UK FIRE ALARM SYSTEMS


This article has been included as it gives a description of the systems available.
Because of this, some of the in-depth technical descriptions and details have been removed.
 

 

POST OFFICE ENGINEERING DEPARTMENT

TECHNICAL INSTRUCTION XVI
FIRE ALARM SYSTEMS

Paper read before the Metropolitan Centre of the Institution of Post Office Electrical Engineers
by J.  Sinnott
-
November 1909

The first application of the Electric Telegraph to the transmission of Fire Alarms was made in Berlin in 1849.  This was followed in 1853 by the installation in that city of a system of street alarms devised by Messrs. Siemens of Berlin. 

Siemens System

The alarm boxes were connected in series in a closed metallic circuit terminating at the Chief Fire Station, where the battery was placed.  Each street post had an automatic telegraph transmitter which, when started by the person giving the alarm, interrupted the permanent current a certain number of times, transmitting a signal in Morse code to the fire station, where it was recorded on a paper tape by an auto-starting Morse register.  A distinctive set of Morse signals was allocated to each street post to indicate the locality of the alarm received.  This system proved of such great utility that, in the course of a few years, similar fire telegraphs were installed in other German Cities, and it was also adopted in Amsterdam and Stockholm.  Although the results of experience and of general progress in electrical science have led to much development of Messrs. Siemens' system, the original general principles have been continued, namely: "closed" metallic circuits for the Street Alarm boxes; and a record in Morse code of all Alarms transmitted.  The Morse code system-of signalling was undoubtedly of great advantage, as it enabled the street alarms to be used by the fire department for the transmission of telegraphic messages in connection with its work.  In this respect the introduction of the telephone has altered matters in recent years, and nearly all German Street Fire Alarms of the present day are fitted with telephone apparatus in addition to the automatic fire telegraph transmitter.  As a consequence Messrs.  Siemens have recently devised alarm boxes with mechanism to signal numbers in place of Morse code.  Each alarm box of an installation is distinctively numbered; the numbers representing the localities of the boxes.

These numerical signals, which are sounded three times on one or more gongs at the fire station, and also recorded three times on paper tape there, are considered to be more easily made out than Morse code signals; numerical signals possess the further advantage that the locality of the alarm given can be displayed visually throughout the fire department by means of plain figures.

The United States of America followed closely, but independently, the course taken by Germany in the matter of Fire Alarm Telegraphs; and this is what might be expected, because, on account of the dryness and high summer temperature which characterize the climate of the United States, fire risks are very serious; fire protection, or fire fighting as Americans term it, being regarded as a very important branch of municipal work.

America has, in fact, been conspicuously in the forefront in both fire alarm and fire brigade work.  Previous to the introduction in 1850 of the Fire Alarm Electric Telegraph, New York was divided into eight fire districts.  In each district a powerful bell was provided in a tower where a watchman was continuously on duty.  Each tower commanded a clear view of its district, and it was the business of the watchman to look out for fires, and, when discovered, to tap with a hammer on his tower bell the number of his district.  The other watchmen repeated the taps on their bells, in this way spreading the alarm over the whole of the city.  The first application of the electric telegraph was to signal the existence of fires from police stations and engine houses to the watchman.
 

Channing and Farmer System

Boston (Mass.) was the first city in the United States to adopt a street Fire Telegraph.  It was designed by Dr. Charming and Professor Farmer and was installed in1852.  The original plant comprised 19 bell strikers and 26 street signal stations.  The alarm boxes depended for their operation upon the turning six times by hand of a crank which had a break circuit wheel fastened directly to its shaft.  One half of this wheel was so toothed that, in revolving, it transmitted signals which were recorded by a tape register and which represented the number of the fire district where the fire alarm was given; the other half of the wheel transmitted a certain number of current pulsations, recording on the register at the Central Station the number of the particular box operated.  The Central Station then transmitted the alarm to the watch tower in the district concerned, where a local alarm to the firemen was given by means of the tower bell.  To ascertain the locality of the alarm a fireman had to go to a street box and count the taps of the small bell inside, these taps being sent from the Central Office when the alarm had been transmitted to the watch towers.  If a fireman on reaching the street box did not find the bell tapping, he signalled the Central Office and the operator there repeated the number.  Notwithstanding the obvious imperfections of this system, reference to it is of importance, as it was the origin of the numerical signal system, the characteristic feature of American lire alarm telegraphy of to-day.

In 1859 Mr. J. Gamewell took over the Channing and Farmer patents and subsequently formed a company, the parent of the present Gamewell Fire Alarm Telegraph Company, for the purpose of improving and developing the fire alarm system.  The work of this Company has been so extensive that for a long time past the word "Gamewell" in the United States has been a synonym for "Fire Telegraph."  It may be mentioned that quite 90 per cent of the Fire Alarm Telegraph Systems in North America are of this company's production.  A description of their modern apparatus and of the principles of their system will be given later.  It may be of interest at this stage to consider the statistics of the Fire Alarm Systems in 1902, compiled by the United States Bureau of Commerce and Labour.  The statistics are contained in the tabular statements at the end of this paper.  Present day figures are not exactly known, but they may be assumed to be at least 25 per cent. greater than those of 1902.

It will be observed that signal boxes are almost exclusively used for the Street Alarms, and that there are but a few of the Annunciator kind.  Signal boxes are those which transmit a definite code of signals when operated; annunciator those which merely close the alarm circuit, dropping an annunciator at the fire station to indicate the alarm affected.

