Design

After the fire protection goals are established – usually by referencing the minimum levels of protection mandated by the appropriate model building code, insurance agencies, and other authorities – the fire alarm designer undertakes to detail specific components, arrangements, and interfaces necessary to accomplish these goals. 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.

Fundamental configuration

• Fire alarm control panel: This component, the hub of the system monitors inputs and system integrity, control outputs and relays information.
• Primary Power supply: Commonly the non-switched 120 Volt Alternating Current source supplied from a commercial power utility. In non-residential applications, a branch circuit is dedicated to the fire alarm system and its constituents. “Dedicated branch circuits” should not be confused with “Individual branch circuits” which supply energy to a single appliance.
• Secondary (backup) Power supplies: This component commonly sealed, lead-acid storage batteries or other emergency sources including generators, is used to supply energy in the event of a primary power failure.
• Initiating Devices: This component acts as input to the fire alarm control unit and are either manually or automatically activated.
• Notification appliances: This component uses energy supplied from the fire alarm system or other stored energy source, to inform the proximate persons of the need to take action, usually to evacuate.
• Building Safety Interfaces: This interface allows the fire alarm system to control aspects of the built environment and to prepare the building for fire and to control the spread of smoke fumes and fire by influencing air movement, lighting, process control, human transport and exit.

Initiating devices

• Manually activated devices; manual pull station are constructed to be readily located (near the exits), identified, and operated.
• Automatically activated devices can take many forms intended to respond to any number of detectable physical changes associated with fire: convected thermal energy; heat detector, products of combustion; smoke detector, radiant energy; flame detector, combustion gasses; carbon monoxide detector and release of extinguishing agents; water-flow detector. The newest innovations can use cameras and computer algorithms to analyze the visible effects of fire and movement in applications inappropriate for or hostile to other detection methods.

Notification appliances

• Audible, visible, tactile, textual or even olfactory stimuli (odorizer). to alert the occupants. Audible or visible signals are the most common and may utilize speakers to deliver live or pre-recorded instructions to the occupants. In the United States, fire alarm evacuation signals are required to use a standardized interrupted three count temporal pattern to avoid confusion with other signals using similar sounding appliances. Other methods include:
• Audible textual appliances, which are employed as part of a fire alarm system that includes Emergency Voice Alarm Communications (EVAC) capabilities. High reliability speakers are used to notify the occupants of the need for action in connection with a fire or other emergency. These speakers are employed in large facilities where general undirected evacuation is considered impracticable or undesirable. The signals from the speakers are used to direct the occupant’s response. The system may be controlled from one or more locations within the building known as Fire Wardens Stations, or from a single location designated as the building Fire Command Center. Speakers are automatically activated by the fire alarm system in a fire event, and following a pre-alert tone, selected groups of speakers may transmit one or more prerecorded messages directing the occupants to safety. These messages may be repeated in one or more languages. Trained personnel activating and speaking into a dedicated microphone can suppress the replay of automated messages in order to initiate or relay real time voice instructions

Building safety interfaces

• Magnetic Smoke Door Holders: Wall or floor mounted solenoids or electromagnets controlled by a fire alarm system or detection component that magnetically secures spring-loaded self-closing smoke tight doors in the open position. Designed to de-magnetize to allow automatic closure of the door on command from the fire control or upon failure of the power source, interconnection or controlling element. Stored energy in the form of a spring or gravity can then close the door to restrict the passage of smoke from one space to another in an effort to maintain a tenable atmosphere on either side of the door during evacuation and fire fighting efforts.
• Duct Mounted Smoke Detection: Smoke detection mounted in such a manner as to sample the airflow through duct work and other plenums specifically fabricated for the transport of environmental air into conditioned spaces. Interconnection to the fan motor control circuits are intended to stop air movement, close dampers and generally prevent the recirculation of toxic smoke and fumes produced by fire into occupied spaces.

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Main characteristics

The aim for passive fire protection systems is typically demonstrate in fire testing the ability to maintain the item or the side to be protected at or below either 140 °C (for walls, floors and electrical circuits required to have a fire-resistance rating) or ca. 550 °C, which is considered the critical temperature for structural steel, above which, it is in jeopardy of losing its strength, leading to collapse. This is based, in most countries, on the basic test standards for walls and floors, such as ASTM E119. Smaller components, such as fire dampers, fire doors, etc., follow suit in the main intentions of the basic standard for walls and floors. Fire testing involves live fire exposures upwards of 1100 °C, depending on the fire-resistance rating and duration one is after. More items than just fire exposures are typically required to be tested to ensure the survivability of the system under realistic conditions.

