In many situations where chemicals are interacting with other chemicals or materials, the interaction is strongly dependent and often correlated with the functional group(s) present. These interactions include chemical reaction, dissolution, and swelling/permeation of polymeric materials. For this reason, it is useful to have a standard means for classifying chemicals.

One application for this classification system is in the selection of chemical protective clothing based on the chemical resistance of the clothing materials. ^{, ,} Chemical resistance data are available for only a very small fraction of the chemicals for which protective clothing is used. However, for chemicals for which no data are available, a knowledge of the chemical class sometimes can give insight into the resistance of a prospective clothing material.

Note 1—The present state of knowledge precludes reliable estimates from chemical class alone.

The classification system also facilitates the development of predictive methodology by researchers in a variety of fields, in addition to protective clothing.

1.1 This standard provides a classification system for chemical compounds whereby chemicals are assigned a 3-digit code based primarily on chemical class. Poly-functional compounds should be classified by all applicable code numbers associated with their component functional groups.