Aside from the objections listed above, blasting probably will not be 
feasible in the subbottom installation excavation because toxic fumes are 
produced, to say nothing of excessive dust. This is usually counteracted by 
ventilating with large amounts of fresh air, which will not be available in the 
subbottom excavation site. If drilling and blasting prove to be the only means 
feasible, development of fume-removal techniques and systems will have to 
precede construction of the first installation. 
Since almost any method of excavation developed will undoubtedly 
produce some fine particulate matter, environmental control (that is, control 
over the quality of air in the excavation) may be required and may prove 
critical in the selection of a disintegration method. While environmental con- 
trol may prove difficult, it should be accomplished with known techniques 
or those under development. Environmental control is a major aspect of the 
research recommended by the NAS study (Hartman, Jacobs, and Williamson, 
1968). 
In conclusion, a note on spoil removal. It is planned to remove spoil 
from the vertical shaft by pumping a slurry of fragments and seawater. Various 
methods have been suggested for excavation in a normal atmosphere and ejecting 
the spoil through water-tight pass-throughs (Figure 61). Unless a second pene- 
tration from the sea bottom is made and connected via lateral passageways, it 
will be necessary to incorporate the spoil removal lock system in the same 
pressure head as is used for ingress—egress from a submersible. 
Improvement in Methods of Rock Fragmentation 
From the earlier discussions in this chapter and under ‘’Spoil Removal,”’ 
it is clear that while it may be practicable to use conventional large-diameter 
boring techniques for drilling into the hard rock bottom of the ocean, it will 
be costly. This is so because available machines are very heavy and complex; 
generally the spoil is removed in large pieces which do not lend themselves to 
slurry pumping. Thrust forces against the work face are very high, as are the 
torque requirements for rotating the cutting assembly against the work face. 
The machines are generally long in the dimension of their rotational axis, and 
guidance is difficult until the penetration of at least one machine’s length is 
made. 
Rock fragmentation (comminution) techniques which will perform 
in a less massive machine would presumably eliminate many of the expensive 
development problems in adapting the established borers to the deep-ocean 
floor. 
77 
