Fire sprinkler systems are necessary for fire protection of property, contents and people. They are designed and installed either to meet regulatory requirements, meet insurers’ requirements or meet business or property risk management requirements. They can be automatic and if so are most commonly wet pipe sprinkler systems. Multiple regulatory factors concern their design and specification. These are building services issues that sprinkler engineers take in their stride. We explain more about them here.
Automatic fire sprinkler systems
Automatic fire sprinkler systems have been used in the US since the 19th Century, initially in factory applications where at the turn of the century fires were often catastrophic in terms of physical and economic loss. The most appropriate automatic sprinkler system should be chosen based on various factors, including location, temperature configuration. There are several types of these systems available for fire-fighting purposes in Chicago including wet pipe, dry pipe, deluge, pre-action systems.
The factors influencing the selection of the commonest of them - wet pipe sprinkler systems - in Chicago, and details of their benefits and limitations, are described in more detail here.
Wet pipe sprinkler systems
Automatic wet pipe sprinkler systems are more commonly specified and installed than any other type of fire sprinkler system. These systems employ automatic sprinklers attached to a water-filled piping system connected to a water supply. Water flows immediately from sprinklers which open individually in response to heat from a fire.
Regulatory backdrop of Wet Pipe Sprinkler Systems in Chicago
Prior to full design and specification of these systems, recourse should always be made to the latest editions of the prevailing fire protection codes, liaison made with applicable fire officers and authorities as necessary and ideally recourse made to professional sprinkler engineers. Some of the regulatory factors influencing the design and specification of wet pipe sprinkler systems are described further here for guidance purposes.
Automatic sprinkler systems are also to be installed in all buildings having a floor area exceeding the maximum areas defined in Chapter 13 of this Code. There also special requirements and hazardous use unit sprinkler requirements under this Code.
Currently, the Illinois Office of the State Fire Marshall enforces the National Fire Protection Association (NFPA)101 - Life Safety Code. Contrary to popular understanding, this does not contain an blanket requirement to provide or to retrofit all buildings with automatic sprinklers. The sprinkler requirement for existing residential high-rise buildings is however likely to re-appeart in Chicago as the NFPA and others call for greater use of sprinklers in residences.
According to the Chicago Municipal Code, a dry pipe system is only permitted only where the temperature is not high enough to prevent water freezing in all or sections of a system. In all other instances a wet automatic system is required, whether wet pipe, deluge or pre-action.
There are additional items to consider when designing the associated equipment involved with wet pipe sprinkler systems, including backflow preventers, sprinkler risers (check valves) and air vents.
Backflow preventers: The installation of water supply and components such as backflow preventers are based on Chicago Municipal Code and NFPA 24 requirements.
Sprinkler Risers: A sprinkler riser is the bridge between the underground and interior piping. This is the point where we supply the cross mains, feed mains and branch piping that make up the wet system piping network. There are two types of wet system sprinkler risers to choose from; a riser alarm check valve assembly or a ported check valve with a flow indicator. Both of these riser assemblies are acceptable configurations to NFPA 13.
- Riser check valve: A riser check valve is an alarm check valve on the riser. Locking water pressure into the system, it prevents water in sprinkler piping from traveling back into the water supply. Although not used as often as it was in the past, Chicago officials or end users may require that it be installed.
- Ported check valve: Technology facilitates the use of electrical devices and fire alarm systems to provide the required alarm signal upon water flow. Using this technology, a sprinkler riser has a less complicated assembly than a full riser check valve.
Many engineer’s specifications include an alarm riser check valve, but this may not be necessary if a water motor gong is not used. A ported check valve can provide the same outcome but costs less in terms of equipment and installation.
Air vent: NFPA 13 requires an air vent be installed for every wet sprinkler system to reduce corrosion activity caused by trapped air. Mounted at high points within such a system, such vents remove air pockets, providing an inexpensive method to remove air in the system and lessen corrosion.
International Fire Code requires water based protection systems, such as wet pipe sprinkler systems, to be inspected, tested and maintained at regular intervals in accordance with NFPA 25. This regulation requires an internal inspection of fire sprinkler system piping every five years.
Three levels of internal pipe inspection are required:
1. Internal Pipe Inspection:NFPA 25 requires the opening of a flushing connection at the end of one main and removal of one sprinkler head near the end of a branch line to check for obstructions
2. Internal Pipe Examination for ‘At-Risk’ Systems:NFPA 25 lists conditions in which this type of internal pipe exam shall be performed, requiring internal exams at four points of a fire sprinkler system: System valve, Riser, Cross main, Branch line.
3. Obstruction Investigation: This is to be performed if foreign organic / inorganic material is found during an internal pipe inspection. NFPA 25 provides the requirements to conduct obstruction investigations.
Regular testing is also required in Illinois through the Illinois Office of the State Fire Marshal’s adoption of NFPA 101.
Benefits of wet pipe sprinkler systems
A wet pipe sprinkler system is the preferred option in a wide range of applications due to the following five core benefits:
1. Reliable: Its only operating components are the automatic sprinklers and commonly an automatic alarm check valve.
2. Fast response time: as stagnant water is present at the location of every sprinkler head in a wet pipe system. Reaction time does not depend on the distance between the activated sprinkler head and the water supply. Most of the time it only takes one sprinkler head to fully extinguish a fire.
3. Simple system to reset: Its only necessary to replace open sprinkler heads and fill the piping with water again.
4. Easy to maintain. The internal corrosion rate in wet pipe systems is much lower (as piping is constantly full of water and the amount of oxygen available for corrosion to occur is lower). This lowers the possibility of pin-hole pipe leaks or other forms of corrosion damage occuring.
Limitations of wet pipe sprinkler systems
The three main limitations of wet pipe sprinkler systems are as follows:
1. Need for ambient temperature 40°F or more: The main limitation of wet pipe sprinkler configuration is that water in piping can freeze at low temperatures, restricting its use in natural or man-made cold environments. These systems cannot be installed where ambient temperatures go below 40°F.
2. Unsuitable for flammable substances: where flammable substances are stored, there can be a need for a special application and a wet system may be required to spray water from all sprinkler heads simultaneously rather than individually.
3. Leak damage threat: There can be severe property damage if a leak or other operational issues occur in piping, especially if the area(s) sprinkler(s) concerned protect contain sensitive content.
While wet pipe sprinkler systems are the commonest automatic sprinkler system type in Chicago, with multiple benefits outweighing their limitations, their application – in terms of their configuration and maintenance – requires consideration of multiple regulatory factors. Their design and specification is therefore best detailed by experts in the field of sprinkler engineering.
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