To Protect or not to protect
Standard AS 1768 provides clear guidelines to take a decision to provide or not to provide lightning protection to a building or structure based on an assessment of risk involved.
The assessment is done in terms of the likelihood of the structure being struck and the consequences of any such strike. The use of the structure, the nature of its construction, the value of the contents and the prevalence of thunderstorms in the area can all be considered in making the assessment.
A decision to provide lightning protection may, however, be taken without any risk assessment, for example, where there is a desire that there should be no risk to a structure at all.
Examples of such structures are:
- Those in or near which large numbers of persons congregate
- Those concerned with the maintenance of essential public services
- Those in areas where lightning is prevalent
- Very tall or isolated structures and
- Structures of historic or cultural importance.
Where it is thought that the consequential effects will be small and that the effect of a lightning flash will most probably be merely slight damage to the structure, it may be economic not to incur the cost of protection but to accept the risk. Even then, it is better to make an assessment so as to give some idea of the magnitude of the risk that is being taken.
The need to protect electronic equipment and to protect persons against potential differences associated with metallic services increases with the building area. In such cases even though the construction of the structure does not warrant protection, appropriate measures must be taken to avoid risk to persons and equipment.
The standard also stipulates that any structure which is entirely within a zone protected by an adjacent object or objects (whether protected or not) should be deemed to be protected, that is no separate protection is necessary for such structures.
References:
- Practical Grounding, Bonding, Shielding and Surge Protection
G. Vijayaraghavan - IEEE Std 80-2000
IEEE Guide for Safety in AC Substation Grounding - IEEE Std 142-2007
IEEE Recommended Practice for Grounding of Industrial and Commercial Power Systems