Chemical protection performance

The route of entry into the body determines the type of protection required. For example, face masks or respirators with different filters are used to protect individuals against exposure due to inhalation. Chemical protective clothing is used to protect against dermal exposure. Chemical protective clothing materials are broadly divided into woven; nonwoven; laminated to microporous or hydrophilic membranes; coated, bonded, or laminated with plastic films or rubber; and films, sheets, or moulded plastic or rubber. The performance of the chemical protective materials varies considerably based on the air permeability, chemical composition, and material characteristics. Penetration, permeation, and/or degradation of the materials are measured to determine the chemical resistance. In general, the physical form of the chemical that poses a potential risk and the type of material determine whether penetration, permeation, and/or degradation tests have to be conducted. Permeation is 'the process by which a chemical moves through a protective clothing material on a molecular level. Permeation involves (i) sorption of molecules of the chemical into the contacted (challenge side) surface of the material; (ii) diffusion of the sorbed molecules in the material, and (iii) desorption of the molecules from the opposite surface of the material'. 5

The permeation rate and breakthrough time are important for measuring permeation. Permeation tests are conducted to determine the performance of non-porous materials such as monolithic films against volatile and non-volatile liquids and gases. It is not used to measure the performance of woven or knitted fabrics. For such porous materials, penetration tests are used to measure performance. Penetration is defined as the 'process by which a solid, liquid, or gas moves through closures, seams, interstices, and pinholes or other imperfections on a non-molecular level, in a protective clothing material or item.' 5 Penetration through a material can be measured by several national and international standards. The selection of a suitable standard depends on the exposure scenario. For example, there are three national and international test methods to measure the penetration of pesticide through textiles.14 Degradation is defined as 'a deleterious change in one or more properties of a material'.15 Materials that have degraded due to chemical exposure, use or exposure to environmental conditions such as sunlight should be discarded, as these affect the fabric performance.

Given below are the ASTM, ISO and EN test standards used to evaluate performance of materials against chemical hazards. In addition to the test methods stated below, national and international standards are also used to measure the performance of whole body ensemble.

• ASTM F1186-03 Standard Classification System for Chemicals According to Functional Groups.

• ASTM F1001-99a Standard Guide for Selection of Chemicals to Evaluate Protective Clothing Materials.

• ASTM F739-99a Standard Test Method for Resistance of Protective Clothing Materials to Permeation by Liquids or Gases Under Conditions of Continuous Contact.

• ASTM F1383-99a Standard Test Method for Resistance of Protective Clothing Materials to Permeation by Liquids or Gases Under Conditions of Intermittent Contact.

• ASTM F1407-99a Standard Test Method for Resistance of Chemical Protective Clothing Materials to Liquid Permeation-Permeation Cup Method.

• ASTM F1194-99 Standard Guide for Documenting the Results of Chemical Permeation Testing of Materials Used in Protective Clothing.

• ASTM F903-03 (2004) Standard Test Method for Resistance of Materials Used in Protective Clothing to Penetration by Liquids.

• ASTM F2053-00 Standard Guide for Documenting the Results of Airborne Particle Penetration Testing of Protective Clothing Materials.

• ASTM F2130-01 Standard Test Method for Measuring Repellency, Retention, and Penetration of Liquid Pesticide Formulation through Protective Clothing Materials.

• EN 943-1:2002 Protective clothing against liquid and gaseous chemicals, including liquid aerosols and solid particles - Part 1: Performance requirements.

• EN 467:1995 Protective Clothing - Protection against liquid chemicals -Performance requirements for garments providing protection to parts of the body.

• EN374-3:1994 Protective gloves against chemicals and micro-organisms -Part 3: Determination of resistance to permeation by chemicals.

• EN ISO 6529 Protective clothing - Protection against chemicals -Determination of resistance of protective clothing materials to permeation by liquids and gases.

• ISO 6530 (1990) Protective clothing - Protection against liquid chemicals -Determination of resistance of materials to penetration by liquids.

• ISO 13994 (1998) Clothing for protection against liquid chemicals -Determination of the resistance of protective clothing materials to penetration by liquids under pressure.

• ISO 17491(2002) Protective clothing - Protection against gaseous and liquid chemicals - Determination of resistance of protective clothing to penetration by liquids and gases.

