A Primer on Permeation, Penetration, and Degradation
Chemical Protective Clothing 101
Correction: The print version of this article incorrectly stated the issue of the Journal of Occupational and Environmental Hygiene in which the paper "Glove Permeation of Chemicals: The State of the Art of Current Practice, Part 1: Basics and the Permeation Standards" is published. The paper appears in the December 2019 issue of JOEH, not November 2019. The digital version of this article has been corrected below.

The mantra is that protective clothing is the “last line of defense” against chemical exposure, used when engineering and administrative controls cannot be applied or when there is a residual risk after their implementation. However, even though IHs are trained to treat chemical protective clothing (CPC) as a last resort, it remains common in many workplace scenarios. For example, handling chemicals at all stages of production and use, from the research lab to the waste facility, is often done manually, with the protection of gloves and garments, so that the risk of potential skin contact cannot be avoided. Furthermore, proper CPC should always be available in the event of a chemical spill or other emergency.
IHs know the importance of CPC, but not always the extent to which CPC materials can resist any of the numerous chemicals present in the workplace, particularly those new to the market. In these circumstances, IHs continually face the problem of how to select appropriate CPC while lacking data on the materials’ chemical resistance. A study reported in the 1971 chapter on protective clothing in the CRC Handbook of Laboratory Safety evaluated the permeation of aromatic amines through the neoprene suits used at a plant where workers experienced cyanosis (blue appearance of the skin, indicating lack of oxygen in the blood). The study determined that butyl was more resistant to amines than neoprene. After the plant changed to butyl suits, cases of cyanosis decreased. The first permeation test cell generated the data to support the permeation resistance of butyl. A standard test method was needed in order to determine permeation resistance. At that time, only the NIOSH criteria documents on various commodity chemicals reported guidance on permeation resistance, recommending simply that workers wear “impervious” protective gloves and suits, often without mention of specific materials. Fortunately, IHs have made great strides since the 1970s and into the 21st century. We are now able to select appropriate protective clothing based on test data generated from standard methods, such as ASTM F739, first published in 1983.  This article focuses on common CPC testing standards.  Not all testing standards are available for all products. The three main types of testing used to assess CPC chemical resistance are penetration, degradation, and permeation. PERMEATION TESTING Permeation is the process by which a liquid or gas moves through a protective clothing material, glove, suit, or other garment on a molecular basis. Permeation requires the sorption of liquid or gas molecules into the outer material surface, diffusion of these molecules through the material, and then subsequent desorption from the opposite side (Figure 1). Under ideal conditions, this process obeys Fick’s Law of diffusion and is very predictable. With chemical permeation, the two key measures are the breakthrough detection time (BT) and the permeation rate (PR). Together the BT and PR provide the end user with critical information on “how soon” and “how fast” the chemical permeates the CPC. Manufacturers that conduct permeation testing with their products often provide this data to customers in chemical resistance charts, along with penetration and degradation data in some cases.
Figure 1. Permeation is the process by which a liquid or gas moves through protective clothing on a molecular basis.
Figure 2. The ASTM F739 test cell.
