Where there is great power, there is great danger.
When the pressure is increased, the danger is increased.
When the pressure is increased, diligence, care and scrutiny should be
increased.
During the twelve years between 1879 and 1891 there were recorded 2,159
boiler explosions; these resulted in the death of 3,123 persons, and in
more or less serious injury to 4,352 others. Besides these there were
innumerable other accidents during the same period, caused by other
means, which emphasizes the gravity of this cautionary “chapter of
accidents.”
Every boiler constructed of riveted plate and carrying a high head of
steam, holds in constant abeyance, through the strength of a disruptive
shell, a force, more destructive in its escaping violence than burning
gunpowder. To the casual observer there is no evidence of this; and it
is only when a rupture takes place of such a character as to liberate
_on the instant the entire contents of the boiler_ that we get a real
demonstration of the fact. Unfortunately a steam boiler never grows
stronger, but deteriorates with every day’s age and labor, subjected,
as it is, to all sorts of weakening influences; and fractures often
occur, which, if not at once repaired, would speedily reduce the
strength of the boiler to the point of explosion.
In the case of a boiler we have, first, a vessel of certain strength,
to resist strains; and second, expansive steam and water contained
therein. It must be plain that if the strength of the vessel is
superior to the internal pressure there can be no explosion, and also,
on the contrary, if we allow the pressure to go above the strength of
the vessel, that there must be a rupturing and an explosion, but it
will be in the weakest place of that vessel.
Experiments by the most eminent men have failed to discover any
mysterious gas formed by boiling water, or by any mixture of air
and water. Boilers have been built for the express purpose of trying
to explode them under various conditions of high and low water,
and nothing in regard to the sudden generation of any gas has been
discovered. Again, disastrous explosions that have occurred have been
of vessels that contained no water, and were not in contact with fire,
flame or heated air, but were supplied by steam some distance away.
The destructive efforts of the vaporization attendant upon explosions
seem to be due to the subsequent expansion of the steam so formed,
rather than to the intensity of its pressure; low or high steam _alone_
has very little to do with boiler explosions; nor high or low water
necessarily.
The one great cause of boiler explosion is the inability of the boiler
to withstand the pressure to which it is subjected at the time, and
this may be brought about by any one of the following causes, viz.:
1. Bad design, in which the boiler may not be properly strengthened
by stays and braces; deficient water space, preventing the proper
circulation of the water.
2. Bad workmanship, caused by the punching and riveting being done by
unskilled workmen.
3. Bad material, blisters, lamination, and the adhesion of sand or
cinders in the rolling of the plate.
4. By excessive pressure, caused by the recklessness of the engineer,
or by defective steam-gauges or inoperative safety-valves.
5. Overheating of the plates, caused by shortness of water. When water
is poured on red-hot surfaces it does not touch the surface, but
remains in the spheroidal state at a little distance from it, being
apparently surrounded by an atmosphere of steam. It assumes this state
above 340°; when the temperature falls to about 288° it touches the
surface and commences boiling.
6. By accumulation of scale, mud, or other deposit, which prevents the
water gaining access to the iron. This causes the seams to leak, the
crown-sheet to bulge or come down.
One is unable to find any proof that boilers do generally explode at
about starting time, nor is that statement, to the best of information,
founded on any basis of fact, but was first affirmed by parties who had
designed a boiler especially arranged to avoid that imaginary danger.
No one supposes that inspection will absolutely prevent all explosions;
but rigid inspection will discover defects that might end in explosion.
Low water is dangerous from the fact that it leaves parts of the boiler
to be overheated and the strength of iron rapidly decreases in such a
case. In fact, an explosion caused by low water might be expected to be
less disastrous than if the water was higher, other conditions being
equal, from the fact of there being less water at a high temperature
ready to flash into steam at the moment of liberation.
Testing new boilers _under steam pressure_ is both dangerous and
unwise—the hot water expansion test is just as efficient, less costly
and safe in every respect—hence, there is no occasion for a steam test.
A manufacturer was testing a boiler in the way mentioned when a rivet
in a brace blew out and the contents of the boiler rushed out, striking
a man in the face, and parboiling him from head to foot. Another who
was inspecting the boiler, was struck on the head and enveloped in
steam and water; another was also scalded from the shoulders down;
another was injured about the arms; a fifth man was scalded and
severely injured about the back. The apartment was so filled with steam
that the victims could not be rescued until all the damage mentioned
had been done to them.
Danger from exploding steam pipes is greater than supposed.
An inspector in a pipe works was testing a tube by means of a
double-action hydraulic pump; the pipe suddenly burst with the
pressure of 5,000 pounds to the square inch, and the water striking the
unfortunate man on his face, he was killed on the spot.
There is a tendency on the part of engineers to trust too implicitly in
their steam gauges. These are usually the only resort for determining
the steam pressure under which the boiler may be working. But the best
gauges are liable to err, and after long use to require a readjustment.
It is fortunate, however, that the error is usually upon the safe side
of indicating more than the actual pressure.
Any boiler that has been standing idle for a few weeks or months is a
dangerous thing to enter, and no one should attempt it until it has
been thoroughly ventilated by taking off all the man hole and hand-hole
plates and throwing water into it. This is due to the presence of a
gas which is generated from the refuse and mud, or scale, which, to a
greater or less degree, remains in all boilers. Contact with fire is
certain to result in an explosion. Not long since a locomotive was in
a roundhouse, where it had been waiting some weeks for repairs. Some
of the tubes were split and a man was pulling them out. He had only
removed one or two when, putting in his lamp to see what remained,
there was a fearful explosion which shook the shop. There are many
other places which are unsafe to enter when they have been long closed,
such as wells, pits of any kind, and tanks. Precisely what the nature
of the gas is no one seems to know, but it is assuredly settled that a
man who goes into it with a light seldom comes out unharmed.
The gas most likely to fill idle boilers in cities is sewer gas, that
gets in through the blow-off pipe, which is left open and generally
connects with the sewer; hence, the connection with the sewer by the
blow-off pipes should receive attention.
Boilers are sometimes unexpectedly emptied of their contents by the
operation of the principle of the syphon; a boiler is so piped that
a column of water may be so formed as to draw out of the boiler its
entire contents. Danger ensues if this is done while the boiler is
being fired.