1.1 This specification covers brick intended for use as the lining in the fireboxes of residential fireplaces.1.2 Firebox brick are manufactured from clay, fire clay, shale, or similar naturally occurring earthy substances and subjected to a heat treatment at elevated temperatures (firing). The heat treatment must develop a fired bond between the particulate constituents to provide the strength and durability requirements of this specification. Note 1—Firebox brick are typ