6.6.1 Definition of terms

The scope of IEC 62305-3 covers not only the protection of buildings and structures against fire and mechanical destruction, but also the protection of people against injury from touch and step voltages in the vicinity of a lightning protection system. 
The maximum permissible values for step and touch voltages are predominantly determined by their duration of current flow in the human body.
The permissible touch voltage depends directly on the length of time a person is exposed to this voltage. The shorter the duration of current flow, the higher the voltage may be without posing a risk of fatality.

Touch voltage
Touch voltage is the voltage that acts on a person between the position where they are standing on the ground and when they touch a down conductor. The current path leads from the hand via the body to the feet (Figure 6.6.1.1). The danger zone for step and touch voltages for persons outside a building is within a distance of 3 m from the building and a height of 3 m. This danger zone corresponds in height to the maximum reach of a person with their hand held upwards (2.5 m) and an additional separation distance s (Figure 6.6.1.2).
Two different physical effects are crucial for protection against contact voltage, each of which poses its own hazards: