What does permeation rate mean when it comes to chemical protective clothing?
Permeation is the process by which a chemical moves through protective clothing and fabric at a molecular level. It is measured in terms of permeation rate: the rate at which a chemical is transferred (in micrograms) through one square centimeter of the fabric in one minute.
Permeation (and the permeation rate) increases with the environmental temperature.
(For related reading, see A Guide to Selecting Chemical Protective Clothing.)
Chemical Protective Clothing and Permeation
So, what does permeation rate mean when it comes to chemical protective suits?
Essentially, the permeation rate tells you how quickly a particular chemical will go through a suit, a fact you need to know in order to decide what level of protection you need. Any chemical protective suit you select must have been tested and deemed safe for use with the particular chemical the worker will be exposed to. Additionally, the contact or exposure time of the PPE to the chemical(s) must be known and factored into the use of the clothing and its life-cycle, including decontamination and disposal of used clothing.
The highest temperature in the work environment that the PPE will have to function in must also be factored in, and the presence of chemical vapors must be addressed in your hazard analysis or risk assessment.
The permeation characteristics of mixtures can often deviate considerably from the behavior of the individual chemicals. Since permeation rate testing is done in a controlled environment, actual 'breakthrough' time will be influenced by environmental factors and chemical characteristics.
“Breakthrough time is not the same as safe wear time. Breakthrough time alone is insufficient to determine how long a garment may be worn once the garment has been contaminated. Safe user wear time may be longer or shorter than the breakthrough time depending on the permeation behavior of the substance, the toxicity of the substance and the exposure conditions.”
Section 8 of an SDS: Exposure Controls/Personal Protection, will define the PPE needed, including breakthrough times. If this information is not on the MSDS/SDS, contact the Supplier for detailed information on permeation and breakthrough rates
In summary, chemical protective suits and clothing require the safety professional to conduct a highly detailed hazard and risk analysis before using any specific PPE product. Also, chemical suits are only a part of the PPE ensemble a worker will need.
Please review the appropriate legislation and information regarding this subject, including but not limited to:
- ANSI/ISEA 105-216. Retrieved from (6)
- ASTM International F739-12e1. Retrieved from (7)
- ATSM F1001 – 12(2017) Retrieved from (8)
It's also valuable to review the OSHA and EPA information below:
The OSHA Technical Manual, Section VIII, Chapter 1, is an excellent resource for understanding this subject and details the use of chemical protective clothing.
The Environmental Protection Agency provides a table detailing their levels of PPE protection, which can be used as a starting point for assembly of protective clothing ensembles. However, each ensemble must be tailored to the specific situation to provide the most appropriate level of protection .
Here are two other terms that are important when it comes to understanding the effectiveness of chemical protective clothing.
- Breakthrough time: The time it takes a chemical to permeate completely through the material.
- Degradation: A measurement of the physical deterioration of the material due to contact with a chemical. The material may get harder, stiffer, more brittle, softer, weaker, or may swell. In the worst cases, the material may actually dissolve in the chemical.
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