Nick Artim, Director
Fire Safety Network
Cultural property management is entrusted with the responsibility of protecting and preserving an institution's buildings, collections, operations and occupants. Constant attention is required to minimize adverse impact due to climate, pollution, theft, vandalism, insects, mold and fire. Because of the speed and totality of the destructive forces of fire, it constitutes one of the more serious threats. Vandalized or environmentally damaged structures can be repaired and stolen objects recovered. Items destroyed by fire, however, are gone forever. An uncontrolled fire can obliterate an entire room's contents within a few minutes and completely burn out a building in a couple hours.
The first step toward halting a fire is to properly identify the incident, raise the occupant alarm, and then notify emergency response professionals. This is often the function of the fire detection and alarm system. Several system types and options are available, depending on the specific characteristics of the protected space.
Fire protection experts generally agree that automatic sprinklers represent one of the single, most significant aspects of a fire management program. Properly designed, installed, and maintained, these systems can overcome deficiencies in risk management, building construction, and emergency response. They may also provide enhanced flexibility of building design and increase the overall level of fire safety.
The following text presents an overview of fire detection, alarm and sprinkler systems including system types, components, operations, and answers to common anxieties.
Before attempting to understand fire detection systems and automatic sprinklers, it is beneficial to possess a basic knowledge of fire development and behavior. With this information, the role and interaction of these supplemental fire safety systems in the protection process can then be better realized.
Basically, a fire is a chemical reaction in which a carbon based material (fuel), mixes with oxygen (usually as a component of air), and is heated to a point where flammable vapors are produced. These vapors can then come in contact with something that is hot enough to cause vapor ignition, and a resulting fire. In simple terms, something that can burn touches something that is hot, and a fire is produced.
Libraries, archives, museums, and historic structures frequently contain numerous fuels. These include books, manuscripts, records, artifacts, combustible interior finishes, cabinets, furnishings, and laboratory chemicals. It should be recognized that any item containing wood, plastic, paper, fabric, or combustible liquids is a potential fuel. They also contain several common, potential ignition sources including any item, action, or process which produces heat. These encompass electric lighting and power systems, heating and air conditioning equipment, heat producing conservation and maintenance activities, and electric office appliance. Flame generating construction activities such as soldering, brazing, and cutting are frequent sources of ignition. Arson is unfortunately one of the most common cultural property ignition sources, and must always be considered in fire safety planning.
When the ignition source contacts the fuel, a fire can start. Following this contact, the typical accidental fire begins as a slow growth, smoldering process which may last from a few minutes to several hours. The duration of this "incipient" period is dependent on a variety of factors including fuel type, its physical arrangement, and quantity of available oxygen. During this period heat generation increases, producing light to moderate volumes of smoke. The characteristic smell of smoke is usually the first indication that an incipient fire is underway. It is during this stage that early detection (either human or automatic), followed by a timely response by qualified fire emergency professionals, can control the fire before significant losses occur.
As the fire reaches the end of the incipient period, there is usually enough heat generation to permit the onset of open, visible flames. Once flames have appeared, the fire changes from a relatively minor situation to a serious event with rapid flame and heat growth. Ceiling temperatures can exceed 1,000° C (1,800° F) within the first minutes. These flames can ignite adjacent combustible contents within the room, and immediately endanger the lives of the room's occupants. Within 3–5 minutes, the room ceiling acts like a broiler, raising temperatures high enough to "flash", which simultaneously ignites all combustibles in the room. At this point, most contents will be destroyed and human survivability becomes impossible. Smoke generation in excess of several thousand cubic meters (feet) per minute will occur, obscuring visibility and impacting contents remote from the fire.
If the building is structurally sound, heat and flames will likely consume all remaining combustibles and then self extinguish (burn out). However, if wall and/or ceiling fire resistance is inadequate, (i.e. open doors, wall/ceiling breaches, combustible building construction), the fire can spread into adjacent spaces, and start the process over. If the fire remains uncontrolled, complete destruction or "burn out" of the entire building and contents may ultimately result.
Successful fire suppression is dependent on extinguishing flames before, or immediately upon, flaming combustion. Otherwise, the resulting damage may be too severe to recover from. During the incipient period, a trained person with portable fire extinguishers may be an effective first line of defense. However, should an immediate response fail or the fire grow rapidly, extinguisher capabilities can be surpassed within the first minute. More powerful suppression methods, either fire department hoses or automatic systems, then become essential.
