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Dilemma- sprinkler addition on a gridded dry system.

Dilemma- sprinkler addition on a gridded dry system.

Dilemma- sprinkler addition on a gridded dry system.


Situation- An existing (circa 1983) 29,400 sq ft open warehouse (235' E-W x 125' N-S) with a 6" dry system. The riser is in the NE corner of the bldg. The new owner wants to add 2,800 sq ft of offices in the SW corner. No problems so far...
The problem is that the dry system is gridded and installed like a wet system. The 6" necks down to 4" at the top of the riser and runs down the north side, with 1 1/2" lines up and over the peak to what amounts to a 3" gang drain on the south side.

One of the first and most basic design rules that I learned was "you don't grid dry systems". Never. From the inception of dry pipe systems the reasons for this have been plain and obvious.

Yet, here is a system with a calculation plate in place for a faulty design that was approved by the city.

So now they want to make changes to the system...where do you start? Yeah, I know what should be done, but I really find it hard to believe that this huge mistake has never caught anyone's attention...for 30+ years.

Alex Traw
Rainbow Fire Sprinklers
Albany, Oregon

RE: Dilemma- sprinkler addition on a gridded dry system.


Either do new riser and complete new system for the addition. Do not come off above that dry valve for the gridded dry system. That is how I would handle it.

I really dislike when people put that gang drain on and claim it is not a grid. You have to put a drain valve at the end of each line before it ties into the gang drain to prevent it from being a grid. No one does that. I'd be interested to know the water delivery time on that project.

Travis Mack
MFP Design, LLC
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...

RE: Dilemma- sprinkler addition on a gridded dry system.

The 3" really appears to be a secondary main for a grid.
You can gang drain multiple adjacent branch lines, but the piping must be 1"

New System.


RE: Dilemma- sprinkler addition on a gridded dry system.


I am almost sure gridded dry was allowed in 83.


RE: Dilemma- sprinkler addition on a gridded dry system.


I was kind of kidding when I called it a gang drain. It isn't. I'm sure it was designed as a bulk main as if it was a wet system. I'm assuming the calcs were done manually and that the numbers on the data plate really don't mean much. I think my calc software would reject this design if I tried to run it as it's built.

It's right on my way home, so I'm going to stop by and get the date off the valve, just so I know.
I intend to do a trip test to see what I'm working with. If it tests out OK, and, well, we'll see...

Alex Traw
Rainbow Fire Sprinklers
Albany, Oregon

RE: Dilemma- sprinkler addition on a gridded dry system.

I agree with Matthew the only way out of this one is to manifold the riser and come off with a new system so you don't get messed up with the old system.

It was back in the 1980's when I designed a good amount of gridded dry systems and I myself never had a problem with trip times.... all you had to do was use your head a little.

For example a side feed grid without a feed main connecting the near and far mains meant you were looking for trip time troubles but if you had an end feed system with a bulk main from the riser feeding both the near and far mains cut trip times considerably.

Sometimes what we intuitively think turns out to be wrong and I believe this happens a lot in our industry especially when it comes to dry pipe systems.

For example I have a horseshoe dry pipe system consisting of a 6" riser, 4" mains and 2" branch lines that looked something like this but bigger than I depict here with a capacity of just under 900 gallons.

As you can see I left myself out "out" I could have cut the system in half adding another riser adjacent to the one I showed in which case the systems would have been < 750 gallons so trip time wouldn't matter.

It was one of those jobs where I wouldn't have staked my life in a guarantee of trip time but based on what I've seen over the years I thought it would be ok.

It was about this time I ran across this article by James Golinveaux who was with Tyco but is now with Viking.

If you haven't read it I would urge all designers to do so because I found it absolutely enlightening.

A Technical Analysis: Variables That Affect The Performance Of Dry Pipe Systems
James Golinveaux, Sr. Vice President,
Research & Development
Tyco Fire & Building Products

According to the Mr. Golinveaux's paper if I simply tied the two far branch lines together with a 1" piece of pipe, shown in green, I could expect a faster time to water to the inespectors test connection. I don't know about you but for me it ran counter intuitive to everything I ever thought I knew. Everyone knows grids and loops take longer, right?

But according to Mr. Golinveaux's paper by tying the two branch lines together I could expect a faster trip time due to compression of the air in the system instead of forcing more of it through the inspectors test.

The guys in the field thought their designer went totally nuts when I told them I wanted to do exactly that... try a trip before tying the two lines together and again after being careful to start at the same air pressure for each test.

Measuring the time by tying the two lines together I cut approximately 12 seconds off time to water through the inspectors test. Without tying them together we were right around 62 seconds for water to the inspectors test but after we tied the lines together we were right at 50 seconds.

I was amazed but if you take time to read the paper it does make sense.

