FIREPROOF BUILDINGS.
I. _General Construction._
When such buildings as the City Flour Mills and the Pantechnicon--types
of many other and similar structures in London and the provinces--are
burnt out, in spite of their supposed fireproof qualities, it becomes a
question of lasting importance as to what is the cause of failure, and
whether any so-called fireproof buildings are really so or not. The
panic caused in many minds by the newspaper reports of such disasters
lasts but a short time, and the true lessons are seldom learnt. With the
object, therefore, of endeavouring to place certain facts and
suggestions on permanent record, I have collected from many sources
various particulars connected with this subject--so intimately connected
with the manufacture of fire-proof receptacles.
Much that has been written on fireproof construction is of little value,
because the practical bearings of the subject have been lost sight of,
and theories of construction are broached that may be good in themselves
but cannot be brought into use, because of expense and other
inconveniences.
I remember, for instance, some gentleman recommended that every room of
a building should have floor, walls, and roof lined with galvanised
tanks of water, connected by an elaborate system of pipes and so
on--not at all a bad idea, but utterly impracticable for business
purposes. Another suggestion was that there must be no windows in a
building, as through them a draught passes to increase fire.
But in these instances, as in many others, the main fact is forgotten,
viz., that what is wanted is the best possible mode of making a
fireproof structure that is also adapted for ordinary business purposes.
This is what I take to be the point. Cases where exceptional security
from fire is needed seldom occur and are more easily met. Dealing,
therefore, with an ordinary warehouse, which is to be a fireproof
building, it should be remembered that its fire-resisting qualities are
determined not only by the materials of the actual structure, but also
by its interior fittings, and, above all, by the goods stored or
manufacture carried on in the place. A house of brick only obviously
will not burn, but fill it with cloth or cotton goods, and the house as
well as the goods may be destroyed. No hard-and-fast line can,
therefore, be laid down, for every case may be different. I will
endeavour to notice the _risks_ of buildings commonly erected and the
remedies for each--a combination of which remedies will make a good
fire-resisting structure. Among the numerous books and papers on fires
to which I have been able to refer I have found no information so clear,
precise, and practical as that to be had from the late Mr.
Braidwood’s[3] paper, read before the Society of Arts in 1856, and the
excellent book entitled ‘Fire Surveys,’ by Captain Shaw, the present
Chief of the Metropolitan Fire Brigade. Mr. Braidwood laid down certain
rules, which have never been improved upon; while both he and Capt. Shaw
express views so alike, and with the confidence of men who have gained
their experience from actual results, that it seems better to be guided
by them than by all other writers put together. Not that I would
disparage these latter, for it is well known that there are architects
and others who have contributed much to the solution of the mystery
which was so long attached to fireproof building. Mr. Braidwood gives a
comparison to demonstrate that what would be safe construction for one
building would not be for another. He says: ‘Supposing an average-sized
dwelling-house, 20×40×50=40,000 cubic feet, built with brick partitions,
stone or slate stairs, wrought-iron joists filled in with concrete, and
the whole well plastered. Such a house will be practically fireproof,
because there is no probability that the flooring in any one room would
make fire enough to communicate to another. But suppose a warehouse
equal to twenty such houses, with floors completely open, supported by
cast-iron pillars, and each floor communicating with the others by open
staircases and wells; suppose farther that it is half-filled with
combustible goods, and perhaps the walls and ceilings lined with wood.
Now, if a fire takes place below, the moment it bursts through the upper
windows or skylights the whole place becomes an immense blast-furnace;
the iron is melted, and in a comparatively short time the building is in
ruins; and, it may be, the half of the neighbourhood destroyed.’
Such a warehouse, as here described, is the type of many now in
existence, and yet people wonder how they can burn. The wonder is rather
why so few are burnt; and one explanation is, that the majority are
scarcely used when gas and lamps are required, the hours when the
workpeople and clerks are about having been so much restricted that for
at least a great part of the year the work does not extend beyond
daylight. When a fire has once got hold of a warehouse, unless it is
built in compartments, the firemen can do nothing but prevent its
spreading to adjoining erections; and, as this cannot always be done
successfully, a badly-built warehouse is likely to bring disaster upon
its neighbours.