A fire can have far reaching impact on the institution's buildings, contents and mission. General consequences may include:
To minimize fire risk and its impact, heritage institutions should develop and implement comprehensive and objective fire protection programs. Program elements should include fire prevention efforts, building construction improvements, methods to detect a developing fire and alert emergency personnel, and means to effectively extinguish a fire. Each component is important toward overall accomplishment of the institution's fire safety goal. It is important for management to outline desired protection objectives during a fire and establish a program that addresses these goals. Therefore, the basic question to be asked by the property's managers is, "What maximum fire size and loss can the institution accept?" With this information, goal oriented protection can be implemented.
A key aspect of fire protection is to identify a developing fire emergency in a timely manner, and to alert the building's occupants and fire emergency organizations. This is the role of fire detection and alarm systems. Depending on the anticipated fire scenario, building and use type, number and type of occupants, and criticality of contents and mission, these systems can provide several main functions. First they provide a means to identify a developing fire through either manual or automatic methods and second, they alert building occupants to a fire condition and the need to evacuate. Another common function is the transmission of an alarm notification signal to the fire department or other emergency response organization. They may also shut down electrical, air handling equipment or special process operations, and they may be used to initiate automatic suppression systems. This section will describe the basic aspects of fire detection and alarm systems.
The control panel is the "brain" of the fire detection and alarm system. It is responsible for monitoring the various alarm "input" devices such as manual and automatic detection components, and then activating alarm "output" devices such as horns, bells, warning lights, emergency telephone dialers, and building controls. Control panels may range from simple units with a single input and output zone, to complex computer driven systems that monitor several buildings over an entire campus. There are two main control panel arrangements, conventional and addressable, which will be discussed below.
Conventional or "point wired" fire detection and alarm systems were for many years the standard method for providing emergency signaling. In a conventional system one or more circuits are routed through the protected space or building. Along each circuit, one or more detection devices are placed. Selection and placement of these detectors is dependent upon a variety of factors including the need for automatic or manual initiation, ambient temperature and environmental conditions, the anticipated type of fire, and the desired speed of response. One or more device types are commonly located along a circuit to address a variety of needs and concerns.
Upon fire occurrence, one or more detectors will operate. This action closes the circuit, which the fire control panel recognizes as an emergency condition. The panel will then activate one or more signaling circuits to sound building alarms and summon emergency help. The panel may also send the signal to another alarm panel so that it can be monitored from a remote point.
In order to help insure that the system is functioning properly, these systems monitor the condition of each circuit by sending a small current through the wires. Should a fault occur, such as due to a wiring break, this current cannot proceed and is registered as a "trouble" condition. The indication is a need for service somewhere along the respective circuit.
In a conventional alarm system, all alarm initiating and signaling is accomplished by the system's hardware which includes multiple sets of wire, various closing and opening relays, and assorted diodes. Because of this arrangement, these systems are actually monitoring and controlling circuits, and not individual devices.
To further explain this, assume that a building's fire alarm system has 5 circuits, zones A through E, and that each circuit has 10 smoke detectors and 2 manual stations located in various rooms of each zone. A fire ignition in one of the rooms monitored by zone "A" causes a smoke detector to go into alarm. This will be reported by the fire alarm control panel as a fire in circuit or zone "A". It will not indicate the specific detector type nor location within this zone. Emergency responding personnel may need to search the entire zone to determine where the device is reporting a fire. Where zones have several rooms, or concealed spaces, this response can be time consuming and wasteful of valuable response opportunity.
The advantage of conventional systems is that they are relatively simple for small to intermediate size buildings. Servicing does not require a large amount of specialized training.
A disadvantage is that for large buildings, they can be expensive to install because of the extensive amounts of wire that are necessary to accurately monitor initiating devices.
Conventional systems may also be inherently labor intensive and expensive to maintain. Each detection device may require some form of operational test to verify it is in working condition. Smoke detectors must be periodically removed, cleaned, and recalibrated to prevent improper operation. With a conventional system, there is no accurate way of determining which detectors are in need of servicing. Consequently, each detector must be removed and serviced, which can be a time consuming, labor intensive, and costly endeavor. If a fault occurs, the "trouble" indication only states that the circuit has failed, but does not specifically state where the problem is occurring. Subsequently, technicians must survey the entire circuit to identify the problem.