It is, perhaps, unfortunate that similar statistical information is not available as to the fire alarm systems in other countries, especially in Great Britain, with which this institution of Post Office Engineers is principally concerned; but it may be stated that the majority of systems in this country are either of the annunciator kind, merely consisting of the dropping of an indicator at the fire station, or more primitive still, of volunteer firemen's bells set in action by an electric hell push or pull contact fixed outside the fire station.  The street fire alarms in use are estimated to number about 3,000 boxes, as compared with the 38,000 of the United States; of the 3,000 only about 500 are of the signalling type, but this number will be increased to 700 when the Manchester installation now in progress is completed.

The history of the fire alarm telegraph in this country is largely that of London Fire Brigade systems, and as the experience of the various systems successively tried is not generally known, it will be of interest to state briefly what has been done.  In the year 1877, Mr. Treuenfeld read to the Society of Telegraph Engineers a most valuable and comprehensive paper on the subject of Fire Telegraphs.  He described the Continental systems, and advocated not so much the introduction of a particular system as the adoption of street alarms generally as a most useful aid in the prevention of serious fires.  His statistics in this paper, and also in another on the subject read in 1888, amply prove his contention, In these days there is no need to adduce further reasons, as the value of fire alarm telegraphs is fully admitted by every municipality that has installed them.
 

Exchange Telegraph Company System

Until the late date of 1880 there was no system of street fire alarms in London, or in fact in any other town in Great Britain.  The system first tried in London was that of the Exchange Telegraph Company.  It was fashioned after the fire alarms then in vogue in America.  "Closed" metallic circuits were used with the fire alarm boxes in "series." The alarm transmitter consisted of a short train of wheels regulated by an escapement.  The main-spring of the train was wound up by pulling a knob after the door was opened or the glass broken.  Geared in this train was an ivory code signalling wheel, the teeth of which differed in each transmitter.  This wheel in rotating interrupted the line current a certain number of times, according to the number and arrangement of the teeth on its periphery.  These interruptions or signals, through the medium of the station relay, were recorded on a Morse embosser and were tapped out by a single stroke bell.  The Morse embosser on starting closed the local circuit of an alarm bell.  The transmitter gave three repetitions of the signals before stopping.  When the signals had been received on the Morse embosser the watchman depressed the plunger switch, which broke the circuit of the alarm hell and reversed the line battery.  The reversal of current acted on the needle, at the transmitting alarm box, bringing a disc in position before an aperture and exposing the words "Signal received"; at the same time an audible acknowledgment was given by a bell in the alarm box.  As long as the door of the alarm box was closed or the glass remained intact, the contact springs in the alarm box were kept in contact, short-circuiting the box.


Bright's System

100 of the Exchange Company's fire alarm boxes, distributed over 14 of the London fire station areas, were installed.  Almost simultaneously with the Exchange Company's system one devised by Mr. E. Bright, Civil Engineer, was fitted up in connection with some of the other London fire stations.  The number of alarm boxes of this type was 160, covering 23 station areas. Bright's system, was based on the application of the differential balance method of locating faults devised by him.  The line circuit with the alarm boxes in series was taken through one coil of a differential galvanometer which also acted as a relay, and was balanced by a compensation circuit connected to the other coil of the Galvanometer.  Normally the fire alarm boxes were short-circuited.  When the handle of an alarm was pulled, it removed the short-circuit on an electromagnet inside the box. The resistance of the coils of this electromagnet upset the line balance at the fire station and caused the galvanometer needle to deflect and ring the station alarm bell.  To stop the ring, the watchman turned a dial resistance in the compensation circuit until.  the galvanometer needle became neutral; the pointer on the dial resistance then indicated the locality of the alarm box pulled, as the resistance of the electromagnet in each box differed from that of the others connected in series with it. The watchman by means of a key in the line circuit caused a pendulum attached to the electromagnet in the alarm box to vibrate; and the movement of a disc attached thereto was intended to inform the caller that the alarm had been received.
 

Spagnolleti System

In 1884 two London fire stations were fitted with a "series" circuit system devised by Mr. Spagnolletti, Engineer to the Great Western Railway; 12 alarm boxes in all were installed.  The system had for a Station Receiver a step by step visual recorder, almost similar to the modern Train.  Describer.  The alarm box contained a step by step transmitter made of two strips of metal connected together by insulating pieces like a ladder, the strips representing the stiles, and the insulating pieces the rungs.  One stile was insulated at various points.  A metal ball lying across the stiles connected electrically one stile to the other.  The ladder was pivoted so that it was tilted when the alarm handle was pulled, the lower portion being caught and retained by a pawl attached to the armature of an electromagnet in series with the line circuit.  The ball ran down the stiles and alternately broke and made the circuit, the pulsations of current actuated the station recorder, step by step and according to their number the pointer stopped on the dial at the name of the locality of the alarm box; the watchman then pressed a switch restoring the station indicator to zero, and also increasing momentarily the line current.  This increased line current released the pawl and allowed the ladder to return by gravity to the normal position, resetting the ball and closing the circuit.  This system gave so much trouble that its use was not extended.
 

Brown System

A series circuit system devised by Mr. A. C. Brown was tried at Great Portland Street Station, five alarm boxes being fixed in connection therewith.  Each alarm box apparatus contained a pendulum contact breaker with a distinctive rate of vibration when set in motion.  When an alarm was pulled its pendulum was set in.  motion, interrupting the current periodically, and affecting at the fire station an electromagnetic indicator with a pendulum armature arranged to respond to the particular rate of current impulse.  The station equipment included a series of pendulum indicators, each of which was regulated to correspond with a pendulum at one of the alarm boxes.  The vibration of the pendulum armature indicated the alarm box pulled and closed the local circuit of the fire bell common to each pendulum receiver.  The pendulum transmitter and receiver were similar to the Pendulum Selector Telephone Call Apparatus described by Preece and Stubbs in their work on Telephony.

