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Fire Alarm SystemsField's Fire Protection, Inc. is proud to distribute the Notifier line of Fire Alarm Systems . Please contact one of our sales representatives with any questions that you may have about the installation, service, or maintenance of your fire alarm system. Fire Alarm Systems in the News Fire Alarm Systems: What do the Codes Say? By Bruce Johnson http://www.nvfc.org/page/626/show_item/800/News.htm Published on the National Volunteer Fire Council web site Fire alarm systems and smoke alarms are life safety systems that save countless lives each year, both civilians and firefighters. The International Residential Code requires interconnected, hardwired smoke alarms in all new construction (Section R313) and the International Building Code and International Fire Code (Section 907.2) call for manual or automatic fire alarm systems in most commercial buildings with high life occupancy or other hazards. In addition to new construction, the International Fire Code also has provisions for fire alarm systems and smoke alarms in existing structures (Section 907.3). There has been a lot of discussion lately concerning residential smoke alarm technology. Americans have relied on low-cost ionization type detectors for more than 30 years. Some new information, however, indicates that ionization technology may be slower in detecting smoldering fires while they are most effective in alerting residents to fast-flaming fires. Photoelectric detection technology has also been available for decades and recent testing indicates this technology may respond faster to smoldering type fires. Because photoelectric technology is several times more expensive than ionization, most homes have the ionization type devices presently installed. Since one can never predict what type of fire may occur, there have been recent recommendations by many fire service organizations to advise the public their best protection is to install both types of smoke detectors or a “dual-technology” detector. Some jurisdictions have introduced legislation that would make the requirement for combined ionization and photoelectric smoke alarms or dual technology laws. While this may seem a logical approach, it has not been fully substantiated by thorough and independent scientific testing, nor has it gone through a consensus process utilized for updating codes or standards. Laws are tough to pass, but even tougher to change once enacted and signed into law. Future information or technology may render these laws effectively obsolete, but still on the books. This is an important consideration for any code-related issues that may seem to be right today but may turn out to be wrong tomorrow. There are many factors that need to be tested and considered by all the technical experts and stakeholders before a change can be made to the International Residential Code to expand its requirements beyond the current requirement for interconnected, hard-wired smoke alarms in each sleeping room, in the hallway outside each sleeping room, and at least one on each floor. The question of how to provide the best possible protection from all types of fires in residential dwellings is an important life safety concern that is best answered through a governmental consensus process, such as those used for changing building codes or installation standards developed by the International Code Council. As a member of the fire service, this is another area where fire service participation in the code development and installation standard development process will be critical in determining the future requirements for smoke alarm technology in homes across America. The International Code Council uses a governmental consensus process that accepts code change proposals and testimony from any interested party, but limits the final vote to determine what is published as requirements in any of the I-Codes to governmental voting members. Governmental members are those who administer building and fire safety codes for their jurisdiction and are “First Preventers” – code officials and other public safety servants as opposed to those representing any special or financial interest. They may go under the title of fire chief, fire inspector, fire marshal, or fire code official, but the labels merely obscure their common mission to prevent harm by ensuring code compliance before a disaster occurs. The fire service is welcome to apply for Code Council Governmental membership and fully participate in code development. Properly installed and maintained manual and automatic fire alarm systems in commercial buildings such as public assembly buildings, high-rises, hospitals, factories, mercantile's, schools, and malls to name a few, are also essential life safety systems. International Building Code and International Fire Code include provisions for the installation, testing and proper maintenance of these systems. These coordinated and companion documents provide the utmost public and firefighter safety when used together. They identify the types of buildings that require a manual and/or automatic fire alarm system based on life risk, building construction features, and/or fire or hazardous material risks. The International Fire Code references the National Fire Protection Association – Standard 72, National Fire Alarm Code for commercial fire alarm system design, installation, and maintenance specifications. Proper installation, correct location of smoke detection devices, and regular inspection, maintenance, and testing of all devices are essential for proper system operation and the prevention of false or nuisance alarms, a potentially dangerous response for fire service and the public. The International Fire Code is written to ensure the fire alarm systems will detect smoke quickly and alert occupants in sufficient time to safety exit the building. These fire alarm systems must be designed by qualified professionals. The permit application must include detailed plans that are reviewed by trained fire and building code plans examiners prior to installation. Qualified (and in some cases certified) installation technicians must complete the installation for acceptance testing by fire inspection personnel. The International Fire Code requires all fire protection systems must be installed, inspected, tested and approved prior to any public occupancy of the building. When the fire alarm system is temporally inoperative for maintenance, repair, or testing, the International Fire Code requires a fire alarm system impairment coordinator is used to ensure occupant and firefighter safety. Building owners are required to follow several basic steps to communicate system impairments and provide alternate means of occupant safety for the duration of the impairment. Finally, the International Fire Code prohibits the use of any device that has