Volume 17, Number 2 .... May 1995

An Introduction to Automatic Fire Sprinklers, Part II

Abstract

Museum management is entrusted with the responsibility of protecting and preserving the institution's 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 its destructive forces, fire constitutes one of the more serious threats.

Collections must be safeguarded from fire. Vandalized or environmentally damaged objects can be repaired and stolen objects recovered, however, fire destroyed items are gone forever. An uncontrolled fire can obliterate an entire room's contents within a few minutes and completely burnout a building in a couple hours.

Fire protection experts generally agree that automatic sprinklers represent the single, most significant aspect of a fire management program. Properly designed, installed, and maintained systems can overcome deficiencies in risk management, building construction, and emergency response. They may also enhance the flexibility of building design and use by increasing the overall safety.

Nonetheless, sprinklers frequently cause considerable debate among heritage facility experts. Typical concerns include the potential for inadvertent operation, increased damage due to water release, and aesthetic impact. As a result many heritage properties have avoided fire sprinkler protection.

This article will present an overview of sprinkler systems including system types, components, operations, and common anxieties.

For Part I see WAAC Newsletter September 1994, Volume 16, Number 3.

1: Fire Growth and Behavior
2: Sprinkler System Benefits
3: Sprinkler System Operation
4: System Components and Types

Part II

5: System Types

There are three basic types of sprinkler systems: wet pipe, dry pipe, and preaction. Each has unique 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 multi-function 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:

• System simplicity and reliability. Wet pipe sprinkler systems have the least number of components and therefore, the lowest number of items to malfunction. This produces unexcelled reliability which is important since sprinklers may be asked to sit in waiting for many years before they are needed. This simplicity aspect also becomes important in facilities where system maintenance may not be performed with the desired frequency.
• Relative low installation and maintenance expense. Due to their overall simplicity, wet pipe sprinklers require the least amount of installation time and capital. Maintenance cost savings are also realized since less service time is generally required, compared to other system types. These savings become important when maintenance budgets are shrinking.
• Ease of modification. Heritage institutions are often dynamic with respect to exhibition and operation spaces. Wet pipe systems are advantageous since modifications involve shutting down the water supply, draining pipes and making alterations. Following the work, the system is pressure tested and restored. Additional work for detection and special control equipment is avoided which again saves time and expense.
• Short term down time following a fire. Wet pipe sprinkler systems require the least amount of effort to restore. In most instances, sprinkler protection is reinstated by replacing the fused sprinklers and turning the water supply back on. Preaction and dry-pipe systems may require additional effort to reset control equipment.

The main disadvantage of these systems is that they are not suited for sub-freezing environments. There may also be a concern where piping is subject to severe impact damage and could consequently leak, e.g. warehouses.

The advantages of wet systems make them highly desirable for use in most heritage applications. With limited exceptions they represent the system of choice for museum, library and historic building protection.

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. Located in a heated space, the dry-pipe valve 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.

Illustrations 5-1 and 5-2 show the typical dry pipe sprinkler system.

Illustration 5-1. Dry Pipe System, Non-Fire.

Illustration 5-2. Illustration 5-2: Dry Pipe System, Discharge.
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. This perceived benefit is due to a fear 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 which must be evaluated before selecting this equipment. These include:

• Increased complexity. Dry pipe systems require additional control equipment and air pressure supply components which increases system complexity. Without proper maintenance this equipment may be less reliable than a comparable wet pipe system.
• Higher installation and maintenance costs. The added complexity impacts the overall dry-pipe installation cost. This complexity also increases maintenance expenditure, primarily due to added service labor costs.
• Lower design flexibility. There are strict requirements regarding the maximum permitted size (typically 750 gallons) of individual dry-pipe systems. These limitations may impact the ability of an owner to make system additions.
• Increased fire response time. Up to 60 seconds may pass from the time a sprinkler opens until water is discharged onto the fire. This will delay fire extinguishing actions, which may produce increased content damage.
• Increased corrosion potential. Following operation, dry-pipe sprinkler systems must be completely drained and dried. Otherwise remaining water may cause pipe corrosion and premature failure. This is not a problem with wet pipe systems where water is constantly maintained in piping.