Addressable or "intelligent" systems represent the current state-of-the-art in fire detection and alarm technology. Unlike conventional alarm methods, these systems monitor and control the capabilities of each alarm initiating and signaling device through microprocessors and system software. In effect, each intelligent fire alarm system is a small computer overseeing and operating a series of input and output devices.
Like a conventional system, the address system consists of one or more circuits that radiate throughout the space or building. Also, like standard systems, one or more alarm initiating devices may be located along these circuits. The major difference between system types involves the way in which each device is monitored. In an addressable system, each initiating device (automatic detector, manual station, sprinkler waterflow switch, etc.) is given a specific identification or "address". This address is correspondingly programmed into the control panel's memory with information such as the type of device, its location, and specific response details such as which alarm devices are to be activated.
The control panel's microprocessor sends a constant interrogation signal over each circuit, in which each initiating device is contacted to inquire its status (normal or emergency). This active monitoring process occurs in rapid succession, providing system updates every 5 to 10 seconds.
The addressable system also monitors the condition of each circuit, identifying any faults which may occur. One of the advancements offered by these systems is their ability to specifically identify where a fault has developed. Therefore, instead of merely showing a fault along a wire, they will indicate the location of the problem. This permits faster diagnosis of the trouble, and allows a quicker repair and return to normal.
Advantages provided by addressable alarm systems include stability, enhanced maintenance, and ease of modification. Stability is achieved by the system software. If a detector recognizes a condition which could be indicative of a fire, the control panel will first attempt a quick reset. For most spurious situations such as insects, dust, or breezes, the incident will often remedy itself during this reset procedure, thereby reducing the probability of false alarm. If a genuine smoke or fire condition exists, the detector will reenter the alarm mode immediately after the reset attempt. The control panel will now regard this as a fire condition, and will enter its alarm mode.
With respect to maintenance, these systems offer several key advantages over conventional ones. First of all, they are able to monitor the status of each detector. As a detector becomes dirty, the microprocessor recognizes a decreased capability, and provides a maintenance alert. This feature, known as Listed Integral Sensitivity Testing, allows facilities personnel to service only those detectors that need attention, rather than requiring a labor and time consuming cleaning of all units.
Advanced systems, such as the FCI 7200 incorporate another maintenance feature known as drift compensation. This software procedure adjusts the detector's sensitivity to compensate for minor dust conditions. This avoids the ultra sensitive or "hot" detector condition which often results as debris obscures the detector's optics. When the detector has been compensated to its limit, the control panel alerts maintenance personnel so that servicing can be performed.
Modifying these systems, such as to add or delete a detector, involves connecting or removing the respective device from the addressable circuit, and changing the appropriate memory section. This memory change is accomplished either at the panel or on a personal computer, with the information downloaded into the panel's microprocessor.
The main disadvantage of addressable systems is that each system has its own unique operating characteristics. Therefore, service technicians must be trained for the respective system. The training program is usually a 3-4 day course at the respective manufacturer's facility. Periodic update training may be necessary as new service methods are developed.
When present, humans can be excellent fire detectors. The healthy person is able to sense multiple aspects of a fire including the heat, flames, smoke, and odors. For this reason, most fire alarm systems are designed with one or more manual alarm activation devices to be used by the person who discovers a fire. Unfortunately, a person can also be an unreliable detection method since they may not be present when a fire starts, may not raise an alarm in an effective manner, or may not be in perfect heath to recognize fire signatures. It is for this reason that a variety of automatic fire detectors have been developed. Automatic detectors are meant to imitate one or more of the human senses of touch, smell or sight. Thermal detectors are similar to our ability to identify high temperatures, smoke detectors replicate the sense of smell, and flame detectors are electronic eyes. The properly selected and installed automatic detector can be a highly reliable fire sensor.
Manual fire detection is the oldest method of detection. In the simplest form, a person yelling can provide fire warning. In buildings, however, a person's voice may not always transmit throughout the structure. For this reason, manual alarm stations are installed. The general design philosophy is to place stations within reach along paths of escape. It is for this reason that they can usually be found near exit doors in corridors and large rooms.
