| Cubic feet of free air per minute. | ||
| 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.
[Accidents.]
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.
The only serious blasting accident in the tunnels occurred on January 26th, 1908, and was due to a premature blast, the cause for which could not be ascertained.