To accomplish these aims, many different types of materials are employed in the design and construction of systems. For instance, common endothermic building materials include concrete and gypsum wallboard. During fire testing of concrete floor slabs, water can be seen to boil out of a slab. Gypsum wall board typically loses all its strength during a fire. The use of endothermic materials is established and proven to be sound engineering practice. The chemically bound water inside these materials sublimes. During this process, the unexposed side cannot exceed the boiling point of water. Once the hydrates are spent, the temperature on the unexposed side of an endothermic fire barrier tends to rise rapidly. Too much water can be a problem, however. Concrete slabs that are too wet, will literally explode in a fire, which is why test laboratories insist on measuring water content of concrete and mortar in fire test specimens, before running any fire tests. PFP measures can also include intumescents and ablative materials. The point is, however, that whatever the nature of the materials, they on their own bear no rating. They must be organised into systems, which bear a rating when installed in accordance with certification listings or established catalogues, such as DIN 4102 Part 4 or the Canadian National Building Code.

Passive Fire Protection measures are intended to contain a fire in the fire compartment of origin, thus limiting the spread of fire and smoke for a limited period of time, as determined the local building code and fire code. Passive fire protection measures, such as firestops, fire walls, and fire doors, are tested to determine the fire resistance rating of the final assembly, usually expressed in terms of hours of fire resistance (e.g., 1/3, 3/4, 1, 1 1/2, 2, 3, 4 hour). A certification listing provides the limitations of the rating.

Contrary to active fire protection measures, passive fire protection means do not typically require electric or electronic activation or a degree of motion. Exceptions to that particular rule of thumb are fire dampers (fire-resistive closures within air ducts, excluding grease ducts) and fire door closers, which must move, open and shut in order to work, as well as all intumescent products, which swell, thus move, in order to function.

Passive fire protection (PFP), as the name suggest remains silent in your coating system till the eventuality of a fire. There are mainly two types of PFP. Intumescent fire protection and vermiculite fire protection. In vermiculite fire protection, the structural steel members are covered with vermiculite materials, mostly a very thick layer. this is a cheaper options as compared to an intumescent one, but is very crude and aesthetically unpleasant. Moreover if the environment is corrosive in nature, then vermiculite option is not an advisable option, as there are possibility of water seeping into (because of the porous nature of vermiculite) and there is little scope to monitor the corrosion aspects. Intumescent fire proofing is a layer of paint which is applied along with the coating system on the structural steel members. The thickness of this intumescent coating is dependent on the steel section used. For calculation of DFT (dry film thickness) a factor called Hp/A (heated perimeter divided by cross sectional area) is used. Intumescent coatings are applied as an intermediate coat in a coating system (primer, intermediate and top/finish coat). Because of the relatively low thickness of this intumescent coating (350-700 micrometers), nice finish, and anti-corrosive nature, intumescent coatings are preferred aesthetically and performance-wise. it should be noted that in the eventuality of a fire, the steel structure will eventually collapse once the steel attains the critical core temperature (around 450 degrees Celsius or 850 degrees Fahrenheit). The PFP system will only delay this by creating a layer of char in between the steel and fire. Depending upon the requirement, PFP systems can provide fire ratings of up to 120 minutes and even more. PFP systems are highly recommended in infrastructure projects as they can save precious human lives and assets.

PFP in a building can be described as a group of systems within systems. An installed firestop, for instance, is a system that is based upon a product certification listing. It forms part of a fire-resistance rated wall or floor and this wall or floor forms part of a fire compartment, which forms an integral part of the overall fire safety plan of the building, which, as a whole, can also be seen as a system.