The advantage of manual alarm stations is that, upon discovering the fire, they provide occupants with a readily identifiable means to activate the building fire alarm system. The alarm system can then serve in lieu of the shouting person's voice. They are simple devices, and can be highly reliable when the building is occupied. The key disadvantage of manual stations is that they will not work when the building is unoccupied. They may also be used for malicious alarm activations. Nonetheless, they are an important component in any fire alarm system.
Thermal detectors are the oldest type of automatic detection device, having origin in the mid 1800's, with several styles still in production today. The most common units are fixed temperature devices that operate when the room reaches a predetermined temperature (usually in the 135°–165°F/57°–74°C). The second most common type of thermal sensor is the rate-of-rise detector, which identifies an abnormally fast temperature climb over a short time period. Both of these units are "spot type" detectors, which means that they are periodically spaced along a ceiling or high on a wall. The third detector type is the fixed temperature line type detector, which consists of two cables and an insulated sheathing that is designed to breakdown when exposed to heat. The advantage of line type over spot detection is that thermal sensing density can be increased at lower cost.
Thermal detectors are highly reliable and have good resistance to operation from nonhostile sources. They are also very easy and inexpensive to maintain. On the down side, they do not function until room temperatures have reached a substantial temperature, at which point the fire is well underway and damage is growing exponentially. Subsequently, thermal detectors are usually not permitted in life safety applications. They are also not recommended in locations where there is a desire to identify a fire before substantial flames occur, such as spaces where high value thermal sensitive contents are housed.
Smoke detectors are a much newer technology, having gained wide usage during the 1970's and 1980's in residential and life safety applications. As the name implies, these devices are designed to identify a fire while in its smoldering or early flame stages, replicating the human sense of smell. The most common smoke detectors are spot type units, that are placed along ceilings or high on walls in a manner similar to spot thermal units. They operate on either an ionization or photoelectric principle, with each type having advantages in different applications. For large open spaces such as galleries and atria, a frequently used smoke detector is a projected beam unit. This detector consists of two components, a light transmitter and a receiver, that are mounted at some distance (up to 300 ft/100m) apart. As smoke migrates between the two components, the transmitted light beam becomes obstructed and the receiver is no longer able to see the full beam intensity. This is interpreted as a smoke condition, and the alarm activation signal is transmitted to the fire alarm panel.
A third type of smoke detector, which has become widely used in extremely sensitive applications, is the air aspirating system. This device consists of two main components: a cotrol unit that houses the detection chamber, an aspiration fan and operation circuitry; and a network of sampling tubes or pipes. Along the pipes are a series of ports that are designed to permit air to enter the tubes and be transported to the detector. Under normal conditions, the detector constantly draws an air sample into the detection chamber, via the pipe network. The sample is analyzed for the existence of smoke, and then returned to atmosphere. If smoke becomes present in the sample, it is detected and an alarm signal is transmitted to the main fire alarm control panel. Air aspirating detectors are extremely sensitive and are typically the fastest responding automatic detection method. Many high technology organizations, such as telephone companies, have standardized on aspiration systems. In cultural properties they are used for areas such as collections storage vaults and highly valuable rooms. These are also frequently used in aesthetically sensitive applications since components are often easier to conceal, when compared to other detection methods.
The key advantage of smoke detectors is their ability to identify a fire while it is still in its incipient. As such, they provide added opportunity for emergency personnel to respond and control the developing fire before severe damage occurs. They are usually the preferred detection method in life safety and high content value applications. The disadvantage of smoke detectors is that they are usually more expensive to install, when compared to thermal sensors, and are more resistant to inadvertent alarms. However, when properly selected and designed, they can be highly reliable with a very low probability of false alarm.
Flame detectors represent the third major type of automatic detection method, and imitate the human sense of sight. They are line of sight devices that operate on either an infrared, ultraviolet or combination principle. As radiant energy in the approximate 4,000 to 7,700 angstroms range occurs, as indicative of a flaming condition, their sensing equipment recognizes the fire signature and sends a signal to the fire alarm panel.
