Year: 1872




gent persons that steam explosions are
often due to mysterious if not unprevcnt-
able causes. An account III IL 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, a brief and concise explana-
tion 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 it 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
negro seated upon the safety-valve--to
point beyond the power of the boiler to
resist In well-made boiler such eX-
plosions require an enormous force-one
that Is much greater than that under
which the boiler is designed to work.
Mr.. Fairbairn 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 ineXcusable care
lessness, if not to wantonness in taking
risks, as in the case that we have men
toned.


2. Unequal expansion in the boiler,
caused by low water, or by the accumu-
lation of mineral scale or sediment upon
parts of its inner surface, is a fertile cause
of explosion. Under such conditions
there may be a difference of two hundred
degrees or more Fahrenheit between the
temperature of the tiues 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





inserted an armful of shavings in either
end of each of the two fues, and set them
on fire, hoping to loosen the incrustations |
upon them in this manner. But present |
ly, by the expansion of the flues, the |
whole head of the boiler was "blown"
of, 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 ut the same temper |
lture, and so avoiding all explosions from
Unequal expansion but we must not stop |
here to explain it.


3. 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
here is no sign of danger, frightful eX-
)losion may occur, as if some new and
irresistible energy were liberated within
,he fated boiler Such is, indeed, the
case, though it is no new explosive COM
pound, generated by the presence of oil
)r other impurities in the water, as some
engineers have argued, that does the mis-
chief. In these cases, some part of the
)oiler below the water-level has become
heated to a higher degree than the water
lbove il. The result is, that the water is
'epelled from the metal, and a thin film
If steam intervenes between the two
lOdies In this condition, which is
Known as the "spherodial state" the
ron may become intensely hot, while the
water remains comparatively cool. But
low let any cause-as, strong circula-
ion of the water in the boiler, where
t lashes around under the fierce heat
md pressure like a tortured animal
orce it into contact with the red-hot
metal. An immense volume of steam is
generated; it throws the water
bove ii with the energy of bullets before
N exploding charge of powder, and the
orce of this tremendous steam hammer Is
utficient to shatter the top of the strong
st boiler in use. These terrible explo-
ions are apt to occur at the moment of
tarting a locomotive or marine engine,
when the escape is shut down and the
PRESSURE is suddenly increased. To pre-
ent them, il is necessary to make sure
hat the fires are of uniform heat through
ut their whole extent, so as to avoid eX-
essive heating in any part of the boiler,
nd also to avoid any too sudden increase
even though it be slight one) of the
ressure in the boiler,


4. In the last class of explosions to be
there is the same shattering of
he upper part of the shell of the boiler as
4 those that we have just described, But
hey are at first sight more mysterious
han those, for in them no evidence can
e found that any part of the boiler has |
cen at all overheated; and, to make sur :
rise still greater, they occur at low (
emperature of the water, and CORE /
low pressure of steam, while !
ct they are of the most frightful vio- :
snce.
AS, under the subject of "nnequal ex- /