemical emerges as a vapor on the inside surface of the material.

Permeation Rate is expressed as micrograms per square centimeter per minute (ie: μg/cm2/min).

NOTE: Permeation is typically NOT VISIBLE to the eye, even when it has occurred.

For example: a permeation rate could be written as 5ug/cm2min. (5 micrograms per square centimeter per minute)

Normalized Breakthrough Time:

The time at which permeation rate reaches .1 μg/cm2/min. Normalized breakthrough times are useful for comparing the barrier performance of fabrics.

System Detection Limit

The sensitivity of the instrument being used to measure permeation. For example: some measuring instruments may be better than others. One instrument being used may be able to detect very small amounts of chemical breakthrough--- .001 ppm, and another instrument may only be able to detect breakthrough of .4 or 3.1 ppm.

This measurement is usually written in parts per million (ppm). The SDL must be determined for each individual test performed. This information is required in order to compare test data accurately.

If ink marks are made on a butyl rubber, PVC, Viton, and film composite materials and a short time has elapsed (approximately 5 minutes), differences in absorption can be observed.

The marks will rub off of the film composite fabrics very easily. With the elastomeric and thermoplastic fabrics, the marks will smear and be difficult, or impossible to remove.

This example illustrates permeation and the absorptive characteristics of elastomeric and thermoplastic materials.

(NOTE: A common complaint from film composite users is that it is difficult to write personal identification marks on these suits, due to their non-absorbent characteristics!)

Permeation Process of Chemical Contact, Molecular Diffusion, Desorption:

Permeation can be explained by considering a common garden hose and on/off valve. Assume that the on/off valve represents the exposure scenario, the water is the challenge chemical, and the hose is the protective fabric. When the water is turned on, the hose begins to fill, representing initial contact of a fabric with a chemical and the beginnings of chemical diffusion through the fabric. As the hose fills, an initial shot of water will be expelled from the end of the hose (i.e. chemical breakthrough). After some time, the flow of water will become constant (i.e. steady state permeation rate). Contamination can be explained as the water inside the hose at any time.

When the valve is shut off, the flow of water will continue, as does permeation, for a period of time after the challenge chemical is removed. Even after the valve is turned off and the flow of water has stopped, a certain amount of water remains in the line and, unless encouraged by lifting one end of the hose, will remain relatively stagnate until disturbed. This water represents residual contamination.

Permeation - Compared To A Sponge

Assuming the sponge is a protective fabric, and water is the chemical. If water is poured on one side of the sponge (chemical contact), it will soak into the sponge (diffusion), and eventually start to come out the other side (breakthrough). When the water has stopped pouring onto the sponge, the sponge is still full of chemical. Even if the sponge is squeezed, it is still damp (residual chemical).

ASTM F903 - CHEMICAL PENETRATION

"Standard Test Method for Resistance of Protective Clothing Materials to Penetration by Liquids"

Explanation of the Test Method:

Material is clamped over opening of a cup. The cup is then placed on its side and filled with liquid. The liquid is forced against material by pressurizing the cell. If liquid droplets are seen on the outside of fabric, the material has failed the test. Test can be used for artificial blood, a suspension of a virus or bacteria, or a chemical.

Penetration Defined:

The physical transport of a chemical from one side of the material to the other side of the material, such as through imperfections, holes, tears, etc. Pass/Fail test determines if a material is porous to a potentially hazardous liquid at a given pressure.

- This measurement is often applied to seams, closures, and interfaces.

- Penetration tests use visible methods of detection to determine failure.

- Used for evaluating splash clothing.

- A liquid's ability to penetrate is related to the liquid's surface tension.

ASTM F1001 - CHEMICAL TEST BATTERY

The ASTM F1001 Chemical Test Battery is a recommended standard list of liquid and gaseous chemicals used for evaluating protective clothing during permeation testing. It provides users a
way of comparing the different chemical holdouts that fabrics offer. The test battery was chosen to provide a broad spectrum of chemical families and some of the most common industrial chemicals used today. The list consists of: Acetone, Acetonitrile, Carbon Disulfide, Dichloromethane, Diethylamine, Dimethylformamide, Ethyl Acetate, Hexane, Methanol, Nitrobenzene, Sodium Hydroxide, Sulfuric Acid, Tetrachloroethylene, Tetrahydrofuran, Toluene. There is also a list of gaseous chemicals consisting of: Ammonia, 1,3-Butadiene, Chlorine, Ethylene Oxide, Hydrogen Chloride, Methyl Chloride. All reagents used in the test must comply with the specifications of the Committee on Analytical Reagents of the American Chemical Society.

ASTM F1670 - SYNTHETIC BLOOD PENETRATION

"Resistance of Materials Used in Protective Clothing to Penetration by Synthetic Blood"

Explanation of Test Method:

A specimen is subjected to synthetic blood at a certain pressure and for a specified time. The test apparatus used is one similar to the apparatus used in the ASTM F903. If any penetration is detected by visual observation then the material fails the test.

detection device is used to detect penetration by the virus even when liquid penetration is not visible.

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