Selecting Protective Clothing for Mixtures
Permeation, Degradation, and Other Complexities
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In most industries, inhalation hazards are typically the top priority for OEHS professionals. Yet data from the United States Bureau of Labor Statistics for the period 2014 through 2019 indicate that dermal diseases among workers outnumbered respiratory diseases, 121,400 to 68,500. In its 2009 publication Current Intelligence Bulletin 61: A Strategy for Assigning New Skin Notations, NIOSH observed that workplace skin diseases account for 15 to 20 percent of all occupational diseases in the U.S. NIOSH also acknowledged that despite the high incidence of workplace dermal diseases, relatively little was known about the risks of skin contact with chemicals.
Although personal protective equipment occupies the lowest rung in the hierarchy of controls and is considered the last line of defense for workers, chemical protective clothing (CPC) is heavily relied upon in many facilities for protection against dermal hazards. But not all CPC is equally protective against all chemicals, and selecting the appropriate garment or glove is even more complicated when the substance of interest is a mixture of multiple chemicals. This article discusses some of the complexities of CPC selection for mixtures.
Selecting appropriate CPC requires knowledge of specific terms that may be confusing to OEHS novices: • Permeation is a chemical’s ability to pass through a material on a molecular level. The concept is very similar to diffusion. • Breakthrough time (BT) is the elapsed time between initial contact of a liquid chemical with the outside surface of a glove or garment and the permeation rate reaching 0.1 mg/m2/sec. When breakthrough is reached, gloves are no longer considered to provide necessary protection. • Degradation is a change in the physical properties of a glove or garment after contact with a chemical. Chemicals can react with or attack glove or garment material in a manner that makes it less protective. Some common examples of degradation are the loss of a glove’s strength or swelling and deterioration over time. A more thorough discussion of these terms can be found in “Chemical Protective Clothing 101,” which appeared in the April 2020 issue of The Synergist. PERMEATION TESTING Selection of protective clothing requires consideration of the chemicals of interest. (Unfortunately, it is not always possible to know the identity of the chemicals.) In most cases, the safety data sheet will indicate whether the substance is a single chemical, a hazardous chemical diluted in water, or a mixture of several hazardous chemicals. Protection against single chemicals is straightforward. With mixtures, solvents are the primary concern and the focus of this article. But the concepts related to protection against solvents also apply to complex mixtures of other chemicals. In the early 1970s, NIOSH published “criteria documents”—documents intended to provide a basis for occupational health and safety standards—on various chemical solvents that were potential carcinogens. Those documents made recommendations for workers to wear “impermeable” protective clothing. At the time, there were no standard permeation test methods and little to no permeation data available. That began to change in 1978, when the American Society for Testing Materials (ASTM) formed Committee F-23 on protective clothing, which eventually developed the first standard permeation test method (ASTM F-739). Still in use today, ASTM F-739 reports permeation breakthrough times and permeation rate through clothing materials. Various organizations followed suit, publishing additional permeation test methods and generating an abundance of data. The first edition of Quick Selection Guide to Chemical Protective Clothing appeared in 1989. It categorized over 1,000 chemicals according to their functional group and presented data from 12 different manufacturers in color- coded tables, with green representing breakthrough times greater than 8 hours, yellow less than 4 hours, and red less than 1 hour. This system was very popular with emergency responders, who needed a quick reference to select gloves or suits while en route to an emergency. Last year the seventh edition of this guide was published with updated data on additional chemicals and new barrier materials.
The general rule “like will dissolve like” is predictable for most polymer barriers and laminates.
Most of the published test data is on pure substances—common solvents used commercially and transported worldwide. Limited data have been reported on common mixtures. Therefore, there is a need for testing with mixtures and with new glove and suit materials, particularly new laminates, that manufacturers have introduced. Some of the ASTM F-23 test methods for degradation, penetration, and permeation were discussed in “Chemical Protective Clothing 101.” Additional information on standardized test methods under development appears in the December 2019 issue of the Journal of Occupational and Environmental Hygiene.
MIXTURES, SOLVENTS, AND PROTECTIVE CLOTHING Mixtures provide an interesting challenge for the selection of appropriate protective clothing. A mixture can comprise different solvents, either in water-soluble solutions of liquids or solids, or organic solvents of various concentrations. Fortunately, all mixtures are required to have an SDS that states the percentage composition, concentration, and physical and chemical properties of each chemical constituent (unless that information is considered to be a trade secret). This information is key to understanding and predicting whether mixtures will permeate the barrier materials consisting of different polymers, like Viton (a fluoropolymer), used in the construction and production of clothing, particularly gloves and suits used for protection against hazardous chemical mixtures containing benzene. Other considerations for glove selection include the anticipated dermal exposures for both incidental scenarios (splashes) and immersion scenarios, the quality of the gloves, and the solubility properties and functional groups that may interact with the gloves.
Figure 1. Photograph of a typical ASTM permeation test cell setup.
