I have an order for designing a large Preaction Fire Sprinkler System in some kind of underground computer farm. Now that I lost most of my capital, I have to work more to remake myself and this high tech thingie seems profitable.
Preaction fire sprinkler systems employ the basic concept of a dry pipe system in that water is not normally contained within the pipes. The difference, however, is that water is held from piping by an electrically operated valve, known as a pre-action valve. Valve operation is controlled by independent flame, heat, or smoke detection.
Two separate events must happen to initiate sprinkler discharge. First, the detection system must identify a developing fire and then open the preaction valve. This allows water to flow into system piping, which effectively creates a wet pipe sprinkler system. Second, individual sprinkler heads must release to permit water flow onto the fire.
In some instances, the preaction system may be set up with a double interlock in which pressurized air or nitrogen is added to system piping. The purpose of this feature is two-fold: first to monitor piping for leaks and second to hold water from system piping in the event of inadvertent detector operation. The most common application for this system type is in freezer warehouses.
Advantages of using pre-action fire sprinkler systems include: • The dual action required for water release - The pre-action valve must operate and sprinkler heads must fuse. This feature provides an added level of protection against inadvertent discharge. For this reason, preaction systems are frequently employed in water sensitive environments such as archival vaults, fine art storage rooms, rare book libraries and computer centers.
Disadvantages of using pre-action fire sprinkler systems include: • Higher installation and maintenance costs - Preaction systems are more complex with several additional components, notably a fire detection system. This adds to the overall system cost. Modification difficulties - As with dry-pipe systems, preaction sprinkler systems have specific size limitations which may impact future system modifications. In addition, system modifications must incorporate changes to the fire detection and control system to ensure proper operation. • Potential decreased reliability - The higher level of complexity associated with preaction systems creates an increased chance that something may not work when needed. Regular maintenance is essential to ensure reliability.
Deluge Fire Sprinkler System A slight variation of pre-action fire sprinklers is the deluge system, which is basically a pre-action system using open sprinklers. Operation of the fire detection system releases a deluge valve, which in turn produces immediate water flow through all sprinklers in a given area. Typical deluge systems applications are found in specialized industrial situations, i.e. aircraft hangers and chemical plants, where high velocity suppression is necessary to prevent fire spread.
On-Off Fire Sprinkler SystemAnother pre-action system variation is the on-off system. This system utilizes the basic arrangement of a pre-action system, with the addition of a thermal detector and non-latching alarm panel. The system functions similar to any other pre-action sprinkler system, except that as the fire is extinguished, a thermal device cools to allow the control panel to shut off water flow. If the fire should re ignite, the system will turn back on.
10 comments:
I was able to wander in the basement of the Mesa City hall here in my hometown a few years ago, and while walking down a hallway I saw the city's computer room. The computer room had a notice on the door warning potential entrants that the room had a Halon fire suppression system. This was about 10 years ago, nowadays such chemicals have been banned (Halon 1301, Halon 1211) under pressure from the Ecopagans as 'damaging the ozone.' So far as I know no one has died from the ozone being depleted, but if the Mesa City Police were to lose their files on dangerous criminals in the area someone might actually get injured. But such is the lunacy of the enviroleft, or as I called them the Ecopagans.
Halon is still used in these parts, but my client specified a water sprinkler system, possibly following American standards. I shall learn more on the subject as I advance in the project.
Halon systems are still in use throughout the world. The only catch is that the refrigerant manufacturing of chemical solutions known as CFC's has was banned some time ago and HCFC's as well as any gaseous solution containing ozone depleting constituants are heavily regulated.
There are many different fixed flooding systems that are designed to use all types of extinguishing agents. Just do the research if you're considering one of these types of systems.
I am considering the use of a preaction system in switch gear rooms which utilize obsolete gear so they are all very expensive to replace. Currently we have wet pipe in most of the rooms. Don't ask why, i wish i knew.
Anyway, Thank you J for your insight on the use of pre-action systems.
Jesse,
In the meanwhile, after designing the preaction double interlock system, the client decided NOT to build it but install a gas system instead. The whole electricity room will be one large electric cabinet. The reason, apparently, was the high cost of preaction, its destructiveness, and the need for an air compressor to maintain pressure in the sprinkler pipes. do you think they are taking the right decision?
Regarding gear room, I understand the flammable material is grease. Grease fire cannot be extinguished by water, can it?
Jesse said...
There are many different fixed flooding systems that are designed to use all types of extinguishing agents.
Do any gas firefighting systems use carbon dioxide as fire suppressant?
Yes, fixed fire suppression systems can use carbon dioxide. This is frequently found onboard ships in the engineroom spaces.
Compared to Halon or Halon replacements such as FM-200, CO2 requires a much higher concentration in air to suppress fire, and consequently is a life hazard to anyone in the space. Halon and FM-200 are safe to breathe at design concentrations, although both can produce toxic byproducts when exposed to flame. The smoke from the fire will kill you first, though.
I am not sure why, but carbon dioxide fire supression systems are less known in Israel than Halon systems. In the project I am working on, the electric transformator room of a large underground computer farm, Halon was selected. I know it is corrosive and harms electronic parts. Thinking about how the decision was adopted, there is also a human angle. In this project the dominant personality is the electric engineer, and he is very familiar with gas systems in electric boards, that are standard and obligatory in Israel. So water was discarded very early in the debate. One thing that disturbs me is the air conditioner system, how does it fit within a gas supression event? I also wonder if Israeli firefighters are trained to enter and treat a fire in room full of toxic gas. I wonder if foam was an option? What do they do in the USA?
I only know about the computer room I saw in the basement of the Mesa City Hall.
I would like to point out that the room may not have much outside ventilation and may not be cooled by a normal central air system. I work in a large store (110k square feet) and we have a small computer room of our own. Since the store already has a centralized refrigeration system the computer room has a refrigeration line feeding coolant to a cooling unit in the top of the room. As such only minimal airflow is needed from outside the room to maintain a proper temperature. The electrical engineer may decide to have a sealed room for the computers with a large set of cooling coils hung from the ceiling to provide climate control. A sealed room prevents outside dirt from fouling the equipment and allows the cool air to stay inside. If the room normally has no employees in it then no outside airflow is needed. A gas fire suppressant may work better if only a small vent is provided to the outside making it easier for Halon to displace the oxygen.
Fire suppression is a lot easier to provide for if you don't normally have to worry about people.
I am just guessing, so please correct me if I am wrong.
Ronduck,
I cannot correct you since my experience in computer farms is rather limited. I shall learn along the way, by doing. There is no other way.
Hello
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