Types of Sprinklers
As the saying goes, you need the right tool for the right job, and this applies to selecting the right types of sprinklers to be used in a sprinkler system. This blog is designed to be a helpful reference and contains most of your sprinkler options along with a helpful description of each.
While there are several different types of sprinklers, each sprinkler will have a characteristic related to their spray pattern, orientation, and response time that can vary and is addressed below. It is also important to note that although there are a wide variety of different nozzles that can be used as part of an NFPA 13 system this blog only addresses sprinklers.
Before we jump into some of the varying characteristics of a sprinkle here is a quick note about basic sprinkler operation. A sprinkler works by having a heat-activated element made of either a glass bulb or a fusible metal link that will activate and discharge water when heated to a designated temperature. Sprinklers are tested and listed for specific uses, and they need to be used in accordance with their listing.
SPRAY PATTERN
When a sprinkler is activated, a plug is released, and water moves through an orifice at a certain flow and pressure. That water then collides with the deflector which is designed to create a certain spray pattern. Most sprinkler spray patterns fall into one of the following categories.
Standard Spray Sprinklers. The standard spray sprinkler is installed in accordance with specific coverage area limitations and is available in pendent, upright, and sidewall configurations. Because the standard spray sprinkler is proven to be effective for a broad range of hazards and applications by adjusting the water discharge density, it is popular and, to a certain degree, serves as the benchmark for sprinkler measurement and performance.
Extended Coverage Sprinklers. As the title suggests, these sprinklers have a larger, or extended, coverage area when they discharge. This can help save material and labor costs because you do not need to install as many sprinklers. The trade-off is that they might require a water supply with a higher pressure to discharge at the higher flow rate necessary to cover the larger area they were designed for. Extended coverage sprinklers also come in several orientations and response types.
Old Type Sprinklers: Old style sprinklers are only permitted for special situations such as the protection of fur storage vaults. These sprinklers have a unique water distribution, where about half the water is directed upwards and half is directed down. This typically allows these sprinklers to be installed in either the pendent or upright position.
SPRINKLER ORIENTATIONS
Sprinklers are designed to be installed in a certain orientation. While this allows additional design flexibility it is also important to ensure that sprinklers are installed in the orientation in which they are designed to be installed.
Pendent Sprinkler: A sprinkler designed to be installed in such a way that the water stream is directed downward against the deflector. Pendent sprinklers are very common but standard pendent sprinklers can’t be used with dry pipe systems because water can get trapped between the sprinkler and branch line piping causing ice to block the flow of water.
Upright Sprinkler: Upright sprinklers have a spray pattern that appears similar to that of a pendent sprinkler. The difference is that upright sprinklers are mounted to the top of branch lines or sprigs and installed in such a way that the water spray is directed upwards against the deflector. Upright sprinklers can be used in dry pipe systems because water can’t get trapped.
Sidewall Sprinkler: Sidewall sprinklers typically are installed along a wall and discharge water away from the wall into the room or space. Sidewall sprinklers can be mounted on the side, bottom, or top of a branch line, as specified in their listings. The discharge pattern resembles one-quarter of a sphere, with a small portion of the discharge directed at the wall behind the sprinkler.
Recessed Sprinkler: A sprinkler in which all or part of the body is mounted within a recessed housing. Some recessed sprinklers are meant to be partially recessed into a wall or ceiling while others are designed to be completely flush with the wall or ceiling. Only sprinklers designed and listed to be installed as a recessed sprinkler can be installed recessed.
Concealed Sprinkler: A recessed sprinkler with cover plate. The cover plate is typically soldered to the frame that screws or pushes into the sprinkler assembly. The solder is designed to melt at a lower temperature than the sprinkler activation temperature. When the solder melts, the cover plate falls off allowing the sprinkler head deflector to drop below the ceiling height and distribute water after the sprinkler activates.
SPRINKLER RESPONSE TYPES
Sprinkler response types are determined by their Response Time Index (RTI). This is a method of measuring thermal sensitivity under standardized test conditions. In addition to sprinkler response time, sprinklers also can have different thermal elements that are designed to activate at varying temperatures. For more information on thermal characteristics of sprinkler check out our latest blog that covers that very topic.
Quick Response (QR) Sprinkler: A type of spray sprinkler that has a thermal element with an RTI of 50 (meter-seconds)1⁄2 or less and is listed as a quick-response sprinkler for its intended use. A quick-response sprinkler is similar to a standard response sprinkler, except that it possesses a fast-response operating element, so when exposed to the same temperature change, a quick response sprinkler will operate faster than a standard response sprinkler. QR sprinkler technology was developed from residential sprinkler technology. QR sprinklers are tested against the same criteria as standard-response sprinklers. The difference in the size of the operating elements of QR sprinklers and standard-response sprinklers should be noted. Where glass bulbs are used for standard spray sprinklers, the diameter of the bulb of a QR sprinkler is typically less than that of a standard-response sprinkler. Where a metallic alloy is used, the operating heat responsive element of a standard-response sprinkler has more mass than the element used in a QR sprinkler.
Standard Response Sprinkler: Sprinklers defined as standard response have a thermal element with an RTI of 80 (meters-seconds)1⁄2 or more.
