What is the difference between penetration and permeation? How do I know which test method to use?
Choosing and evaluating the right protective clothing is critical. Not choosing correctly and failing to evaluate and test can have serious consequences. There are two primary test methods for protective clothing designed to protect from liquid chemicals. Each method has its strengths and weaknesses.
Permeation testing evaluates the way in which chemicals are absorbed by and move through the surface of protective clothing. It evaluates how the chemical in contact with the clothing is absorbed into the protective clothing through its imperfections and pores, how it spreads through the barrier and how it reacts with the person wearing it.
The military test protective garments this way by spotting them with chemicals, the theory being that in the field the material is more likely to be spotted with a chemical. This may not mirror your application and therefore may not be an effective evaluation method.
In some methods of permeation testing the protective clothing is splashed at periodic intervals.
The important thing is to evaluate how much exposure your clothing will likely experience, including the duration, temperatures, etc. Will it just experience occasional spotting, periodic splashing or be continuously coated in a chemical? Determine what is the worst-case scenario and base your testing on that.
If you want the most thorough and effective permeation testing, it involves coating the entire surface of the protective material in the chemical you want to protect from. Set up a tank of the chemical, use the material as a barrier, leave it for a predetermined time and evaluate if the chemical permeates through the material.
Choosing the permeation method that works for you will depend upon your assessment of the level of protection that you require.
Penetration testing evaluates defects in the protective clothing. It tests the ability of a chemical to pass through protective clothing at the joints, stitching, gussets, closures and interfaces between articles of clothing. Some items to consider when conducting a penetration test are:
- Duration of the test
- The type of chemical being used and its viscosity, surface tension and other physical characteristics
- Reaction of the chemical with the protective clothing
Pressure is used with penetration testing to attempt to exert pressure on the material and force the chemical through its imperfections. Variations in pressure can affect the results of the testing significantly, as can the characteristics of the chemical, duration of the test and chemical reactions with the material. It is important to establish to what degree you need to test your protective clothing based on the above criteria and test at defined intervals. Chemical substitutes with similar characteristics can be used but will not be able to test for things like reaction of the chemical with the material being tested. The most effective penetration test, where possible, involves testing with the actual chemical or combination of chemicals that your protective clothing will be exposed to.
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