According to IEC61643-11, Type 1 surge protective device should be tested by 10/350μs waveform and Type 2 SPD should be tested by 8/20μs waveform.

10/350μs waveform is a surge which reaches peak value at 10μs and it reduces to half of peak current at 350μs. Take BR-25GR type 1 SPD as an example, the product was tested at waveform which reach 25kA in 10μs which reduces to12.5kA at 350μs.

As comparison, 8/20μs waveform is a surge which reaches peak value at 8μs and reduces to half of peak current at 20μs. Take BR-40 type 2 SPD as an example, this product was tested at waveform which reach 40kA in 8μs which reduces to 20kA at 20μs.

As you can see from the above picture, 8/20μs waveform has much shorter time than the 10/350μs waveform. As energy equals to current square multiplied by resistor and time (E=I²Rt) and the time difference between the two wave is very big, therefore, a type 1 25kA SPD can discharge much more energy than a type 2 40kA SPD.