What is a fire sprinkler system?
A fire sprinkler system is a method to limit the damage to life and property by fire. A sprinkler system does not prevent fire, but rather works to suppress a fire. Fire suppression isn’t fire prevention, it’s fire protection.

A fire system uses pressure and flow rate of water or approved designated chemicals through a pipe system to suppress a fire upon activation. At specified spaced intervals on these pipes, sprinklers (also called sprinkler heads, or just heads) are placed to disperse the fire-retardant. Water is the most common type of fire-retardant used in commercial and residential systems.

Contrary to the Hollywood depiction, most sprinkler systems do not use a single sprinkler head to set off an entire system. Most systems used today require a single head that activates independently and as needed. This method limits damage to property that is not affected by fire, and helps to maximize the available water pressure over the point of the fire’s origin. So you can’t just hold up a lighter to one sprinkler head and expect the entire system to activate.

How does a sprinkler system work?
Sprinkler systems are designed to control a fire and/or to suppress a fire. A control mode sprinkler system is designed to control a fire in order to limit the spread of a fire. It will pre-wet combustible materials and work to prevent the physical collapse of the building. The system controls the fire until the fire department arrives and effectively extinguishes the fire and/or until burning combustibles are exhausted.

Early Suppression Fast Response (ESFR) systems (also known simply as Suppression systems) are designed for sudden reduction of fire and to completely extinguish a fire prior to manual intervention.

A typical sprinkler head for commercial use disperses about 20-40 gallons of water per minute. Suppression systems can release a higher rate of flow at 100 gallons per minute. Compare that to the stream of water from a fire hose which can disperse 250 gallons of water per minute.

The type of building and what is stored within the building will determine the hazard level, which dictates the type of sprinkler system required. A residential system will not require a more expensive EFSR system. But if that residential building is a nursing home, where medical chemicals might be found, the hazard level maybe raised and therefore a simple sprinkler system may not be sufficient for the purpose and use of that building.

The delivery of the suppression retardant is made by the sprinkler head. Each sprinkler head is held closed by a glass bulb or a two-part metal link. These ‘links’ or ‘bulbs’ use pressure to hold a cap in place which acts as a plug-in the system. These links are designed to break at a specified temperature, releasing the plug and allowing water to disperse over the flames.

What makes a sprinkler system so valuable is the amount of time it takes to activate and hopefully control the fire, as opposed to the time for suppression of the fire by the fire department. A typical sprinkler system will activate within 4 to 5 minutes of detection. Once a fire alarm has been activated, the fire department is notified. An additional 5 to 10 minutes will pass as the local fire department arrives at the location. An additional 10 minutes can pass as these first responders assess the fire, set up equipment and apply water to the fire.

This additional time allows a fire to grow, thereby doing more damage and requiring more water to suppress the flames. Which can cause additional water damage to equipment and property. The additional time can also create a greater danger for the loss of life. The fire department arrives as quickly as they can and get to work as quickly as possible, but they are at a disadvantage by not being at the fire when it begins. Where as a sprinkler system is already there.

Today’s Fire Protection Systems
There is very little Federal legislation regarding sprinkler system design and installation. Building codes are generally left to local jurisdictions and that includes the specifications for sprinkler systems. The Federal government has used its funding and monetary clout to strongly encourage fire safety standards however. But the main emphasis for the details, are set by local governments.

In 1895 the National Fire Protection Association (NFPA) was founded in Boston by Frederick Grinnell, a pioneer in the fire protection industry. It was the first time anyone had set and implemented standards for the installation of automatic fire sprinklers. His venture proved to be greatly successful and the NFPA standards became the uniformed installation requirements for the United States and Canada. These are the standards that are still utilized today by local governments to set fire protection requirements.

Even with all the improvements and desires to protect life through fire protection and suppression systems, nothing impacts standards more than a catastrophe. The MGM Grand Hotel fire in Las Vegas in 1980 was such an event. 85 guests and workers died during the fire captured on TV by local, national and even worldwide news agencies. The tragedy resulted in one of the nations first fire sprinkler retrofit ordinances for high-rise buildings.

Many see this fire as the event that set off some of the first federal legislation for building safety. In 1990 the US Congress passed PL-101-391, better known as “The Hotel and Motel Safety Act (of 1990)”. This law requires that any hotel, meeting hall, or similar institution that receives federal funds (i.e. for a government traveler’s overnight stay, or a conference, etc.), must meet fire and other safety requirements. Included in these conditions is the implementation of working sprinklers.

The NFPA
On their website, NFPA explains their codes and standards this way:
Virtually every building, process, service, design, and installation is affected by NFPA’s 275+ codes and standards. Our codes and standards, all available for free online access, reflect changing industry needs and evolving technologies, supported by research and development, and practical experience. (nfpa.org/Codes-and-Standards)

Codes and Standards are constantly evaluated and updated accordingly every 3 to 5 years. The Codes are issued in a handbook (ie: NFPA 13, Standard for the Installation of Sprinkler Systems, 2019 Edition). They also provide information through their magazine the NFPA Journal.

