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November 2013: Sprinkler Heads Technology & Terminology

In times gone by, sprinkler heads came in basic flavors, with a few relatively limited options and permutations available: 1/2 inch orifice, 17/32 inch orifice, low, medium, or high temperature.

Today, like much else in the world, choosing sprinkler heads for system involves a dizzying array of choices and options. The basic types of sprinkler systems available include wet pipe, dry pipe, anti-freeze, pre-action (with several variations) and deluge. With the exception of foam/water systems and water mist which require separate discussion, all of these are designed to discharge water as the extinguishing agent. At the heart of every system is the sprinkler head, which determines how water is discharged.

In many cases, the occupancy to be protected will dictate the type of system to be used. For example, an office occupancy will almost always utilize a basic wet pipe sprinkler system, a frozen foods facility would typically require a double interlock pre-action sprinkler system, and open head deluge systems are common in outdoor chemical facilities. The choice of sprinkler head technology to use with the base system can be much more complex, and will ultimately affect the design of the system.

Things get complex with storage occupancies, particularly rack storage. With the advent of the industrial age and the ability to mass produce products, came the need to store goods to ever increasing heights. Along with this, the use of plastics (petroleum in solid form) further complicates the picture.

It is in the storage warehouses that the biggest challenges and changes have been required. The sprinkler system which was capable of protection wooden toys stored on 10 ft. high shelves in 1945, was not adequate to protect 20 ft. high rack storage of plastic toys in 1970, and even more inadequate for the storage of foam mattresses to 45 ft. high in an automatic retrieval racking system in 1995.

Through the 1970's, sprinkler systems remained largely unchanged from their ancestors developed in the 1890's; however as fire protection challenges grew, the demands being placed on traditional sprinkler systems were quickly becoming impractical. Advocates of sprinkler protection recognized this problem, and in the 1970's and 1980's embarked on conducting basic research to further understand the mechanisms of fire protection which make sprinkler protection either successful or unsuccessful.

One of the early practical outcomes of this research was the Large Drop (LD) sprinkler head, which proved to be successful in many higher challenge storage applications. Later on, this initial work was a foundation for the development of the Early Suppression Fast Response (ESFR) sprinkler head.

The ESFR sprinkler was a true departure from traditional sprinkler design. ESFR sprinkler heads were based on much larger orifices (higher K factors), had fast response elements, allowing the sprinkler to operate more quickly than its predecessors, and had deflector designs specifically engineered to achieve appropriate water droplet sizes for penetration of the fire plume.

However, physical features aside, the most significant change in design was the way in which sprinkler design was to be calculated. For these new "Suppression Mode" sprinkler system technologies, effective design was no longer based on the traditional density/area design basis on which virtually all prior sprinkler systems were based. Calculations now considered K factor and pressure, using a fixed number of sprinklers - typically 12 sprinklers. This design had the rudimentary difference of "suppression" of a fire at an early growth stage versus the traditional density/area design which was for "control" of a fire pending arrival of the fire department. Control versus Suppression is a fine, but very important distinction.

Below is a limited glossary of sprinkler types and terms which may be encountered. Rather than alphabetize the list, we have grouped similar and complimentary terms together for reference to one another.

Control Mode Sprinklers - Sprinklers which operate in the "control mode" will control a fire until the arrival of the fire department. The control mode sprinklers included Control Mode Density Area (CMDA) sprinklers and Control Mode Specific Application (CMSA) sprinklers. In part, the success of these density/area type of sprinkler systems is the ability to pre-wet adjacent materials that the fire has not yet reached, and to cool the building's structural components.

Suppression Mode Sprinklers - Suppression mode sprinklers will act to suppress a fire at an early stage before it becomes fully established. If fire development is beyond early stage growth and suppression sprinklers have not already operated, it is likely that they will no longer be able to control fire growth. Suppression mode sprinklers have very stringent installation and obstruction rules which most be followed to ensure proper operation and fire suppression.

Storage Sprinklers - FM Global and others have now adopted the term "Storage Sprinklers" to include both Control Mode (CMDA and CMSA) and Suppression Mode sprinklers designated for protection of storage. The Storage Sprinkler terminology therefore also includes ESFR sprinklers and Large Drop sprinklers.

Large Drop Sprinklers (LD) - LD sprinkler heads, also known as High Challenge, were the precursor of ESFR sprinklers. They now fall into the classification of a CMSA type sprinklers. LD sprinklers have larger orifices and produce larger water droplets for better penetration of the fire plume. LD sprinklers typically have a K factor of 11.2, and remain a viable option for protection of storage applications.