From various obvious causes these "series" circuit systems gave so much trouble that in 1886 the London Fire Brigade authorities decided to discard them altogether and to substitute the "Open" circuit system with a separate wire to each box.

Mr. A. C. Brown invented the system adopted, a single wire with earth return being used for each circuit.  The alarm box apparatus was of a simple character.  The handle of the alarm when pulled closed the line circuit through a retaining relay, a small bell of the short-circuiting type being in series.  Closing the circuit dropped an indicator at the Fire Station and actuated a shut-circuiting type of bell, common to all indicators on the alarm receiver board.  The bell in the alarm box rang until the watchman depressed a plunger switch, cutting off the battery and releasing the armature of the retaining relay at the alarm box.  The cessation of the ring given by the bell of the alarm box was intended to intimate that the call had been received.  The system, later, had telephone apparatus included, this being added about 1898.


 

Stuart and Moore System

Two "open" circuit Alarm systems designed by Messrs. Stuart and Moore were also tried by the London Fire Brigade.  The alarm box in the first system of Messrs. Stuart and Moore was arranged so that when the handle was pulled it closed the line circuit.  The handle was retained in the pulled out position by the armature of an electromagnet in circuit with the line.  At the fire station a drop indicator and fire bell were actuated.  The watchman then by means of a switch increased the line current and caused the electromagnet in the alarm box to attract the armature and release the handle.  A hammer attached to this armature struck one blow on a gong; this was the reply signal.

The other system of Messrs. Stuart and Moore was of the pendulum type, and was tried at two fire stations.  The alarm transmitter consisted of a pendulum which was set in motion by pulling the handle.  The pendulum in motion intermittently earthed the circuit causing a relay at the fire station to ring a fire bell intermittently.  The object of the regular intermittent rings was to distinguish genuine calls from false rings brought about by earth faults.  An indicator was provided for each circuit.  When the watchman answered the call, by pressing a switch, the line current was increased to an extent sufficient to actuate a single stroke bell in the alarm box, the beats corresponding to the vibrations of the pendulum, and in this way giving the reply signal or acknowledgment.  Messrs. Stuart and Moore's alarms were eventually abandoned in favour of Mr. A. C. Brown's apparatus; the London Fire Brigade authorities having decided to have only one style of alarm apparatus for all their fire stations; but the pendulum system is maintained by the Post Office at Newport, Monmouth, and Lewes, Sussex.

Stuart and Moore fire alarm indicator with telephone 22+22

 

Stuart and Moore fire alarm indicator with telephone 22+22
Internal view

A. C. Brown's system, which, in common with the previous London systems, was installed and maintained by the Post Office, is still in exclusive use by the London Fire Brigade.  Until recently it was subject to the defect of not providing any dependable means in the fire station for distinguishing false signals due to electrical faults, from the genuine calls caused by the operation of the alarm boxes.  As this defect came increasingly into prominence with the extension of the system, it will be of interest at this stage to give certain particulars of the experiences in this regard of the London Fire Brigade.  The number of street call points in service each year since 1880 is as follows:-
 

Year   Number   Year   Number   Year   Number   Year   Number
1981 - 44   1888 - 358   1895 - 570   1902 - 801
1982 - 77   1889 - 365   1896 - 580   1903 - 927
1983 - 153   1890 - 385   1897 - 592   1904 - 1078
1984 - 220   1891 - 502   1898 - 600   1905 - 1150
1985 - 263   1892 - 546   1899 - 61`3   1906 - 1246
1986 - 347   1893 - 563   1900 - 675   1907 - 1285
1987 - 349   1894 - 565   1901 - 694   1908 - 1317

In 1888 the Chief Officer, Captain Sir E. M. Shaw, reported that during the preceding year 2,365 fire calls had been received by the fire brigade; of these 1,195 were given by the street alarms, but of this number, 362 were false and were set down to the following causes: 170 were malicious; 91 due to lines out of order; 13 to men working on wires; 14 to collisions of vehicles with the street fire posts; 74 were not definitely traceable, but probably the majority were due to undetected electrical faults.  Captain Shaw, whilst acknowledging the valuable services rendered by the street fire alarms, considered that the false alarm trouble was the most serious drawback to the extension of the system.

During the period 1900-1904, false alarms were unfortunately very frequent, owing to the fact that the provision of the Post Office Telephone Exchange System then in active progress necessitated considerable overhauling of the wire routes, mostly underground, on which the fire alarm circuits were carried.  In recent years, although there has been a marked improvement in the maintenance of the wires, the number of false alarms continues large.

For the year 1908, the Chief Officer reported that of the 5,811 calls received, 3,236 were given by the street alarm boxes, 1,949 by strangers, i.e., by persons calling at the fire stations; 477 by Telephone Exchange subscribers; 62 by police and salvage corps telephones; 52 by private fire telephones; 12 by automatic alarm systems, and 23 by public telephone call offices.  Out of the 3,236 street fire calls, 530 were false, due to electrical faults.

