The united opinion. [volume] (Bradford, Vt.) 1881-1970, 1895-03-22
IN THE CAISSON.
What Lis the Greatest Air Pressure That
Man Can Stand? (.


Man Can Stand?
Messrs. Sooysmith q Co. OF New
York. the we'll known contracting engi-
neers who for years have made special
ty of difficult foundations and tunnel
ing requiring the use of compressed air,
tell us that the full ability of properly
equipped and properly behaved men,
under the most favorable condition, to
resist caisson disease has never been
tested. The highest working pressures
recorded have been close to 80 pounds
per square inch, but with extreme care
in the selection of men and correspond
ing care on the part OF the men it is
very probable that this limit may be
considerably exceeded. For the average
pressure man under average conditions
the top limit may BIO placed at about
As pounds, the time Of working varying
from four to six hours per shift, accord
ing to conditions In the cases where
higher pressures might be used the
shifts for the men should be restricted
TO two of two hours each, separated by
a considerable interval As an example
of heavy pressure work under favorable
conditions as to ventilation without
very bad effects on the men, Messrs.
Sooysmith g. Co. had an experience
with work on which men were engag-
ed in six hour shifts separated into two
parts by half hour intervals for lunch.
This work was exoavating in open,
seamy rock, carried on for several weeks
under about 45 pounds pressure.
The character of the material through
which the caisson is being sunk or upon
which it may be resting at any time
bears quite largely upon the ability of
the men to stand the pressure necessary
to hold back the water at that point Ii
the material be so porous as to admit
considerable leakage of air through it,
there will naturally result a continuous
change of air in the working chamber
and corresponding relief of the men
from the deleterious effects which are
produced nearly always by overused
air. In other words, a system Of ventl-
lation is kept up by the porous material.
On the other hand, if the caisson is
passing through an impervious sub
stance, such as tough clay, ventilation
is much INSTRUCTED, and the consequent
bad effects on the men are very notice.
able AS it is usually necessary to carry
the highest pressure when the caisson
has reached its final position and while
the air chamber is being filled with
concrete and sealed up, the worst results
usually result at these times. Thus very
often at the time when the pressure is
greatest the ventilation is the worst
AS an example, experience has shown
that in one known instance at least dur
ing rock excavation at great depths the
leakage of air through the seams and
crovices of the rock permitted of the men
standing very high pressures. The phys
ical condition of the men is an impor-
tant factor in the whole matter. Men
who are thoroughly sound organioally
and who are not fieshy can endure much
higher pressures than men who have
not these physical conditions Moreover,
the degree to which pressure men OBJ
serve hygienio rules, preserve regularity
OF conduct and abstain from dissipation
affects largely their capacity to endure
the effects of compressed air. The extent
also to which pressure men adhere to
the rules for entering pressure, for con-
duct while at work, for exit to the or
binary atmosphere and for behavior inn
mediately after coming out influence
their physical sensitiveness to these ef-
feots -Cassier' Magazine.