The following data have been extrapolated from CEI 42-4 standards:

• 1 The distinction between atmospheric and shunting impulses is made on the basis of the front duration. The pulses whose front has a duration of less than 20 µsec. are defined as atmospheric impulses, while those with a longer duration, as maneuver impulses.
• 1.1 Full atmospheric impulse. A full atmospheric impulse is a lightning impulse that is not truncated by a disruptive discharge (as shown in the figure)
• 1.2 Truncated atmospheric impulse. A truncated atmospheric impulse is a lightning impulse during which a disruptive discharge causes the voltage to drop to practically zero. The truncation can take place on the front, on the crest, on the tail.
• 1 Normalized atmospheric impulse. The normalized atmospheric impulse is a full impulse with a front duration of 1.2 µsec. It is described as impulse 1.2/50.