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Research indicates that permeation is somewhat predictable based on polymer solubility factors such as molar volume and intermolecular bonds. Following Fick’s law of diffusion, the thicker the barrier material, the longer the breakthrough time. Other characteristics of solvents that contribute to permeation include concentration (viscosity), size, shape (chemical structure), functional groups (classes), and molecular weight. The general rule “like will dissolve like” is predictable for most polymer barriers and laminates. For example, gloves made of polyvinyl alcohol (PVA), a polymer made from PVC with an alcohol group (OH) polar, are not recommended for use when handling polar molecules such as alcohols, acids, or bases; for the same reason, water and aqueous solvents will dissolve PVA gloves over time. Another example is neoprene (polychloroprene), a synthetic nonpolar polymer made from butadiene, an alkene with strong double bonds. Neoprene gloves are recommended for use with concentrated acids and bases that are polar molecules. In the painting industry, butyl rubber gloves are recommended for use with methyl ethyl ketone (MEK). Butyl gloves are made from isobutylene and isoprene, both large, linear, unsaturated nonpolar molecules with double bonds that resist permeation to ketones that have a small molar volume and single bonds with alkyl groups.
Another general rule concerns solvents used to prepare agricultural pesticides, herbicides, and fungicides to spray on fields and crops: if the solvent will permeate the clothing, it will act as a carrier to allow the pesticides, herbicides, and fungicides to break through as well. This should not be considered unusual since the dissolved component (pesticide, herbicide, or fungicide) must be in solution to spray it.
OEHS professionals should consider contracting out or performing their own permeation testing when data from the manufacturer is unavailable, when multiple chemicals (mixtures) are involved, or when they have questions regarding the various glove options and their properties. While these general rules are predictable in many cases, it is important to recognize that different manufacturers use different glove materials. For example, nitrile gloves from different manufacturers can have different copolymers. Therefore, it is important to verify the material with the manufacturer. These companies are usually willing to provide samples of their material for you to test or will have tests done on their product.
MIXTURES AND DERMAL HAZARDS Multiple approaches can be used to address the dermal hazards that chemical mixtures present to the worker. One approach includes using multiple types of gloves based on the properties of the chemical components in the mixture. Some common examples are the use of nitrile, PVC, or butyl gloves over a secondary inner glove such as a mylar glove.
There are two accepted methods of selecting gloves for use with mixtures. The first is to base selection on the component in the mixture that is present in the highest concentration. The second approach is to base selection on resistance to multiple chemicals in the mixture and use the glove that has the most conservative breakthrough time for those chemicals. Additional consideration should be given to chemical compounds in mixtures that have skin notations. The SDS and the ACGIH TLV book are good sources of information on the dermal route of entry.
Also, if the breakthrough times are uncertain, it is essential that OEHS professionals consider testing of gloves either on their own or by utilizing a well-qualified private glove testing company. If you choose to do your own testing, it is best to use methods developed by volunteer standards-setting organizations such as ASTM International and the European Committee for Standardization (CEN).
TESTING METHODS One such test method includes using colorimetric indicator tubes connected to the ASTM F-23 permeation test cell to measure breakthrough time and permeation rates following the procedures outlined in the F-739 method. You can also use a control sample to determine which interferences are present ahead of testing. Since colorimetric indicator tubes are readily available for a number of solvents, they can be used to identify breakthrough time and concentration for specific components in mixtures. Figure 1 depicts a photograph of a typical ASTM permeation test cell setup.
Another glove permeation tool the industrial hygienist can use is the NIOSH Permeation Calculator. This user-friendly tool automates permeation test analysis and allows users to avoid intensive manual calculations involving the various permeation parameters.
Other resources of interest include AIHA’s IHSkinPerm tool, which can be downloaded from the AIHA website; EPA’s dermal exposure assessment tools; and the NIOSH skin notation profiles.
PPE SELECTION A lot of information and data is involved in selecting the right PPE for people to use. This article is not meant to be exhaustive; it is instead a sampling of available information that should be used to select PPE.
PPE selection is important because it is the last line of defense between the user and the chemical of concern. A PPE ensemble should not be selected randomly or just because a vendor says it will work. Workers’ well-being and even their lives may be at risk if PPE is not properly selected.
CHRIS BRENNAN, MSPH, CIH, CSP, is a senior industrial hygiene specialist at Huntsman Corporation in The Woodlands, Texas.
NORMAN W. HENRY III, MS, CIH, FAIHA, is a consultant for Safety and Health by Protection (SHBP).
CRAIG WILLEY, CIH, CSP, is corporate manager for Health and Chemical Hygiene at Cambrex in Charles City, Iowa.
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AIHA Journal: “The Use of Detector Tubes Following ASTM Method F-739-85 for Measuring Permeation Resistance of Clothing” (June 1989).
ASTM International: “Selection and Use of Molecular Parameters to Predict Permeation Through Fluoropolymer-Based Protective Clothing Material” in Performance of Protective Clothing: Fourth Volume (1992).
Bureau of Labor Statistics: “Occupational Injuries and Illnesses Industry Data (2014 Forward)”: Private Industry-Total Cases of Skin Disease and Private Industry-Total Cases of Respiratory Illnesses.
Journal of Occupational and Environmental Hygiene: “Glove Permeation of Chemicals: The State of the Art of Current Practice, Part 1: Basics and the Permeation Standards” (December 2019).
NIOSH: Current Intelligence Bulletin 61: A Strategy for Assigning New Skin Notations (July 2009).
The Synergist: “Chemical Protective Clothing 101” (April 2020).
Van Norstrand Reinhold Publications: Quick Selection Guide to Chemical Protective Clothing, 1st ed. (1989).
Wiley Publications: Quick Selection Guide to Chemical Protective Clothing, 7th ed. (2020).