ESFR Sprinklers (Early Suppression Fast Response) - ESFR sprinkler technology was a continuing evolution of Large Drop (LD) sprinklers, combining them with a quick response element. These sprinkler heads were the first generation of what are now known as Suppression Mode sprinklers. The development of ESFR sprinklers largely eliminated the need for in-rack sprinklers. The installation guidelines for ESFR sprinklers are stringent and have little room for deviation. ESFR sprinklers are typically available with K factors of 14.0 to 25.2

Extended Coverage (EC) Sprinkler Heads - Traditional sprinklers were based on a nominal spacing of 100 sq. ft. per sprinkler head (typically 10 x 10 ft.), and generally allowed for spacings between 64-225 sq. ft. (8 x 8 ft. to 15 x 15 ft.) per sprinkler head. EC sprinklers allow for spacings up to 400 sq. ft. (20 x 20 ft.), thus extending the traditional coverage limits. EC sprinklers are available in K factors from 5.6 to 25.2. The design basis uses a modified density/area calculation method, requiring a minimum operating pressure at the design spacing. EC sprinklers are generally limited to light and ordinary hazard occupancies; however several models are approved for storage occupancies. In addition to pendant &and upright sprinkler configurations, EC sprinklers are also available in sidewall configurations with spacings up to 16 x 24 ft.

Extra Large Orifice (ELO) Sprinkler Heads - ELO sprinkler heads are another flavor of EC type sprinklers designed to provide coverage of up to 400 sq. ft. per sprinkler head. EC sprinklers are available in K factors from 11.2 to 14.0. The design basis uses a density/area calculation method.

In-Rack Sprinklers - The development of Suppression Mode type sprinkler systems has dramatically reduced the need for in-rack sprinkler heads. However, situations still remain where ceiling sprinkler systems alone are not adequate to protect rack storage. In these instances, in-rack sprinklers may be required to provide adequate protection. In fact, the combination of adequately designed in-rack and ceiling sprinklers is generally felt to provide better fire control that the use of adequately designed ceiling sprinkler systems alone. In rack sprinklers typically have integral water shields and are available in either pendant or upright models with K factors of 5.6-8.0. The design basis is similar to Suppression Mode sprinklers, requiring a minimum flow or pressure for a minimum number of operating sprinklers.

Dry Pendant - Dry pendant sprinklers are a specialty sprinkler head with a short air filled barrel for use in environments subject to freezing. They are installed on wet pipe systems, where the piping above must be kept from freezing. Typical installations might include a restaurant freezer or an entry vestibule.

Residential Sprinklers - This class of sprinkler head is designed for use in residential dwellings. This can include single family homes, townhouses, condominiums, and hotel guest rooms and corridors. These sprinklers are designed specifically to enhance occupant survivability and egress. Therefore, the sprinkler heads have a quick response element with a low temperature rating for fastest operation thereby allowing maximum egress time. These sprinklers generally have relatively low water flows with K factors ranging from 1.2 to 5.6. They are not generally suitable for use in occupancies other than residential.

Special Sprinkler Heads - There are numerous specialty sprinkler heads available, including: Attic Sprinklers (for installation within peaked attic spaces of wood frame construction), Window Sprinklers (for installations at windows where exposure protection is needed), Concealed Space Sprinklers (for limited spaces such as under combustible floors, K2.8-5.6), Institutional Sprinklers (jails and institutions where tampering is an issue), Special Construction Sprinklers (stainless, aluminum, titanium), Coated Sprinklers (wax, Teflon, plastic, coatings for use in harsh environments), Cooling Tower Sprinklers (protection of combustible cooling towers) and On-Off Sprinklers (where there is a desire to limit waterflow after the fire).

K factor - Sprinkler head K factor is the orifice flow coefficient, and remains constant for the range of pressure over which sprinkler systems are anticipated to operate. This terminology has largely replaced the orifice size as a more accurate way of characterizing the amount of water of which a sprinkler is capable of flowing. K factor is one of the most important features to consider when choosing sprinkler heads today. K factor can be computed by the basic hydraulic equation of Q=K√P, where Q is the waterflow in gallons and P is the sprinkler pressure in psi. As seen by this equation, the K factor is proportional to both the operating pressure and the flow. K factors typically range from 1.4 for some residential sprinklers, to 5.6 for common 1/2 inch orifice sprinklers, up to 25.2 for storage sprinklers.

