Fire Alarm System Design and Installation Consideration

One of the most important aspects of a building structure is notably a fire alarm system. A good fire alarm system can save your life and protect your property. Many years ago, when fire alarm systems did not existed, fires swallowed large buildings, and had even caused to wipe out its entire neighborhood. A fire alarm system is generally required to be installed as part of fire certificate required by the Fire Precautions Act or the workplace regulations after an audit of a fire risk assessment.

It is surprising to realize how many people think the fire alarm systems are installed exclusively in corporate buildings and businesses. It is much more important to think about fire alarm system that would work at your home than anywhere else, as your main concern is the safety of your family and your property.

Planning the Fire Alarm System

The decision of whether a fire alarm system is required or the type of category should not normally be the responsibility of the designer, customer/installer. The local authorities should take these decisions for enforcing legislation in buildings. With all fire alarm systems there should be an exchange of information and decision process; a typical example would be building control officers, fire authorities, statuary and insurance requirements etc…

This is normally because the designer, customer/installer tends to underestimate safety or generally the public quickly forget the big disasters and just do the planning for the necessity only. And also a fire hazard in a building will not only be a threat to itself but also to the near by property, so it's a need of a community.

When sufficient information and level of category has been obtained then the fire alarm system can be designed.

Basically there are two categories of protection for which fire alarm systems are employed, Property Protection and Life Protection.

The Importance of Effective Fire Alarm Placement

When it comes to installing a fire alarm or smoke-detector, many people are not sure where, exactly, they should be placed. It is extremely important that all fire alarms are placed in the right locations around the home so that, in the event of a fire, any people in the home can be alerted of the situation as quickly as possible, giving them the most time to get out of the home safely before the fire or deadly smoke reaches them. So when a person is installing new fire alarms in a home, there are several things that they should keep in mind when it comes to their placement. Obviously, the placement of fire alarms and the number of them that are going to be needed will vary greatly based on the size of the living space. 

Moreover a fire alarm is to be never installed near any kind of heating or cooling vents in the home. If one is located near a vent and the vent is turned on during a fire, the smoke may actually be blown away from the alarm, resulting in it not sounding off. And, fire alarm systems should be tested every once in a while to make sure that they are in working order. Batteries should be replaced often to make sure that the fire alarm is not dead. However, for the most part, fire alarms and smoke detectors do not require a whole lot of maintenance, especially considering that they can be life saving devices.

The basic elements of fire alarm systems are as follows :

n             Call Points : While deciding on the positions of call points the following guidelines are to be considered.

l               Call points should be fitted in conspicuous and easily accessible points on escape routes, mounted at 1.4 metres +/- 0.2m above floor level.

l               Call points should be located at the exits to the open air and all storey exits on each floor.

l               You should not have to travel more than 45 meters to operate a call point or 25 meters in any special hazards or high-risk areas.

n             Smoke Detectors : There are different types of smoke detectors : l Optical/ multi-sensor l Beam detectors.

Optical detectors : Optical smoke detectors operate on the principle of infra red light refracting off smoke particles entering the chamber. Hence these types of detector are more sensitive to smoldering fires such as modern fabrics or furnishings. Optical detectors are more prone to false alarms from steam or dusty environments (outside bathroom/building works).

Beam Detectors : Beam detectors comprise of a transmitter and a receiver. The transmitter emits an infra red beam from the TX (transmitter) to the RX (Receiver); the beam detects obscuration by the smoke.

Heat Detection : There are three main types : l Rate of rise heat detectors l Fixed temperature heat detectors l Rate of rise cum Fixed temperature heat detectors.

Rate of rise heat detectors :  These types will respond to a sudden increase in temperature but also have a fixed element in case of a slow smoldering fire. Rate of rise detectors are most suitable for areas where a smoke detector is undesirable such as warehouse, go down etc. where the environment is dusty or humid.

Fixed temperature heat detectors : This type have a sensing element fixed at a particular temperature, when this is reached, the detector operates. Fixed temperature is ideal for kitchens, boiler room where a rate of rise heat detector would be unsuitable.

Rate of rise cum fixed temperature heat detectors : This is a combination of both the above heat detectors. These are used in places where combined protection is required such as ware house storing slow burning goods which may not trigger a rate of rise heat property.

