It is easy to account for explosions of boilers on the hypothesis of
too great pressure; but it is hardly ever very easy--frequently utterly
impossible--to account for the causes which induce that overpressure.
There are, to be sure, a number of reasons which may be advanced. The
engineer may have screwed the scales down too much, and thus, the
safety-valve not operating to let off the surplus steam, a force may be
generated within the boiler of such tremendous power that the strong
iron will be rent and torn like tissue-paper. This I say may occur, but
in my experience I never knew of such a case. Then again, the water may
get so low in the boiler that, on starting the engine and injecting
cold water upon the hot plates, steam will be generated so suddenly as
not to find vent, and in such enormous quantities and of so high a
temperature as to explode the strongest boiler. Again, the water may be
allowed to get low in the boiler, and the plates getting extremely hot,
the motion of the train would generate steam enough by splashing water
against them to cause an explosion. A proper care and due attention to
the gauges would obviate this, and render explosion from these causes
impossible. A piece of weak or defective iron, too, may have been put
into the boiler at the time of its manufacture, and go on apparently
safe for a long time, until at last it gives way under precisely the
same pressure of steam that it has all along held with safety, or it
may be with even less than it has often carried. How the engineer is to
obviate this most fruitful cause of explosions, for the life of me I
cannot see; still if his engine does blow up, everybody and their wives
will believe that it happened entirely through his neglect. A person
who has never seen an explosion, can form no idea of the enormous
power with which the iron is rent. I saw one engine that had exploded,
at a time too when, according to the oaths of three men, it had a
sufficiency of water and only 95 lbs. of steam to the square inch, and
was moving at only an ordinary speed, yet it was blown 65 feet from
the track, and the whole of one side, from the "check joint" back to
the "cab," was torn wide open--the lower portion hanging down to the
ground, folded over like a table-leaf, and the other portion lay clear
over to the other side, while from the rent, the jagged ends of more
than half of the flues projected, twisted into innumerable shapes. The
frame on that side was broken, and the ends stuck out from the side at
right angles with their former position. I saw another, where the whole
boiler front was blown out and the engine tipped clear over backwards
on to the tender and freight car, where the engineer and fireman were
found, crushed into shapeless masses, lying in the midst of the wreck.
The engine Manchester exploded while standing at a station on the H.
R. R. R., and killed two out of five men, who were standing together
beside the tender. Two of those who were left, deposed, on oath, that
not three minutes before the accident occurred, the engineer tried the
water and found fully three gauges, while there was a pressure of only
ninety-five pounds to the square inch, and it was blowing off.
How to account for it no one could tell, so every one who knew any
thing whatever in regard to such things, called it "another of the
mysterious visitations of God." But the newspapers called it an
evidence of gross carelessness on the part of the engineer.
Several explosions have been known where the upper tubes were found
unhurt, while the lower ones were, some of them, found badly burnt. The
conclusion in these cases was that the tubes were too close together,
and the water was driven away from them; consequently the starting
of the engine, or the pumping of cold water into the boiler, was
sufficient to cause an explosion.