These false alarms cannot be regarded as indicative of a low standard of wire maintenance, if it is borne in mind that quite 1,000 miles of wire is involved and that an earth fault of only a few seconds duration is sufficient to cause a false alarm.  In fact, it is doubtful whether with the fire alarm system just described, it would be possible to reduce the trouble very materially, even if routes specially reserved for fire alarm wires were provided.  The cost of such routes would be so great as to restrict the extension of the street alarm system, which would, be more disadvantageous to the community than the present fire alarm trouble.  For this reason an attempt is now being made to overcome the trouble, and it is hoped that this will be done without appreciably diminishing the efficiency of the fire alarm, which it need scarcely be said is the most important factor in determining the value of any system.  The London Fire Brigade accordingly decided to try at Islington Fire Station a modification of the Fire Alarms on a plan similar to one which proved satisfactory at Newcastle-on-Tyne.  The Islington trial was commenced in 1907.  It has been attended with such good results that the Fire Brigade has asked that the remainder of their fire alarms shall be altered similarly.

The modified system of Mr. A. C. Brown will be supplied to new fire stations.  It will be observed that the bell in the alarm box has been replaced by a vibrator, or buzzer, as it is usually termed.  The handle of an alarm box when pulled, trips the reed of the buzzer, starting it in vibration; this vibration is then maintained by an electromagnet, through which the line circuit is closed in shunt with the retaining relay.  The main battery current passes through a milliamperemeter, a combination of relays termed a "Relay Buzzer Selector," and through an indicator; there is a separate indicator for each alarm box circuit.  The "Relay Buzzer Selector" separates, as it were, the rapid vibratory current pulsations set up by the transmitting reed from the steady line current.  The vibratory component actuates a special form of relay which controls the ringing of the fire hell, and also operates a slow action relay which is referred to on the diagram as a "Circuit Silencer." The armature lever of the slow action relay is attached to an air dashpot to retard the return of the lever when the controlling electromagnet is de-energised.  This relay closes the local circuit of the local alarm bells in the fire station for about 20 seconds.  If a leakage of current takes place owing to a line insulation fault the buzzer selector "steady current" relay is actuated, causing the fault bell to ring and draw attention to the fault.  This fault bell is also used for telephone calls made by the Fire Brigade from the street alarms.  The operation of the Relay Buzzer Selector may be briefly described as depending upon the successive pulsations of current setting up minute, but continuous vibration of a lightly balanced lever, one end of which rests on the diaphragm of a relay made like a telephone receiver.  The fire bell relay is short-circuited by the contact between the diaphragm and the lever.  The effect of the vibratory motion of the lever is to increase the resistance of this contact sufficient to admit current to the fire bell relay.  The latter relay closes the local circuit of the fire bell through a slow action relay, the object of which is to prevent a momentary impulse starting the local alarm slow action relay.

Practically at the moment a street fire alarm is pulled the fire station bells start to ring, and if desired the emergency lights can be switched on automatically as well.  In addition to these advantages the trouble of false alarms due to electrical faults is eliminated.  The return call key is provided in order that the fire station watchman may call the attention of a fireman if in the vicinity of a fire alarm post: the calling signal is produced from the telephone receiver, which is caused to set up a loud buzzing sound by means of the vibratory current applied to the line when the return call key is pressed.

The transformer on the fire alarm switchboard is used when it is required to speak from a street alarm to another fire station.  It connects the street alarm circuit with the telephone intercommunication switching system, which is in use between the headquarters fire station and the superintendents' stations, and between the latter and the various out stations of the brigade.  This intercommunication telephone system is a most important factor in the working of the London Fire Department.  Considerable attention has been given to the acceleration of the transmission of messages over this intercommunication system, so much so that the time now taken to get a reply to a brief message sent from headquarters to a superintendent's station is about six seconds, and from headquarters to an out station about 20 seconds, although in this latter case a switching operation is necessary at a superintendent's station to get through to the out station.  However, in mobilising rapidly the various sections of the brigade in the case of serious fires the 20 seconds taken to call an out station would not be wholly wasted.  When a fire signal key on the intercommunication switchboard at a superintendent's station is pressed, the firemen's bells at the out station are instantly set in action, and as a rule, by the time the watchman on duty has received by the telephone full particulars of where they are wanted the men and equipment are ready to go out.


 

British Post Office System

Systems almost similar in character have been installed by the Post Office Engineering Department for the corporation of Belfast and Newcastle-on-Tyne in these cities.  In the Newcastle-on-Tyne system, although the buzzer type of alarm is employed, a buzzer relay selector is not used as a receiver; the buzzing signals are rendered audible at the fire station by means of a specially constructed .telephone receiver fitted under the alarm bell.  This bell can be temporarily stopped by pressing the short-circuiting button if it is required to render the "hooty" sound of the receiver more audible.  At Belfast the system is practically similar to that now being superseded in London, with the exception that instead of fixing the local reply bell in the street alarm box itself, it is fitted outside close to the top of the lamp standard carrying the street alarm, the object being to call the attention of the police with a view to the arrest of persons pulling the alarms without proper cause.

At both places the alarm circuits are wholly metallic, and on that account are not liable to get out of order through earth faults to the line wires as in the case of the London system.  Of the simple forms of Fire Alarm Systems which have been installed by the Post Office in small towns it will suffice to describe that known as type G, which is an open-circuit system.  When the alarm handle is pulled, the line is earthed through a shunted trembler bell; the handle in the pulled out position is locked by a latch which cannot be released until the fire brigade arrives and unlocks the alarm door.  Closing the circuit in this way draws current from the central battery at the fire station through a non polarised drop indicator provided with a local battery circuit to which the firemen's bells are connected.  These bells are fixed in the men's houses, one circuit usually serving several bells.  At the fire station the bell circuits are bunched together and connected through to the common local circuit of the drop indicators on the switchboard.  An "electromagnetic indicator key" is provided for each alarm box circuit in order that the ringing of the bells may be stopped until the street alarm can be reset, during this period the indicator affected shows a white star.  When the box is reset and the circuit is thereby broken, the indicator key restores the normal condition of the circuit, the white star indication disappearing.  A telephone jack is connected across the indicator of each circuit so that a telephone receiver may be plugged in to detect the pulsations of the local trembler bell in the alarm box and in this way confirm that the call is due to the alarm box having been actuated.

