The maximum requirements of air at this end were primarily estimated as follows:
Central Shaft, four headings 24 drills. Hackensack, two working faces 20 drills. ---------- Total 44 drills.
44 Slugger drills (25 by 174) require 4,350 2 Steam shovels 1,600 Pumps and machine-shop, say 1,000 4 Hoisting engines, placing concrete 2,000 4 Derricks 2,000 ------ Total 10,950
The theoretical capacity of the whole eight compressors was:
1250 × 8 = 10,000 cu. ft. of free air per min.
It was considered that not more than two-thirds of the above equipment would be working at the same time; the actual requirement, therefore, was taken at about 8,000 cu. ft. of free air per min., thus leaving a margin of one spare compressor.
As actually worked out, there were probably never more than eight drills working at any one time at the Central Shaft, and this work was entirely suspended in June, 1907, before there was any demand for power in connection with the tunnel lining. The heaviest actual requirement, therefore, was approximately as follows:
40 Drills (22 by 174) 3,828 2 Shovels 1,600 Pumps and machine-shop, say 1,000 2 Derricks 1,000 ----- Total 7,428
(_B_) _After November, 1907_ (_after completion of enlargement of Central Shaft headings_): Cubic feet of free air per minute.
32 Drills (17 by 174) 2,958 2 Shovels 1,600 Pumps, etc 1,000 3 Hoisting engines on concrete, each working one-third time 500 2 Derricks 1,000 ----- Total 7,058
The average number of drillers per shift was about 25 at the two main working faces. There were also from 5 to 10 drills trimming and cleaning up for concrete, say an average of 7, making 32 in all.
After November 1st, it actually required three boilers under steam all the time, and not less than seven compressors running at full capacity, to keep the air at proper pressure, the theoretical capacity of the compressors being 8,750 cu. ft. of free air per min., as against 7,000 to 7,400 cu. ft., the theoretical maximum requirement.
Some of this deficiency was due to losses in transmission, part also was due to the fact that the actual was probably considerably below the theoretical capacity of the compressors.
Two accidents occurred to the powder magazines, the causes of which were never absolutely determined. The first occurred on January 10th, 1907, when the dynamite burned up without exploding. The second accident was on March 3d, 1907, when an explosion occurred which damaged property over a very large area, but did not involve any serious injury to persons, only one man being slightly hurt.