Real world conditions produce a vast array of waveforms having pulse widths ranging from tens of nanoseconds to tens of milliseconds in duration. The graph in Figure 1 relates peak pulse power vs time for 600W suppressors.
Similar graphs depict power vs time for TVSs rated at other power levels.
The graph illustrates at 20 us the PPP rating is 3.2kW, or 5.3 times its rating at 1000us. Hence the IPP rating of an SMBJ12C would increase by a factor of 5.3 from 27.3A to 145A for a 20us pulse. For longer pulses, the TVS will withstand lower IPP values. The IPP for an SMBJ12C would be reduced by a factor of .33, from 27.3A to 9.1A for a 10,000us pulse. This applies to all devices in the 600W series regardless of their operating voltage.