Scheduling of Pole Line Inspections

In 1920 only ten per cent of the 14 million poles in line owned wholly or in part by the Bell System were treated full-length with preservatives. Of this ten per cent, most were creosoted southern pine poles. In 1960 about eighty per cent of the 23 million Bell System poles were pressuretreated southern pine poles; the majority of the others were Douglas fir and other western or Rocky Mountain species. Early pressure treatments used creosote; later, pentachlorophenol-petroleum solutions were also in common use. Today a creosote-penta mixture is specified for southern pine. Early untreated poles, notably cedar and chestnut, had a much greater natural resistance to decay than untreated southern pine poles. They had relatively thin layers of sapwood surrounding the highly decay1737 1738 T H E B E L L SYSTEM T E C H N I C A L J O U R N A L , NOVEMBER 1962 resistant heartwood, whereas today's southern pine poles consist largely of sap wood. Untreated southern pine poles might be expected to give less than five years service in the deep South, and but little more in the North. Treatment with preservatives toxic to decay fungi and insects prolongs the lifetime of poles with thick sapwood for many decades. The effectiveness of such treatment is reflected in the average physical lifetime, which is taken to mean the average time from placement until failure due to decay (or insect attack). Physical life is to be contrasted with service life. Service life, which averages about 25 years, is defined as the time from placement until replacement, regardless of whether replacement is for reasons of decay or for obsolescence, line relocation, fire, lightning, collisions, tornados, wind accompanying sleet, etc.