Examples

• fire-resistance rated walls
• Firewalls not only have a rating, they are also designed to sub-divide buildings such that if collapse occurs on one side, this will not affect the other side. They can also be used to eliminate the need for sprinklers, as a trade-off.
• Fire-resistance glass glass using multi-layer intumescent interlayer technology to meet ASTM-E119 test standards. The glass is optically clear, and can be used in 60 minute and 120 minute fire resistance rated assemblies. The International Building Codes (IBC) allows this glass to be installed as a fire-rated wall.
• fire-resistance rated floors
• occupancy separations (barriers designated as occupancy separations are intended to segregate parts of buildings, where different uses are on each side; For instance, apartments on one side and stores on the other side of the occupancy separation.
• closures (fire dampers) Sometimes firestops are treated in building codes identically to closures. Canada de-rates closures, where, for instance a 2 hour closure is acceptable for use in a 3 hour fire separation, so long as the fire separation is not an occupancy separation or firewall. The lowered rating is then referred to as a fire protection rating, both for firestops, unless they contain plastic pipes and regular closures.
• firestops
• grease ducts (These refer to ducts that lead from commercial cooking equipment such as ranges, deep fryers and double-decker and conveyor-equipped pizza ovens to grease duct fans. In North America, grease ducts are made of minimum 16 gauge (1.6 mm) sheet metal, all welded, and certified openings for cleaning, whereby the ducting is either inherently manufactured to have a specific fire-resistance rating, OR it is ordinary 16 gauge ductwork with an exterior layer of purpose-made and certified fireproofing. Either way, North American grease ducts must comply with NFPA96 requirements.)
• cable coating (application of fire-retardants, which are either endothermic or intumescent, to reduce flamespread and smoke development of combustible cable-jacketing)
• spray fireproofing (application of intumescent or endothermic paints, or fibrous or cementitious plasters to keep substrates such as structural steel, electrical or mechanical services, valves, liquefied petroleum gas (LPG) vessels, vessel skirts, bulkheads or decks below either 140 °C for electrical items or ca. 500 °C for structural steel elements to maintain operability of the item to be protected)
• fireproofing cladding (boards used for the same purpose and in the same applications as spray fireproofing) Materials for such cladding include perlite, vermiculite, calcium silicate, gypsum, intumescent epoxy, DuraSteel (cellulose-fibre reinforced concrete and punched sheet-metal bonded composite panels), MicroTherm
• enclosures (boxes or wraps made of fireproofing materials, including fire-resistive wraps and tapes to protect speciality valves and other items deemed to require protection against fire and heat—an analogy for this would be a safe) or the provision of circuit integrity measures to keep electrical cables operational during an accidental fire.

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Categories of Active Fire Protection

Fire suppression

Fire can be controlled or extinguished, either manually (firefighting) or automatically. Manual includes the use of a fire extinguisher or a Standpipe system. Automatic means can include a fire sprinkler system, a gaseous clean agent, or fire fighting foam system. Automatic suppression systems would usually be found in large commercial kitchens or other high-risk areas.

Sprinkler systems

Fire sprinkler systems are installed in high rise buildings, department stores, warehouses and other similar buildings. They are usually located at ceiling level and are supplied by a central system of water pumps and a reservoir. The sprinkler system operates usually when heat at the site of a fire causes a glass component in the sprinkler head to fail, thereby releasing the water from the sprinkler head. This means that only the sprinkler head at the fire location operate – not all the sprinklers on a floor or in a building. (This is a common misconception which stems from action movie scenes). Sprinkler systems help to reduce the growth of a fire. Sprinkler systems are evolving into water mist systems which give finer water droplets.

Fire detection

The fire is detected either by locating the smoke, flame or heat, and an alarm is sounded to enable emergency evacuation as well as to dispatch the local fire department. An introduction to fire detection and suppression can be found here. Where a detection system is activated, it can be programmed to carry out other actions. These include de-energising magnetic hold open devices on Fire doors and opening servo-actuated vents in stairways.

Construction and maintenance

All AFP systems are required to be installed and maintained in accordance with strict guidelines in order to maintain compliance with the local building code and the fire code. An example treatise on code compliance in Miami Dade County can be seen here. Code authorities can encourage compliance through open communications, such as an invitation for code questions or an invitation to participate or an explanation of the code development process

AFP works alongside modern architectural designs and construction materials and fire safety education to prevent, retard, and suppress structural fires.

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Sprinkler systems offer several benefits to building owners, operators, and occupants. These benefits include:

• Immediate identification and control of a developing fire – Sprinkler systems respond at all times, including periods of low occupancy. Control is generally instantaneous.
• Immediate alert -  In conjunction with the building fire alarm system, automatic sprinkler systems will notify occupants and emergency response personnel of the developing fire.
• Reduced heat and smoke damage -  Significantly less heat and smoke will be generated when the fire is extinguished at an early stage.
• Enhanced life safety – Staff, visitors and fire fighters will be subject to less danger when fire growth is checked.
• Design flexibility -  Egress route and fire/smoke barrier placement becomes less restrictive since early fire control minimizes demand on these systems. Greater utilization of exhibition and assembly spaces is usually a benefit.
• Enhanced Security – A sprinkler controlled fire decreases demand on security forces, minimizing intrusion opportunities.
• Decreased insurance expenditure – Sprinkler controlled fires are less damaging than fires in non-sprinklered buildings. This results in lower insurance reimbursements. Insurance underwriters will usually offer reduced premiums in sprinkler protected properties which can save a large amount of capital. This is especially important when funds are limited.