Fire sprinkler application and installation guidelines, and overall fire sprinkler system design guidelines, are provided by the standards set in several NFPA sections. The most common standards for Fire Protection are found in NFPA 13, NFPA 13D, NFPA 13R, NFPA 14, NFPA 20 and NFPA 24. These specifications define the accepted minimum requirements for building codes that are set by local jurisdictions in the United States. Many local jurisdictions add-on to these requirements and various state jurisdictions include additional requirements within state-wide building codes.

Because of these additional regulations, fire sprinkler contractors must attain a state license in order to operate in that state. These licenses require proof of knowledge and understanding of that state’s building codes and requirements. Because of this, designing and installing a sprinkler system should only be done by a licensed sprinkler contractor. While a plumber might have the knowledge to fit pipe, they may not understand all the requirements behind a sprinkler system and it’s installation.

Today, most states rely on The National Institute for Certification in Engineering Technologies (NICET) whose function is to evaluate the qualifications of those who voluntarily apply for certification in engineering technology fields. Some states prefer to create their own evaluation process for licensure. In either case, part of the evaluation process includes successful passage of an exam to assess and provide proof of knowledge before a license is granted.

How is a sprinkler system designed?
Most of today’s commercial and industrial sprinkler systems are designed with an area and density approach. Early Suppression Fast Response (EFSR) systems are designed with a special area in mind. ESFR is calculated based on flowing 4 heads on 3 adjacent lines. Residential systems are generally created in a room design method. The building itself, how the building will be used and what contents will be maintained or stored in the building, all determine the appropriate design of the sprinkler system. This information is used to define the fire hazard classification and the type of fire classification which dictate the specifications of the sprinkler system design, installation and operation.

The first part of this design is determining the Fire Hazard.

Fire Hazards:
NFPA 13 defines fire hazards into 4 main groups, two of which have sub-classifications described in NFPA 13 Chapter 4.3 Classification of Hazard.

• General Hazard (NFPA 4.3.1)
  • Miscellaneous Storage
  • Low-Piled Storage
  • Miscellaneous Fire Storage
  • In-Rack Sprinklers
• Light Hazard (NFPA 4.3.2) occupancy is defined as:
  • The Combustibility of the contents is low, and
  • The Quantity of the combustible is low, and
  • There are Low rates of heat release.
• Ordinary Hazard
  Group 1  (NFPA 4.3.3)
• Hazard is defined as:
  • The Combustibility of the contents is low, and
  • The Quantity of the combustibles is moderate, and
  • The Moderate heat release rates, and
  • The Height of storage is 8 feet or less.
  Group 2 (NFPA 4.3.4) Hazard is defined as:
  • The Combustibility of the contents is moderate to high, and
  • The Quantity of the combustibles is moderate to high, and
  • The Moderate to high rates of heat release, and
  • The Storage height is 12 feet or less.
• Extra Hazard
  Group 1 (NFPA 4.3.5) Hazard is defined as:
  • The Combustibility of the contents is very high, and
  • The Quantity of the combustibles is very high, and
  • The High rates of heat release, and
  • The Quantity of flammable and/or combustible liquids small.
  Group 2 (NFPA 4.3.6) Hazard is defined as:
  • The Quantity of flammable or combustible liquids is moderate to high, or
  • The Extensive shielding of the combustibles is present.

Fire Classifications:
Jurisdictions often set classifications for the types of fire hazards contained in buildings. These classifications are basic definitions and maybe enhanced or further classified by local jurisdictions and building codes. These classifications help define the standard requirements for designing and implementing fire protection systems.

Type of Fire	North America
Fires that involve flammable solids such as wood, cloth, rubber, paper, and some types of plastics.	Class A
Fires that involve flammable liquids or liquefiable solids such as petrol/gasoline, oil, paint, some waxes & plastics, but not cooking fats or oils	Class B
Fires that involve flammable gases, such as natural gas, hydrogen, propane, butane
Fires that involve combustible metals, such as sodium, magnesium, and potassium	Class D
Fires that involve any of the materials found in Class A and B fires, but with the introduction of an electrical appliances, wiring, or other electrically energized objects in the vicinity of the fire, with a resultant electrical shock risk if a conductive agent is used to control the fire.	Class C
Fires involving cooking fats and oils. The high temperature of the oils when on fire far exceeds that of other flammable liquids making normal extinguishing agents ineffective.	Class K

System Calculations
Once these classifications have been determined, the design area and required density are defined, the system is then calculated. Calculations are made to determine the sprinkler layout and pipe sizes required to protect a building for a given occupancy hazard. Calculations cover the pressure loss due to friction and elevation. Calculations for gains occur if the flow goes through a fire pump, or if there is a decrease in elevation. However it is pretty rare for there to be a decrease in elevation.

What are the types of sprinkler systems?
There are several types of sprinkler systems. Most are water based, but some special hazards may require non-water spray systems. Most jurisdictions require remote monitoring of all sprinkler systems except 13-D types.

