FIRE-ALARMS AND AUTOMATIC FIRE EXTINGUISHERS
Assuming that a town has a well-appointed fire brigade, equipped with
the most up-to-date engines, it still cannot be considered efficiently
protected against the ravages of the fire-fiend unless the outbreak
of a fire can be notified immediately to the stations, and local
mechanical means of suppression come into action almost simultaneously
with the commencement of the conflagration. "What you do, do quickly"
is the keynote of successful fire-suppression; and its importance has
been practically recognised in the invention of hundreds of devices,
some of which we will glance at in the following pages.
The electric circuit is the most valuable servant that we have to warn
us of danger. Dotted about the streets are posts carrying at the top
a circular box, which contains a knob. As soon as a fire is observed,
anyone may run to such a post, smash the glass screening the knob,
and pull out the latter. This action flashes the alarm to the nearest
fire-station, and a few minutes later an engine is dashing to the
rescue. Help may also be summoned by means of the ordinary telephone
exchanges or from police-stations in direct telephonic communication
with the brigade depôts.
All devices depending for their ultimate value on human initiative
leave a good deal to be desired. They presuppose conditions which _may_
be absent. For instance, an electric wire in a large factory ignites
some combustible material during the night. A passer-by may happen to
see flames while the fire is in an early stage. On the other hand, it
is equally probable that the conflagration may be well established
before the alarm is given, with the result that the fire brigade
arrives too late to do much good.
What we need, therefore, is a mechanical means of calling attention to
the danger automatically, with a quickness which will give the brigade
or people close at hand a chance of strangling the monster almost as
soon as it is born, and with a precision as to locality that will save
the precious time wasted in hunting for the exact point to be attacked.
Mr. G. H. Oatway, M.I.E.E., in a valuable paper read before the
International Congress of Fire Brigades in London in 1903, says that
the difference between the damage resulting from a fire signalled in
its early stage, and the same fire reported when it has spread to two
or three floors, is often the difference between a nominal loss and
a "burn out." The reformer, he continues, who aims at reducing fire
waste must turn his attention primarily to hastening the alarm. The
true cure of the matter is, not what quantity of gear it takes to deal
with huge conflagrations, but how to concentrate at the earliest stage
upon the outbreaks as they occur, and to check them before they have
grown beyond control. He cites the fire record of Glasgow of 1902, from
which it appears that three fires alone accounted for 40 per cent. of
the year's total loss, ten fires for 73 per cent., and the other 706
for only 27 per cent., or an average of £72 per fire. Had the first
three fires only been notified at an earlier stage, nearly £72,000
would have been saved. Captain Sir E. M. Shaw, late Chief of the London
Fire Brigade, has put the following on record: "Having devoted a very
large portion of the active period of my working life in bringing into
general use mechanical and hydraulic appliances for dealing with fires
after they have been discovered, I nevertheless give and have always
given the highest place to the early discovery and indication of fire,
and not by any means to the steam, the hydraulic, or the numerous other
mechanical appliances on which the principal labours of my life have
been bestowed."
A fire given fifteen minutes' start is often hard to overtake. Imagine
a warehouse alight on three floors before the alarm is raised! Engines
may come one after another and pour deluges of water on the flames, yet
as likely as not we read next morning of "total destruction." No stitch
in time has saved nine!
The sad part about fires is that they represent so much absolute waste.
In commercial transactions, if one party loses the other gains; wealth
is merely transferred, and still remains in the community. But in the
matter of fire this is not the case. Supposing that a huge cotton
mill is burnt down. The re-erection will, it is true, cause a lot of
money to change hands; but what has resulted from the money that has
_already_ been put into the mill? Nothing. So many hundred thousands of
pounds have been dematerialised and left nothing behind to represent
them. The great Ottawa fire of a few years ago may be remembered as a
terrible example of such total loss of human effort.