SPECIAL SPRINKLERS
Residential Sprinkler: A type of fast-response sprinkler having a thermal element with an RTI of 50 (meters-seconds)1⁄2 or less that has been specifically investigated for its ability to enhance survivability in the room of fire origin and that is listed for use in the protection of dwelling units. Residential sprinklers are designed to prevent flashover, so the spray pattern throws water much higher. Residential sprinklers are required to pass wall wetting tests in addition to floor distribution.
Dry Sprinkler: Sometimes referred to as dry barrel sprinklers, dry sprinklers are used in areas where the sprinklers and piping are subject to near-freezing temperatures such as freezers or balconies. A dry sprinkler or dry barrel sprinkler is a sprinkler that is secured in an extension nipple that has a seal at the inlet end to prevent water from entering the nipple until the sprinkler operates. Dry sprinklers are used so a wet pipe system can serve an area that is subject to freezing by holding the water back in a space that can be maintained above freezing.
Open Sprinklers: Open sprinklers are used in deluge systems. They are not activated by individual thermal elements, instead the system water supply is held back by a deluge valve that is automatically opened (most often by activation of a heat detection system). This is meant to deliver a large amount of water over a specific area in a short amount of time. They are typically used for protection against high-hazard or rapidly spreading fires.
Institutional Sprinkler: Installing sprinklers in a correctional or institutional facility can be tricky since they need to be tamper-proof. Institutional sprinklers are specially designed to prevent people from attaching anything to it that could inflict harm on themselves or others. They are also made with components that cannot be easily converted into makeshift weapons.
Corrosion Resistant Sprinkler: A sprinkler fabricated with corrosion-resistant material, or with special coatings or platings, to be used in an atmosphere that would normally corrode sprinklers. Corrosion-resistant sprinklers are either covered with a decorative or corrosion-resistant coating or are designed for a specific function. Additional consideration of corrosion resistance should be given to any attached escutcheon. Stainless steel and aluminum escutcheons are often preferred over mild steel in harsh environments.
STORAGE SPRINKLERS
Most sprinklers are designed to control a fire. This means that they apply water to a fire to prevent it from growing out of control. This is done in order to allow the occupants to evacuate the building and firefighters to arrive and fully extinguish the fire. There is only one type of sprinkler that is designed to fully extinguish a fire. When it comes to the sprinklers used in the protection of storage areas you will notice that the names of the sprinklers indicate whether they control the fire (control mode) or suppress the fire (early suppression).
Control Mode Density Area (CMDA): A type of spray sprinkler intended to provide fire control in storage applications using the density/area design criteria.
Control Mode Specific Application (CMSA) These are designed for applications such as storage occupancies. These designs, along with most other types of sprinklers, are intended to control the fire, not suppress it. CMSA sprinklers are a type of spray sprinkler that can produce characteristic large water droplets and that is listed for its capability to provide fire control of specific high-challenge fire hazards. This term is meant to incorporate a wide variety of sprinklers capable of fire control in high challenge fire scenarios. Note that CMSA Sprinklers are tested for use in specific storage configurations and need to be used in accordance with their listing. You might hear some people refer to CMSA sprinklers as large-drop sprinklers.
Early Suppression Fast Response (ESFR). Similar to CMSA sprinklers ESFR sprinklers are designed for storage occupancies. Although, ESFR sprinklers are designed for fire suppression rather than control. These are designed to protect rack storage without the need for in-rack sprinkler protection. The ESFR concept is to apply enough water to the burning fuel during the early phases of a fire and penetrate the developing fire plume, achieving suppression. ESFR sprinklers have a thermal element with an RTI of 50 (meters-seconds)1⁄2 or less and are listed for their capability to provide fire suppression of specific high-challenge fire hazards. Caution must be exercised to avoid confusing ESFR sprinklers with other types of sprinklers that are equipped with fast-response operating elements. A non-ESFR sprinkler with a fast-response element is not specifically designed to achieve fire suppression. The relationship among thermal sensitivity, actual delivered density, and required delivered density needs to be considered.
Intermediate Level Sprinkler: A sprinkler equipped with integral shields to protect its operating elements from the discharge of sprinklers installed at higher elevations. Intermediate Level Sprinklers are typically designed for use in rack storage sprinkler systems where their thermal elements need to be shielded from the water spray of sprinklers above. Other applications where one might find Intermediate Level Sprinklers include areas beneath open gridded catwalks.
RECENT TECHNOLOGY
Here are some additional sprinkler types that have recently been brought to the market, they are not as common as some other types of sprinklers but it is important to be aware of them.
Polymer sprinklers: A residential fire sprinkler comprised of mainly polymeric materials. These are typically slightly lighter than metallic sprinklers and are lead free, allowing them to be used in a system that uses potable water. As of the writing of this article these sprinklers are limited to being used in NFPA 13D systems.
Electrically Operated Sprinklers: Electrically operated sprinklers are a technology in which the primary means of operation is through an electrical signal provided by an electronic control system using specialized detection and control algorithms. These systems are typically used in high challenge storage applications. The systems utilize a combination of heat and smoke detectors to pinpoint the precise location of a fire, which enables the system to actuate (open) the proper number of sprinklers to control and/or suppress the fire.
If you enjoyed this blog be sure to check out our blog on the Thermal Characteristics of Sprinklers as well as our blog on the different Types of Sprinkler Systems.
Important Notice: Any opinion expressed in this blog is the personal opinion of the author and does not necessarily represent the official position of NFPA or its Technical Committees. In addition, this piece is neither intended, nor should it be relied upon, to provide professional consultation or services.
