6.6.2 Measures to protect against touch voltages

Even if a lightning protection system (LPS) has been designed and installed in accordance with the requirements of the relevant documents, there may still be a risk of fatality if people are present near down conductors under normal conditions. The aim is to reduce this risk to an acceptable level.

The risk is considered to be reduced to an acceptable level if one of the following conditions is met:

• Avoiding the presence of people (minimum distances) 
  Under normal operating conditions, no people are permitted within a radius of 3 m of the down conductors (Figure 6.6.2.1). In addition, down conductors and metal installations that are connected to the equipotential bonding system should not be installed in areas accessible to the public.
• Intrinsic down-conductor systems 
  An "natural" down-conductor system consists of at least 10 supports of the extensive metal framework of the structure or at least 10 columns of the interconnected steel of the structure, whereby electrical continuity is ensured. 
  Note: The effectiveness of this measure described in IEC 62305-3 is assessed differently by international lightning protection experts. Although the risk is reduced in buildings with reinforced concrete/steel frame construction and very good lightning current distribution, a system with at least ten down conductors is not recommended as the sole measure for preventing dangerous step and touch voltages.