Response Time Index (RTI) - The amount of time it takes a sprinkler head to respond to fire is the RTI. In its simplest form, sprinkler heads are rated as Quick Response (QR) and standard response (SR). Quick Response sprinkler heads were initially developed for use in residential occupancies where the quicker response results in increased life safety. QR technologies have since been adapted to all sprinkler uses, including storage occupancies. Sprinkler designs can be critical with respect to the use of quick response technology. QR has become the preferred term, but some past literature has used the term Fast Response (FR).

Density - Sprinkler design density, sprinkler density, or merely density is the amount of water to be delivered to a 1 sq. ft. area over 1 minute. This is specified as gpm/sq.ft., and for a density/area sprinkler system will be applied over the entire design operating area. Typical densities for density/area sprinkler systems range from 0.10 to 0.60 gpm/sq. ft. Densities both higher and lower than this range exist for some specific application designs.

Operating Area - Operating area is a primary design feature of density/area type sprinkler systems. For example, a design operating area of 2,000 sq. ft. is used for a sprinkler system with sprinkler heads on a 10 x 10 ft. spacing (100 sq. ft.). Thus the number of sprinkler heads inside the operating area is 20 sprinkler heads (2,000 sq. ft. / 100 sq. ft. per sprinkler). For successful fire control by a density/area system, the number of operating sprinklers should be equal to, or less than the design operating area. In this example we would anticipate the operation of not more than 20 sprinkler heads for successful fire control.

Density/Area - Density/Area type sprinkler systems may also be known as Conventional or Standard sprinkler systems. These systems specify a minimum sprinkler density over an operating area (ex. 0.35gpm/sq. ft. over 2000 sq. ft.). Density/area systems remain in common use and provide good fire protection if appropriately designed for the fire hazard.

Clearance To Sprinklers - For sprinkler heads to develop a spray pattern, they require a minimum clearance between the sprinkler deflector and the storage to be protected. For non-storage sprinklers this clearance is typically 18 inches, and for storage sprinklers this clearance is 36 inches. In storage applications, a clearance of 3-5 ft. is ideal, a clearance of 5-10 ft. is normal, and a clearance of >10 ft. may be excessive clearance possibly requiring special measures.

Sprinkler Orientation, sidewall/upright/pendant - This denotes the orientation of the sprinkler head's deflector with respect to the ceiling or wall. In some instances (such as protecting a combustible roof) this can be a critical choice, but mostly it is not a major factor, and is often an aesthetic or practicality choice.

Spray Pattern, SSU, SSP Sprinklers - Standard Spray Pendant (SSP) and Standard Spray Upright (SSU) sprinklers may also simply be called "Standard Sprinklers." They were designed for use with non-combustible roofs or ceilings and deflect approximately 90% of the waterspray pattern downwards. These sprinkler heads account for the vast majority of density/area sprinkler installations.

Spray Pattern, Old Style/Conventional - Old Style sprinklers, or also known as Conventional sprinklers, are still available in upright and pendant models. These sprinkler heads were designed for installation under combustible roof decks and are therefore designed to spray 40-60% of the waterspray pattern upwards towards the roof deck. Although these sprinklers receive relatively little new installation use in the absence of heavy wood construction, they can be highly desirable in specialty applications.

Temperature Rating - Sprinkler heads have traditionally been manufactured with a temperature rating of low temperature (135-170°F), medium (175-225°F), or high (175-300°F). There is also a variety of very high temperature ratings available for specialty industrial uses, such as inside ovens. The temperature rating denotes the temperature at which the sprinkler will operate to flow water. The sprinkler temperature rating can be critical, but is generally not as critical as it was once considered. Other design factors have increased in importance over temperature ratings.

Glass Bulb vs. Fusible Link - Fusible link sprinkler heads utilizing a metallic solder link with a specified melting point have been in continuous use since the first sprinklers were developed in the late 1800's. The glass bulb sprinkler is a later innovation, and contains a colored glycol liquid inside a glass bulb in place of the solder link. The thermal expansion of the liquid will cause the glass to break at the specified temperature. From a fire protection standpoint there are generally no advantages of one type over the other; however from aesthetic or other usage constraints, there may be a preference. Depending on what is available from the manufacturer, either type may be used in most situations.

Since the 1980's a myriad of choices has become available with respect to sprinkler systems and installations. This allows the property owner much greater flexibility than has ever been available in the past. However the sheer number of choices, permutations and combinations which become available make choosing the best sprinkler system for a given application a crucial matter. Risk Logic Inc. is available to evaluate and discuss your needs with respect to sprinkler and fire protection systems for all size, scale and types of projects.