But a building may be built to give security; and Mr. Braidwood’s
opinion was ‘that the real fireproof construction for such buildings is
brick arches, supported on brick pillars only.’ This mode of building,
however, involves so much expense, and occupies so much space, that it
cannot be used with advantage. The next best plan is to build warehouses
in compartments of moderate size, divided by party walls and double
wrought-iron doors, so that if one of these compartments takes fire
there may be a reasonable prospect of confining the fire to that
compartment only.
Cast-iron is largely used in building because of its cheapness; but it
is exceedingly dangerous, for it gives way from so many different causes
that it is impossible to calculate _when_ it will give way. The castings
may have flaws in them, or they may be too weak for the weight they may
have to support, being sometimes within ten per cent. or less of the
breaking weight. The expansion of girders may thrust out the side-walls.
For instance, in a warehouse 120 ft. × 75 × 80 ft. there are three
contiguous rows of girders on each floor, with butt-joints; the
expansion in this case may be 12 inches. The tie-rods to take the strain
of the flat arches must expand and become useless, and the whole of the
lateral strain be thrown on the girders and side-walls, perhaps weak
enough already. Again, throwing cold water on the heated iron may cause
an immediate fracture. For these and similar reasons the firemen are not
permitted to go into warehouses supported by iron _when once fairly on
fire_. The effect of fire on cast-iron, as stated by the late Sir
William Fairbairn, F.R.S., of Manchester (Seventh Report of the British
Association, vol. vi. p. 409), is, that the loss of strength in
cold-blast cast-iron, in a variation of temperature from 26° to 190° =
164° Fahr., is 10 per cent., and in hot-blast at the variation of from
21° to 169° Fahr. is 15 per cent. Now, if the loss of strength advances
in anything like this ratio the iron will be totally useless as a
support long before the fusing-point is attained. Respecting the
strength of cast-iron columns here alluded to, I may state that Capt.
Shaw says: ‘At a temperature of 212° Fahr., or the boiling-point of
water, cast-iron loses 15 per cent. of its strength. At the temperature
of molten lead, 612° Fahr., it has probably no strength at all; and at
the temperature 2,787° Fahr., which is probably much below that of the
centre of a large building, it becomes liquid.’ A very clear proof of
the inability of cast-iron to resist the effects of fire was given at
the destruction of a chapel in the Liverpool Road, Islington, on Oct. 2,
1848. The chapel was 70 feet in length and 52 feet in breadth, and was
completely burned down by a fire which commenced in a cellar. After the
fire it was ascertained that of thirteen cast-iron pillars, used to
support the galleries, only two remained perfect; the greater part of
the others were broken into small pieces, the metal appearing to have
lost all power of cohesion, and some parts were melted. It should be
observed that these pillars were of ample strength to support the
galleries when filled by the congregation, but when the fire reached a
certain point the pillars crumbled under the weight of the timber only,
lightened as it must have been by the progress of the fire. In spite of
such a case as this, which is but an example of what has often happened
to other buildings, cast-iron continues to be used not only for ordinary
purposes but actually for so-called fireproof buildings. It may safely
be asserted that _no place in which there are unprotected iron-supports
can possibly be fireproof_; and if this test is applied to many
erections thought to be secure, it will soon be seen how few there are
that can be relied upon to withstand excessive heat.
The reckless mode of running up houses, as speculative builders appear
to delight in doing, and supporting the front on light columns, is a
most dangerous proceeding. Capt. Shaw has cited a case of a corner
building lately put up, 90 ft. long and 70 to 80 ft. high, supported
entirely on iron columns, without any wall, wood, or brickwork. There is
no doubt that at the ordinary fire temperature of 600° to 700° Fahr. the
whole building must inevitably fall down, and such a heat could easily
be created by the combustion of a very small quantity of household
furniture. The fashion of having all the available space for large
shop-fronts gives rise to this dangerous work. Most of the elaborate
shops and offices lately built in London depend entirely upon iron
supports; and some day, when a fearful accident is the result, the
public will appreciate the danger.
In the early part of this year large corner premises were built not far
from the Elephant and Castle, in the South of London, and I watched
their erection with some interest. The house of four storeys was run up
(a better term than built) in a month. The corner angle is supported by
two thin iron columns, and between these and the other ends of the
building are two wooden posts, but the weight chiefly rests upon the
iron columns, which are most certainly unable to sustain the tons of
brickwork above it in case of severe fire. As long as architects and
builders and their employers give up security for the sake of economy
and space, this sort of work will continue to be put up, unless
interfered with by a new Building Act.