These benefits should be considered when deciding on the selection of automatic fire sprinkler protection.

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A fire sprinkler system is an active fire protection measure, consisting of a water supply, providing adequate pressure and flowrate to a water distribution piping system, onto which fire sprinklers are connected. Although historically only used in factories and large commercial buildings, home and small building systems are now available at a cost-effective price.

Sprinklers may be required to be installed by building codes, or may be recommended by insurance companies to reduce potential property losses or business interruption. Building codes in the United States for places of assembly, generally over 100 persons, and places with overnight sleeping accommodation such as hotels, nursing homes, dormitories, and hospitals usually require sprinklers either under local building codes, as a condition of receiving State and Federal funding or as a requirement to obtain certification (essential for institutions who wish to train medical staff).

If building codes do not explicitly mandate the use of fire sprinklers, the code often makes it highly advantageous to install them as an optional system. Most US building codes allow for less expensive construction materials, larger floor area limitations, longer egress paths, and fewer requirements for fire rated construction in structures protected by fire sprinklers. Consequently, the total building cost it is often less by installing a sprinkler system and savings money in the other aspects of the project, as compared to building a non-sprinklered structure. In the UK, since the 1990′s sprinklers have gained recognition within the Building Regulations (England and Wales) and Scottish Building Standards and under certain circumstances, the presence of sprinkler systems is deemed to provide a form of alternative compliance to some parts of the codes. For example, the presence of a sprinkler system will usually permit doubling of compartment sizes and increases in travel distances (to fire exits) as well as allowing a reduction in the fire rating of internal compartment walls.

Renewed interest in and support for sprinkler systems in the UK, largely as a result of effective lobbying by the National Fire Sprinkler Network, the European Fire Sprinkler Network and the British Automatic Fire Sprinkler Association, has resulted in sprinkler systems being more widely installed. In schools, for example, the Department of Children, Families and Schools has issued strong recommendations that most new schools should be constructed with sprinkler protection. In Scotland, all new care homes are sprinklered as are sheltered housing and high rise flats. Most local authorities in Scotland have a policy of fitting sprinklers to new schools and to most of their own new buildings.

Operation

Each closed-head sprinkler is held closed by either a heat-sensitive glass bulb (see below) or a two-part metal link held together with fusible alloy. The glass bulb or link applies pressure to a pip cap which acts as a plug which prevents water from flowing until the ambient temperature around the sprinkler reaches the design activation temperature of the individual sprinkler head. Because each sprinkler activates independently when the predetermined heat level is reached, the number of sprinklers that operate is limited to only those near the fire, thereby maximizing the available water pressure over the point of fire origin.

A sprinkler activation will do less damage than a fire department hose stream, which provide approximately 900 liters/min (250 US gallons/min). A typical sprinkler used for industrial manufacturing occupancies discharge about 75-150 litres/min (20-40 US gallons/min). However, a typical Early Suppression Fast Response (ESFR) sprinkler at a pressure of 50 psi (345 kPa) will discharge approximately 100 US gallons per minute, (380 litres per minute). In addition, a sprinkler will usually activate between one and four minutes, whereas the fire department typically takes at least five minutes to arrive at the fire site after receiving an alarm, and an additional ten minutes to set up equipment and apply hose streams to the fire. This additional time can result in a much larger fire, requiring much more water to achieve extinguishment.

Design intent

Sprinkler systems are intended to either control the fire or to suppress the fire. Control mode sprinklers are intended to control the heat release rate of the fire to prevent building structure collapse, and pre-wet the surrounding combustibles to prevent fire spread. The fire is not extinguished until the burning combustibles are exhausted or manual extinguishment is effected by firefighters. Suppression mode sprinklers (formerly known as Early Suppression Fast Response (ESFR) sprinklers) are intended to result in a severe sudden reduction of the heat release rate of the fire, followed quickly by complete extinguishment, prior to manual intervention.

Types of Sprinkler System

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