The Londonderry sifter. (South Londonderry, Vt.) 1883-19??, 1895-05-10
m TIE CAlSSoN.
What Is the Greatest Air Pressure That
Mao Can Stanl9

What Is the Greatest Air Pressure That
Man Can Stand?
seSessrs. Sooysmith & Co, Of New
York, the woll known contracting engt
neers who for years have made a special
ty of difficult foundations and tunnel,
ing requiring the uso of compressed air,
tell MS that the full ability of properly
equipped and properly behaved men,
under the most favorable condition, to
resist caissol disease has never been
tested. The highest working pressures
recorded have boen close to 90 pounds
per square inch, but with extreme care
in the selection of men and correspond
ing care on the part of the tnen it is
very prohkNlo that this limit may BIO
considerably exceeded. For the average
pressure man under average conditions
the top limit may DO placed at about
40 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 tho men, Messrs.
Sooysmith 81 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 40 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 If
the material be so porous as to admit a
considerable leakage of air through it,
there will naturally result 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, system of venti-
lation is kept up by the porous material.
On the other hand, if the caisson is
passing through an impervious sub
stance, snch 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 tho 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 organically
and who are not feshy can endure much
| higher pressures than men who have
not these physical conditions Moreover,
the degree to which pressure men OBJ
serve hygienic rules, preserve regularity
of conduct and abstain from dissipation
affects largely their capacity to endure
tho effects of compressed air. The extent
also to which pressure men adhere tt
the rules for entering pressure, for con
duct whilo at work, for exit to the or
binary atmosphere and for behavior i'm
mediately after coming out influence
their physical sensitiveness to these eff
feots. CASTER Magazine.