the appearance of a life safety device (i.e. smoke detector, heat detector, manual pull station, etc.) for any other purpose. This includes covert security equipment that is disguised to look life part of the fire alarm system. When commercial fire alarms systems are properly installed and maintained, they perform very well. When they are not, the public and fire service are subject to unnecessary “false alarms” that puts everyone at risk. The public may be slow to respond to the home smoke detector or commercial fire alarm if it is “always going off” with no smoke or fire condition. The fire service may be at risk of injury during response and may also suffer from false alarm syndrome; becoming complacent that the response for the activated fire alarm will turn out to be a false activation and not taking the same safety precautions we would take for a confirmed fire. These human responses defeat the effectiveness of fire alarm systems and smoke detectors as life safety systems. The fire service will need to pay special attention to fire alarm maintenance requirements and periodic inspections as the national economic recession may lead business owners to cut back on the required maintenance to balance their budgets. Work with your fire inspectors to promptly inspect premises with a sudden increase in fire alarm activity to avoid potential problems. Fire Alarm Systems Fire Alarm Control Panels Conventional Traditional fire alarm panels that were the primary installed fire alarm panel prior to 1998 were conventional zone panel. In a zoned system, fire alarm devices in a common area or floor of a facility are connected to the same alarm initiating circuit. Each zone requires its own circuit conductors. This arrangement allows alarm annunciation to be reported by areas of the building to identify what device is in alarm. Conventional panels are often used in small facilities where a few zones can provide sufficient alarm annunciation.
Addressable With the advent of microprocessors and digital electronics, addressable fire alarm control panels and devices have become more common than conventional systems for medium and large-sized facilities. They have even become more cost effective in some small applications as well.
Addressable fire alarm systems use digital encoding and multiplex technology to more accurately identify alarm locations and device conditions. Each fire alarm device in a system is programmed with an unique address. The fire alarm control panel is capable of communicating with a single address or a group of addresses depending on the functions required. The communication is often multi-plexed over a common cable, sometimes referred to as the signaling line circuit (SLC). This arrangement significantly reduces the amount of cabling necessary to install the system. The communication channel allows two-way communication, thus enabling the fire alarm control panel to control as well as monitor fire alarm devices. A significant component of addressable fire alarm system is the software programming necessary to make the system function correctly. The programming allows for flexible applications where you want to have specific control over the inputs and outputs. The communication technologies employed in addressable system allow for advanced features (e.g. self-adjusting smoke detectors) to accommodate sensitivity changes due to age and accumulation of dust prior to maintenance. These features are not available with the standard conventional system. Fire Alarm Devices Automatic Detection Components of a fire consist of:
Fire detection devices are built to detect one or a combination of these components. While all components are necessary for a fire to exist, all components may not exist at a detectable threshold. Detectors will be selected that will detect the elements that may exist in a fire for the ambient conditions that are present. It also should be realized the similar non-fire components might exist in the same ambient conditions, which could cause unfavorable false alarm conditions. Devices used for fire detection include smoke detectors, thermal detectors, flame detectors, fire-gas detectors, and other devices.
Each detector is further divided into line, spot, and air-sampling.
Detectors may be further classified as restorable or non-restorable types:
Smoke Detectors There are three types of smoke detectors, ionization, photoelectric, and combination. Ionization The ionization smoke detector is widely used. Its capability to detect smoke originating from fire is best utilized for clean-burning fires that produce small particles during combustion.
The typical ionization type of smoke detector consists of an alpha particle producing a radioactive source, a smoke chamber, and charged detector plates.
Advantages of Ionization style smoke detectors:
Disadvantages of Ionization style smoke detectors:
Typical locations or hazards for ionization detection:
Photoelectric Photoelectric type smoke detectors are the most common smoke detector used today. It detects smoke by using either the principle of light obscuration or light scattering. Its capability to detect smoke originating from fire is best utilized for fires that produce large particles during combustion.
Spot-type photoelectric smoke detectors using the light obscuration princliple have a light emitting device, usually a light-emitting diode (LED), a smoke chamber, and a photosensitive device that receives the light directly from the light source and produces a monitored current. Smoke that enters the smoke chamber reduces the intensity of tech light reaching the photosensitive device, which reduces the monitored current. When the intensity drops below a certain level, the sensor control circuitry detects a drop in the current produced by the photosensitive device. When the current falls below a preset threshold, the smoke alarm is triggered. Spot type photoelectric smoke detectors that use the light scattering principle are constructed similar to the detectors that use the light obscuration principle except that the photosensitive device is set so that it cannot see the light source directly. When smoke enters the chamber, the smoke particles reflect the light from the source into the photosensitive receiver. When sufficient light intensity is detected, the alarm is triggered. Advantages of Photoelectric style smoke detectors:
Disadvantages of Photoelectric style smoke detectors:
Typical locations or hazards for photoelectric detection:
Beam Detector Beam smoke detectors are line-type photoelectric detectors consisting of a separate light source and photosensitive receiver. These devices are usually installed in large open areas where there is an unobstructed line of sight between the light source and the receiver and where the use of spot-type detectors would be economically unfeasible due to the number of detectors required.
