Design and Construction of Fire Alarm System in a Two Storey Building

Design and Construction of Fire Alarm System in a Two Storey Building

Chapter One of Design and Construction of Fire Alarm System in a Two Storey Building

INTRODUCTION

BACKGROUND OF PROBLEM

Fire detection system are safety system. They monitor rooms and buildings continuously for indication of fire outbreak and give alarm directly if one occurs.

Both the British Factory Acts 1961 and the officers shops and railway premises Acts 1963 stiputed minimum requirements in the case of fire that there shall be clear and audible warning throughout the building. Also, an earlier statutory requirement (section 36[7] of the factories Acts 1937) states that in any factory, hospitals, market places, homes etc. Where more than 20 persons are employed that place should be effective provision for giving warning signal in case of fire outbreak and that it shall be clearly audible throughout the building.

STRUCTURE OF THE PROBLEM

The alarm is given locally (visually and audibly) in order to mobilize internal auxiliary personal e.g the works fire brigade) and inform them as to the seat of the fire. A control center performs the organization of the alarm, that is, it makes available operational aids for the fire fighting measures and automatically bring the fire protection equipment into operation. Fire detection system must be tailored to the geographical and operational conditions in each individual case fore detection system, and must be installed in accordance with the relevant regulations.

OBJECTIVE OF THE STUDY

In the past and present years now, there have been serious occurrences of fire outbreaks, each of which causes destruction of articles work millions of naira. In the past few months, there was fire outbreak in NITEL Exchange building at Apapa and Ikeja all in Lagos, destroyed materials estimated to be about N2.5 million.

These ugly situation of fire outbreak always result in frustration, instabilities and disconsolations to the individuals involved and the country at large.

It is therefore, on the recognition of this fact that we initiated the idea of constructing the fire alarm system, which is to alert the security men or fire service men in the event of any fire outbreak.

SCOPE AND LIMITATION

There are two main parts of fire alarm systems:

(a) The public fire alarm system

(b) The private fire alarm system.

The public fire-alarm boxes are connected to the fire station by dedicated lines. These alarms boxes also perform the function of relaying calls initiated from private fire detection system to the fire station automatically. The private fire alarm detections system are used to monitor particular limited properties. They are installed in among other places, offices and business premises, industrials and commercial undertakings, theatres, cinemas department stores, schools, old people homes, hospitals and hotels.

Fire detection system consist of the control centre including its power supply (mains equipment and battery) with the principal functions of indication control activating alarms and system management, the alarm units connected through call circuits, the monitored and unmonitored lines for controlling the local alarm and information equipment, the fire protection equipment and the circuit to the fire brigade.

Fire alarm units are in the form of automatic fire detectors or of press bottom alarm boxes. Base of these, we extended our attention on the form and nature of a fire alarm system that will give the desired result. Careful study was extended also to such areas as choice of components, portability, durability, economic choice and of course engineering efficiency. We also did our very best to ensure that the circuit wiring conformed with set standards with regard to requirements rules and regulations of electrical installation.

The position of the sensory unit of fire alarm system found convenient on the corridors, rooms, bath rooms or any strategic position where it is likely to be any fire outbreak. However, the sensory unit of the system should be kept at some convenient distance from the kitchen, because of the thermal characteristics of some of the relay component. Although, if installed in the kitchen should be well safeguarded against the heat that normally comes from the kitchen and should be at least 1.5 meters above the floor to avoid children’s reach.

IMPORTANCE OF THE STUDY

It is hoped that the fire alarm unit will find useful application in homes, offices, hospitals, restaurants, market places, service centers etc to reduce the outbreak of fire.

DEFINITION OF TERMS

SWITCH

TYPES OF MECHANICAL SWITCH

(a) Push-bottom switch

(b) Slide switch and toggle switch

(c) Micro switch

(d) Water switch

(e) Electromagnetic relay

(f) Read switch

FUSE

A fuse is a device for opening a circuit by means of conductor designed to meet when on excessive current flow. The fuse comprises of all the parts that form the complete device. There are three types of fuses.

(a) Rewireable fuses

(b) Catridge fuses

(c) High breaking capacity (HRC) fuses.

CONDUCTOR

This is a device or material which offer a low resistance to the flow of current. A conductor must be:

(a) Of low electrical resistance

(b) Mechanically strong and flexible

(c) Relatively cheap

CABLE

A cable is of long insulated single conductor solid or stranded) or of two or more such conductors, each provided with its own insulation, which are laid up together. Basic parts of cable are:

(a) The conductor

(b) Insulator

A.C. CONTACTORS

These are mechanical devices whose function in any given system is for making and breaking of circuits on receipt of electrical signals (current) from the supply. They depend for their operation on the electromagnetic principles.

However, it can also be defined as a device for repeatedly establishing and interrupting an electric power circuit. It can be seen from the meaning of contactor that it’s principle function is to carry the current when the contacts are closed and to interrupt the circuit by opening the contacts.

Contactors may be of various types

(a) Manually operated

(b) Electrically operated, that operated by air cylinder. They may be of various sizes and details of construction.

SOUNDERS

These are devices in which electrical signals are converted into sound signals, e.g. bells, boosters, sirens etc. The types and the locations should be such that alarms are clearly audible to people using the building. They must not have a similar sound to any other device on the premises.

MANUAL (BREAK THE GLASS)

They are coloured red, and are located so that no person has to travel more than 30m from any position within the premises in order to raise the alarm. They are located on exist routes and in particular on floor landings of staircases and exit to streets. They should be fixed at a height of 1.4 above the floor at easily accessible, well illuminated, conspicuous positions free from obstruction.

DESIGN OF THE SYSTEM (DESIGN PROCEDURE)

In the design of this circuit, much care was taken to ensure correct polarity which in effect determines the continuity of the circuit. This was also made possible by numbering each connections.

Nevertheless, the approach to the design of this system involve trial and error methods. After the initial design was completed, the model was set up to task the behaviour of the initial system configuration and was by no means satisfactory, and was re-designed and corresponding analysis completed.

This process of design and analysis was repeated until a satisfactory workable system was obtained. Then a prototype physical system was constructed, built and tested to see whether or not it is satisfactory.

LAYOUT FOR THE CONSTRUCTION

The layout for this construction is based on the inter-connection of the circuit components of fig. 1.1 to achieve the desired function.

From fig 1.1, the switch unit comprises of the main switch S

The control cabinet is made of polished plywood. Wires are connected from the contactors to the connector. The connector terminals have been numbered for easy and correct connection between the control cabinet/display cabinet and the house. The control cabinet consists of three (3) contactors each controlling each floor. The siren (horn) is connected from a loop on the three contactors so that whichever contactors that is energized, the siren together with the bell of the particular floor must be on.

Also, from fig 1.1, it is seen that the supply from the A.C mains is connected to terminals 1 and 4 of the connector wires. The wires from the A.C source is connected to the contactors and the three contactors connected in parallel.

The cabinet contains the detectors switches which are connected in parallel for each floor. Their connections are brought out to the connectors according to their numbers.

The bell and the bulb on the control cabinet are connected in parallel, each being connected to the connector number outside it. The detectors and test bottoms on the cabinet are connected in parallel and each connection brought out losing the flexible wire to the connector number.

The connector serves the purpose of disconnecting the switch unit from the rest of the building and also for correct and easy connection between the control cabinet and the house cabinet.

DIAGRAM

DIAGRAM

DIAGRAM