WAACNewsletter
Volume 17, Number 2 .... May 1995

An Introduction to Automatic Fire Sprinklers, Part II

by Nick Artim

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:

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.

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

[Dry Pipe System, Discharge]
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:

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.

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

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

[Pre-Action System, 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:

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:

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.

Table 6-1: Fire Suppression Water Application Rates.

Delivery Method

Liters/min.

Gallons/min.

Portable Fire Extinguisher/Appliance

10

2.5

Occupant Use Fire Hose

380

100

Sprinkler (1)

95

25

Sprinkler (2)

180

47

Sprinkler (3)

260

72

Fire Dept., Single 1.5" Hose

380

100

Fire Dept., Double 1.5" Hose

760

200

Fire Dept., Single 2.5" Hose

950

250

Fire Dept., 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.

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.)

[Decorative Ceiling]
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:

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:

Additional Information.

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

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