DEPARTMENT OF COMMERCE Technologic Papers OF THE Bureau of Standards S. W. STRATTON, Director No. 56 PROTECTION OF LIFE AND PROPERTY AGAINST LIGHTNING BY 0. S. PETERS, Assistant Physicist Bureau of Standards [ISSUED DECEMBER 15, 1915] WASHINGTON GOVERNMENT PRINTING OFFICE 1915 ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT 35 CENTS PER COPY .. .. PROTECTION OF LIFE AND PROPERTY AGAINST LIGHTNING By O. S. Peters CONTENTS Page I. Introduction 4 1. Early history of the lightning rod 4 2. Present status of the practice of protection against lightning 7 3. Lack of attention by the public to protection against lightning. 8 4. The need for investigation and spreading information concerning protection against lightning 9 5. Object of this paper 10 II. Desirability of protection against lightning 11 1. Lightning as a cause of fire and damage to property 11 2. Lightning as a cause of injury and loss of life 16 III. Efficiency of lightning rods 24 1. Results of the use of lightning rods in the United States 25 2. Results of the use of lightning rods in Europe 28 IV. Some points of disagreement among various authorities 30 1. Notes on causes and supposed causes of damage to protected buildings 31 2. Iron conductors versus copper conductors 34 3 Systems of protection against lightning with points versus systems without points 35 4. Use of insulators between rods and buildings 36 V. Characteristics of lightning flashes 37 1. Current intensities of lightning flashes 38 2. Frequency and duration of lightning flashes 41 3. Potentials of lightning flashes 47 4. Shifting of the path of lightning flashes by the wind 47 5 Some conditions to be considered in designing a protective system 49 (a) Heating effects 49 (6) Potentials 53 (c) Relative skin effects 53 VI. Relative liability to damage by lightning of different classes of buildings and other forms of property 54 1. Fire hazard to oil tanks and their protection 57 2. Fire hazard from lightning in bams and houses 59 3. Life hazard in unprotected houses struck by lghtning 60 3 . 4 Technologic Papers of the Bureau of Standards Page VII. Materials and construction of lightning rods 61 i. Properties of the metals available for lightning conductors 61 (a) Copper 61 (b) Aluminum 62 (c) Iron 63 2. Mechanical construction of lightning rods 66 (a) Contact of metals having different galvanic potentials. 66 (6) Joints and couplings for lightning rods 67 (c) Fasteners 69 (d) Protection from corrosion by smoke and gases 70 (e) The shape of the cross section of the rod 71 VIII. Earth connections for lightning rods 73 1. Resistance of earth connections 77 2. Methods of measuring the resistance of earth connections 79 3. Materials and construction of rods for earth terminals 81 IX. Aerial terminals with points for lightning rods 82 1. Points 89 2. Aerial terminals 90 X. Arrangement of rods and aerial terminals on buildings and the intercon- nection of metallic masses 92 1. Location of aerial terminals 92 2 Location of rods 94 3. Interconnection of metallic masses 94 XI. Question of cost 96 XII. Protection of live stock in fields 98 XIII. Safeguarding human life 100 Location of greatest safety during a thunder storm 100 XIV. Summary 101 Appendixes 107 Appendix I. Rules concerning the installation and maintenance of light- ning rods 107 Appendix II. First aid to persons injured by lightning 122 Appendix III. Bibliography 126 I. INTRODUCTION 1. EARLY HISTORY OF THE LIGHTNING ROD The conception of the lightning rod dates from the summer of 1750. During that year Benjamin Franklin, in letters to his friends, Peter Collinson and Dr. Mitchel, Fellow and Member, respectively, of the Royal Society of London, reported some of the results of his researches in electricity which had led him to infer the identity between electricity and lightning. In one of those letters he suggested that damage by lightning to buildings, and other objects upon the surface of the earth, might be pre- vented by the erection upon their summits of sharp-pointed iron Protection Against Lightning 5 rods, the lower ends of which should be extended into the ground. In June, 1752, Franklin performed his well-known kite experi- ment, which was the means of fully establishing the tentative conclusions he had drawn from the results of his previous researches. In the summer of 1753 he erected on his house in Philadelphia the only lightning rod then in existence. This rod, which was of iron, extended 5 feet into the ground, and had a sharp point raised 7 or 8 feet above the roof. It was evidently intended by its inventor to serve both as a protection against lightning, and as a means of observing the effects of atmospheric electricity. Franklin's con- fidence in the protective properties of his lightning rod was such that he persuaded several of his friends to allow him to erect sim- ilar rods on their houses in