Chemical Barrier Protection: What You Need to Know
From assessing workplace risks and the likelihood for hazard exposures to understanding OSHA standards and EPA Protection Levels, the job of selecting the right chemical protective apparel appears to be a complex job. And, in fact, many people charged with apparel selection are operating under some fairly common misconceptions when it comes to matching the right protective garment for a specific work task.
Part of the problem stems from the lack of an established U.S. standard for protective apparel. While the National Fire Protection Association (NFPA) had previously addressed clothing worn for hazardous materials emergency response operations under its standards NFPA 1991, 1992, and 1993, no standard exists for the majority of chemical protective clothing worn by the U.S. workforce. And, although OSHA provides references to many applicable performance-based standards for certain types of personal protective equipment (PPE) (i.e., eye and face protection), there is a void in its regulation with respect to the performance of protective clothing used within general industry.
Hazard Analysis and Risk Assessment
Many PPE users look exclusively at the hazardous chemicals in the workplace to drive their garment selection decisions. And while identifying the hazardous chemicals and substances in the work environment is a key part of the hazard analysis process, narrowing apparel selection to just looking for a >480 minutes break-through time for a specific chemical leaves many options unexplored.
The entire process of hazards analysis and risk assessment influences PPE selection. The details of the application and a realistic understanding of the likelihood for exposure to the chemical are just as important as the chemical itself.
For example, there is a great deal of difference in the PPE required for a worker exposed to a quart of acetone in a well-ventilated room compared with one who is exposed to a large vat of acetone in an enclosed space. Similarly, if a worker’s daily job involves cleaning parts with a solvent, exposure to that solvent is likely and usually controlled. It is an expected part of the job. However, a chemical pipe burst during a repair operation would be considered less likely to happen, but would be potentially more severe in terms of the consequences and may require a greater degree of protection. The protective equipment selected should be adjusted to meet the practical demands of the task.
Two Tests to Know
There are two primary ways to evaluate chemical barrier performance – permeation testing and the less-known and less-understood penetration testing. Permeation testing typically applies to Level A garments that protect against unknown hazards or gaseous/vapour phase chemicals that represent the highest level of respiratory and skin threats. The penetration test method applies to Level B and C garments that protect against moderate-skin-threat liquid chemicals. (It is important to note here that there is no difference in EPA garment recommendations between Level B and Level C protection, because both levels provide protection from moderate skin threats. The difference is the type of respiratory protection provided.)
In the selection of chemical protective suits for most industrial applications, many in the industry overemphasize permeation performance over penetration performance. The result is a garment selection process that is overprotective, creating undue worker stress and productivity loss, as well as higher cost.
Permeation Resistance
Permeation testing measures a chemical’s movement through a material on a molecular level. The American Society for Testing and Materials (ASTM) has created ASTM F739 as a standard test method for measuring permeation resistance. Apparel manufacturers typically test the permeation of their garments’ materials against 21 representative liquid and gaseous chemicals as recommended in ASTM F1001.
The permeation test is conducted for up to eight hours (480 minutes), during which the chemical remains in continuous contact with the garment material specimen at full concentration.
This testing scenario is much more severe than situations typically found in industrial settings, where only splash or intermittent contact occurs. In fact, the test is equivalent to being fully immersed in a liquid chemical or being in a gaseous environment at 100 percent concentration for an entire work shift.
In reality, most high-level (Level A) garments are worn for an hour or less due to time limitations in SCBA air supply, or to prevent heat stress and exhaustion in the wearer.
Permeation Testing Results
The permeation test provides two types of results – permeation breakthrough time and permeation rate. Normalized breakthrough time is the elapsed time between the start of chemical exposure and the point when the amount of chemical permeating the material reaches a rate of 0.1 micrograms per square centimetre per minute.
To put this into perspective, at the time of breakthrough, the rate of permeation is so small, it’s equivalent to one grain of sand falling through a one square inch net each minute.
The reported permeation rate is the maximum speed at which the chemical comes through the material during the test.
Penetration Resistance
A second type of chemical barrier test – penetration testing – is more appropriate for testing chemical barrier when splash exposure is anticipated, which is far more likely in industrial settings than full immersion in a liquid.
Many safety professionals may be unfamiliar with penetration testing. Reference for its use in determining chemical splash protection for emergency response applications can be found in the National Fire Protection Association (NFPA) Standard 1992.
Penetration is defined in ASTM Test Method F903 as the bulk flow of liquids through a material or seam in the garment. When testing penetration, a garment material is exposed to a concentrated liquid chemical for one hour. The material is then observed for any sign of liquid coming through the fabric. (Note that sometimes, blotting paper may be used to see if any liquid wets the material.)
Penetration Testing Results
Any detectable sign of chemical passage through the fabric is reported as a failure. This is a key advantage of penetration testing over permeation testing: the test results are not open to interpretation. Instead, results are presented as either PASS or FAIL for each chemical tested.
To aid in the assessment process, some garment manufacturers offer additional information in their chemical resistance guides to indicate which of the chemicals tested for penetration are carcinogens or have skin notations. These indications may warrant the use of permeation resistance data because of the potential for higher skin threat.
Applying Chemical Resistance Data
After understanding the difference between permeation and penetration resistance testing, it should be clear that permeation is more appropriate for evaluating Level A garments. These garments are designed to protect against truly unknown hazards and chemicals presenting the highest level of skin threat.
For example, permeation resistance data should be applied if the hazardous chemical is a gas, such as chlorine or ammonia, against which the skin must be protected. Permeation resistance data also should be applied for liquid chemicals that produce hazardous vapours, such as benzene and acrylonitrile, both of which have skin notations and are classified as carcinogens.
It should also be clear that penetration resistance testing is most appropriate for evaluating Level B and C garments, where the garments are worn to protect against chemicals presenting moderate skin threats, primarily in situations involving splashes or limited exposure.
Penetration resistance testing is an appropriate garment evaluation method for protection against liquid chemicals whose vapours are not hazardous through skin absorption. It is also appropriate when the liquid does not produce vapours, but users are exposed to the liquid, primarily through splashes, and those splashes are harmful to the skin, such as with nitrobenzene or sulfuric acid.
Keep in mind that with many cases of liquid chemical splashes and sprays, the liquid either evaporates quickly or runs off the garment before having the chance to penetrate through the garment and reach the skin.
Conclusion
Some in the chemical protective clothing industry overemphasize permeation resistance data in the selection of protective clothing. The result is insufficient focus on garments that provide appropriate protection and may actually improve worker comfort and productivity.
One big advantage of applying penetration resistance data is the ability to evaluate more comfortable, lighter weight clothing with acceptable splash protection, versus heavier weight, high-permeation-resistant clothing.
Understanding when to apply permeation and when to apply penetration data is key to choosing the best garment that is ideal in all aspects…protection, productivity and cost-savings.
Chemical Selection Tool
Use our Chemical Resistance Database to help you choose the correct PPE for your needs.
Note: This tool sits on the K-C Professional US site. Not all products shown are available in Australia and New Zealand.
