Whether a building needs protection against lighting is matter of judgment on the part of designer; obviously it depends on the probability of a stroke and acceptable risk levels. For example, a higher risk is presumably acceptable for an isolated small bungalow than, say, for a children’s hospital. Whilst no exact rules can be laid down which would eliminate the designer’s judgment entirely, certain steps can be taken for an objective assessment of the risk and of the magnitude of the consequences. As an aid to making a judgment, a set of indices is given in table-1 and elaborated below for the various factors involved.
Usage of structure
The lightning hazard to human being within structure or a building is a very important in deciding how far to go in providing lightning protection. Schools, hospitals, auditoriums, railway stations etc., are places where a large number of people congregate and, therefore, would in general be structures of greater importance than small buildings and houses.
Type of construction
The type of construction of the structure has a large influence upon the extent of protection to be provided. A steel framed building to some extent is self-protecting and may not generally required additional protection, while brick buildings or buildings with thatched roof require greater degree of protection.
Contents or consequential effects
In addition to direct loss due to destruction of buildings by lightning, fire resulting from lightning, killing of livestock etc. there may be indirect losses which sometimes accompany the destruction of buildings and there contents. An interruption to business or to firming operations, especially at certain times of the year, may involve losses quite distinct form, and in addition to losses arising from the direct destruction of property. There are also cases where full community depends for safety and comfort in some respect on the integrity of a single structure, as for instance on the brick chimney of a water pumping plant. A lightning strike to it may have a serious consequence due to disruption of sanitary facilities, drinking water, water for irrigation, fire protection etc. the contents of buildings should also be considered as to whether they are replaceable, explosive, combustible, flammable vapor or explosive dust. These may present a hazard in a building that is otherwise immune to lightning. Contents like hay or cotton may make protection measures especially desirable.