With the exception of unheated building spaces and freezer rooms, dry pipe systems do not offer any significant advantages over wet pipe systems. Their use in heritage buildings is generally not recommended.

The third sprinkler system type, pre-action, 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 pre-action valve. Valve operation 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. Illustrations 5-3 through 5-5 show the operation of a typical preaction system.

Illustration 5-3. Pre-Action System, Non-Fire.

Illustration 5-4. Pre-Action System, Pre Discharge.

Illustration 5-5. Pre-Action System, Discharge.

In some instances, the preaction system may be set up with a double interlock in which pressurized air or nitrogen is added to system piping. The purpose of this feature is two-fold: 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 pre-action system is the dual action required for water release: the pre-action valve must operate and sprinkler heads must fuse. This feature provides an added level of protection against inadvertent discharge. For this reason, preaction 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 pre-action systems. These include:

• Higher installation and maintenance costs. Preaction systems are more complex with several additional components, notably a fire detection system. This adds to the overall system cost.
• Modification difficulties. As with dry-pipe systems, preaction sprinkler systems have specific size limitations which may impact future system modifications. In addition, system modifications must incorporate changes to the fire detection and control system to ensure proper operation.
• Potential decreased reliability. The higher level of complexity associated with preaction systems creates an increased chance that something may not work when needed. Regular maintenance is essential to ensure reliability. Therefore, if the facility's management decides to install preaction sprinkler protection, they must remain committed to installing the highest quality equipment, and to maintaining these systems as required by manufacturer's recommendations.

Provided the application is appropriate, preaction systems have a place in heritage buildings, especially in water sensitive spaces.

A slight variation of pre-action sprinklers is the deluge system, which is basically a pre-action 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 pre-action system variation is the on-off system. This system utilizes the basic arrangement of a pre-action system, with the addition of a thermal detector and non-latching alarm panel. The system functions similar to any other pre-action 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, however, care must be exercised when selecting this equipment to ensure that they function 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.

6: Sprinkler Concerns

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:

• When one sprinkler operates, all will activate. With the exception of deluge systems (discussed later in this article), only those sprinklers in direct contact with the fire's heat will react. Statistically, approximately 61% of all sprinkler controlled fires are stopped by two or less sprinklers.
• Sprinklers operate when exposed to smoke. Sprinklers function by thermal impact against their sensing elements. The presence of smoke alone will not cause activation without high heat.
• Sprinkler systems are prone to leakage or inadvertent operation. Insurance statistics indicate a failure rate of approximately 1 head failure per 16,000,000 sprinklers installed per year. Sprinkler components and systems are among the most tested systems in an average building. Failure of a proper system is very remote.

Where failures do occur, they are usually the result of improper design, installation or maintenance. To avoid problems, the institution should carefully select those who will be responsible for the installation and be committed to proper system maintenance.

The 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, pharmaceutical, clean rooms, or high tech manufacturing. Companies including AT&T, Merck, and IBM have very stringent sprinkler installation requirements. If a sprinkler contractor has demonstrated success with these type 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 the average and the highest quality components is minimal, however the long term benefit is substantial. When considering the value of a facility and its contents, the extra investment is worthwhile.

• Sprinkler activation will cause excessive water damage to contents and structure. Water damage will occur when a sprinkler activates. This issue becomes relative, however, when compared to alternative suppression methods. The typical sprinkler will discharge approximately 25 gallons per minute (GPM) while typical fire department hoses delivers 100-250 GPM. Sprinklers are significantly less damaging than hoses. Since sprinklers usually operate before the fire becomes large, the overall water quantity required for control is lower than situations where the fire continues to increase until firefighters arrive. Table 6-1 shows approximate comparative water application rates for various manual and automatic suppression methods.

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.

• Sprinkler systems look bad and will harm the buildings appearance. This concern has usually resulted from someone who has observed a less than ideal appearing system, and admittedly there are some poorly designed systems out there. Sprinkler systems can be designed and installed with almost no aesthetic impact.