The advantage of flame detection is that it is extremely reliable in a hostile environment. They are usually used in high value energy and transportation applications where other detectors would be subject to spurious activation. Common uses include locomotive and aircraft maintenance facilities, refineries and fuel loading platforms, and mines. A disadvantage is that they can be very expensive and labor intensive to maintain. Flame detectors must be looking directly at the fire source, unlike thermal and smoke detectors which can identify migrating fire signatures. Their use in cultural properties is extremely limited.
Alarm Output Devices
Upon receiving an alarm notification, the fire alarm control panel must now tell someone that an emergency is underway. This is the primary function of the alarm output aspect of a system. Occupant signaling components include various audible and visual alerting components, and are the primary alarm output devices. Bells are the most common and familiar alarm sounding device, and are appropriate for most building applications. Horns are another option, and are especially well suited to areas where a loud signal is needed such as library stacks, and architecturally sensitive buildings where devices need partial concealment. Chimes may be used where a soft alarm tone is preferred, such as health care facilities and theaters. Speakers are the fourth alarm sounding option, which sound a reproducible signal such as a recorded voice message. They are often ideally suited for large, multistory or other similar buildings where phased evacuation is preferred. Speakers also offer the added flexibility of emergency public address announcements. With respect to visual alert, there are a number of strobe and flashing light devices. Visual alerting is required in spaces where ambient noise levels are high enough to preclude hearing sounding equipment, and where hearing impaired occupants may be found. Standards such as the Americans with Disabilities Act (ADA) mandate visual devices in numerous museum, library, and historic building applications.
Another key function of the output function is emergency response notification. The most common arrangement is an automatic telephone or radio signal that is communicated to a constantly staffed monitoring center. Upon receiving the alert, the center will then contact the appropriate fire department, providing information about the location of alarm. In some instances, the monitoring station may be the police or fire departments, or a 911 center. In other instances it will be a private monitoring company that is under contract to the organization. In many cultural properties, the building's inhouse security service may serve as the monitoring center.
Other output functions include shutting down electrical equipment such as computers, shutting off air handling fans to prevent smoke migration, and shutting down operations such as chemical movement through piping in the alarmed area. They may also activate fans to extract smoke, which is a common function in large atria spaces. These systems can also activate discharge of gaseous fire extinguishing systems, or preaction sprinkler systems.
In summary, there are several options for a building's fire detection and alarm system. The ultimate system type, and selected components, will be dependent upon the building construction and value, its use or uses, the type of occupants, mandated standards, content value, and mission sensitivity. Contacting a fire engineer or other appropriate professional who understands fire problems and the different alarm and detection options is usually a preferred first step to find the best system.
For most fires, water represents the ideal extinguishing agent. Fire sprinklers utilize water by direct application onto flames and heat, which causes cooling of the combustion process and prevents ignition of adjacent combustibles. They are most effective during the fire's initial flame growth stage, while the fire is relatively easy to control. A properly selected sprinkler will detect the fire's heat, initiate alarm, and begin suppression within moments after flames appear. In most instances sprinklers will control fire advancement within a few minutes of their activation, which will in turn result in significantly less damage than otherwise would happen without sprinklers.
Among the potential benefits of sprinklers are the following:
These benefits should be considered when deciding on the selection of automatic fire sprinkler protection.
Sprinkler System Components and Operation
Sprinkler systems are essentially a series of water pipes that are supplied by a reliable water supply. At selected intervals along these pipes are independent, heat activated valves known as sprinkler heads. It is the sprinkler that is responsible for water distribution onto the fire. Most sprinkler systems also include an alarm to alert occupants and emergency forces when sprinkler activation (fire) occurs.
During the incipient fire stage, the heat output is relatively low and is unable to cause sprinkler operation. However, as the fire intensity increases, the sprinkler's sensing elements become exposed to elevated temperatures (typically in excess of 57–107°C (135–225°F), and begin to deform. Assuming temperatures remain high, as they would during an increasing fire, the element will fatigue after an approximate 30 to 120 second period. This releases the sprinkler's seals allowing water to discharge onto the fire and begin the suppression action. In most situations less than 2 sprinklers are needed to control the fire. In fast growing fire scenarios, however, such as a flammable liquid spill, up to 12 sprinklers may be required.
In addition to normal fire control efforts, sprinkler operation may be interconnected to initiate building and fire department alarms, shutdown electrical and mechanical equipment, close fire doors and dampers, and suspend some processes.
