Fire Alarm Panel Introduction Introduction:
Many fires not discovered in their early stages by occupants of the premises involved but are revealed only when they have developed sufficiently to become noticeable and have caused considerable damage. In view of the above fact, it will be appreciated that automatic detection and alarm systems offer particular advantage with their potential for quick detection and automatic alarm. This is becomes very essential in premises which are unoccupied at night, week-ends and during holiday periods.
Automatic fire detection forms part of the whole process of fire prevention and fire fighting. Selection of automatic fire detection equipments must be considered in relation to the whole system.
Points of considering while recommending Fire Detection and Alarm System :
The prime function of a fire detector is to detect one or more changes in the protected environment indicative of the development of a fire condition.
To consider all situations where appropriate detection equipment may help prevent a fire starting or developing. Listed below are seven such situations with suggested automatic detection devices :
The fire alarm system can accommodate various devices and sensors. Manual Call Points, Isolators, Hooters and Response Indicators are treated as devices.
1. Manual Call Point :
Manual Call Point is a device meant for human beings to operate in the event of visual fire or smoke where the sensors failed or delayed to operate. MCP is also interfaced with the main fire alarm system. Typically these devices are installed near the exit door / corridor / staircase.
2. Isolator :
3. Response Indicator :
Normally these indicators are fitted outside the closed rooms, so that the person can ascertain the status in the event of alarm condition. This reduces the time consumption while searching for the doubtful location.
4. Hooter or Sounder :
Generally the device is designed such that the current consumption is low with high volume and no additional power supply is required.
Effective detection :
The effectiveness of detection system depends upon few considerations which are as follows :
Choice of Detectors
The detectors working on different principles of operation will respond differently to a given fire situation. Also a particular type of detector cannot detect a fire equally efficiently in all situations. The following variable factors that define a fire situation have influence on choice and situation of detectors in particular premises.
A. The burning behavior of combustible contents.
B. Structural characteristics of the area to be protected.
C. Environmental conditions.
D. Processes carried out,and.
E. Ventilation including forced air flow.
Different Types of Fire Detection and Alarm Systems
There are four types of systems available today. They are,
1. Conventional System
2. Addressable System.
3. Analog Addressable System.
Comparison of all types of detection system
Comparison of Typical Conventional, Addressable, Analogue Addressable and Intelligent Systems.
Specification of Relevant Standard
Equipment specifically manufactured for these purposes are selected and standardized installation methods are anticipated during the design. In the United States, NFPA 72, The National Fire Alarm Code is an established and widely used installation standard.
There are a number Indian Standard Specifications and code of practices dealing with automatic fire detection and alarm systems, a few of which are stated below :
NFPA Code number 74 requires that battery-operated units meet the following requirements:
The alarm must be capable of producing an alarm signal of 85 decibels for four consecutive minutes. The batteries must meet all power requirements for at least one year, including routine testing. A distinctive, audible trouble signal must be given at least once per minute for seven consecutive days before the batteries are incapable of operating (from aging, terminal corrosion, etc.). The unit must also be capable of producing the alarm signal for four consecutive minutes during the seven days of trouble signal.
Battery-operated smoke detectors have two advantages and one disadvantage when compared with detectors operated from the dwelling’s electrical power. One advantage of battery-powered units is that if the electrical power in the dwelling should be off due to an interruption from the utility company or from a fire within the dwelling, the detector will still function. Some manufacturers are now manufacturing units with a battery backup in case power is lost.
The other advantage is that you can install a smoke detector in an existing dwelling where an appropriately placed electrical outlet is not available.
The major disadvantage is that the batteries need to be replaced once a year.