What ought, then, to be used for supports? If the brick columns are
inadmissible, then, strange to say, wood posts are the best, or an iron
support, well protected by brickwork, cement, or plaster. The fact is,
though iron is incombustible, it is itself not fireproof; and, on the
other hand, though wood is combustible, it may be used in such a manner
as to resist fire for a great length of time. Capt. Shaw’s recent
experiments with a wooden post had such an extraordinary result that,
with his permission, I append the particulars, from a letter of his
inserted in ‘The Times’:--
‘A few months since a fire occurred in one of the enormous warehouses
for which the docks in this metropolis are remarkable, and raged with
great fury from a little before six in the morning till about eleven in
the forenoon, when it was extinguished, and a very large proportion of
the building and its contents saved. The warehouse was constructed of
brick walls; it had wooden floors, supported on wooden beams, which, in
their turn, were carried on wooden storey-posts about twelve inches
thick; and although serious damage was done, not one portion of the
heavy woodwork was destroyed. After the fire I was allowed to remove one
of the storey-posts, with a section of the beams, and other parts
surrounding it above and below. This post had been subjected to the full
action of the fire during the whole of its duration, as already
mentioned; or, making full allowance for everything, including the delay
of the fire attacking the particular spot on which it stood, and the
time at which the cooling process commenced, certainly not less than 4½
hours.
‘As we had used large quantities of water, and it was probable that the
wood might have been somewhat saturated, I had it carefully dried for
several days before a strong fire until not a trace of moisture remained
in it.
‘I then set it on end in an open yard exactly as it had stood in the
warehouse, with the pedestal underneath, the cap above, and the beam
across the cap; placed more than a ton of shavings, light wood and heavy
wood, round it, and after saturating the whole heap with petroleum
applied a light to it. After this I kept men pumping petroleum on it
until my stock was exhausted. At the end of 2½ hours I withdrew the
post, beam, and other parts from the fire, and within a few minutes from
the time they were withdrawn they ceased to burn.
‘I then sawed off, horizontally, a few feet of that part which had
suffered most from the flames, and afterwards split the same piece
longitudinally with steel wedges, in order to examine its condition.
‘The post was of pitch-pine, about the most inflammable wood I know, and
yet after exposure to fire for seven hours, the fury of which could not
be exceeded except in blast-furnaces, it contained, and still contains
within it, a quantity of uninjured and apparently fresh wood, probably
capable at this moment of supporting the whole weight which the original
post may have been designed to carry.
‘Immediately after the saw-cut, and again after the cleaving with steel
wedges, I carefully examined the centre, and found it just perceptibly
warm to the touch, but nothing more, thus proving that the fibre, in
which the strength lies, must have been quite uninjured.
‘The lessons to be drawn from this I take to be as follows: A massive
storey-post of even the most inflammable wood is absolutely and
perfectly proof against any heat that can be applied to it--will not of
itself burn at all, but requires a continual supply of highly
inflammable substance to keep it burning, and when the supply is
withdrawn ceases to burn; and lastly, after being exposed to flames for
seven hours of very great intensity, is not injured to a greater depth
than about two inches from the original outer surface, and still shows
a centre as clean and fresh as when it was first put in.
‘There may be other materials suitable for this purpose which are
capable of resisting the effects of heat, and, if so, I hope we may one
day hear of them; but, in the meanwhile, I venture to submit what I
consider to be strong practical testimony in favour of massive timber
for the internal supports of heavily-loaded buildings. Oak or elm is the
best wood to use, and will defy destruction for hours.’
Messrs. Dennett, whose name is better known in connection with the
Dennett Arch, have introduced a new mode of covering up iron columns in
such a manner that they stand through intense heat, and have the
advantage of being small in bulk. The accompanying engraving will make
the following explanation clear.
Strips of corrugated hoop-iron are fastened at intervals by wire close
to the iron column, and all is then encased with concrete 3½ inches in
thickness, made as described on page 86. An experiment was tried at
Nottingham with one of these columns placed in a fire of wood and
shavings saturated with gas-tar, and allowed to burn with a fierce heat
for a space of 4½ hours. When half the time had elapsed the column was
thrown over, so as to lie horizontally in the fire, and have its whole
length exposed to the flames. The fire was at length extinguished by
water being thrown on, in order to make the test still more severe, but
on examination the concrete casing had not cracked or broken in any
part, while the column underneath, as soon as a portion of its covering
could be removed, was cool enough to be handled with impunity. It will
be interesting to note the development of this invention; for in the
event of farther tests in actual practice being as satisfactory as that
already named, it is likely to come into very prominent use.
