An Engineer's Perspective on FDCs (Part I)

​Why are fire department connections (FDCs) so important to a suppression system?

They are the link between initial response and supplemental help.

Despite appearances, sprinkler systems are not intended to discharge forever. Their goal is to suppress long-enough that firefighters can take over and finish the job.

Standpipe systems exist to extend the reach of the fire department in tall, wide or complex buildings. Manual standpipes depend upon pressure and flow from the fire department. What single piece of equipment is relied upon to make the transfer? The FDC.

This week's article is an overview of fire department connections from an engineer’s perspective. It is one part of a two-part series covering fire department connections. Read more from a supplier’s perspective at Quick Response Fire Supply here.

Authority Intervention Needed
Fire department connections are a unique piece of a suppression system in that they’re not just governed by the designer and code. NFPA 13 and 14 require that fire department connection type and location is coordinated with the Authority Having Jurisdiction.

Early in design, prior to bid, I’ll call the local fire marshal and coordinate each of the following big-picture elements:

Coordination Item 1: Type of Fire Department Connection
The most popular types of FDCs? Siamese (2 x 2-1/2" threaded connection) and Storz (4" or 5" with or without 30-degree elbow).

In my very unscientific study of jurisdictions I call (nearly half are local to my area), I've found the following; 73% use Siamese-type 2-1/2” fire department connections, 11% use 4” Storz connections, and the remaining 16% use 5” Storz connections.

Of these, 13% have special requirements such as Knox Locking caps, 30-degree elbows, or irregular threading.

There’s no right or wrong answer here – I just want to be sure what I’m calling for or showing on plans match what the jurisdiction uses.

Large diameter Storz-type fire department connections have become more common for their ability
​to quick-connect a single hose and flow large amounts of water.

 
Coordination Item 2: Location of Fire Department Connection
The most obvious coordination during design is the location of the fire department connection.
 
My design preference, driven by installation effort and cost, is typically in the following order:
 
1. Wall-mounted FDC, adjacent to the sprinkler riser
2. Wall-mounted FDC, remote from the riser (such as the front of the building)
3. Freestanding FDC, downstream of a site backflow pit or hotbox
4. Freestanding FDC, connected underground into the sprinkler riser room
 
The first couple options are not always workable and depend on the building.
 
Sometimes the water supply and riser room are in the back of a building inaccessible to the fire department. This would be a bad place for an FDC.
 
Sometimes the front face of a building is "grand view" with large glazed curtain walls and no room to mount a fire department connection. This comes up with large offices or modern schools.
 
Sometimes a building-mounted FDC doesn’t make sense with major hazards; why risk firefighter safety in these cases? High-rises, for instance, require multiple FDCs due to the potential for falling glass that could injure firefighters or sever hoses. If there's potential for wall-collapse (think high-hazard warehouse wall) then a wall-mounted FDC also may not make sense. Freestanding FDCs can make a lot of sense for projects like these.
 
Considering most of my work is two stories or less and light commercial, it may not be surprising that roughly 85% of projects include building-mounted FDCs. The remaining 15% have necessitated freestanding FDCs.
 

Some jurisdictions require freestanding fire department connections, but it typically
​depends on the type of building and hazard presented.

 
Coordination Item 3: Distance of FDC to Nearest Hydrant
As a designer it would be great if I could operate in the dark. Send me all the information I need to do a design, I do it, and everyone’s happy.
 
If it were that simple, though, we’d probably already have machines design and do it without downing two bags of Doritos and a half hour of facebook each day.
 
Back to the topic: FDC-to-hydrant distance has an impact on the tactical approach in firefighting.
 
Many designers & installers in our field are current or former firefighters. They could readily speak to this. I’m not one of them, but I can imagine that having to shut down a major roadway or cross a parking lot with hundreds of feet of hose quickly during an emergency is not exactly the easiest thing to accomplish.
 
As a result I like to ask AHJs what distance the FDC should be to the nearest hydrant.
 
Of my highly unscientific and locally-biases results, 41% of jurisdictions require a hydrant to be within 100 feet of the FDC or less, 47% require a hydrant to be within 150 feet, and only 16% of jurisdictions require a hydrant within 200 feet or more of the FDC.
 
These three elements are a part of my code calls. Next week I'll distribute my FDC Cheatsheet that outlines requirements for FDCs across NFPA 13, 13R and NFPA 14. If you haven't already subscribed, consider doing so here.
 
What do you look to coordinate with the AHJ? Discuss your experience here.

​Want more coverage on fire department connections? See the other half of our two-part series on fire department connections here: Quick Response Fire Supply.