Reverting to the subject of the "closed" circuit alarm systems, upon which principle fire alarm practice outside this country is almost exclusively based, it might be thought that the experience of the London Fire Brigade is condemnatory; but on reviewing that experience it appears possible that if the work awl apparatus generally had been up to present day standards, the conclusions would have been reversed. 

German and American authorities are of opinion that the "closed" metallic circuit principle should alone be employed, in view of the nature of the conditions to be met in.  fire alarm telegraphy.  The street fire alarm differs essentially from other telegraphic signalling systems in that it is very infrequently used.  Even when tested daily there is no certainty with an "open" circuit arrangement that the alarms may be in order at the moment when required to transmit a fire call, as disconnections of line wires and battery leads cannot be made to give dependable automatic notification of their occurrence; and in connection with matters of such vital importance as the transmission of fire alarms automatic safety and control devices to provide against these contingencies are generally considered indispensable.  Although a "closed" circuit system possesses the great advantage that such devices can he readily applied, its application to circuits with one call point each would be costly.  It is therefore the practice with a "closed" circuit system to connect in series in each circuit as many call points as a reasonably safe length of line will admit.  This in itself is a very desirable feature.  It reduces to a minimum the cost of the external wiring of a system, especially where metallic circuits are desired; and it may be stated as a general principle, that whether a system is of the "open" or of the "closed" circuit type, it is advisable that it should be completely metallic and not employ earth return.  "Earth" return means not only that the signals may be closely if not exactly imitated in certain circumstances by line insulation faults, but also that the circuits may be more often out of order, the insulating material of wires being mechanically the weakest portion of every electrical system.  Reference was made at the outset to the "closed" circuit series system of Messrs. Siemens; and although several other such systems are in existence, further reference will be limited to a description of that of the Gamewell Company, which is so widely in use in America, and which in recent years has been installed in several of the large towns in this country.

 

Fire Alarm Indicator 6/10 with telephone Fire Alarm Indicator 11/16 with telephone
   

Fire Alarm Indicator 11/20 with telephone

Fire Alarm Indicator 12/20 with telephone

 

Fire Alarm Indicator 30/30
 

Gamewell System

It is stated that one of the first objects of Mr. Gamewell's invention was to provide for the mechanism of the street fire alarm box being adequately protected against the extreme weather conditions of the United States.  This he did in a simple but effective way, by mounting the signal mechanism in a metallic case insulated from and enclosed in an outer metallic case.  In the company's modern boxes, which now contain more intricate mechanisms, the signal portion is mounted in the interior of a triple metallic case.  Although the cases are made practically dust tight, it is the air partitions between the several cases that protect the signal mechanism from the effect of changes of temperature which might lead to the deposition of moisture through condensation from the atmosphere; this has probably contributed a great deal to the success of the system, as the effects of condensation on the signal mechanism would be most deleterious.  Almost from the outset the Gamewell Company decided not to use mechanisms maintained in motion by electrical means.  In their designs the various electromagnets are employed simply to set in action or to control the forces of springs or weights.  An important feature is that of the automatic mechanical restoration of the armature lever of each electromagnet to the "no current" position after its lever has been fully retracted by its spring; consequently an electromagnet when energised by the closed circuit current has merely to attract its armature a very short distance.  This permits the use of strong retractile springs on the armatures, and reduces to a minimum the effect of variations in the strength of the electromagnets; the adjustments of the apparatus are, therefore, very robust, and when once properly set up rarely required to be altered.  Another feature of the system is the employment of a uniform current strength of 100 milliamperes in every line circuit, a strength which avoids the need of delicately constructed electromagnets in the mechanisms.  Reference has already been made to the principle of signalling the number of an alarm box when it is set in operation; the adoption of the numerical code was probably a consequence of the adaptation of electrical means to do what had previously been done by hand in the manner already described.  If so, it was a rather fortunate circumstance; no more simple or certain means could have been adopted to provide against false alarms being given by reason of electrical faults happening to the circuits, especially having regard to not impairing the efficiency of the alarm system in the many adverse conditions likely to arise in the course of its existence.

The record of the signals at the fire stations is made on a paper tape either by a punching or by an ink register.  These instruments are designed to make the record of each individual signal similar in length, although variations in the duration of the "breaks" of the circuit may be made by the alarm box transmitter.  With a Morse Code System variations in the lengths of the recorded signals are likely to occur from this cause, and in consequence may give rise to uncertainty as to the locality of the alarm.  For this reason the Gamewell System is undoubtedly superior to any in which ordinary Morse recorders are used to record signals, whether in Morse or in numerical code.  In American practice it may be stated that all street fire alarm circuits in a town or city are connected to a central station, where all fire alarms are received and retransmitted, in some cases manually, in others automatically, to the engine house, hook and ladder companies, and to the other departments of the brigade.  This is generally the plan also adopted in Germany.  The object is to centralize the control of the brigade as a whole.  For small towns with volunteer brigades, a fire alarm system usually consists of a single closed circuit for the street boxes, or fire telegraph stations as they are termed.  The alarm circuit is connected to operate electrically and automatically either an electro mechanical tower bell striker or an electrically controlled steam siren by which the alarm is sounded, announcing to all concerned the section of the town where the fire has been discovered.  The employment of such means of spreading an alarm is not favoured by fire brigades in this country; the adverse reason advanced being that the attention of the idle and curious would be attracted, and that this would hamper the operations of the brigade.  Therefore when a British municipality decides to make a start with electrical fire alarms, it is, as a rule, with the object of providing an electrical bell at each of the firemen's residences to dispense with the use of either maroon rockets or of large mechanical bells or hooters for spreading the alarm.