Advantages of Beam style smoke detectors:
Disadvantages of Beam style smoke detectors:
Typical locations or hazards for beam detectors:
Air Sampling Smoke Detectors For environments where detection of smoke is most critical, an air-sampling system provides the earliest possible detection. An air sampling or aspirating type fire detection system is a self-contained smoke detection package compromised of five primary components:
It uses a network of pipes to continuously draw air samples and direct them to a central smoke detector.
The system operates with a network of sampling pipes that extend into the protected area. The pipes are usually made of a thermoplastic material. An internal aspirator continuously draws air into the piping network. The systems use either a filter assembly or laser particle counting technology to filter out airborne dust and debris particles, which helps to eliminate false readings. Typical locations or hazards for Air-Sampling smoke detectors:
Thermal Detectors Fixed Temperature Fixed Temperature Thermal detectors can respond to:
Typical fixed temperature spot-type smoke detectors contain a bimetallic switch element that closes at a specified temperature limit. The switch is normally composed of two metals, each having a different temperature coefficient of expansion. As this bimetallic element heats, the metal with higher coefficient of expansion causes the switch to bend or curve closing the switch; thus indicating an alarm condition.
Line type thermal detectors are cables that detect heat along their entire length. A line type thermal detector may consist of two wires that are separated by an insulator. After the heat builds to a certain level the insulation melts, allowing the wires to touch and current to flow, initiating an alarm. Bimetallic spot and coaxial style thermal detectors are self restoring. Fusible link and melting insulation types of line thermal detectors are not self-restoring. Fixed Temperature Spot Type Thermal Detector Classification
Advantages of Fixed Thermal detection:
Disadvantages of Fixed Thermal detection:
Rate of Rise Rate-of-Rise Thermal detectors measure the rate at which the air temperature changes during an fire event. Measuring the change in temperature provides a faster alarm response than measuring the temperature level in a space. The rate-of-rise detector measures the change in the temperature of the space through the use of a differential pressure switch. This switch contains an air chamber separated for the air in the ambient space by a flexible diaphragm. As air in the ambient space changes temperature, the air pressure increases, creating a differential pressure across the diaphragm.
The air chamber is constructed with a calibrated leak so that normal temperature and pressure fluctuations within the room space adjust across both sides of the diaphragm and will not cause the alarm contacts to close. During a fire, the air temperature rises at a rate faster than normal, causing an increase on the room side of the diaphragm. The faster than normal, causing an increase in pressure on the room side of the diaphragm. The leak cannot compensate, and therefore the diaphragm moves and closes the detector contacts. Combination rate-of-rise and fixed temperature thermal detectors are also manufactured and have both technologies built in. Advantages of Rate-of-Rise Thermal detection:
Disadvantages of Rate-of-Rise Thermal detection:
Rate Compensated Rate-compensated thermal detectors are devices that are designed to activate at a predetermined temperature in a space regardless of the rate at which the temperature in the space increases. This is accomplished by compensating for the thermal lag between the room temperature and the interior of the device. Construction consists of an outer metal tube that expands at a fixed rate. Within this tube, alarm contacts close when a certain expansion distance is reached, but this expansion is opposed by another metal device. At a slow rate-of-rise in temperature, the outer tube expands drawing the contacts closer together. The inner metal device exerts a counter force, keeping the contacts separated until the entire device has been heated to its rated temperature. At a rapid rate-of-rise in temperature, the outer tube expands faster than the inner device can compensate. Therefore, the alarm contacts close when the entire device has been heated to a lower level, thus compensating for thermal lag. Advantages of Rate Compensated Thermal detectors:
Disadvantages of Rate Compensated Thermal detectors:
Typical Uses:
Flame Detector Flame detectors are used to detect the light radiation component of a fire. Typical detectors of this type detect the wavelength of either IR or UV or a combination of these two. These detectors are extremely fast acting and are used in areas where rapidly occurring fires or explosions could occur.
Advantages of Flame Detection:
Disadvantages of Flame Detection:
Typical Uses:
Fire-Gas Detector These detectors respond to the various gases produced during the combustion process.
The Fire-Gas detector employs two types of technology to predict the fire. One method uses a semiconductor material that changes the metals conducting potential in a fire situation. The other method uses a catalytic element encased in an aluminum bead. Advantages of Fire-Gas Detection:
Disadvantages of Fire-Gas Detection:
Manual Pull Stations
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