Sprinkler System Basics

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A fire protection and life safety consultant describes the basics of automatic sprinkler systems.

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December 9, 2009

Inventors began experimenting with automatic sprinklers around 1860. These systems started out as pipes with holes drilled in them. When a fire occurred, the water was turned on to control the fire.

Until the 1940s, most sprinkler systems were installed in industrial and commercial facilities. Since then, however, sprinkler systems have been installed in nearly all occupancies, including schools, hotels and motels, places of assembly, offices and, more recently, residences.

Sprinklers have developed beyond the original drilled pipe into a variety of devices that operate at different temperatures and positions. The operation of a sprinkler is simple, as it "puts the wet stuff on the red stuff."

Throughout the past 100 years, sprinkler systems have been successful in saving lives and properties. Automatic sprinkler systems can react in the early stage of a fire to minimize the fire’s impact.

TODAY’S SYSTEMS

Sprinkler systems for fire-protection purposes consist of a city water supply or pumping system that is connected to an underground fire main that supplies overhead piping in the building. The piping is sized based on the hazards within the building. The sprinklers themselves are attached to the piping. Because the piping system is connected to a water supply, the pipes are filled with water. When the sprinkler is activated, water is immediately delivered to the area.

The sprinkler is a simple device that features a fusible element in the center that melts when exposed to excessive heat, allowing water from the piping system to flow. The fusible element is designed to operate at a specific temperature. The designer takes the ambient temperature in the building into account when selecting the sprinkler. The standard sprinkler operates at 165 degrees Fahrenheit (74 degrees Celsius).

Because each sprinkler has a fusible element, only the sprinklers in the immediate area of the fire will operate. When the sprinkler operates, it discharges water in a circular pattern that rains down in the shape of an umbrella.

Depending on the facility’s conditions and requirements, different types of sprinkler systems are used. A wet pipe system, which has water in the piping up to the sprinkler, is standard. If the building or room in question experiences temperatures below 40 degrees Fahrenheit (4 degrees Celsius) for more than eight hours daily, a dry pipe system must be installed. The dry pipe system has air pressure that keeps the water out of the system until a sprinkler is activated, releasing the air and allowing the water to flow.

Other types of systems are available for specific applications, but they are not applicable to this discussion.

BEYOND APPEARANCES

It is common to conclude that your facility is protected from fire if it is equipped with sprinklers and piping. However, this may not be the case. Not all sprinkler systems are created equal. Just because your facility is equipped with sprinklers that will discharge water in the case of a fire does not mean the system will be able to control a fire.

When you are in the process of buying or leasing a building and you see that the building has a sprinkler system, it does not mean that the system is adequate for your occupancy. It may be acceptable for a shredding operation but may not be adequate for rack or pile storage. Prior to settling on an existing building, it is important to ask what the density of the current sprinkler system is and what it is designed to protect. You would hate to get locked into a lease or buy a building only to find out that you have to put $150,000 to $300,000 into the sprinkler system before you can occupy the building.

KEY CONSIDERATIONS

What are the benefits of properly designed sprinkler systems? First and foremost, a properly designed sprinkler system provides life safety to a building’s occupants. When a sprinkler operates, an alarm notifies the occupants of the fire hazard, and water discharges to reduce the fire’s size, controlling it until the fire department can arrive to manually fight it.

Having a properly designed sprinkler system may mean the difference between staying in business and not being able to recover from a devastating loss. Your insurance company may cover a portion of the loss as the result of a fire, but could you survive the loss of business clients, downtime and future clients that you cannot service because you do not have a building in which to operate?

It is extremely important that a sprinkler system be properly designed for the business operations or materials being stored as well as for the height and method of storage. You cannot expect a sprinkler system designed for light manufacturing to control a fire in rack or pile storage at a height of 20 to 30 feet.

For those records center operators who do not want a water-based sprinkler system because they are concerned about water damage or what would happen if a sprinkler accidentally went off, wetting items in storage, I’d like to remind you that sprinklers have been manufactured for more than 100 years and don’t just go off. Sprinklers operate because of a fire, as a result of physical damage or because an employee has played with the sprinkler to "see what will happen."

While chemical or gaseous fire extinguishing systems have specific applications, generally there is no substitute for a water-based sprinkler system.

Remember, smoke detectors are an excellent tool that provides an early warning that there is a fire, giving you the time to evacuate the building and notify the fire department. However, smoke detectors will not extinguish the fire or reduce its progress.

Fires grow exponentially. In a matter of minutes, a fire will double in size and double again and again until water is applied. If a sprinkler system is not properly designed, the fire can easily overcome the system, and your building could burn down.

Sprinkler systems are designed for a "normal" fire, or a fire that starts accidently in a single location. Sprinkler systems are not designed to combat arson, because the arsonist may start multiple fires or a large fire, use accelerate or tamper with the system. Any of these conditions could overcome the sprinkler system even if it is adequately designed.

DESIGN GUIDELINES

A properly designed sprinkler system is your best defense against accidental fire. What constitutes a properly designed sprinkler system? Several factors must be considered when selecting the system for your facility, such as the material being stored, the method of storage, the height of the racking system and the height of the building. Specific standards, particularly National Fire Protection Association (NFPA) 13, Standard for the Installation of Sprinkler Systems, govern the design of sprinkler systems.

NFPA first developed NFPA 13 in 1896. This standard has been used by the industry for the last 113 years to design and install sprinkler systems. The NFPA has kept records on fires for most of those years and has found that sprinkler systems save lives and protect property.

A fire protection consultant can assist you in the selection process.

A facility’s protection requirements increase as the combustibility of items within the facility increase. For instance, plastic fittings will burn rapidly and produce a significant amount of heat compared with metal fittings. Controlling or extinguishing this type of fire will require a lot of water.

The same concept applies to the method of storage. If materials are stored in piles on the floor, the specific density is different from that of a facility in which material is stored on racks. Then there are the dreaded words "in-rack sprinklers," which may be required because of the height of the racking and items in storage.

The height of storage and the height of the building are key elements in selecting the correct sprinkler system density. As the storage gets higher, the amount of combustibles increases, and the farther away the sprinklers are from the base of the fire, necessitating an increase in the water flow to the sprinkler system.

Fire officials or contractors will indicate that a sprinkler system’s density must meet certain requirements, such as 0.3 gallons per minute (1.14 liters per minute) per square foot for the most remote 2,000 square feet (186 square meters).

What does the word "density" mean? Density is the quantity of water that must be delivered over an area. This is the quantity of water that must be delivered out of each sprinkler within a 2,000-square-foot area; the contractor anticipates the 2,000 square feet is located in the most remote part of the building. The contractor designs the pipe size based on this water flow requirement.

If you do not have a sprinkler system or if the system you have is improperly designed and a fire occurs, your building likely will burn down.

I hope this information assists you in understanding sprinkler systems and in discussing your fire protection system needs with fire officials or consultants. n

The author is a principal with Fire Protection International Consortium Inc., Concord, Calif. He can be contacted at w.comeaux@the-fpi.com.