SAFES AGAINST FIRE.
Perhaps there is a greater demand for fire-resisting than for
thief-resisting safes, and certainly it is in the former character that
they are most often put to the test. The consideration, therefore, of
what is the best form of construction to cope with fire is most
important; while it is also a much simpler matter than when strength
against thieves is required.
In fire we have an element whose character is known, and which cannot
attack us in some new way for which we are not fully prepared. All that
it can do to a safe is to exercise upon it a certain heat, the intensity
of which may be pretty nearly determined, and which cannot in actual
practice last beyond a certain time. Probably heat that will melt iron
in a large mass is seldom produced in the burning of an ordinary
dwelling-house; but in a warehouse with inflammable contents such fierce
heat often exists, so that a safe should be proof against it for two or
three hours. Unless a safe were very bulky it could not well preserve
its contents without any damage for a much longer time; and indeed it is
not necessary, for no safe is very likely to be exposed to an intense
all-round fire longer than three hours; by that time it will either have
fallen into rubbish, or the _débris_ from above will have covered it in,
and protected it from immediate contact with the fire. It will be seen
from this that it is advisable not to build a safe partially into a
wall or recess; the chances being that it will be kept in its place long
enough to have the full force of the fire expended upon its exposed
portion, and then fall a greater distance and upon harder material than
if it had fallen when the wooden floor first gave way.
The first quality that a fire-resisting safe should possess is strength
in its construction sufficient to prevent its being damaged by a heavy
fall, or sustaining injury through the plates warping from heat. This
cannot be obtained unless the outer plates are at least a quarter of an
inch thick (or upwards, in big safes), strongly joined at all the edges
by stout angle-irons well rivetted to them. Other and more expensive
methods are used to join the edges, and are doubtless better than the
foregoing; but this is at once a cheap, effectual, and most generally
used method.
Secondly, it is essential to make the safe as nearly airtight as
possible, to do which it is only necessary that the door should fit very
closely at its edges, and that its inside face touches at every possible
point the interior of the safe.
The third thing to be considered is the fire-proofing--the most
important feature of the safe. Almost everything that one can think of
has been either proposed or used for proofing--water, wood, paper,
plaster-of-Paris, chemicals of all sorts, and many other things besides.
But of all these what may be termed a combination of water and wood, in
the forms of alum and sawdust, has been most extensively used.
There are two walls of wrought iron in the safe, and the intervening
space has to be filled with a fire-resisting material, which may be
either of a refractory nature, such as fire-clay, sand, or any other
practically infusible slow conductor of heat; or it may be an absorbent
substance containing chemicals that will evolve moisture when heated.
The former of these two methods is now seldom used except by makers of
cheap common safes, who sometimes use clay, ashes, or mould. The
evaporating system is generally adopted, and as a rule the absorbent
material is common sawdust, with which is mixed ordinary alum, the water
of crystallisation in the alum being gradually parted with under the
continued heat generated by fire. Mahogany sawdust is preferred, as
being less combustible than that of white woods.
At one time tubes of glass or fusible metal containing alkaline
solutions were imbedded in the sawdust and were supposed to burst or
fuse at a given temperature, but it was found that the glass
accidentally broke or the fusible metal became corroded, and allowed the
liquids to escape, thus damping the contents of the safe. But the
mixture of alum with sawdust is open to two objections. Owing to the
hygroscopic nature of sawdust the alum is liable to decomposition,
thereby producing a certain moisture in the safe; and, secondly, there
is of course a limit to the production of moisture from the alum when
under the action of fire, after which the sawdust will become gradually
dry, and although it may not actually ignite, it will become charred,
and even red hot, under sufficiently continued heat. It is but fair,
however, to say, as I have previously suggested, that such instances of
continued heat are but rarely probable; yet, for the before-mentioned
reasons, I prefer and use an _incombustible_ material, very light and
absorbent, and which does not possess the bad qualities of sawdust, but
which is more expensive. Supposing the alum to become exhausted, there
still remains the protection of a substance which is both infusible and
a bad conductor of heat.
Of course the actual amount of resistance to fire depends largely on the
capacity of the proofing chambers. When advisable the thickness of
these may be increased to any extent desired, or the safe may have
several chambers, all containing proofing, or intermediate ones left as
air-chambers only.
