378 BELL SYSTEM TECHNICAL JOURNAL 



less important than the thoroughness with which it is distributed 

 throughout the non-durable sapwood of the poles. 



The overall summary in Table I for the 2393 poles in line 10 years 

 or less shows average values for penetration in sound poles and in poles 

 with internal sapwood decay. The summary suggests the existence 

 of the very important relationship between penetration and decay 

 that is definitely shown in detail in Fig. 3. All of the internally de- 

 caying poles shown in this figure had penetration less than 2.3 inches 

 and 70 per cent of the sapwood thickness. Furthermore, all except 

 six of these decaying poles and all except one of the poles that failed 

 had penetration less than 1.8 inches and 60 per cent of the sapwood 

 thickness. The group defined by the latter figures may be considered 

 as the "risk group," i.e., poles which by reason of poor penetration 

 may become infected with wood-destroying fungi within 10 years. 

 The 286 poles in this group in Fig. 3 were 11.9 per cent of the 2393 

 inspected poles that had been in line 10 years or less. The poles 

 making up this 11.9 per cent were possible early failures, but the in- 

 spection revealed that only 63 of them, or 22.2 per cent, had actually 

 begun to decay. Of these 63 poles with internal sapwood decay only 

 35, or 55.5 per cent, failed in service. The distinction between in- 

 fection and failure is important. In terms of the whole 2393 poles 

 2.6 per cent were infected with internal decay and only 1.4 per cent 

 failed. 



The external decay at the ground line indicated in Figs. 3, 4, and 5 

 apparently did not exceed one half inch in depth. It was typical of 

 the superficial rot usually found after the ground line of a pole has been 

 raised following a few years of service. During these years the creosote 

 in the exposed outer layers of the wood is depleted, and the favorable 

 moisture conditions at the new ground line facilitate fungous infection 

 of the poorly protected wood. 



Another group of poles somewhat above the risk poles in quality 

 may be defined as having penetration more than 1.8 inches and 60 

 per cent but less than 2.5 inches and 85 per cent of the sapwood 

 thickness. Some of these poles are subject to infection prior to the 

 fifteenth year. The data in Figs. 3, 4, and 5 show that decay developed 

 in 11, or 2.98 per cent, of the poles in this group, and that only 1, or 

 0.27 per cent, failed in service. 



The data in Figs. 6 and 7 and in Table II, show in a striking way 

 the stability of the line when the per cent of poles having penetration 

 greater than 2.5 inches or 85 per cent of the sapwood thickness is 

 relatively large. Not a single pole in this group in the sample from the 

 19-year old line (Fig. 6) showed any indication of internal sapwood 



