Grade

The three classes of fire-resistant glasses are further classified into Grade I, Grade II, Grade III and Grade IV according to various levels of protection which is measured in terms of Integrity, Radiation and Insulation. The Table interpreting Class Vs Grade Vs Time is just for reference. Glass resists more than 90 min (could be as high as 180 min.), is classified into higher levels. There are also Classes E and EI which perform much better and are more safety for fire protection.