3.1 The presence of certain impurities in silica brick tends to lower their refractoriness and service limits. This classification permits those familiar with refractories to predict the refractoriness of silica brick from their alkali and alumina contents.

1.1 This classification is limited to silica brick meeting the following requirements:

Alumina (Al₂O ₃) content of less than 1.50 %.
Titania (TiO₂) content of less than 0.20 %.
Iron oxide (FeO₃) content of less than 2.50 %.
Calcium oxide (CaO) content of less than 4.00 %.
Average modulus of rupture of not less than 500 psi (3.45 MPa).

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.