Protection Against Lightning.

Pelorus Guardian and Miners' Advocate., Volume 29, Issue 37, 15 May 1917, Page 2

Protection Against Lightning.

The United States Bureau of Standards has made an exhaustive investigation on the subject of protection against lightning. Some of the conclusions arrived at are most interesting. During each year, it is stated, there are approximately 1,500 persons affected by lightning stroke in the United States, about one-third of thin number being killed' and the rest subjected to injuries which in many cases are permanent. Nine-tenths of these accidents occur in rfiral districts. Such evidence as is available on the effectiveness of lightning rods indicates that, taking rods as they come in the general run of installations, they reduce the fire hazards from lightning by 80 to 90 per cent, in the cases of houses, and by as much as 99 per cent, in the case of barns. The same is undoubtedly true in the case of other buildings having characteristics similar to those of barns and houses.

In the event of equal and large numbers of unprotected barns and houses being struck by lightning, about four times as many barns as houses would he fired.

There are no data to show that different objects equally exposed to lightning as to height, configuration, and other characteristics are not equally liable to he struck. From theoretical considerations it would appear that highly conducting bodies are more likely to be struck than insulating bodies ; but there are no data available to show to what extent this is the case. The impression that some objects are more liable to lightning stroke than others undoubtedly arises from the fact that some are more susceptible to damage by lightning than others. Such statistics as are available seem to show that when a stroke of lightning falls upon an unprotected house sheltering a family of an average number of persons, the chances are about even that one or more of the members will be injured or killed; but because of the fact that cases of lightning stroke on houses in which no serious damage to the building nor injury to persons occurs are very unlikely to be reported, it is quite likely that the chances are much less than even.

The metals commercially available as materials for lightping rods and which meet all the other requirements in greater or less degree are copper, aluminium, and iron.

Tite most important property which must be possessed by the metal of which a lightning rod is made is resistance to atmospheric and soil corrosion. To impart this property to iron it must be galvanised. Good mechanical construction is quite essential to permanency in a lightning-rod system, but at the present time it is not as a rule given the attention it should have. The impression that a defective rod is necessarily a menace, however ie false ; even a defective rod is generally better than no rod at all.

The return on an investment in lightning rods may be expected in two ways ; In a sense of personal security from lightning and in actual security to both life and property. The property loss by lightning is not sufficient to cause protection against lightning always to be a paying investment. Protection against lightning is justified as an investment only where risk is high enough to make protection against lightning cheaper than insurance.

The loss of live stock in fields can be reduced by earthing wire fences by means of galvanised-iron pipe or posts at intervals of 100 yards or so, and breaking up the electrical continuity of the fence at intervals by inserting sections of non-conducting wood in place of the wire. No place to which a person may ordinarily retire can be considered absolutely safe from lightning. The place of greatest safety which is ordinarily accessible is a well-rodded building ; the next safest is undoubtedly an unprotected house, which mayj be regarded as much safer than in the open or in small unprotected buildings.