Spacing of Detectors

A smoke detector under a flat ceiling has a radius of 10 meters.  Heat detectors have a radius of 7 meters. A detector radius should reach every part of the room. Detectors should be located a minimum 500mm away from walls. (See fig. 02)


Spacing between                 Spacing between

smoke detectors                  heat detectors

There should be a 500mm clear space below and around the detector. Detectors should be located at least 1 meter from air conditioning units. If an obstacle (for example, beam) is less than 10% of the ceiling heights then, ignore. If it is more than 10% of the ceiling height, treat it as a wall for detector spacing locations. Obstructions from floor to ceiling is more than 300mm, then ignore, and if less than 300mm then treat it as a dividing wall. In a pitched ceiling or in a roof void the spacing of the detector can be increased for 1% for every degree of the pitch angle up to a maximum of 25%. For this increase to be implemented, detection should start at the apex.

Detection in Voids

If the system category requires automatic detection in areas where there is a void greater than 800mm then fire detection should also be provided in the void. Voids less than 800mm generally do not need to be covered with the following exception.

l               If a fire or smoke can spread especially between rooms or compartments before detection.

l               Or there is high risk which should be determined by a risk assessment as to warrant protection in the voids.

Ceiling Heights

As the time taken for smoke and heat to reach the detector increases with ceiling height, and usually a maximum ceiling height of 12 feet is assumed beyond which closer spacing of detector will not help simply because the heat or smoke may not reach the detector in time.

Audible Alarms

One sounder should be located near the control panel or entrance on a separate circuit. Addressable systems should be wired from the control to a sounder protected by a short circuit isolator. All the sounders should sound similar to avoid confusion. A minimum of 65 dB is required in general areas or 5 dB above any background noise which persists for more than 30 seconds. Where high noise levels exist, visual indication such as strobes may be required.  Where sleeping people are to be woken then 75 dB is required at the bed head.  A loss of 30 dB per door should be allowed for, to guarantee 75 dB at the bed head a sounder per bedroom is recommended. For areas where there are people with impaired hearing (say, special school for the hearing impaired etc…), the approval of devices would subject to the consultation with the users. The decibel level decreases -6dB from a sounder every time the distance is doubled.

Control Equipment

The equipment should be generally accessible on the ground floor next to the entrance to the building to enable the occupier and the fire brigade to quickly identify the zone in fire. A plan of the building should be displayed close to the control panel showing entrances, escape routes and zones. Operating instructions and logbook should also be available. And in case of multiple entrances all the entrances other than the main entrance (where the main control panel is placed), should have a repeater panel so as to avoid the search for the main control panel; because in an emergency every second counts.

Power Supplies

The power supply for the control panel should be exclusive to the fire alarm system.  This should be secured from unauthorized use and labeled “FIRE ALARM DO NOT SWITCH OFF”. Upon a mains failure the batteries should continue to power the system for a minimum of 24 hours plus 30 minutes alarm duration after that. For unoccupied premises the battery backup should be up to 72 hour plus the 30 minute alarm duration. For over 72 hours the system should be monitored by a central station.

Maintenance and Documentation

Upon completion of system testing, there are often deficiencies that are found. While these must be corrected immediately, if possible, sometimes this cannot be done right away. However, it is incumbent on the building owner to ensure that the system is fully operational within a reasonable period of time. Most preventative maintenance is often easy to perform. Depending on the environment in which the equipment operates, it can consist of simply blowing the smoke detectors out with compressed air to more frequent and intensive cleanings based upon location. In the end however, the technician should always follow the manufacturer's recommendations in order to be completely sure that proper maintenance is being performed. Upon completion of system testing and maintenance, the servicing organization must complete a maintenance form and leave it on site with the building owner or his duly authorized representative. It is imperative that the required documentation be kept available at all times. In addition, the owner must retain records of inspection, testing and maintenance for the life of the system.


Most importantly, the simple fact is that fire alarm systems save lives, and their proper operation should be of the highest priority.

The fire alarm system is seen as an unnecessary expenditure in many commercial establishments and in domestic sector. But in fact the fire alarm system must be a part of the long term planning and investment. It helps in preventing a mishap which otherwise would spoil an entire life time efforts and it helps in being prepared for the unexpected. And in many cases the points mentioned in the article are tampered with and people compromise with the safety. I hope this would help make the fire alarm systems better equipped to protect life and property.