In June 2020, Wiley will publish an updated Quick Selection Guide of Chemical Protective Clothing, 7th Edition. It provides permeation data on approximately 1,000 chemicals, brands, and mixtures for 27 representative barrier materials produced by manufacturers. Breakthrough Time The BT is the time to first detection, in minutes, of the chemical passing through the material to the inner side. Due to the differences in sensitivities of analytical methods, BT is often normalized (NBT) to represent detection of a specific amount in µg per cm2 of material. Caution must be exercised when comparing BT data, as detection limits vary among sources. The value of having a BT, or better yet, an NBT, is that it provides an indication of how long the material will resist a chemical before it contacts the underlying skin. However, BT does not indicate the amount of a chemical that will permeate in a given amount of time or account for the chemical’s toxicity or any hazard associated with it. Permeation Rate The PR, in units of µg/cm2/min, is either a maximum rate of permeation or the rate at equilibrium (known as the steady-state permeation rate or SSPR). The permeation rate indicates how fast the chemical will move through the material following breakthrough, which can be of importance with more hazardous substances. Where the BT provides a lag-time for exposure, the PR can give a more reliable indication of potential skin exposure over time. For More Information on Standards The American National Standards Institute, ASTM International, the International Organization for Standardization, and the National Fire Protection Association have published permeation standards. Unfortunately, despite recent efforts, they are not well harmonized. For a complete review of current practices and test methods for chemical permeation, we recommend “Glove Permeation of Chemicals: The State of the Art of Current Practice, Part 1,” published in the December 2019 issue of the Journal of Occupational and Environmental Hygiene. The paper compares various standards for testing, identifies research gaps, and even discusses the value of whole glove testing and simulated movement. The authors state that ASTM F739 and the original 1-inch test cell (Figure 2) should be the primary permeation test cell for all the standards. They also recommend harmonization among standards, especially in the determination of a normalized BT and SSPR.  Harmonization and further improvement will likely simplify CPC selection, help expand existing databases, and instill more confidence among end users, but use of more innovative equipment and analytical instrumentation for testing would add cost to products. For now, we must select appropriate protective clothing using the current available test methods for permeation, with an understanding that different manufacturers use different test methods.  PENETRATION TESTING  Penetration is the flow of a chemical through zippers, weak seams, pinholes, cuts, or imperfections on a non-molecular level. Penetration of chemicals through protective clothing can result in dermal exposures, but typically on a larger scale than is seen with permeation.  Standard test methods for determining penetration include ASTM F903 and ISO 13994, which focus on penetration by liquid chemicals. Solids, gases, and biological materials can also penetrate CPC but are evaluated by different methods.  The F903 and ISO 13994 methods test penetration by applying the challenge agent to the outside surface of a test specimen of a protective garment within a special test cell. Typically, the challenge agent is also slightly pressurized for part of the test cycle. Several different pressure or time sequences for different situations are listed in the standard. For example, Procedure C, specified by NFPA for testing protective garments for emergency response, calls for 0 pounds per square inch gauge (psig) for 5 minutes, followed by 2 psig for 1 minute, followed by 0 psig for 54 minutes. The test lasts for 60 minutes and results in either a “pass” or a “fail.” (Observation of the challenge agent on the inside surface of the test specimen results in a fail.) The time needed to reach this point is recorded for the chemical in question, and the manufacturer reports to customers. Use of Penetration Data Often, the best source of penetration data is the manufacturer of the protective garment in question. However, recognizing whether the provided data is for penetration as opposed to permeation, and understanding the difference between the two, can be difficult for end users selecting CPC. Manufacturers of protective garments often provide penetration data for products intended for chemical splash situations where actual exposure is unlikely. In the event of chemical contact, the expectation is that the wearer will stop the task and doff the contaminated garment before the chemical permeates it. In contrast, manufacturers of garments for severe scenarios where contact is expected likely provide permeation data instead of penetration data. 
Ideally, the data will be clearly identified as either permeation or penetration, but users should also pay attention to any footnotes or comments that identify the test method used. As discussed in this article, ASTM F903 is commonly used for determining resistance to penetration while ASTM F739 is the method of choice for determining resistance to permeation.  DEGRADATION TESTING Chemical degradation is a change in one or more physical properties of a material following contact with a chemical. It is an indication that certain chemical action on the material will degrade its desired barrier properties. The data may be useful to end users, but more so for manufacturers to ensure that reliable chemical permeation testing can be performed. In most testing strategies, the chemical is immersed or put in contact with one side of the material for a set time, at an elevated temperature, and then evaluated for changes in weight, thickness, volume, tensile properties (associated with molecular structure), or other physical characteristics such as color or shape. The results can indicate chemical incompatibility and potential for product failure but may not correlate with the product’s barrier properties under use. The three common testing standards used with CPC are ASTM D471, ANSI/ISEA 105, and EN 374-4. ASTM D471 The ASTM D471 method is often used with rubber-like elastomers and coated fabrics. The chemical contact time and temperature varies, so results are not comparable from one dataset to the next. Interpretation of the results is not well defined, and performance ratings can vary. The AIHA Chemical Protective Clothing book provides an example (Table 1) of how one manufacturer rated degradation based on weight change. 
Table 1. Degradation Ranking Based on Weight Change
Source: AIHA Chemical Protective Clothing, 2nd Edition
Tap on the table to open a larger version in your browser.