To sum up the qualities which are requisite to make a safe proof against
an ordinary fire, it must, first, be made entirely of wrought iron;
secondly, the outer plates must be at least a quarter of an inch thick;
thirdly, there should be a space of three to four inches all round it of
an evaporating non-conducting composition. With such a safe as this,
properly put together, the general run of fires may be defied; but there
are cases where extra precaution should be taken, and the safe kept in a
brick, stone, or iron strong-room. No safe inside a strong-room has, to
my knowledge, ever been destroyed; but many--always light ones--in
warehouses or offices have had their contents burnt.
And here I would caution those not acquainted with the subject to put
little faith in the tests, either public or private, that are sometimes
made, unless they are conducted by persons quite disinterested. When it
is done in this way of course the result is one that may, if certain
conditions are fulfilled, be valuable; but so frequently are these
‘tests’ arranged, either by making a safe specially for a trial, by
carefully packing its contents, or by constructing the fire in a
particular mode, to turn out such wonderful successes, that it will be
well not to rely upon anything but actual experience gained from the
result of safes which have been known to be subject to an ordeal in the
ordinary course of things. Plenty of such instances can be investigated,
but it will obviously be unadvisable to give here the numerous results
that have from time to time been chronicled by the daily papers and
other publications.
It should be borne in mind that certain things are less liable to
injury from heat than others; and therefore it is that books will
sometimes sustain no injury, whilst loose papers in the same safe may be
more or less damaged. For this reason it is advisable that all
parchments and papers be kept in a drawer or cupboard of a safe, as the
second enclosure (though with no more fire-proofing round it) gives a
slight extra security.
Another caution I would give is that, after being in one fire, a safe
should not be relied on to resist fire again until it has been examined
and re-proofed by the maker or a thoroughly competent person. The
resisting properties are certain to be damaged, if not destroyed
altogether; and although I know of safes still in use that have not been
renovated since preserving their contents, I would not place any faith
at all in their power to prove again successful.
The destruction of the Pantechnicon has presented an opportunity of
fairly ascertaining the effect of great heat upon various safes, and,
strange as it may seem, scarcely one of the many safes survived the
conflagration without injury. One French safe had nothing but its four
sides left intact, its front, back, and inside having disappeared as if
driven out by a cannon-ball. The cast-iron safes, of which there were
several, proved, as might be expected, utterly useless, being found when
pulled out of the ruins twisted into all sorts of shapes, or cracked and
broken like glass. Other safes, by makers whose reputation can hardly be
affected by damage done in such an unprecedented fire, had their
contents very seriously injured; and only a few safes came out of the
trial in at all a satisfactory state.
Speaking of French safes, I may here say that, as a rule, they and most
of the Continental safes cannot be trusted in English fires, nor against
the more advanced skill prevailing among our English thieves. Without
offence their character may be summed up as being really
‘French’--pretty in outward appearance (which is more than can be said
for our safes), with peculiar locks requiring no keys, and certain other
un-English things about them; they are quite unsuitable for our market,
and _vice versâ_ our British safes find little sale in France.
Safes and other receptacles to contain gunpowder and preserve it from
explosion have recently been talked about; and there is no doubt that
one result of such a calamity as the late Regent’s Canal explosion will
be to expedite legislation on the subject of the transit and storage of
gunpowder and other explosives. It may appear curious that gunpowder can
be preserved from damage by fire with much greater ease than such a
substance as parchment, but the former can only be destroyed by being in
contact with actual fire, or becoming subject to a most intense heat
(about 560 degrees); while a moderate heat or exposure to steam, such as
is necessarily generated by the fire-proofing of a safe, often
irretrievably damages parchment. A well-made safe, on the principle of
evaporation already described, may be relied on to preserve gunpowder
from considerable heat, but to avoid the possibility of flame or sparks
entering the space round the door, a second safe of lighter make may be
placed inside the ordinary one. Major Majendie, in a recent report to
the Government on this subject, suggests that there should be public
trials by the various makers, of safes, such as they severally think
most suitable for this special purpose. It remains to be seen if this
advice will be followed, and if so, upon what principle the trials will
be conducted, and whether the safes or chests so tested will be
precisely the same as the makers intend to retail, or are made specially
for the occasion. It is extremely doubtful if the Government would be
acting wisely in affording facilities at the public expense for private
firms to experiment with safes the merits of which are pretty well
known; but should the trials take place, no doubt the results will, in
some instances, be of a nature to astonish those not practically
familiar with the action of fire in such cases.