The relation between penetration and decay in creosoted southern pine poles

Poor penetration of the non-durable sapwood is the most important factor in the decay of creosoted southern pine poles. Over 3000 such poles that had been treated with coal tar creosotes of varying types at thirteen creosoting plants in the South have been critically inspected to determine when and where decay started. The poles had been in line from five to twenty-six years under widely diverse climatic conditions in scattered localities east of the Mississippi River. Ninety-five per cent of the failures were poles in which the creosote had penetrated less than 1.8 inches and 60 percent of the sapwood thickness. No failures were found in poles that had been penetrated more than 2.1 inches and 75 per cent of the sapwood thickness. The current Bell System treating specifications require a penetration of 2.5 inches or 85 per cent of the sapwood thickness. The hazard of failure by decay during the ordinary service life of a line is reduced to a practical minimum in poles produced under these specifications.