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FT 41AUTOMATIC ALARM SYS

MANUALLY OPERATED FIRE ALARMS

OBJECTIVE

1. To explain the manually operated fire alarm system that fixed to a building and thatare listed under f ixed installation.

REFERENCE

2. a. Manual of Fireman ship Book 9.b. Fire College Notes.

CONTENTS

3. Introduction. In the introduction earlier, the point was made that a fire alarm can beraised automatically by a detections system or manually by a person in the affected building.This chapter examines the means available to a person in the affected building for raising analarm. These means will generally be either manual or manual/electric, not forgetting that analarm can always be raised vocally.

4. Manual Systems. The purely manual means for raising an alarm involve the use ofbasic devices which in clued the following:

a. Rotary gongs which are sounded by simply leading the handle around the rimof the gong.

b. Hand strikes e.g. iron triangles suspended from a well accompanied by ametal bar which is used to strike the triangle and produce a loud clanging noise.

c. Hand bells.

d. Whistles.

5. These devices are normally found on the walls of corridors, entrance halls andstaircase a situation where they are readily available to anyone who may need to raise analarm.

6. It is, of course, relatively cheap to provide devices. While they give an alarm over alimited area, operation of one of them is not adequate to give a general alarm throughout the

premises; nor do they necessarily convey the alarm to a central point from which the firebrigade can be speedily summoned.

7. As a person in required to operate them a continuous alarm cannot be guaranteedfor as long as may be necessary. Because of these restrictions in their use it is unlikely (andin certain instances undesirable) that these devices will be the sole means of rising alarmsexcept perhaps in low risk areas.

8. Manual/Electric System. There are system which, although set in motion manually,operate as part of an electrical alarm circuit. Manual call points can, in fact, be incorporatedwith detectors into a comprehensive fire alarm system which allows for automatic and/ormanual rising of an alarm.

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9. The call points in a manual/electric system are invariably small, wall mounted boxes.They are designed to operate either:

a. Automatically, when the glass front is broken orb,. When the glass front is broken and the button push pressed in.

10. The majority of available models are designed to operate immediately the glass front

is broken.

Basic Illustration of a Fire Alarm Call Point

11. Contact (1) (picture above) is connected to one side of the electrical circuit; contact

(2) is connected to the other side. The movement of contact (1) is governed by the springloaded button which is maintained in position by the glass front. In the healthy situationcontact (1) is therefore held off spring-loaded button outward, allowing contact (1) to engagewith contact (2) thus completing the electrical circuit and raising the alarm.

12. As an alternative this type of call-point can be fitted so that the electrical circuit iscomplete in the health state, a relay being incorporated to hold off the alarm. On breakingthe glass the circuit is broken, the relay de-energizes and the alarm sound.

13. In either case, accidental breaking of the glass will, of course raise a false alarm.This is most likely to happen in a situation where various goods and materials are beingmoved about (e.g. in workshop and storage areas). In these situations the problem can be

overcome by installing a call-point in which the push button has to be manually pressed in toraise the alarm after the glass has been broken.

14. To help with the breaking of the glass in call points most manufacturers will provide, ifrequested, a small chromium-plate hammer for attaching by chain to the box. In lieu of thehammer some manufacturers will score a circle in the glass for easier breakage; in onecase sufficient to broken by a blow with the tips of the fingers.

15. Obviously these arrangements are desirable only when the possibility of accidental ormalicious breaking is minimal.

16. Where neither hammer nor scored glass is available a blow with a covered elbow, ashoe heel or other sharp object will be effective.

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17. In certain types of occupancy (e.g. mental hospitals) or in situations where vandalismis likely, a modified call point is often fitted. It can be seen that these points have a soliddoor with a keyhole. When the key is inserted and turned the electric circuit is completedand an alarm is raised.

18. The key will normally be in the possession of or accessible to, authorized personalonly.

19. Recommendations on the installation of manual call points a given in British StandardCode of Practice 1019. In general terms they should obviously be fitted conspicuouspositions, usually on escape routes, where anyone operating them is not exposed tons duerisk.

20. Miscellaneous. In addition to the facilities specifically designed for raising an alarmit is possible to use facilities which may already be installed in a building for other purposes,e.g. a telephone or public address system.

21. Which automatic telephone systems arrangements can be made for a particular

dialing code to be reserved for use when reporting a fire? Use of such a code on connectthe caller to a person (normally the operator) responsible for ceiling the fire brigade andsounding the general alarm; alternatively it can be arranged that use of the codeautomatically sounds the general alarm.

22. While such systems are useful as back-up services it can be unwise to rely on themas the sole means of raising an alarm. The have two main disadvantages.

a. Delay - the delay that can occur between the person detecting the firecontacting the person at the switchboard or public address system; the further delaythat can occur between this contact and the actual raising of the general alarm.

b. Familiarity (particularly with a public address or manual telephone system) -

the fact that people are familiar with these systems being used for other purpose maymean that they treat them with less urgency than deserved when they are used asfire alarms.

23. Restricted Alarms. In order to avoid unnecessary disturbance in hospital and otherlarge installations it may be desirable to resist an initial alarm to the locality in which it arisesor restrict it to a small number only if a duty officer considered it desirable to do so.

24. Single light systems which are often installed for summoning staff for variouspurposes, can be for restricted alarms; operating of the call point producing a certain lightcode signal. These lights are installed at warden trances (in the case of hospitals) atpassage intersection and other places where they are conspicuous to staff.