order that he might have a better opportunity to observe their effects. After many months of pa- tient waiting his confidence in his new device was found to be justified. During a severe thunderstorm several persons plainly saw lightning strike a rod on the house of a Mr. West. The flash was carried off without damage to the building, and the only ob- servable evidences of its passage were a slight melting of the- rod at its point and a disturbance of the earth about the place where it entered the ground, which was afterwards found to be very dry. When Franklin felt that the usefulness of his invention had been fully established by experiment and observation, he began at once to devote a great deal of his time to advocating the use of light- ning rods as a means of protecting buildings against lightning. In this he was ably assisted by many friends both in America and Europe, but the progress made was far from satisfactory. In America rods were often erected in a haphazard manner by un- skilled persons, and many grievous calamities resulted. Certain individuals, whose counterparts have always been associated with the lightning-rod business, went traveling about the country sell- ing rods and soon made themselves notorious as "lightning-rod men;" their fraudulent operations causing much prejudice against lightning rods to arise among people who would otherwise have been kindly disposed toward the new device. In England light- ning rods were looked upon coldly by the Royal Society, although Peter Collison and Dr. Mitchel worked hard to secure the Society's recognition of their worth. On account of this attitude of the 6 Technologic Papers of the Bureau of Standards Royal Society very little general notice was taken of the invention of the Philadelphia printer. This indifference was changed later into strong opposition on the part of many influential English people. In France the inventor and his invention were very cor- dially received in many quarters. This kindly feeling, however, was more than offset by the opposition encountered among the representatives of religious orders of all kinds, in Europe as well as in America, many of whom regarded Franklin as an infidel in the act of proposing to interfere with the operations of what they imagined to be a Divine instrument for the punishment of sinners. Because of this religious prejudice a great many years passed before lightning rods were used to any extent for the protection of church buildings, although during the same time the ringing of bells was recommended by certain of the clergy as efficacious in dispelling thunderstorms and warding off lightning strokes. In many instances progressive persons erected lightning rods only to have them torn down later by an angry populace which imagined them responsible for crop failures, earthquakes, and other evidences of what seemed to them to be Divine displeasure. In line with this attitude of the general public toward lightning rods, it is reported that on a certain occasion an Englishman, who was residing in St. Omer, France, erected a lightning rod over his house. When this fact became generally known a great public disturbance arose and the rod was torn down and carried away. The Englishman took his case before the courts, and after pro- tracted pleadings the French tribunals decided that, inasmuch as there was nothing in the statutes which prohibited the attachment of metal rods to buildings, such rods might be attached, provided that certain precautions were observed in so doing. The lawyer who conducted the case for the plaintiff was Robespierre, then a very young man, and at that time unknown to fame. 1 The first recognition of the worth of lightning rods by any Government of Europe, or, indeed, of the world, was given when the Senate of Venice, on May 9, 1778, ordered the erection of lightning rods throughout the Republic. A complete history of the lightning rod would illustrate in a striking manner the gradual vanishing, during the last century, 1 Richard Anderson, Lightning Conductors, p. 35. Protection Against Lightning 7 of the superstitions formerly held by civilized people regarding the phenomena of nature. 2. PRESENT STATUS OF THE PRACTICE OF PROTECTION AGAINST LIGHTNING After more than 160 years of use, in which the usefulness of the lightning rod has been demonstrated in a very practical manner, there is at present hardly any electrical device about which there is a greater diversity of opinions or in the application of which a greater number of diametrically opposite methods are used to accomplish the same results. As an example of this diversity of opinions, it may be stated that in some localities in the United States the impression is prevalent that the presence of a lightning rod is a menace to property, whereas in others lightning rods are generally believed to be a great protection.