THE HISTORY OF FIRE-ALARMS
The first recorded specification for an automatic detecting device
bears the date 1763. In that year a Mr. John Greene patented an
arrangement of cords, weights, and pulleys, which, when the cord burnt
through, caused the movement of an indicating semaphore arm. As this
action appealed only to the eye, it might easily pass unnoticed, and we
can imagine that Mr. Greene did not find a gold mine in his invention.
Twenty-four years later an advance was made when William Stedman
introduced a "philosophical fire alarum." "His apparatus consisted of
a pivoted bulb having an open neck, and containing mercury, spirit
or other liquid. As the heat of the room increased, the expansion of
the fluid caused it to spill over, release a trigger, and allow a
mechanical gong to run down. This arrangement, whilst an advance upon
the first referred to, is quite impracticable. Evaporation of fluid,
expansion of mercury, a stiff crank, or other causes which will readily
occur to you, and the thing is useless."[14]
In 1806 an automatic method for sprinkling water over a fire appeared.
The idea was simplicity itself: a network of water mains, with taps
controlled by cords, which burnt through and turned on the water.
William Congreve patented, three years later, a sprinkler which was
an improvement, in that it indicated the position of the fire in a
building by dropping one of a number of weights. But string is not to
be relied upon. It may "perish" and break when no fire is about, and
any system of extinction depending on it might prove a double-edged
weapon.
The nineteenth century produced hundreds of devices for alarming and
extinguishing automatically. All depended upon the principle of the
expansion or melting of metal in the increased temperature arising
from a fire. At one time the circuit-closing thermometer was popular
on account of its simplicity. "Its drawback," says Mr. Oatway, "is the
smallness of its heat-collecting surface, its isolation, and, last and
worst of all, its fixity of operation. In thermometer or fuse-alarm
practice it is usual to place the detectors at intervals of about
ten feet or so, so that a room of any size will contain a number.
If a fire breaks out, the ceiling is blanketed with heat, and every
detector feels its influence. Each is affected, but none can give the
alarm until some one of the number absolutely reaches the set point or
melts out. Having no means of varying the composition of the solder or
shifting the wire, an actuating point must be selected which is high
enough to give a good working margin over the maximum industrial or
seasonal heat of the year; and thus it comes about that if the fire
breaks out in winter, or when the room is at its lowest temperature,
the amount of loss is considerably and quite unnecessarily increased.
In a device set to fuse at 150° Fahrenheit, it will be clear to
every one that the measure of the damage will depend upon the normal
temperature of the room at the time of the outbreak. If the mercury is
in the nineties, there is only some sixty degrees of a rise to wait
for; whilst if it happens to be a winter's night, the alarm is held
back for a rise of perhaps 120°. What chance is there in this case for
a good stop?"
Mr. Oatway has examined the fuses under different conditions, and his
conclusions are drawn from practical tests. Great intelligence will
not be required to appreciate the force of his arguments. Inasmuch as
the rise of temperature caused by a fire is relative, during the early
stages at least, to the general heat of the atmosphere, it becomes
obvious that an automatic fire-alarm should be one which will keep
parallel, as it were, with fluctuations of natural heat. Thus, if the
"danger rise" be fixed at 100°, the alarm should be given on a cold
night as certainly as at midday in summer. It was the failure of early
patterns in this respect that led to their being discredited by the
fire-brigade authorities.
The writer already quoted has laid down the functions of a perfect
alarm:--
(a) To detect the fire at a uniformly early period, under all
atmospheric and industrial conditions.
(b) To give the alarm upon the premises, and simultaneously to the
brigade, by a definite and unmistakable message.
(c) To facilitate the work of extinction by indicating the position
of the outbreak in the building attacked.
The "May Oatway" alarm has got round the first difficulty in a most
ingenious manner by adapting the principle of the compensation methods
already described in connection with watches.
The alarm consists of a steel rod of a section found to be most
suitable for the purpose. To the side is attached by screws entering
the rod near the ends a copper wire, which is long enough to sag
slightly at its centre, from which depends a silver chain carrying a
carbon contact-piece. A short distance below the carbon are the two
terminals of the electric circuit which, when completed by the lowering
of the carbon, gives the alarm. Now if there be a very gradual change
of temperature the steel rod lengthens slowly, and so does the copper
wire, so that the amount of sag remains practically what it was before.
