How can I determine PD for given impulse, based on transient thermal impedance for BJT?
Looking at this graph and assuming the duty cycle is low (say 0.05) then, the transient thermal impedance for 100 ms is 20 K/W: -

That means it would warm by 400 K (in 100 ms) and that would be unacceptable by a mile. Even if the duty cycle were virtually zero, the impedance would only drop to about 12 K/W at 100 ms and it would still warm by 240 K.