The careless way in which chimneys are built is the cause of frequent
danger. By communicating with each other in the same gable, fire will
often spread and wrap the whole house in flames. One of the principal
streets in Edinburgh had scarcely a chimney-head that was not in this
condition. The ends of joists or pieces of timber are sometimes allowed
to protrude into chimneys, and then it is generally by accident if the
building does _not_ catch fire.
[Illustration: HORIZONTAL SECTION OF COLUMN A.]
[Illustration: PART ELEVATION OF COLUMN A.]
Buildings full of these and other ‘scamping’ work, and so likely to
spread fire around, are certainly opposed to the rule that ‘a man may
burn himself and his own property, but he shall not unduly risk the
lives and property of his neighbours.’
Covering timber--that is, joists or the thin wood of partitions--with
sheet-iron is often done, but it is quite useless. When it is known that
the Pantechnicon floors were so covered, proof of its uselessness will
be at once admitted.
It may be thought that an important fire-resisting substance has been
omitted to be mentioned, namely, stone; for in many books, and even in
Acts of Parliament, the expression ‘stone, or other fireproof material,’
may be found. But all competent authorities are now agreed that stone of
nearly every kind is incapable of resisting the heat of ordinary fires;
and when used for supporting weights, or even if hanging unsupported, as
in a staircase, frequently is a source of great mischief and probable
danger. A flight of stone steps, heated by the conflagration of the
house in which it was situated, has been known to collapse immediately
upon the admission of cold air through the outer door being suddenly
opened.
Stone is therefore inadmissible for fireproof purposes, and should not
be used for strong-rooms, or as supports for joists or for any part
excepting the floor, where it may crack or crumble without affecting the
rest of the building. Granite is, as far as experience goes, capable of
resisting immense heat; and it is said the great fire at Boston, U.S.,
in 1873, was stopped when it came to a huge granite warehouse. But the
cost of this material and working it are too great for it ever to be
extensively used.
Concrete has been lately brought forward as a good, cheap, and fireproof
material for making walls and floors, but if used it should be most
carefully made; if broken limestone is used it will not be fireproof;
but with a mixture of flints, brickbats, sandstone, pebbles, and cement
in suitable proportions, a good wall may be erected. One advantage it
has over brick is, that being stronger (if plenty of hoop-iron is used
as a bond), it occupies less space, and no plastering, or very little,
is needed inside.
There has been no case, as far as I am aware, of a large concrete
building being subjected to a severe test; therefore, unless other
objects were aimed at, I should prefer a brick building. But some
warehouses and mills are so large that brick cannot be used internally
in arches; and a subdivision by party walls would destroy the business
purpose of the building, and allow of only small compartments in it.
Cannot iron girders be used in _any_ way to make them safe? To a certain
extent they can, if protected over the entire surface by cement or lumps
of fire-clay. There should be but few employed, and allowance must be
made for the girders, in case they get heated, to expand without
thrusting out the walls. They should be supported on corbels of brick,
and be as light as possible consistently with the strength required. If
used as means to carry a wall they must be covered as suggested, and
with the utmost care, for in this case any twisting or bulging sideways
will endanger the wall above.
Whatever system of construction is adopted, there are three things not
yet mentioned of high importance to the fireproof quality of the
building; namely, the communication between the various floors, the
style of window, and the construction of the roof. With regard to the
first of these, there is little doubt that the ordinary staircase and
the open lift are important aids to the spread of fire; by them the
various floors of a warehouse are, when combustion begins, converted
into so many furnaces with a connecting flue, and the extension of fire
is accelerated by the draught rushing upwards. Though the stairs may be
uninflammable and even indestructible, they will be in some measure a
source of weakness, unless completely separated from the open rooms, as
shown in the designs engraved in the Appendix. For these designs of a
thoroughly fire-proof warehouse, I am indebted to Mr. E. Hoole, of
Russell Square, London; who has succeeded in planning a building adapted
to commercial requirements, and yet possessing the necessary elements of
a fireproof structure.