But in event of a fire the copper expands much more quickly than the
steel, and sags until the carbon completes the circuit. The whole thing
is beautifully simple, very durable, quite consistent, and reliable. As
soon as the temperature diminishes, on the extinction of the fire, the
alarm automatically returns to its normal position, ready for further
work.
Now for the second function, that of giving the alarm in many places
at once. The closed circuit does not itself directly cause bells to
ring: it works a "relay," that is, a second and more powerful circuit.
In fact, it is the counterpart of the engine driver, who does not
himself make the locomotive move, but merely turns on the steam. An
installation has been introduced in the Poplar Workhouse--to quote an
instance. Were a fire to break out, one of the 276 detectors would soon
set twenty-five bells in action, one in each officer's room. Similarly,
in the Warehousemen's Orphanage at Cheadle Hulme, every dormitory would
be aroused, and every officer, including the Principal in his house
some distance away. Messrs. Arthur and Company, of Glasgow, have a
warehouse fortified with 600 of these "nerve centres," all yoked to
four position indicators, three of which actuate a "master" indicator
connected with the central fire-station. There is no hole or corner in
this huge establishment where the fire-demon could essay his fell work
without being at once spied upon by a detector.
We may glance for a moment at the mechanism which sends an unmistakable
message for help. At the brigade station there is a number of small
tablets, each protected by a flap, on the outside of which is the
word SAFE, on the inside FIRE. Normally the flap is closed. As soon
as the circuit is completed, a magnet releases the flap, and a bell
begins to ring. Now, it is possible that the circuit might be closed
accidentally by contact somewhere between the premises it serves and
the fire-station. So that the official on guard, seeing "J. Brown and
Company" on the uncovered tablet, might despatch the engines to the
place indicated on a wild-goose chase.
To prevent such false alarms the transmitter not only rings the station
up, but automatically sends an unmistakable message. When a fire occurs
an automatic printing machine is set in motion to despatch a cipher in
the Morse code _four times_ to the station. An accidental circuit could
not do this; therefore, when the officer sees on the receiving tape the
well-known cipher, he turns out his men with all speed.
On arriving at their destination the firemen receive valuable help from
the "position indicator," which guides them to their work. On a special
board is seen a row, or rows, of shutters similar to those already
mentioned. Each row belongs to a floor; each unit of the row to a
room. A glance suffices to tell that the trouble is, say, in the most
southerly room of the second floor. No notice is therefore taken of
smoke rolling out of other parts of the building, until the danger spot
has been attacked.
That the firemen appreciate such an ally goes without saying. Every
fire extinguished is a point to their credit. Also, the risks they
run are greatly diminished, while the wear and tear of tackle is
proportionately reduced. The fireman is noted for his courage and
unflinching performance of duty. The discomforts of his profession
are sometimes severe, and its dangers as certain as they are at times
appalling. Therefore we welcome any mechanical method which at once
shortens his work, lessens his peril, and protects property from damage.
Mr. Oatway draws special attention to the need for simultaneous warning
on the premises and at the fire-station. "I remember," he says, "many
cases, but perhaps no better illustration need be looked for than
the case of a cotton mill in Lancashire about two years ago (1901).
The fire was seen to start at a few minutes past seven; a fuse blew
out, and sparked some cotton; but it looked such a simple job that
the operatives elected to deal with it. At twenty minutes to eight it
dawned upon somebody that the brigade had better be sent for, because
the fire was getting away; and in due course they arrived; but the
mill, already doomed, became a total loss. In every centre similar
instances can be quoted. There is nothing in any automatic system to
discourage individual effort. Inmates can put the fire out, if able;
but in any case the brigade gets timely and definite notice, and if on
their arrival they find the fire extinguished, as Chief Superintendent
Thomas put it when we opened the Dingle Station after the fatal
train-burning, 'So much the better, we shall get to our beds all the
quicker.' This is the common-sense view of it. Helpers work none the
less intelligently because they know the brigade is coming; and it is
necessary to provide some automatic method of calling them, because you
can never rely upon anybody who is unfamiliar with fire doing the right
thing at the proper time."