The plan of interconnecting electrically the various component items of a Gamewell fire alarm installation is quite a simple matter.  The street fire alarm boxes are connected in series with each other and with the fire station receiving apparatus and the closed circuit battery proper to the particular circuit, each circuit being treated independently.  It will, therefore, be sufficiently explanatory of the Gamewell system to describe separately the principal up-to-date apparatus items usually employed.

Fire Alarm Boxes
The
Gamewell Company have devised from time to time several types of street alarm box, to meet, no doubt, different conditions as experience revealed their existence.  It is proposed to deal in this paper with only two of these types.

Sector Non-Interference Pull Box
The picture below shows the external appearance of this box with the key protected by a key guard with glass door.  In some circumstances this key guard is omitted, keys distinctly numbered being given to the police and to certain of the townspeople.  When a box is unlocked by one of these keys, the key is trapped in the lock and cannot he released except by means of a master key held by the Fire department.

Gamewell Sector Box
Front view showing key in door lock


Gamewell Sector Box
View of front door
showing the glass key guard broken and the key exposed


Gamewell Sector Box
Shown the door open with the inner box and pull-down hook in view.


Gamewell Sector Box
Both inner and outer doors shown opened; the keys for the inner door are used only by the fire department.

The view above shows the bell, telephone jack, telephone signal key fixed below the bell dome; and the special fire signal key used by the fire department in special circumstances.  This latter key is mounted on the terminal connection block.  The inner circular box contains the automatic signal mechanism which is operated by the external pull-down lever.
 

Gamewell Sector Box
Vi
ew of the automatic signal mechanism.

The telephone call key when depressed, opens the short circuit of a 250ohms resistance coil in the line circuit, which reduces the permanent line current to an extent sufficient to release the armature of a telephone relay in the circuit at the fire station, but the current is not reduced low enough to allow the fire alarm receiving apparatus to be actuated.

The object is to admit of telephone calls being made to the fire station without disturbing the fire alarm apparatus proper.  By means of the test switch in the alarm box the signal mechanism can be proved locally, no alarm signal being given.  When the switch lever is pulled forward, a resistance of 19ohms is connected across the line connections, shunting the break wheel, bell and signal key.  During the revolution of the character wheel of the signal mechanism the periphery is in contact with an earthed spring to admit of signals being transmitted by earth return should the line circuit become disconnected.  In the event of such disconnection occurring a signal would be automatically received at the station; it would then be necessary for the watchman to turn a switch, which would earth one pole of the battery and bunch the outgoing and incoming wires of the circuit to the receiving apparatus connected to the other pole.  The circuit would in this way be made good temporarily and alarms would be transmissible, using earth return to complete the circuit.  The plug switch in the alarm box is provided so that either the incoming or outgoing line can be earthed; if the corresponding terminal is earthed in  the adjoining box, the section of wire between these two boxes can be subjected to the operations of wiremen without risk of interference with the alarms.

The pull-down lever is connected to lever on the inside of the inner door; this latter lever through a pawl engages with a lever attached to the train of wheels, the lever being connected with the axle of a segmental gear wheel.  This wheel is fitted with a powerful main spring after the manner of the main driving wheel of a clock.  The gear wheel is in mesh with a ratchet and this ratchet drives a toothed wheel, which carries on its spindle the character wheel.  The toothed wheel is in gear with a reduction wheel, the teeth of which engage with the rocking lever pallets, forming the escapement to regulate the motion of the train of wheelwork.  The ratchet is arranged to engage with the toothed wheel only when given 'a complete turn, which ensures at least one complete revolution of the character wheel, if the outside lever is pulled down sufficiently; when this lever is pulled down to the full extent, four complete revolutions of the character wheel will be made before the main wheel returns to rest.  When the pull-down lever is let go, its pawl cannot re-engage with the lever, until the lever returns to the rest or normal position.  This ensures that once the mechanism has been started, it is not possible to interfere in any way with the regular motion of the character wheel by subsequent pulling of the outside lever.  The bell hammer in the alarm box strikes the bell dome on the release of the armature of the electromagnet, one ring being given for each break of the circuit made by the character wheel and in this way striking out the number of the box to indicate locally that the alarm is being transmitted.  There is no provision in this type of box for preventing interference with its signals should another box on the same circuit be pulled at the same time.  The risk of such interference causing a complete confusion of the received signals is considered extremely improbable, and is quite confirmed by experience.

