The Idaho Springs siftings-news., 1919-11-14
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termine the distances which the shock
resulting from the discharge of various explosives
could be heard. A brief investigation of the
factors influencing the transfer of energy from a
mining tool to the clay coal were also made In
order that recommendations could be made to
the type of mining machine which could be used
TO accomplish the most work with the least noise.
In this connection it found that sounds
were transmitted only about half far in clay
as In shae strata and about one-quarter as far in
clay as in coal. To give some idea of the sensi-
tiveness of the instrument it may be said that
pounding with pick the bituminous coal can
be detected for distance of 900 feet, and the
direction determined. and that pounding with
sledge can be heard far 1,150 feet. These
measurements were made in the Pittsburgh coal
seam in the vicinity Of Pittsburgh where the coal
Is somewhat harder than In most other btuminous
coal beds. The explosion Of n one-ounce charge
of dynamite was detected distance of 1900
feet through the shale strata.
Sound Tells the Implement
One interesting feature of the instrument is
that the sound transmitted to the ear is charac-
teristic of the implement producing the sound To
Illustrate: Twelve mining and carpenterng
operations carried out the coal rib An
engineer of the bureau of mines who had never
used the geophone and who did not know what
tools were to be operated able to recognize
and name nine of the implements at a distance of
several hundred feet through the strata. The
other three sounds were accurately described, but
the tools were not Identified.
Now that the war Is over, the bureau has turned
to the development of the instruments for peace
time For one thing, II is believed that they
will be of great value to mine-rescue crews who
may be entering mines for exploration and to
locate miners who may have been entombed after
disaster. The tests so far made In the vicinity
of Pittsburgh show that pounding on the
coal rib with pick, piece of timber sledge can
be detected and located from a point 600 to 200
feet distant This distance depends greatly on tne
character of coal upon which the man is pounding.
and nrfri inc to hnxo
surprisingly little effect upon the distance the
determination of direction.
Pounding with a sledge be heard from 200
TO 300 feet through the mine cover, depending
upop the auietness of the day outside, since any
wind greatly interferes with the successful opera
tIon Of the instruments. 1t will at once be seen
that when mines are not too deep they can be
"expored" from the surface and it will thus be
possible to find and locate miner who Is pound
ing At the experimental mine in Bruceton, "a,
n man has frequently been located through l4o
foot of cover within 80 feet of the exact point
where he was pounding.
A study is also being made of the distances that
nounding on rails and pipes can be heard Since
rails are generally buried in the earth or dust In
the entries of a mine and since this dust daInpens
the transmission of the sound, the SOUNDS are not
transmitted very well. The same Is true OF pipe
lines However if the pipe lines are not buried.
hrt ,,re laid on blocks and ties. the pounding can
be heard great distances. So far no lines have
heen found long enough to show the limit OF the
,,aonbope 1t is known, however that tne ndkeu
- con oct sounds farther than 1000 feet
Used to Guide Tunnel Work
In metal mines expensive surveys have some
,e n, bn made in order that the approaching
t,nnal headings may be brought together ac-
at ta,v Since direction be determined so
vol, with the geophones, IT is thought that they
90, he used to guide such work II wouic ohls
~, - oc.cs.rv to 20 into each heading and locate
tha direction from which pounding in the other
h,a,linp was coming.
Observations made in metal mine recently
,ad that direction be determined much
snN LIZ, IN rock than in coal This Is prob
III, dne TO the fact that there Is some reveroera-
a, ~ the sound from hammer blow on coal.
uhile on stone the sound is clean cut. 1t so nap
pened that in this mine raise was pene ahsst
- hont six or eight feet distant from smart.
nhservatfons were made in the drift of tine soas.