Year: 1872




THERE is an impression among intelli-
gent persons that steam explosions are
often due to mysterious if not unprevcnt-
able causes. An account In weekly
journal of some recent experiments upon
this subject declared that, ''to the aston
ishment of the experimenters," certain
boilers used in the investigation blew up
"under very low pressure OF steam"
The causes of such explosions are, in
deed, not generally known. But to
readers who live in a country where
steam explosions are subject of such
serious importance to the public as they
are with us, brief and concise eXplana-
tiJn of the main causes of these explOs-
ions can hardly fail to be of interest.
Such an account, freed from technical
ties, we propose TO give in the present
paper. Among other forms of explosion,
we shall show how, on the one hand, an
open pan of boiling water may explode
fatally; and how, on the other, boiler
without single drop of water in it may
be shattered TO fragments by the action
of heat alone.


1. The first and simplest cause of boiler
explosions, frequent though ii is, need
not long detain us. 1t is the gradual in
crease of steam pressure-as in the case
of racing steamboats,, with the traditional
riegro sested upon the safety-valve-to a
point beyond the power of the boiler to
resist In wellmade boiler such ex-
plosiOns require an enormous foree-One
that is much greater than that under
which the boiler is designed to work.
Mr.. Fairfairn concluded, from his expert
ments, that one of the low-pressure
boilers which he burst could not have
given way at a pressure of less than three
hundred and fifty pounds to the square
inch. Explosions of this sort are, more
than any other, due to inexeusable care
lessness, if not TO wantonness iii taking
risks, as in the case that we have merl-
TONED.


9. Unequal expansion in the boiler,
caused by low water, or ~ The accumu-
lation of mineral scale or sediment Upon
parts of its inner surface, is fertile cause
OF espiosiou, Under such conditions
there NAV be difference of two hundred
degrees or more Fahrenheit between the
temperature of the fiues and of the boiler
shell and the unequal expansion of the
metal thus caused is enough to rupture
the toughest iron. As already stated,
this may happen without the pressure of
steam TO aid it. Near Grand Rapids,
Michigan, boiler twenty feet long was
opened for The purpose of cleaning the
fiues. The man intrusted with this duty
inserted an armful of shavings id either
end of each of the two fiues, and set them
on fire, hoping to loosen the incrustations
upon them in this manner. But present
", by the expansion of the fiues, the
whole head of the boiler was "blown y
off, and driven through the walls of the
building into the adjoining field. An
American engineer, Mr.. Wizard, claims
to have devised method of keeping
every part of boiler at the same temper
ature, and so avoiding all explosions from
unequal expansion but we must not stop
here TO explain it.


8. Explosions caused by the "repul-
sion of the water" are of special interest
because they form one class of the So
called mysterious explosions. In these
cases no excessive pressure of steam or
heat of fires is apparent the gauges
stand at their usual level; and yet, while
there is no sign of danger, a frightful ex-
plosion may occur, as if some new and
irresistible energy were liberated within
the fated boiler. Such Is, indeed, the
case, though it Is no new explosive COM
pound, generated by the presence OF oil
or other impurities in the water, rs some
engineers have argued, that does the mis-
chief. In these cases, some part OF the
boiler below the water-level has become
heated to a higher degree than the water
above it. The result is, that the water is
repelled from the metal, and thin film
of steam intervenes between the two
bodies. In this condition, which is
known as the "spherodial state" the
iron NAV become intensely hot, while the
water remains comparatively cool. But
now let any cause-as, a strong clrcula-
ton of the water in the boiler, where
it lashes around under the fierce heat
and pressure like n tortured animal
force IL into contact with the red-hot
metal. An immense volume OF steam is
instantly generated; it throws" the water
above il with the energy of bullets before
an exploding charge of powder, and the
force of this tremendous steam hammer is
sufficient to shatter the top of the strong
est boiler in use. These terrible explo-
sions are apt to occur at the moment OF
startinga locomotive or marine engine,
when the escape is shut down and the
pressure is suddenly increased. To pre-
vent them, il is necessary to make sure
that the fires are of uniform heat through
out their whole extent, so as to avoid eX-
cessivc heating in any part of the boiler,
and also to avoid any too sudden increase
(even though il be a slight one) OF the
pressure in the boiler.


t. In the last class of explosions TO be
considered. there is the same sLattering oil
the upper part of the shell of the boiler as
in those that we have just described. But
they are at first sight more mysterious
than those, for in them no evidence can
he found that any part of the boiler has
been at all overheated; and, to make sur
prise still greater, they occur at low
temperature of the water, and a CORE
spondingly low pressure of steam, while
vet they are of the most frightful vlo'
/ lence. ,.--.,