In Germany, where nearly all closed circuit systems are subject to a similar limitation, it is stated by Mr. Treuenfeld that no case of interference was on record up to the date of his paper, which was delivered in 1888.  Chicago installed about 1,500 of these sector No. 2 boxes in 1901 and in a discussion of the Chicago System before the Western Society of Engineers, Journal 7, pages 623-650, December 1902, the following statement was made.  At one time "non-interference" boxes were in use to provide that if two boxes should be simultaneously pulled one should not interfere with the other.  These were found unnecessary.  It is now arranged that the consecutive numbers of boxes likely to be pulled at the same fire are different or have distinct features, so that the operator receives intelligible signals sufficient for the occasion.  Notwithstanding this experience, the risk of two boxes on the same circuit being pulled at the same moment must be admitted, and it is considered that in towns having more than, say, twenty-five alarm boxes, the non-interference type should be employed.  The opinion of the Fire Alarm Committee of the New York underwriters is, that in all large cities the succession non-interference box should be installed.  The sector box is now constructed so that it is only necessary to substitute the signal mechanism in the inner circular box to convert it to the succession non-interference type, which is the present standard box of the Gamewell Company.  An installation can therefore be commenced with sector boxes, and as the system is extended or other conditions render it desirable, the signal mechanisms can be substituted by those of the succession non-interference type. 

Succession Non-Interference Fire alarm Box
With this style of box it is possible to start simultaneously all the alarm boxes of the system without risk of interference and to receive signals correctly in succession from any two, four, six or eight of the boxes, according to whichever number of "Successive" signals is stipulated for by the fire department at the outset.  The order in which the successive signals will be received if boxes are simultaneously set in action is that of number, the lowest number coming in first.

This shows a recent style of Gamewell Succession box as installed in Bristol.
The pull-down lever is folded back against the door of box and kept in position by a glass slide.

 

Gamewell Succession box
Inner and outer doors open exposing the telephone call key, test switch and fire signal key in position.
The automatic signal mechanism is mounted in a glass fronted cylindrical compartment.

When the glass slide, on the outer door, is broken the the pull-down lever is automatically projected ready for pulling down.  A slight pull downwards of the lever is sufficient to start the internal signal mechanism, and after breaking the glass, this is all that a person giving an alarm has to do.

The pull down lever which when pulled trips the trigger hook projecting through the slot in the inner box.

The succession box is also made with a "keyless" door, the turning of a handle outside the door not only rings a loud-sounding mechanical gong in the door to call the attention of the police to the fact that the alarm box is being operated, but also pulls down the starting hook inside the box.  Two styles of "keyless" door are made.  In one the work of pulling down the handle sets in action the inside gong, the ringing of which continues until the inside pull-down hook is actuated.  In the other, the gong is not started until the pull-down hook has been actuated.  This latter style of door will be fitted in Manchester.

If two or more boxes start exactly at the same instant, it is plain that as the circuit is broken in each box at the same moment, only one signal can be received by the fire station apparatus for each disconnection, no matter whether the disconnection may consist of several breaks in series.  The box with the lowest first series of breaks, constituting the first digit of its number, disconnects the circuit for a certain interval after the first series has been signalled; but during this interval the other boxes will have their non-interference electromagnets de-energised, and if their signal levers are raised the non-interference levers will fall back and lock the signal levers, keeping the contacts closed.  In this way these latter boxes are kept out of the circuit until the one with the lowest number has finished signalling.  The succession alarm box and those types in which the train of wheel work is driven by a wound-up spring can be actuated from an auxiliary closed circuit not connected electrically with the street alarm circuit.  The auxiliary circuit is led into a building or private premises fitted with alarm boxes of simple construction.  If an auxiliary alarm box is pulled it actuates an electromagnet in the street box, raising the trigger of the latter and setting its wheel work in motion.  The brigade on arriving at the street box can ascertain readily whether it has been operated by the auxiliary system.  This method of putting premises in communication with the fire department is advantageous.  In the first place a firm desiring the facility usually installs a street fire alarm box which is available for the protection of the immediate neighbourhood, and secondly, the expense of separate wires to the fire station is avoided.  The auxiliary circuit is kept closed and maintained under test by a permanent current from a small battery.  The starting of the street box is obtained by increasing this permanent current sufficiently to operate a special electromagnet fitted in the street box. 

An alarm is given by pulling the ring of the box.  This throws an "open" circuit augmenting battery in series with the closed circuit battery.  When the street box starts it opens the auxiliary circuit, and the buzzer in.  the auxiliary box is thereby set in action.  The buzz informs the person giving the alarm that the street box, mechanism has been started.  A local fire bell in the premises protected is rung when an auxiliary box is pulled.  The "disconnection" bell is to indicate a disconnection or cross of the wires of the auxiliary circuit.

Central Station Receiving Apparatus
The receiving apparatus may be divided into three classes, audible,
visual and recording.  The recording apparatus may be either an ink or a punching register.  In the case of the former a separate ink marking disc controlled by an electromagnet is provided for each street alarm circuit.  Each mark is produced at the instant the circuit is broken, the armature lever being restored by the mechanical action of the register to the "No current" position.  Ink registers are made in sizes to record from one up to ten circuits.  The punching register is made only for one circuit, but where there are several alarm circuits, and where a repeater is employed for repeating alarms to the firemen's gong, one of the gong circuit positions can be allocated to the punching register, and the latter will in that case record all calls dealt with by the repeater.  This is the arrangement adopted in the Willesden and Bristol municipal installations.

There is a punching register with an automatic date and time stamp in-position for timing alarms.  The record on the slip is that of box No.  53 and it will be observed that this is stamped 09.11.20 A.4 05/06 which means that the alarm was received at 4.5 a.m. on the 20th November 1909.  Audible indications of the alarm signals are given by electro-mechanical bells.  These are made with various sizes of gongs, the smallest, 6-inch, being used for firemen's quarter, and the largest sizes, from 12-inch to 36-inch, being fitted in engine houses.  The smaller bell is mounted in a glass fronted wooden case.

