"Heroes with grimy faces" - Sir Winston Churchill

"Heroes with grimy faces" - Sir Winston Churchill

July 13, 2005

FIRE ALARM SYSTEM




(Photos: Bob's Telephone Files web site)

British firefighters call fire alarms ``Shouts.'' That probably goes back to the days when peopled shouted ``Fire! Fire!'' to bring out the brigade. In the 19th century and early 20th century, the fire alarm telegraph was introduced in London and other cities worldwide.

As technology advanced, ``corner call box'' systems became obsolete to be replaced by today's emergency telephone lines such as 999 in the United Kingdom and 911 in the U.S.

In January 1938, Volume 30 of the Post Office Electrical Engineer's Journal discussed the ``modernization'' of London's fire telegraph alarm system in the years leading up to World War II. The article, written by C.H. Wright, explained the evolution of the alarm system - and also provided a glimpse at pre-war LFB operations.

Excerpts follow:

Introduction

The ceremonial opening of the new Fire Brigade Headquarters, Albert Embankment, by His Majesty the King on July 21st 1937 marked the completion of the initial stage in the London County Council's programme to provide London with an up-to-date fire alarm system. For the past 37 years or so London has been protected by the "Brown" fire alarm system which has been rented by the Council from the Postmaster General. This system, which was invented by the late A. C. Brown, is the acme of simplicity and has faithfully fulfilled its purposes.

In the "Brown" system each street post is connected by a direct pair to a common battery at the station via a flap indicator. When a point is "pulled" the line circuit is closed, causing the flap of the indicator to fall, exposing its designation and a line jack, and actuating the station alarm bell. The contact is kept closed by an electromagnet within the head, until released by the watchroom attendant plugging into the line jack and disconnecting the line current. Each street point is also equipped with a buzzer which produces a distinctive signal when the point is pulled enabling the attendant to distinguish between genuine and false calls.

In 1913 as the result of an unfortunate fatality the Brigade intimated that they had ceased to place reliance in the buzzer signal and from that date they have turned out for any and every indication what so ever.


In 1900 there were 675 posts. They had increased to 1,300 in 1928 and 1,732 in 1936. The number of calls received in 1936 was 9,297. Of these, 5,875 were genuine and 3,422 false. The false calls were divided between 1,304 malicious calls, and 2,118 calls due to electrical defects and other causes. Of the latter figure approximately 1,000 were attributed to electrical faults.
It was with a view to reducing the number of abortive turnouts and the annual costs to the Brigade in rentals that in 1928 the Council approached the Post Office to aid them in providing their own system and the Post Office readily agreed to place its experience at the disposal of the Council.

Following protracted cost studies the Council decided to accept the Gamewell, code signalling, closed circuit, system which was considered to be the most satisfactory, and an experimental system of 26 street boxes arranged on two loops, was provided and installed in 1931 by Messrs. Standard Telephones & Cables, Ltd., at the late Headquarters station in Southwark. The Post Office conducted the negotiations and the placing of the contract, supervised the installation and the acceptance of the equipment, and recovered the cost, which included a nominal percentage service charge, from the Council under a repayment order. The line wires were of course rented from the Post Office which also undertook the maintenance of the equipment on rental terms. The system functioned satisfactorily and in 1936 the Council decided to proceed with the conversion programme commencing with the new Headquarters Station at Lambeth, to be followed by the "B" District. They expressed a wish, however, for certain later developments which were covered by patents associated with the apparatus manufactured by Messrs. Automatic Telephone & Electric Co., Ltd., to be incorporated in the street boxes. The contractors were approached and by agreement with the Council it was decided to accept street boxes of Messrs. Automatic Telephone & Electric Co.'s design and station equipment designed by Messrs. Standard Telephones & Cables. This has resulted in a division of the work between the two contractors.

Work has been completed in the "B" District and the equipment was brought into use in November. There are ten stations including Clerkenwell, which is the superintendent station, and 299 street boxes. Messrs. Standard Telephones & Cables are installing the equipment at Whitefriars, Cannon Street, Redcross Street, Soho and Holloway, and Messrs. Automatic Telephones and Electric Co. have Clerkenwell, Euston, Islington, Camden Town and Kentish Town in hand.

Instructions have also been received to proceed with the installations for Battersea and Shadwell new fire stations.

Organisation of the London Fire Brigade


The L.C.C. area is divided into six districts A-F, each in charge of a superintendent station which controls the outstations in the respective districts. The superintendent stations are Manchester Square, Clerkenwell, Whitechapel, New Cross, Southwark and Clapham. The station at the Fire Brigade Headquarters is an outstation on Southwark.

