ROCKY MOUNTAIN MINE TIMBERS. 



15 



Table 9. — Reported life of untreated round mine timbers in coal mines (mostly 5 to 7 



inches diameter). 



Conditions in mine. 



Average 



Poor ventilation. 

 Good ventilation . 

 Exceptional 



Doug- 

 las fir. 



Years. 



5 



2 



10 



25 



Pine.i 



Years. 

 4 

 1 



Engel- 

 mann 

 spruce. 



Years. 

 4 



1 



Alpine 

 fir. 



Years. 

 3 



Pifion. 



Years. 

 4 

 1 

 6 



1 Includes lodgepole pine and western yellow pine. 



Table 10. — Reported life of untreated round mine timbers in metal mines (mostly 8 to 10 



inches diameter). 



Conditions in mine. 



Douglas 

 fir. 



Western 

 yellow pine 



Lodgepole 

 pine. 



Engelmann 

 spruce. 



Average 



Very poor ventilation . 

 Constantly wet 



Years. 

 9 

 2 to 5 



20 to 40 



Years. 



lto 3 

 15 to 25 



Years. 

 7 

 lto 2 



Years. 



lto 2 

 15 to 20 



The conditions under which the estimates were made vary so much 

 that the relative life of the different species is probably not reliable. 

 For example, several operators reported that under the same condi- 

 tions Douglas fir outlasts lodgepole pine or spruce two to three times; 

 yet the average values show comparatively little variation among the 

 species. 



The factors that cause variation in the life of the timbers are prin- 

 cipally ventilation, moisture, acid mine water, and the condition 

 of the timbers when placed. The influence of fresh and compara- 

 tively dry air was clearly indicated in several mines which reported 

 a life fully four times as long for the timbers in the intake shaft as 

 for those in the return shaft (8 and 2 years, respectively). Several 

 operators reported that they had increased the life of their timbers 

 from two to three times by peeling and seasoning them before place- 

 ment. Certain mines reported that their timbers were sound after 

 standing from 25 to 35 years under conditions where they were nearly 

 always wet, and in one or two cases the water was stated to contain 

 "sulphuric acid" or "copper and arsenic," which probably acted as 

 an antiseptic. Both constantly wet and constantly dry conditions 

 appear, from the replies, to be favorable to a long life, while damp- 

 ness, due to stagnant air, or alternating dryness and wetness, appears 

 to furnish the best conditions for the growth of wood-destroying fungi. 



PRESERVATIVE TREATMENT. 



Preservative treatment to prevent decay was not regularly prac- 

 ticed at any of the mines reporting. Sixteen operators referred to 

 some use of preservatives, though none had had a long enough expe- 

 rience to furnish data on the increased life from such treatment. The 

 methods spoken of were dipping in creosote or crude oil, and brush 