Gamewell Fire Alarm System
Punch register, time stamp and automatic paper winder.
The picture above shows a later style at Windsor Castle - the 1909 version was very similar

A visual indicator of the signal, which can be combined with the bell gong, is made for those fire departments requiring an automatic visual indication of the number of the signal box; the indication remains in view until the resetting lever of the indicator is pulled downwards.

Gamewell Fire Alarm System
External view of the indicator

Gamewell Fire Alarm System
Door open exposing mechanism

Automatic repeater
Where there is more than a single circuit alarm system, and where it is necessary to provide for the repetition of signals received at the Central Office to the firemen's gong circuits or to sub-fire stations in the district, an automatic repeater is used to re-transmit the alarms to the sub-stations from the Central Office.  Repeaters are made in several sizes to take from two to twenty street alarm circuits as may be required.  As the transmission of alarms from the street circuits is effected by interrupting the closed circuit current a prearranged number of times, it follows that if a disconnection of a circuit should take place a single signal
would be received at the Central Office and retransmitted over the system by the repeater.  This would not derange the other circuits, as the repeater is designed to throw out of action a disconnected circuit and to take it into service again immediately after repair.  These actions are entirely automatic.  The repeater dispenses with the need of a watchman at the Central Office so far as the retransmission of street alarms is concerned. 

Gamewell Fire Alarm System
View of an automatic repeater for three circuits

Gamewell Fire Alarm System
Close up view of the automatic repeater for three circuits
The two pictures above were taken in Windsor Castle

There is a separate electromagnet for each circuit, mounted on a common base.  No local batteries are used as in the case of telegraphic relays.  The power to actuate the repeater is obtained from three heavy weights each acting independently through a separate train of wheels.

In large Central Offices with connection to a number of fire stations in a district in place of an automatic repeater it is usual to install manual transmitters by means of which operators at the Central Office are able to send out to the fire stations concerned the alarm calls received at the Central Office and also any code signal 15 messages which may be sent in by the fire department when dealing with serious fires.  For this purpose the special signalling key in the fire alarm box is used to give a prefix signal such as two twos, after which the alarm box is pulled to indicate the locality.  These prefix signals are drawn up to indicate the kind of assistance required at the scene of operations, and they cover practically every contingency.

Gamewell Fire Alarm System
Power Board, Repeater and Punch Register at Hampton Court Palace (picture dated 1921)


Supply of Electric Current for working the Alarm System

Wherever an electric light or power supply is available it is usual to utilize such supply to charge sets of small size accumulators to provide the currents required for the various fire alarm circuits of an installation.  The Gamewell Company have designed switchboards which enable the charging of the cells to be done in an economical, safe and convenient manner.  The switchboards are made suitable for charging-from any direct current supply of up to 500 volts pressure; where the supply is alternating, a rectifier would have to be provided in addition.  Duplicate sets of batteries are required for each circuit in order that one set may be charged whilst the other set is feeding the circuits.

Where no power supply is available the necessary current is obtained from primary batteries.  In this case Daniell Batteries are almost invariably employed on account of the constancy of their electro motive force.  In the United States the form of Daniell battery used for the purpose is the Gravity, as its internal resistance is low.  The Gravity cells are mounted on racks conveniently accessible.  It may be mentioned that if these batteries receive periodic frequent attention their upkeep is quite satisfactory; but it is found that in the primary battery installations maintained in this country by the Post Office that such frequent attention would be rather costly, hence the trough type of Daniell is used; two sets of troughs being connected in multiple.  Even this arrangement, by reason of the loss of power due to the high resistance of the cells, is not a desirable one and it is thought that it would tend to economy if the municipal body were to arrange for the necessary maintenance of Gravity cells to be carried out by the firemen as is done by the Blackpool Fire Department.  It would not be a difficult task for a linemen to impart the necessary instructions and to inspect from time to time the condition of the batteries.  Where primary batteries are employed it is desirable that underground conductors of not less than 40 lbs. copper to the mile and aerial wires of not less than 150 lbs.  copper to the mile should be employed for the external wiring.  It is thought that the description given of the Gamewell Company's apparatus is sufficient to show that an extraordinary amount of mechanical skill and ingenuity has been expended in the design of the system since it was first invented over 50 years ago.  An inspection of the apparatus will be still more convincing on this point.  It may be considered at first that the mechanism employed is unnecessarily complicated for the objects to be achieved; that it resembles clockwork and is liable to be easily deranged; but there is an essential difference between the train of wheels employed in the Gamewell signal mechanism and that of clockwork.  In the latter the driving force is slipped down by the train of wheels to a strength just sufficient to impart the feeble impulse necessary to maintain a pendulum in motion.  In the Gamewell wheel mechanism the force supplied to the escapement is appreciably strong, and judging by the experience of accurately made clockwork there is no mechanical reason why it should not continue in unimpaired condition for a considerable number of years.  In conclusion it is hoped that Post Office engineers will always bear in mind the importance of maintaining the fire alarm systems entrusted to their care at the highest possible standard of efficiency, remembering that the term "maintenance" is to be looked upon from the fire department's point of view, which is that of continuous availability to the public of every alarm box to transmit without fail or delay an alarm at any moment, especially as the prompt transmission of an alarm may mean the saving of human lives from the great danger of fire, a danger which is by no means negligible in this country, seeing that within the County of London alone there are about 100 human lives lost annually through this cause.

Gamewell Fire Alarm System
Power Board at Windsor Castle

 

 

 
BACK Home page BT/GPO Telephones Search the Site Glossary of Telecom Terminology Quick Find All Telephone Systems

Last revised: July 17, 2021

FM2