The criterion: breakthrough time
What decides a chemical protective glove is neither its thickness nor its colour but its breakthrough time: how long the chemical takes to permeate the material at molecular level and reach the inner surface. That time is measured in the laboratory for a chemical–material pair and classified. The same glove may hold for hours against one chemical and be through in minutes against another.
The material follows the chemical
Nitrile, neoprene, butyl, fluoroelastomer, natural rubber and laminate each have chemical families they resist and families they do not. The right question is not “which glove is good” but “which material and which thickness for this chemical”. The answer is in the manufacturer's data for that chemical, not in a general catalogue sentence.
The form of contact changes the choice
- Splash and immersion are not the same; immersion consumes the time quickly and makes cuff length matter.
- Mixtures can be more aggressive than their components; without data for the mixture, select against the worst component.
- Mechanical stress — cutting, abrasion — ends the chemical protection too: the breakthrough time of a punctured glove is meaningless.
Wear time and change-out
Breakthrough time is a clock, and it starts when contact does. The change-out rule is therefore written in advance against the duration of the task; “change them when they look dirty” ignores a passage that is invisible. Removing a contaminated glove is part of the training as well — done wrongly, it contaminates the hand that was being protected at the very last step.
The link with the safety data sheet
A chemical's safety data sheet is the starting point for suitable protective equipment. But the sheet usually names a material family, not the thickness and time this particular task needs; the selection is completed by reading the sheet together with the manufacturer's permeation data.