• ISO 22608 (2004) Protective clothing - Protection against liquid chemicals -Measurement of repellency, retention, and penetration of liquid pesticide formulations through protective clothing materials.

Permeation data is generally available for commonly used chemical protective clothing materials. Breakthrough time, the time taken by the chemical to pass through the material, is commonly used to measure permeation. In addition, permeation rate, which is the rate at which the chemical moves through the material, is also recorded. Chemical resistance data can be obtained from published guidelines as well as from manufacturers of the chemical protective clothing. 'Guidelines for the Selection of Chemical Protective Clothing' and 'Quick Selection Guide to Chemical Protective Clothing'15'16 include color-coded recommendations for sixteen commonly used barrier materials. The color codes and corresponding breakthrough times used in the guidelines are green for breakthrough detection time of >4 hours of continuous contact (a >8 is used when the breakthrough is greater than eight hours); yellow with breakthrough detection time between 1-4 hours; red with breakthrough times of less than one hour. White is used when no data is available for the material. Testing the material against the challenge liquid is recommended prior to use. Contact between the material and the chemical may result in degradation of the material or the breakthrough may be a result of the degradation of the material. It is important to note that the data reported in the guidelines is a compilation of published and unpublished permeation test data obtained from various sources. The authors of the publication state that at least 90% of the tests were conducted using ASTM F739-99, Standard Test Method for Resistance of Protective Clothing Materials to Permeation by Liquids or Gases Under Conditions of Continuous Contact. 5 The majority of the data for generic materials is a summary of results from different sources. According to the OSHA technical manual, 'The major limitation for these guidelines are their presentation of recommendations by generic material class. Numerous test results have shown that similar materials from different manufacturers may give widely different performance. That is to say manufacturer A's butyl rubber glove may protect against chemical X, but a butyl glove made by manufacturer B may not'.1

A majority of manufacturers test the materials against a battery of liquid and gaseous chemicals, which represent a wide range of commonly used chemicals in different classes. Often the recommended chemicals published by national and international standards organizations are used by the manufacturers as a common group of chemicals. The recommended list of challenge chemicals as well as the chemical class that is published by ASTM International is included in Table 4.1.17 The performance data, based on tests conducted by independent laboratories, is publicly available through a manufacturer's website. This data is specific to the material manufactured by the company, and so may be different from that obtained from the above mentioned publications. Often information regarding compliance with minimum requirements is also provided by the manufacturers.

However, judicious use of such data is important, as there are numerous protective clothing and chemical combinations. The data from the recommended list should not be a basis for selecting material for protection against chemicals not represented on the list or against a mixture of chemicals. To the extent

Table 4.1 List of Recommended Gaseous and Liquid Test Chemicals (extracted with permission, from F 1001-99a Standard Guide for Selection of Chemicals to Evaluate Protective Clothing Materials, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19462.)

Chemical

Class

Gaseous test chemicals

Ammonia

Strong base

1,3-Butadiene

Olefin

Chlorine

Inorganic gas

Ethyl oxide

Oxygen heterocyclic gas

Hydrogen chloride

Acid gas

Methyl chloride

Chlorinated hydrocarbon

Liquid test chemicals

Acetone

Ketone

Acetonitrile

Nitrile

Carbon disulfide

Sulfur-containing organic

Dichloromethane

Chlorinated hydrocarbon

Diethylamine

Amine

Dimethylformamide

Amide

Ethyl acetate

Ester

n-Hexane

Aliphatic hydrocarbon

Methanol

Alcohol

Nitrobenzene

Nitrogen-containing organic

Sodium hydroxide

Inorganic base

Sulfuric acid

Inorganic acid

Tetrachloroethylene

Chlorinated hydrocarbon

Tetrahydrofuran

Oxygen heterocyclic

Toluene

Aromatic hydrocarbon

possible, the selection of textile materials should be based on test data for the potential challenge. Materials manufactured to provide protection against specific chemical hazards require the use of challenge liquids that represent the potential risk. For example, a pharmacist working with drugs for chemotherapy needs protective clothing and accessories that protect the individual from those drugs. A garment that provides general protection against commonly used chemicals may not be recommended for this use. Special testing would have to be conducted for the proposed end use.

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