As fire fighters arrive their efforts will focus on ensuring that the system has contained the fire, and, when satisfied, shut off the water flow to minimize water damage. It is at this point that staff will normally be permitted to enter the damaged space and perform salvage duties.
System Components and Types
The basic components of a sprinkler system are the sprinklers, system piping, and a dependable water source. Most systems also require an alarm, system control valves, and means to test the equipment.
The sprinkler itself is the spray nozzle, which distributes water over a defined fire hazard area (typically 14–21 m2/150–225 ft2) with each sprinkler operating by actuation of its own temperature linkage. The typical sprinkler consists of a frame, thermal operated linkage, cap, orifice, and deflector. Styles of each component may vary but the basic principles of each remain the same.
Upon reaching the desired operating temperature, an approximate 30 second to 4 minute time lag will follow. This lag is the time required for linkage fatigue and is largely controlled by the link materials and mass. Standard responding sprinklers operate closer to the 3–4 minute mark while quick response (QR) sprinklers operate in significantly shorter periods. Selection of a sprinkler response characteristic is dependent upon the existing risk, acceptable loss level, and desired response action.
In heritage applications the advantage of quick response sprinklers often becomes apparent. The faster a sprinkler reacts to a fire, the sooner the suppression activity is initiated, and the lower the potential damage level. This is particularly beneficial in high value or life safety applications where the earliest possible extinguishment is a fire protection goal. It is important to understand that response time is independent of response temperature. A quicker responding sprinkler will not activate at a lower temperature than a comparable standard head.
A sprinkler that has received wide spread interest for museum applications is the on/off sprinkler. The principle behind these products is that as a fire occurs, water discharge and extinguishing action will happen similar to standard sprinklers. As the room temperature is cooled to a safer level, a bimetallic snap disk on the sprinkler closes and water flow ceases. Should the fire reignite, operation will once again occur. The advantage of on/off sprinklers is their ability to shut off, which theoretically can reduce the quantity of water distributed and resultant damage levels. The problem, however, is the long time period that may pass before room temperatures are sufficiently cooled to the sprinkler's shut off point. In most heritage applications, the building's construction will retain heat and prevent the desired sprinkler shut down. Frequently, fire emergency response forces will have arrived and will be able to close sprinkler zone control valves before the automatic shut down feature has functioned.
On-off sprinklers typically cost 8–10 times more than the average sprinkler, which is only justifiable when assurance can be made that these products will perform as intended. Therefore, on/off sprinkler use in heritage facilities should remain limited.
Selection of specific sprinklers is based on: risk characteristics, ambient room temperature, desired response time, hazard criticality and aesthetic factors. Several sprinkler types may be used in a heritage facility.
All sprinkler systems require a reliable water source. In urban areas, a piped public service is the most common supply, while rural areas generally utilize private tanks, reservoirs, lakes, or rivers. Where a high degree of reliability is desired, or a single source is undependable, multiple supplies may be utilized.
Basic water source criteria include:
Sprinkler water is transported to fire via a system of fixed pipes and fittings. Piping material options include various steel alloys, copper, and fire resistant plastics. Steel is the traditional material with copper and plastics utilized in many sensitive applications. Primary considerations for selection of pipe materials include:
The benefits and disadvantages of each material should be evaluated prior to selection of pipe materials.
Other major sprinkler system components include:
There are three basic types of sprinkler systems: wet pipe, dry pipe and preaction, with each having applicability, depending on a variety of conditions such as potential fire severity, anticipated fire growth rates, content water sensitivity, ambient conditions, and desired response. In large multifunction facilities, such as a major museum or library, two or more system types may be employed.
Wet pipe systems are the most common sprinkler system. As the name implies, a wet pipe system is one in which water is constantly maintained within the sprinkler piping. When a sprinkler activates this water is immediately discharged onto the fire. Wet pipe system advantages include:
The main disadvantage of these systems is that they are not suited for subfreezing environments. There also may be concern where piping is subject to severe impact damage, such as some warehouses.
The advantages of wet systems make them highly desirable for use in most heritage applications, and with limited exception, they represent the system of choice for museum, library and historic building protection.
