Numerous factors such as the available water supply type of sprinklers, building construction features, and the anticipated fire hazards must be considered in the design of automatic sprinkler systems.
The selection of sprinkler type will vary with occupancy. Where more than one type of sprinkler is used within a compartment, sprinklers with similar response characteristics should be used (i.e. standard response). However, some hazards might benefit from designs that include the use of both standard and quick response sprinklers. Examples include rack storage protected by standard response sprinklers and quick response in-rack sprinklers.
Today, many varieties of sprinklers are available in the market. As said earlier, there may be 2000 varieties of sprinklers available in international market. Thus, certain criteria have to be fixed to enable a designer to decide which sprinkler to be used in a particular application.
Selection on Type of Use
This section attempts to categorize sprinklers into various types and the application where each type can be used. These include.
i. Upright and pendant spray.
ii. Sidewall spray.
iii. Extended coverage.
iv. Open type.
v. Residential type.
vi. Early suppression fast response.
vii. Large drop type.
viii. Special sprinklers.
i. Upright and Pendant Spray Sprinklers
These type of sprinklers are the most common type and can be used in all occupancies and construction types. The application of this type of sprinkler shall be decided in relation to K-factor (explained in articles to follow). General storage, rack storage, rubber storage baled cotton storage which requires spray density of 13.9 mm/min, standard response sprinkler with K-factor of 115 or larger shall be used.
While for spray densities greater than 13.9 mm/min, the K-factor of 160 or larger shall be used.
For densities of 8.2 mm/min or less, standard response sprinklers with a K-factor of 80 shall be permitted.
Experiments have shown that sprinklers with large orifice, i.e. K-factor of 115 or large perform better during storage fires because due to less velocity, water droplets become large and penetrates more readily in the fire core and allow more water to reach fire seat. The distribution pattern of these kind of sprinklers.
ii. Sidewall Spray Sprinklers
These sprinklers shall be installed only in light hazard occupancies with smooth, flat ceilings. These sprinklers can be used to protect areas below overhead doors. The discharge characteristics of sidewall sprinklers are not as effective as those of upright and pendant sprinklers for all applications. Thus, their use is limited to light hazard occupancies. In addition to this limitation, sidewall sprinklers shall not be installed below sloped ceilings.
These sprinklers are generally used in retrofit situations where access to ceilings cannot be permitted.
iii. Extended Coverage Sprinklers
These sprinklers are limited to a construction consisting of flat, smooth ceilings with a slope not exceeding 1:6
These sprinklers have to be specifically mentioned for such constructions. The area coverage with EC sprinklers is larger than the area permitted for other types. The extended coverage allows fewer sprinklers to be used.
However, discharge from an EC sprinkler has a longer, flatter throw than a standard upright or sidewall sprinkler. This pattern is affected by obstructions and slope of ceiling more than other types. That is why, EC sprinklers are limited for use to smooth flat ceiling with relatively small slopes.
iv. Open Sprinklers
These are used in deluge system to protect special hazards or exposures. These are spray sprinklers with their operating element removed. Aircraft hangers require foam water deluge systems which utilize open sprinklers as the predominant means of fire protection.
v. Residential Sprinklers
These sprinklers are tested using a residential fire scenario and hence are to be used in residential portion these sprinklers can be used in dwelling units and their adjoining corridors. Residential sprinkles are intended to prevent flashover in the room of fire origin, thus improving the chance for occupants to escape.
The residential sprinklers are so selected that its area of coverage is equal to or greater than both the length and width of the hazard area. For example, if hazard area to be protected is 4.4 x 5.6 m (13' 6" x 17â 6ââ), sprinklers to be selected shall have a coverage area of 4.5 x 5.8 m (14âx 18') or 5.8 x 5.8 m (18âx 18').
Vi. Early Suppression Fast Response Sprinklers (ESFR)
ESFR sprinklers use fast response operating elements and are designed to respond very quickly to a fire. Occupancies where fire can grow extremely fast with large increase in heat release rates over a short period of time, the quickness with which water is applied is critical. ESFR sprinklers are used in such type of applications.
Sloped roofs tend to cause a skewed distribution of heat from a fire burning beneath the roof. Thus, ESPR sprinklers shall not be used in such places.
Vii. Large Drop Sprinklers
These sprinklers are used where fire grow in an exponential manner. A substantial escalation in heat release rates and thermal velocities would be expected in relatively short time periods.
viii. Special Sprinklers
As the name indicates, these are the sprinklers which are designed for specific applications. But these sprinklers shall nevertheless maintain orifice size, temperature rating, and protection area of coverage as defined in various standards.
Nowadays, to provide more aesthetic look, sprinklers are mounted concealed inside the false ceiling. In these kind of sprinklers, all or part of the body, other than the shank thread, is mounted within a recessed housing.
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