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.

Illustration 6-1 provides an example of a well installed sprinkler in an architecturally sensitive space. (Note, the sprinkler is in one of the plaster ceiling rosettes.)

Illustration 6-1. 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.

7: Water Mist

One of the most promising extinguishing technologies involves the use of fine water droplets, known as micromist.

This technology represents a potential solution to the protection void left by the environmental concerns, and subsequent demise of Halon 1301 gas.

Micromist systems discharge limited water quantities at very high release pressures (approximately 1,000 psi). This produces droplets of less than 20 microns diameter, resulting in exceptionally high efficiency cooling and fire control with significantly little water. Initial system tests have demonstrated successful fire extinguishment in hotel room scenarios, mockup library bookstacks, computer rooms and underfloor cable spaces. In most situations these fires have been extinguished with 1-5 gallons of water. Many of the test scenarios have been suppressed in less than 1 minute, with all fire scenarios extinguished within 5 minutes. Water saturation, often associated with standard firefighting procedures, is avoided. Other anticipated micromist benefits include: lower installation costs, minimal aesthetic impact, and known environmental safety.

The micromist system consists of:

• Water supply: Water may be provided by either the piped building system or a dedicated tank arrangement. System operating pressure is produced by a high pressure pump.
• Piping and nozzles: Piping is generally 1/2 inch diameter stainless steel, which is clean and easily installed. This material comes prefabricated from the factory, with final site assembly performed using simple compression fittings. Welding, brazing, or threading operations are avoided. Nozzles are approximately the size of a pencil eraser.
• Detection and control equipment. Micromist discharge is controlled by selected, high reliability intelligent detectors or by an advanced technology VESDA smoke detection system. These systems represent the premier, state-of-the-art, fire detection technology. Thus, the probability of inadvertent discharge is drastically reduced.

A leading micromist system is under joint development by Baumac International, Reliable Automatic Sprinkler Corporation, Marriott Hotels, and the University of Maryland Fire and Rescue Institute. Equipment controls are being developed by Fire Control Instruments (FCI), Notifier Corporation and IEI North America. To date, this consortium has compiled an extensive data base, testing micromist is a variety of "live fire" situations.

While success has been impressive, several questions remain regarding mist capabilities and constraints. In particular, what factors impact mist success and, what is the level of collateral content damage upon extinguishment? Several cultural heritage fire problems will be simulated and analyzed during upcoming tests. Representative heritage collections will be placed in a micromist discharge. Following micromist suppression each item will be removed and examined by collections management experts for damage and establishment of required restoration effort.

Several heritage institutions are providing materials and technical expertise for the test program. These include the National Gallery of Art, the National Library of Canada, the Field Museum of Natural History, the National Archives of Canada, the Library of Congress, the Architect of the Capitol, the National Library of Scotland, and the National Park Service. With their input, the ultimate benefit of micromist will be established.

Additional information on this technology will be forthcoming as developments progress.

8: Summary:

In summary:

• Heritage management must identify the desired objectives which the selected fire suppression system is to attain. Once these issues have been established, protection systems can be selected to accomplish target goals.
• Automatic sprinklers often represent the most important fire protection option 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.
• Pre-action 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 (micromist) represents a very promising alternative to gaseous agent systems. This technology is under development with availability anticipated in 12-18 months.
• Most system failures are the result of improper system maintenance. Management must remain committed to providing proper system maintenance to ensure reliability, and avoid the temptation to cut back on system service.

Additional Information.

The following information sources are available to assist with selection of fire sprinkler systems:

• Fire Safety Network; Post Office Box 895; Middlebury, Vermont 05753; USA. Telephone 802/388-1064.
• National Fire Protection Association; Batterymarch Park; Quincy, Massachusetts 02269; USA. Telephone 617/770-3000.
• Reliable Automatic Sprinkler, Inc.; 1800 Sandy Plains Parkway, Building 100, Suite 108; Marietta, Georgia 30066; USA. Telephone: 800/652-1819 or 404/421-1633. Attention: Mr. Thomas L. Multer, Special Hazards Manager.