The next system type, a dry pipe sprinkler system, is one in which pipes are filled with pressurized air or nitrogen, rather than water. This air holds a remote valve, known as a dry pipe valve, in a closed position. The drypipe valve is located in a heated area and prevents water from entering the pipe until a fire causes one or more sprinklers to operate. Once this happens, the air escapes and the dry pipe valve releases. Water then enters the pipe, flowing through open sprinklers onto the fire.
The main advantage of dry pipe sprinkler systems is their ability to provide automatic protection in spaces where freezing is possible. Typical dry pipe installations include unheated warehouses and attics, outside exposed loading docks and within commercial freezers.
Many heritage managers view dry pipe sprinklers as advantageous for protection of collections and other water sensitive areas, with a perceived benefit that a physically damaged wet pipe system will leak while dry pipe systems will not. In these situations, however, dry pipe systems will generally not offer any advantage over wet pipe systems. Should impact damage happen, there will only be a mild discharge delay, i.e. 1 minute, while air in the piping is released before water flow.
Dry pipe systems have some disadvantages that must be evaluated before selecting this equipment. These include:
With the exception of unheated building spaces and freezer rooms, dry pipe systems do not offer any significant advantages over wet pipe systems and their use in heritage buildings is generally not recommended.
The third sprinkler system type, preaction, employs the basic concept of a dry pipe system in that water is not normally contained within the pipes. The difference, however, is that water is held from piping by an electrically operated valve, known as a preaction valve. The operation of this valve is controlled by independent flame, heat, or smoke detection. Two separate events must happen to initiate sprinkler discharge. First, the detection system must identify a developing fire and then open the preaction valve. This allows water to flow into system piping, which effectively creates a wet pipe sprinkler system. Second, individual sprinkler heads must release to permit water flow onto the fire.
In some instances, the preaction system may be set up with an interlock feature in which pressurized air or nitrogen is added to system piping. The purpose of this feature is twofold: first to monitor piping for leaks and second to hold water from system piping in the event of inadvertent detector operation. The most common application for this system type is in freezer warehouses.
The primary advantage of a preaction system is the dual action required for water release: the preaction valve must operate and sprinkler heads must fuse. This provides an added level of protection against inadvertent discharge, and for this reason, these systems are frequently employed in water sensitive environments such as archival vaults, fine art storage rooms, rare book libraries and computer centers.
There are some disadvantages to preaction systems. These include:
Provided the application is appropriate, preaction systems have a place in heritage buildings, especially in water sensitive spaces.
A slight variation of preaction sprinklers is the deluge system, which is basically a preaction system using open sprinklers. Operation of the fire detection system releases a deluge valve, which in turn produces immediate water flow through all sprinklers in a given area. Typical deluge systems applications are found in specialized industrial situations, i.e., aircraft hangers and chemical plants, where high velocity suppression is necessary to prevent fire spread. Use of deluge systems in heritage facilities is rare and typically not recommended.
Another preaction system variation is the on/off system which utilizes the basic arrangement of a preaction system, with the addition of a thermal detector and nonlatching alarm panel. The system functions similar to any other preaction sprinkler system, except that as the fire is extinguished, a thermal device cools to allow the control panel to shut off water flow. If the fire should reignite, the system will turn back on. In certain applications on/off systems can be effective. Care, however, must be exercised when selecting this equipment to ensure that it functions as desired. In most urban areas, it is likely that the fire department will arrive before the system has shut itself down, thereby defeating any actual benefits.
Several common misconceptions about sprinkler systems exist. Consequently, heritage building owners and operators are often reluctant to provide this protection, especially for collections storage and other water sensitive spaces. Typical misunderstandings include:
The table below shows approximate comparative water application rates for various manual and automatic suppression methods.
Table 31: Fire Suppression Water Application Rates
|Portable Fire Extinguisher/Appliance||10||2.5|
|Occupant Use Fire Hose||380||100|
|Fire Department, Single 1.5 Hose||380||100|
|Fire Department, Double 1.5 Hose||760||200|
|Fire Department, Single 2.5 Hose||950||250|
|Fire Department, Double 2.5 Hose||1900||500|
One final point to consider is that the water damage is usually capable of repair and restoration. Burned out contents, however, are often beyond mend.
To ensure proper design, the institution and design team should take an active role in the selection of visible components. Sprinkler piping should be placed, either concealed or in a decorative arrangement, to minimize visual impact. Only sprinklers with high quality finishes should be used. Often sprinkler manufacturers will use customer provided paints to match finish colors, while maintaining the sprinkler's listing. The selected sprinkler contractor must understand the role of aesthetics.