Messrs. May and Oatway, who give their name to the alarm described
above, first introduced their apparatus in New Zealand, from which
country it has spread over the British Empire. The largest installation
is at Messrs. Clark and Company's Anchor Mills, Paisley. The whole
of the immense block of buildings, the greater part of which was
previously protected by "sprinklers" only, is now electrically
protected also; and connected up with the fire brigade, and through
their station with the sleeping quarters of every fireman. Some
figures will be interesting here. There are 119 _miles_ of internal
alarm circuits; 5-1/4 miles of underground cable between buildings; 19
automatic telegraphs; 21 automatic position indicators; 20 alarm gongs
a foot in diameter.
Early in January, 1905, a fire broke out in these buildings during the
dinner hour, when most of the works' firemen were at their midday meal.
The alarm sounded simultaneously at the works' fire-station and at the
firemen's houses, which are situated on the other side of the street
from the mill. The firemen were on the spot immediately, and were
enabled to subdue the flames, which had broken out in the building
occupied as warehouse and office, before it had got a firm hold of the
inflammable material, although not before one of the large stacks of
finished thread was ablaze. The brigade, however, were soon masters
of the situation, and the damage done was under £100. There is little
doubt, had the alarm been left to the ordinary course, the building
would have been totally destroyed.[15]
In those few minutes the installation saved its entire cost many times
over. Truly
"A little fire is quickly trodden out,
Which, being suffered, rivers cannot quench."
Here, in a Shakespearean nutshell, is the whole science of fire
protection.
AUTOMATIC SPRINKLERS
As these have been referred to several times a short description may
appropriately be given. The building which they protect is fitted
with a network of mains and branches ramifying into each room. At the
end of each branch is a nozzle, the mouth of which is bridged over by
a metal arch carrying a small plate. Between the bridge and a glass
plug closing the nozzle is a bar of easily fusible solder. When the
temperature has risen to danger point the solder melts, and the plug is
driven out by the water, which strikes the plate and scatters in all
directions.
This device has proved very valuable on many occasions. The
_Encyclopædia Britannica_ (Tenth Edition) states that, in the record
of the American Associated Factory Mutual companies for the 5-1/2
years ending January 1, 1900, it appears that out of 563 fires where
sprinklers came into play 129 were extinguished by one jet; 83 by two
jets; 61 by three; 44 by four; 40 by five.
The fire-bucket is the simplest device we have as a first aid; and very
effective it often proves. Insurance statistics show that more fires
are put out by pails than by all other appliances put together. The
important point to be remembered in connection with them is that they
should always _be kept full_; so that, at the critical moment, there
may be no hurried rushing about to find the two gallons of liquid which
each is supposed to contain permanently. In _Cassier's Magazine_ (vol.
xx. p. 85) is given an account of the manner in which an ingenious mill
superintendent ensured the pails on the premises being ready for duty.
The hooks carrying the pails were fitted up with pieces of spring steel
strong enough to lift the pail when nearly empty, but not sufficiently
so to lift a full pail. Just over each spring, in such a position
as to be out of the way of the handle of the pail, was set a metal
point, connected with a wire from an open-circuit battery. So long as
the pails were full, their weight, when hung on their hooks, kept the
springs down, but as soon as one was removed, or lost a considerable
part of its contents by evaporation or otherwise, the spring on its
hook would rise, come into contact with the metal point, thus close the
battery circuit and ring a bell in the manager's office, at the same
time showing which was the bucket at fault. The bell continued to ring
till the deficiency had been made right; and by this simple contrivance
the buckets were protected from misuse or lack of attention.
FOOTNOTES:
[14] Mr. W. H. Oatway.
[15] _Glasgow Evening News._