All openings must be fitted with _double_ iron doors if perfect security
is required, but with a single door if only ordinary risk is to be
guarded against. The construction and fixing of these doors are a most
important matter, and should be quite as carefully attended to as if the
doorway were to a strong-room. Details of fixing them will be found in
the chapter on strong-rooms, and the strength of doors should be the
same as there shown. The outer plate of door being a half-inch solid
boiler-plate, there must be an air-space behind it, partly occupied by
the working parts of the lock, and inside that a casing of
non-conducting material. The bolts should be six in number, three in
front and three at the back, secured by a lock; and the frame into which
they fasten must be solid iron, well built into the wall. The price of
such a door, 6 feet high by 2 feet 4 inches wide, is 22_l._ 10_s._, and
money thus spent would many a time have saved thousands in property.
The Building Act can be complied with by providing a sheet-iron door
with a plain barrel-bolt, such a division forming no security whatever,
as the iron immediately warps, and allows flame or heat to pass through
the opening. In this particular the Act has done much harm, for a false
sense of security has been felt when its provisions have been met, and
money has been wasted in buying, and labour constantly lost in closing
and opening doors that are unable to hinder fire from spreading and
ensure safety. Cast-iron hinges are sometimes used for these doors,
giving another element of danger. Not long since I saw the ruins of a
building which had been divided in its various blocks by such doors.
Most of the doors were down in the rubbish, while the openings where
they had been high up on the walls had the broken hinges left in the
brickwork.
No regulations for fireproof building can be complete without most
stringent rules for using the best fire resisting doors, for what the
door of a boiler-furnace is to the fire within, the door of a room is to
combustion going on inside: it will, if insecure, allow air in to feed
the flames so long as there is fuel to burn.
But there are other openings necessary to warehouses; and this leads to
the subject of the windows, which are in the fireproof sense a necessary
evil. The danger consists in the draught which comes through to feed the
fire; but the risk can be lessened by using very thick glass, in small
squares, and taking care that no broken panes are allowed to remain in
the windows. If anyone takes the trouble to notice such a thing, he will
scarcely find a warehouse without some broken squares, which will admit
air enough to fan a fire to the temperature of a blast-furnace in a very
short time.
Iron sashes should be used; and iron shutters may be also used to cover
the windows, capable of being opened easily on the outside by firemen if
required. Capt. Shaw states that heavy losses have been caused through
the firemen being unable to open iron shutters from the outside, in
consequence of their expansion from heat. He also gives a warning
against the too common practice in cheap buildings of using glass with
bullseyes or dents, through which the rays of the sun become
concentrated and set fire, as has been the case, to the interior.
Projecting or bow-windows must not be adopted, as fire can more easily
pass in this way from one opening to another.
The remaining particular to be noticed is the construction of the roof,
by the falling in of which the destruction commenced below it is so
often completed. The high Mansard roofs appear to have largely
contributed to the destruction of Chicago and other American cities. It
is somewhat alarming to see the extent to which they are being employed
in England; but whatever form of roof is used, the materials of which
the framing is composed should be incombustible, and the ceiling beneath
it ought to be perfectly fireproof, so that fire beneath cannot ascend
to the roof, or descend from the roof to the rooms. A fireproof ceiling
is also valuable for preventing the building being deluged with water
from the engines, when fire has attacked the roof only. If any openings
to the roof are necessary, they must be constructed with care and placed
in a room--not at the top of a staircase, as is so frequently done,
where the draught of air is likely to be concentrated.
A mill at Leeds, at which a fire took place in 1827, was, with the
exception of the roof, supposed to be wholly fireproof. The upper floor
was filled with flax. The roof fell in, and the heat so affected the
iron beams of the floor as to cause them to give way and involve the
whole building in destruction.
In concluding the particulars of the general construction of fireproof
buildings, I would again urge the use of brick, as the best known
material for the purpose of resisting heat; or failing this, iron,
protected by plaster, concrete, or brickwork. During the space of a few
months there were calamitous fires in some large waterside premises, and
at each of them Capt. Shaw states the following results were observed:
‘The bricks were uninjured, the wood was seriously damaged, but only
partially consumed; the iron was fractured, and consequently rendered
worthless; and the stone was shivered into fragments and totally
destroyed.’