Depending on periods of resistance, glasses can be produced as 30 min, 60 min, 90 min, and 120 min. 

In fire glass classifications, there are three different markings.

E = It protects product integrity during period of flame resistance.
W = It avoids certain radiation during period of radiation restriction.
I = It does not transmit the heat forming during period of isolationto the other side.

EW = Integrity and reduction of radiation: With the feature of heat reflection coating that these glasses have, they avoid not only for flames and fume that occur during a fire but also the radiant heat to pass to the other side.

EI  = Integrity and Insulation: These glasses act in the form of a heat shield and they avoid for flames, fume, toxic gases and radiant heat which come out during a fire incident, to pass to the other side. After fire temperature reaches a certain degree, special foam that is between the glass layers cause for the glass to opacify.

For example;

Glasses that are within E30 class, only avoid for the passage of flames and fumes for a period of 30 minutes and they enable for their integrity to be protected.

Glasses that are within EW60 class avoid passage of radiant heat together with the passage of flames and fume for a period of 60 minutes and they enable for their integrity to be protected.

Glasses that are within EI90 class avoid passage of flames, fume, toxic gases, radiant heat and temperature completely for a period of 90 minutes.