ANSI/ISEA 105 The ANSI/ISEA 105 degradation method relates more to testing chemical protective gloves and puncture resistance, but results can indicate chemical degradation and incompatibility. Significant changes in puncture resistance can indicate chemical action on the material and changes in its molecular structure. More notably, the method provides a consistent set of testing conditions and a rating scale ranging from one to nine, which allows end users to compare and choose products that meet their needs. EN 374-4 The EN 374-4 method is similar to ANSI/ISEA 105 but does not include a rating scale and also allows for evaluating weight change. The percent change may not be reported to end users.  PROTECTING THE SKIN
The skin is the second most important route of exposure in the workplace. While IHs are well aware of chemical protective clothing, they may not be as knowledgeable of the tests used to determine CPC performance. Knowing the basics of permeation, penetration, and degradation can help IHs and end users select the best garments for protecting against dermal exposures.   NORMAN W. HENRY III, MS, CIH, FAIHA, is a consultant for Safety and Health by Protection (SHBP). CURTIS HINTZ, CIH, CSP, is an industrial hygiene manager with The Dow Chemical Company in Freeport, Texas.   ROBERT N. PHALEN, PHD, CIH, FAIHA, is an associate professor of Occupational Safety and Health at University of Houston-Clear Lake in Houston, Texas. Send feedback to The Synergist.
AIHA: Chemical Protective Clothing, Second Edition (2003). AIHA: Personal Protective Clothing in The Occupational Environment: Its Evaluation, Control and Management, Third Edition (2011). American National Standards Institute: ANSI/ISEA 105, American National Standard for Hand Protection Classification (2016). ASTM International: ASTM D471, Standard Test Method for Rubber Property—Effect of Liquids (2016). ASTM International: ASTM F739, Standard Test Method for Permeation of Liquids and Gases Through Protective Clothing Materials Under Conditions of Continuous Contact (2012). ASTM International: ASTM F903, Standard Test Method for Resistance of Materials Used in Protective Clothing to Penetration by Liquids (2018). CRC: “Protective Clothing” in CRC Handbook of Laboratory Safety (1971). International Organization for Standardization: ISO 13994, Clothing for Protection against Liquid Chemicals—Determination of the Resistance of Protective Clothing Materials to Penetration by Liquids Under Pressure (2005). International Organization for Standardization: ISO EN 374-4, Determination of Resistance to Degradation by Chemicals (2013). 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). Wiley: Quick Selection Guide to Chemical Protective Clothing, Sixth Edition (June 2014).
Although the print version of The Synergist indicated The IAQ Investigator's Guide, 3rd edition, was already published, it isn't quite ready yet. We will be sure to let readers know when the Guide is available for purchase in the AIHA Marketplace.
My apologies for the error.
- Ed Rutkowski, Synergist editor
Disadvantages of being unacclimatized:
  • Readily show signs of heat stress when exposed to hot environments.
  • Difficulty replacing all of the water lost in sweat.
  • Failure to replace the water lost will slow or prevent acclimatization.
Benefits of acclimatization:
  • Increased sweating efficiency (earlier onset of sweating, greater sweat production, and reduced electrolyte loss in sweat).
  • Stabilization of the circulation.
  • Work is performed with lower core temperature and heart rate.
  • Increased skin blood flow at a given core temperature.
Acclimatization plan:
  • Gradually increase exposure time in hot environmental conditions over a period of 7 to 14 days.
  • For new workers, the schedule should be no more than 20% of the usual duration of work in the hot environment on day 1 and a no more than 20% increase on each additional day.
  • For workers who have had previous experience with the job, the acclimatization regimen should be no more than 50% of the usual duration of work in the hot environment on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.
  • The time required for non–physically fit individuals to develop acclimatization is about 50% greater than for the physically fit.
Level of acclimatization:
  • Relative to the initial level of physical fitness and the total heat stress experienced by the individual.
Maintaining acclimatization:
  • Can be maintained for a few days of non-heat exposure.
  • Absence from work in the heat for a week or more results in a significant loss in the beneficial adaptations leading to an increase likelihood of acute dehydration, illness, or fatigue.
  • Can be regained in 2 to 3 days upon return to a hot job.
  • Appears to be better maintained by those who are physically fit.
  • Seasonal shifts in temperatures may result in difficulties.
  • Working in hot, humid environments provides adaptive benefits that also apply in hot, desert environments, and vice versa.
  • Air conditioning will not affect acclimatization.
Acclimatization in Workers