Water spray
All water based systems are considered to be “Water Spray” systems. These systems use specified spray patterns to control or suppress a fire. Spray patterns can be oval (the most common), fan, full circle and narrow jet. The amount of water dispersed often defines the main characteristic of the type of water spray system.

Wet pipe systems
These are the most commonly used water spray systems. Water is fed into the piping and remains under pressure until a sprinkler head is activated. When activated the pressure forces the water out through the head and suppresses a fire. Larger wet pipe systems are often monitored by a fire alarm control panel. Additional types of communication control panels are available based on hazard and need. For high rise buildings or buildings/hazards that require higher than normal water pressure or volume, a wet pipe system may include a fire pump.

Dry pipe systems
A dry pipe sprinkler system uses pressurized air, rather than water within the piping system. This is often used in places where the temperature outside or around the pipe has the potential of freezing the water within the pipe. Obviously freezing would be a bad thing as it would render the sprinkler system inoperable and/or could potentially cause the pipes to rupture creating a catastrophic failure of the system. Not to mention the subsequent water damage.

In a dry pipe system, the air pressure holds a valve (known as a dry pipe valve) in the closed position. The dry pipe valve is protected by being located in a heated space. When a fire causes one or more of the sprinkler heads to activate, air pressure is released which activates the dry-pipe valve. The valve opens and allows water from the heated part of the pipe system to enter the pipe, flowing through open sprinklers onto the fire.

Dry pipe systems are typically installed in unheated spaces, such as attics, unheated warehouses, commercial freezers or for outside loading docks.

Deluge systems
This is the Hollywood example of a complete system activation. Deluge systems work pretty much like the name implies. They douse an area quickly with a deluge of water to suppress a fire. They are typically used in extra-hazard areas such as power generation stations, petrochemical facilities, aircraft hangers and other similar warehouse or storage areas. Deluge Systems can include a manual, pneumatic, hydraulic, or any type of electric detection/release system.

Water is not present in the piping until the system operates. A deluge valve holds back the water from the open piping system. The deluge valve is activated by a fire alarm system that has been initiated by a fire detection device (smoke detector, heat detector, or optical flame detector). The initiating device signals the fire alarm panel, which in turn signals the deluge valve to open. The detection device used is determined by the type of hazard within the building.

The deluge valve is used at the water supply connection and mechanically latched. When activated the valve stays open, meaning it cannot be reset and stays open once it’s tripped.

Pre-Action Systems
Pre-action Systems are most frequently used to protect against accidental water discharge when that is a great concern. Keep in mind, all pipe systems have the potential for issues over long periods of time and accidents caused by tenants within the building/area where the sprinklers are installed. Pre-Action systems help to minimize accidental events and are often used in museums, libraries, data centers or where electrical or computer equipment are used.

Pre-action systems are hybrids of wet, dry, and deluge systems. There are two primary sub-types of pre-action systems: single interlock and double interlock. The only practical pre-action system is the double interlock design, primarily because the point of pre-action is to make absolutely sure there’s actually a fire before operating.

Double-Interlocked Pre-action Systems require activation of both the detection system and a sprinkler before allowing water to flow into the piping system. When the alarm system and a sprinkler both activate, the pre-action valve will trip and water will enter the open piping system and disperse water on the coverage area. Double interlock systems are considered to be dry systems in terms of water delivery times, and similarly require a larger design area.

The Single-Interlocked Pre-action System utilizes a pre-action valve which is mechanically latched similar to a deluge valve. The pre-action valve will not open due to loss of air pressure in the pipe system. Activation of the pre-action valve occurs when a detection system (fire, smoke alarm etc.) denotes a fire. Water then flows into the pipes, changing the piping system from a dry system to a wet system. Water is held in the system until a sprinkler opens and allows water to flow into the coverage area. This method of delivery protects against the accidental loss of air pressure in the piping system.

Foam water sprinkler systems
A foam system is a special application system using a mixture of water and low expansion foam concentrate to suppress a fire. These systems are used for special high hazard fires such as flammable liquids, in airport hangers and alike. Additional components are added to the sprinkler system for foam operation. This includes bladder tanks that hold the foam concentrate and are connected to the sprinkler system riser. Concentrate control valves are used to isolate the sprinkler system from the foam until activation. Pro-portioners are used for mixing the appropriate amount of foam with the water supply before dispersal.

Non water based sprinkler systems
Special hazards may require the use of non water based sprinkler systems. These hazard areas include places where water will increase the chance or size of a fire, instead of suppress it. These systems maybe used in electrical switch gear rooms, where lithium, sodium or other sensitive chemicals are stored. For example, when exposed to water lithium will ignite. It’s not a place where you want a water sprinkler system.

HFP has designed several commercial, industrial and residential sprinkler systems for our clients. We have the knowledge and experience to help you lay out a plan and design a system that’s right for your business or home. You can learn more about HFP, our experience and services by visiting our Home page or calling us at 704.877.2553

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