A catastrophic pipe failure during a pneumatic pressure/leak test could result in an explosive release of energy. For example, did you know…
An explosion of 200 ft of NPS 36 line (i.e., 36″ pipe) containing air at 500 psig can create a blast wave roughly equivalent to 80 lbs of TNT. This hazard is proportional to both the volume and the pressure.
Source: The complete Guide to ASME B31.3, Charles Becht IV, 2002