What Does Chemical Resistance (CR) Mean?
Chemical resistance (CR) refers to the ability of a material to withstand exposure to a chemical substance without being degraded by that substance and without that substance permeating the material.
This means that the material must not react significantly with the chemical substance (which causes degradation), and it must act as a sufficient barrier to prevent the substance from permeating through it.
Safeopedia Explains Chemical Resistance (CR)
Chemical resistance is an important attribute of personal protective equipment (PPE) that is worn to protect workers against exposure to harmful chemicals. Because chemicals do not react equally to different substances, the chemical resistance of a product is a term that must be understood relative to the substance that it could be exposed to. The use of safety equipment that can sufficiently resist exposure to substances that may be present in the workplace is an important part of an employer's safety obligations, which include requirements to provide workers with appropriate PPE and to limit exposure to harmful chemicals.
The determination of a material's chemical resistance is done through tests that are subject to existing technical standards from recognized standards organizations such as ASTM International. PPE manufacturers validate the chemical resistance of their products by measuring the permeation rate, breakthrough time, and degradation rate of a product when exposed to a specific chemical. The breakthrough time refers to the time it takes for a test chemical to be detected on the other material being tested, while the permeation rate reflects the highest flow rate of a test chemical across the material within a six- or eight-hour test period.
Degradation refers to the process of a material reacting with a chemical. This may cause some of the material to be lost, potentially creating holes in the material, or it could result in changes to the material’s physical properties in a manner that makes it more permeable. Materials that are heavily degraded by a substance may be referred to as being “attacked” by that substance.
An example of the manner in which chemical resistance is substance-specific can be found when reviewing the properties of material used in protective gloves. Latex gloves provide strong resistance to acetone, while nitrile gloves provide poor resistance; however, latex has poor resistance to diesel fuel, while nitrile provides strong resistance.