in the " hazardous area classification" whats the meaning of T1 or T2 .... etc ???

In hazardous area classification, T1, T2,...,T6 stands for temperature class.

It is the maximum temperature that an equipment's outer surface can reach when it is in running condition. (For motors, it can be the temperature when there is locked rotor condition for 5 seconds)

T1 corresponds to 450 deg.C and is the least stringent. T6 corresponds to 85 deg.C and is the most stringent.

When you are using an electrical equipment in hazardous area, you have to check for the temperature class of the equipment.

For example, if the hazardous gas in the hazardous area has an ignition temperature of 200 deg.C, then you have to choose an equipment having temperature class less than 200 deg.C. (i.e) you can select T4 (135 deg.C).