4.1 This classification categorizes the defined types of refractory brick, with the exception of chrome brick, into distinct classes based on a nominal and minimal value for magnesium oxide content. Chrome brick are treated as a separate class without reference to magnesium oxide content. Such classes have historically been generally useful in relating the defined types to specific industrial applications and in developing product or purchasing specifications.

1.1 This classification categorizes machine-made refractory brick defined as chrome, chrome-magnesia, magnesia-chrome, and magnesia brick (see 3.1). It does not cover products made from electrically fused magnesium oxide or to products made by fusion casting. Its purpose is to describe classes distinguished by obvious differences in magnesium oxide (MgO) content except for chrome brick.

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.