There are 52 outstations and each has a direct telephone line to its superintendent station, each of which has in turn direct communication with the control room at headquarters, Lambeth. Each superintendent station has a direct line numbered 2222 to every telephone exchange in its district. Outstations have no direct exchange line, so that fire calls originated by the public over the telephone exchange network must necessarily be advised to the superintendent station. The alarm is then transmitted to the outstation concerned from the superintendent station by a fire signal over the direct telephone line, which rings the station alarm bells. While the firemen are manning the appliances ready to depart, the watchroom attendant ascertains the particulars of the fire and passes them to the station officer who rides on the first appliance to leave.

An indicator at the superintendent station associated with the fire signal key is operated and remains in view until it is restored manually upon receipt of the advice from the outstation that the appliance has returned.

If a call is received at an outstation from one of its street points the watchroom attendant transmits a fire signal to the superintendent station, which rings a local alarm bell only, and passes over details of the call. The indicator signifying "appliance out" is again operated and remains so until the appliance returns. The superintendent thus knows at any time the disposition of the fire fighting appliances in his area.

The Brigade is organised so that as some stations are deprived of their apparatus in response to calls others are re-distributed to cover those stations. Particulars of all fires and the appliances attending them are notified to headquarters where a mobilisation map is marked to show the seat of the fires and the appliances attending.

Fires which are beyond the capacity of an outstation to deal with become district calls upon which the district appliances are concentrated. If these cannot gain control over the conflagration a brigade call is circulated and appliances are drawn from the stations throughout the London area under the direction of the Mobilisation Officer at headquarters. This may mean as many as 60 pumps, escapes, etc., being employed. The remaining appliances are re-distributed over the area.

The present equipment of the Brigade includes 68 pumps, 55 dual purpose appliances (escape and pumps), 35 escape vans and turntable ladders, 26 other appliances and 3 river floats. There are 31,311 fire hydrants and 52 miles of hose. The personnel comprises 1,980 uniform staff and 163 administrative, technical and other ranks.

The `Gamewell' System

Since its introduction into this country in 1900, the Gamewell System of Fire Alarms has remained basically unchanged. The street fire alarm boxes differ in detail, but the modifications which have been introduced from time to time by the various manufacturers have all been in the nature of refinements, or added facilities. The fundamental principles of the system are as follows :-

1. It is a closed circuit system. The diagram shows the electrical circuit in its simplest form.

2. The street fire alarm boxes are arranged in groups. The boxes forming a group, maximum 20, are connected in series by a single wire which passes progressively from one box to the next.

3. A small current of 50 milliamps is maintained around the loop by a battery at the fire station. The maximum permissible voltage of the battery is 50 volts.

4. Each box contains a powerful clockwork mechanism which is employed to drive a code wheel which transmits signals to the fire station.

5. The various electromagnets in the recording equipment at the station are employed to release the energy of coiled springs.

6. Each box bears a code number of two, three, or four digits. The highest digit is 6.

7. Normally, the mechanism of each box is short- circuited by contacts held closed within the box.

8. When a box is "pulled" it commences to send its code after a short test interval. Impulse contacts in series with the line are intermittently made and broken in accordance with the code number of the box. A box coded 214 would transmit two impulses, followed by one and then by four. Between digits the circuit is disconnected.

9. The code number is sent three times, whereupon the mechanism stops and the short-circuit is restored. The signals are transmitted at a speed of 3 impulses per second.

10. Suitable apparatus is located at the fire station which gives visible and audible indication of the call.

11. A disconnection on the line due to a fault is recorded on the station apparatus and a " patching" switch is operated automatically, which earths the station battery and connects both ends of the fire loop bunched, to the recording apparatus. The system resorts temporarily to earth working.

12. The use of code signalling prevents a fault from being mistaken for a genuine call.

13. Calls can be received without loss of impulses under anyone of the following fault conditions:-
Circuit brokenCircuit broken and earthed at the same pointBox or boxes short-circuitedCircuit earthing

14. Calls incoming from the Gamewell loops can be automatically repeated to a central or superintendent station over a repeat loop.

15. Two types of alarm boxes are used.


(a) Plain Sector.
(b) Non-interference Succession.


The plain Sector box is employed on small installations where the possibility is remote of two boxes on the same loop being pulled simultaneously. On large installations this condition is more likely to arise, and from a consideration of the diagram above, it will be seen that if a second box is pulled while one is already transmitting, they world interrupt each other's signals and the record at the station would be unintelligible.

To prevent this, the succession box was introduced. With this type more than one box can be pulled simultaneously on the same loop without interference. The succession feature causes each box to await its turn to transmit its code, the order of succession being controlled strictly in accordance with the chronological order in which the boxes were pulled. When a box is once "pulled" further operation of the handle cannot affect the working of the mechanism, until it has transmitted its code and reset itself.