To help ensure overall success, the sprinkler system designer should understand the institution's protection objectives, operations, and fire risks. This individual should be knowledgeable about system requirements and flexible to implement unique, thought-out solutions for those areas where special aesthetic or operations concerns exist. The designer should be experienced in the design of systems in architecturally sensitive applications.
Ideally, the sprinkler contractor should be experienced working in heritage applications. However, an option is to select a contractor experienced in water sensitive applications such as telecommunications, pharmaceuticals, clean rooms, or high tech manufacturing. Companies including AT&T, Bristol Meyers Squibb, and IBM have very stringent sprinkler installation requirements. If a sprinkler contractor has demonstrated success with these type of organizations, then they will be capable of performing satisfactorily in a heritage site.
The selected sprinkler components should be provided by a reputable manufacturer, experienced in special, water sensitive hazards. The cost differential between average and the highest quality components is minimal. The long term benefit, however, is substantial. When considering the value of a facility and its contents, the extra investment is worth while.
With proper attention to selection, design, and maintenance, sprinkler systems will serve the institution without adverse impact. If the institution or design team does not possess the experience to ensure the system is proper, a fire protection engineer experienced in heritage applications can be a great advantage.
One of the most promising automatic extinguishing technologies is the recently available fine water droplet, or mist systems. This technology represents another tool that can provide automatic fire suppression in some cultural property applications. Potential uses include locations where reliable water supplies do not exist, where even sprinkler water discharges are too high, or where building construction and aesthetics impact the use of standard sprinkler pipe dimensions. Mist systems may also be an appropriate solution to the protection void left by the environmental concerns, and subsequent demise, of Halon 1301 gas.
Mist technology was originally developed for offshore uses such as on board ships and oil drilling platforms. For both of these applications, there is a need to control severe fires while limiting the amount of extinguishing water, which could impact vessel stability. These systems have been extensively approved by a number of domestic and international marine organizations, and have been a protection standard for the past 8–10 years. They have a solid track record dealing with maritime fires. These systems have also been used in several land based applications, and have a number of listings, primarily in Europe, where their effectiveness has been recognized. Some systems have recently received approvals for North American land based uses.
Mist systems discharge limited water quantities at higher pressures than sprinkler systems. These pressures range from approximately 100 to 1,000 psi, with the higher pressure systems generally producing larger volumes of fine sprays. The produced droplets are usually in the 50 to 200 micron diameter range (compared to 600–1,000 microns for standard sprinklers), resulting in exceptionally high efficiency cooling and fire control, with significantly little water. In most situations, fires are controlled with approximately 10-25% of the water normally associated with sprinklers. Water saturation that is often associated with standard firefighting procedures is decreased. Other benefits include lower aesthetic impact and known environmental safety.
Typical water mist systems consist of the following components:
At this point, one of the main drawbacks to mist systems is their higher cost, which can be 50–100% greater than standard sprinklers. This cost, however, may be reduced due to possible installation labor savings. In rural applications, where reliable sprinkler water supplies can be expensive, mist systems may be comparable or less than standard sprinklers. Another problem is that these systems do not have the variety of approvals and listings commonly associated with sprinklers. As such, they may not be as recognized by fire and building authorities. In addition, the number of contractors who are familiar with the technology is limited. These concerns are diminishing, however, as use of these systems becomes more widespread.
In summary, automatic sprinklers often represent one of the most important fire protection options for most heritage applications. The successful application of sprinklers is dependent upon careful design and installation of high quality components by capable engineers and contractors. A properly selected, designed and installed system will offer unexcelled reliability. Sprinkler system components should be selected for compliance with the institution's objectives. Wet pipe systems offer the greatest degree of reliability and are the most appropriate system type for most heritage fire risks. With the exception of spaces subject to freezing conditions, dry pipe systems do not offer advantages over wet pipe systems in heritage buildings. Preaction sprinkler systems are beneficial in areas of highest water sensitivity. Their success is dependent upon selection of proper suppression and detection components and management's commitment to properly maintain systems. Water mist represents a very promising alternative to gaseous agent systems.
The following information sources are available to assist with selection of fire sprinkler systems: