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What is a combined sprinkler and standpipe system, and how does it work?
INTRODUCTION A Sprinkler system is a heat-operated fire protection system that applies water to the fire source by itself. When the temperature of a sprinkler’s fusible link or it’s glass bulb reaches a pre-set temperature – bang – sprinkler activation and water right at the fire. A standpipe system is a network of piping that provides water for manual firefighting for its trained personnel, or firefighters. A standpipe is fixed in place, and helps transport water from the outside of a building to locations that are much closer to the fire, without having to drag hundreds of feet through the building. Let’s look at these two diagrams. In the one on the left, we have a sprinkler system only. You can see an underground service, backflow preventer, fire department connection, and a sprinkler riser that goes up vertically and feeds each floor level’s sprinkler system. This is our standalone wet pipe sprinkler system for a multi-level building. On the right, we have a standpipe system. This is a manual, wet standpipe. It has an underground water service, backflow preventer, fire department connection, and vertical standpipe risers that feed hose connections on each floor. So, what happens when we combine the two? What are the benefits of combining them? And how does it affect the system design? SHARED PIPE For low-rise structures, a combined sprinkler/standpipe system will be equipped with a lot of the same components. A larger pipe fed from the incoming water supply, or fire pump discharge, will provide a constant source for both the sprinkler system and the standpipe. Combining the systems means we’re using one large diameter feed main instead of two. Of course, this saves on material and labor, so there’s a cost advantage to combining them. Also, in a combined system we use the same fire department connection to serve both the sprinkler and standpipe system. This can increase the volume and pressure available to both systems. This is huge. CLARITY The fire department doesn’t have to decide which fire department connection to use, or have to decide whether to first fight a fire using sprinklers or feed water to their hose stations – they get both. With a single fire department connection, there’s less hoses to connect to the building. There’s less time involved in connecting to the building. All around, it’s faster and simpler. Now again that may not seem like a big deal, but we’re awake, cognizant, and have already had coffee for the day. Fires happen at 2 am or during storms or at other unpredictable times. Making things as clear as possible for firefighters goes a long way in helping have an effective response of response. MINIMUM PIPE SIZES What code impacts does a combined system have? The combined sprinkler and standpipe systems have different pipe size requirements than a standalone standpipe system. The minimum standpipe size for a combined system is required to be 6” for Class I and III and 4” for Class II, as well as the system is still required to be able to deliver the larger of the sprinkler or standpipes flow requirements. This comes from NFPA 14. The standpipes are also required to be interconnected, typically at the lowest level of the building, allowing the fire department connection to supply all aspects of the standpipe system and sprinkler system though one set of fire department connections. One question that seems to come up a lot when coordinating standpipes with fire departments is whether the standpipes will all be interconnected. They are, and they’re required to be interconnected under NFPA 14. Unless we get into very tall structures where there are different pressure needs, or have different standpipes for separate buildings, our standpipe hose connections will all be fed from the same mains and same FDC. Functionally, how are these constructed? We’ve talked about shared feed mains, and the cost savings from having a shared supply. The contractor only has to install one network of pipe up through the building in the same manner as a standalone standpipe system. Typically, from there, the sprinkler system at each floor or zone is fed off of the standpipe riser with an isolation valve, check valve, and flow switch complete with its testing orifice and drain. The sprinkler system begins at this point. This makes access to each sprinkler zone fairly easy, yet shares the supply. A combined sprinkler and standpipe system takes the goals of each and combines them into a shared water supply and fire department connection. Essentially, we achieve the benefits of both sprinkler and standpipe but are able to cut costs by using many of the same components for both systems. They still work as if they were independent, only with a shared water supply. I'm Chris Logan, this is MeyerFire University.
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