Now what I am wondering is what would happen if we added 40 feet of 6" cross main at the end of the far main? We wouldn't add any lines so the inspectors test would remain where shown... we'd simply have a reservoir for trapped air.... would trip time go up or go down?

James Golinveaux will be a speaker at the Florida Fire Sprinkler Association in Boca Raton later this month, I got to go to keep our Florida license. I'm going to try to corner him so we can talk for about eight hours. It's a tough part of the job someone has to do it. Anyone else from here going to be there?

RE: Dilemma- sprinkler addition on a gridded dry system.

Thanks SD2 for the wealth of information. I'm reading through the article now but your example is fascinating and like you say, counterinuitive from everything I've learned.

So, my system dates to 1989. Looking at the trip test record, other than one noted accelerator failure, water to test conn. times run in the 40-45 second range.

I've looked back through past editions but I can't find when the "no gridded dry systems" line first appeared. It's not important to anyone but me, really. I'm not making changes to the original overhead system in any case.
If it was right then, it's right now, according to my grandfather.

Figuring out where to supply the office infill from is my focus now.

Replicating the overhead on the computer would be simple enough, so calculating the office infill should be within the realm of possibility, right?

Alex Traw
Rainbow Fire Sprinklers
Albany, Oregon

RE: Dilemma- sprinkler addition on a gridded dry system.

Your grandfather is correct; it it was right when installed it is right today unless there was a published interim similar to what we have on anti-freeze systems.

When you think about it if we were to install a 2"x2"x1" tee off the branch line near the inspectors test connection then immediately increased the size to 8", using an 8"x1" reducing coupling, followed by installing 21' of 8" pipe it appears we could expect a lower trip time water to the inspectors test. The 8" empty pipe would give a place for the air to compress and wouldn't be forced out through the 1/2" inspectors test orifice.

But wouldn't that look weird? Everyone in the company, including the owner, would think you were nuts.

The first time dry grids were mentioned was the 1980 edition of NFPA #13 which we called "the little red book" that you could literally fold in half to put it in your back pocket. 116 pages if we don't include the appendix. The "little red book" measured 7 1/2" x 5".

I am looking for my 1974 edition... it has to be here somewhere but there wasn't any mention of grids and when you calculated a system, these were all by hand which is why we didn't do grids until 1980, we calculated the entire branch line because the 1.2*sq root of area didn't exist. You could end up with calculating 12 heads on a line.

Who remembers the "phantom" areas? What a phantom area was is if you had heads spaced 10' apart on lined spaced 12' apart we had 120 sq ft per head. But what do you do if the branch line in the back is just 1'-0" off the wall? Back then we would count each head in the back row as covering 120 sq ft even if it didn't. To cover 1,500 sq ft you calculated 13 sprinklers even though 13 heads didn't come close to covering 1,500 sq ft. The area beyond the wall was the 'phantom" area.

Reflecting on the changes what you had to know in 1974 to do the job and what you need to know today is light years apart.

RE: Dilemma- sprinkler addition on a gridded dry system.


I still see guys trying to apply that "phantom area" allowance in systems. It drives me crazy. And these aren't even the same guys stating there is a limit of 32 fps for all systems. Some days are just too much smile

Travis Mack
MFP Design, LLC
"Follow" us at https://www.facebook.com/pages/MFP-Design-LLC/9221...

RE: Dilemma- sprinkler addition on a gridded dry system.

I've got a 1973 copy of 13, and 5-2.3.1 has no mention of gridded systems.

Yeah, I've been reading through other parts of the 1973 handbook, just to get some perspective, not to mention that it's a quick read. The old style line drawings and the overall brevity invokes a word I seldom use; it seems very quaint.

Alex Traw
Rainbow Fire Sprinklers
Albany, Oregon

RE: Dilemma- sprinkler addition on a gridded dry system.

Thanks SD2 for reminding me I'm old. Is that the first $1 you made?

RE: Dilemma- sprinkler addition on a gridded dry system.

Stookey, that's my weekly allowance my wife allows me to have. Wanted to depict the actual size of the little red book.

But it really was easy back then with 95% of our jobs pipe schedule using schedule 40 for everything with threaded fittings for all.

It really was easy. I left flying for sprinklers and inside of two months I was laying out my first systems. I started June 1, 1976 and in November they sent me up to Hastings to take Jack Wood's three day class on hydraulic calculations. It was either three or four days, memory slips me, and I remember people flying in from all over the country to learn how to do these new fangled hydraulic calculations.

It was the day of the K-Mart expansions where it seemed K-Mart was building in every city in the nation and in February and March I was in charge of laying out an entire system for a K-Mart for FM approval pretty much on my own. Nine months experience and in charge!

It was Ohio and nobody but ISO, IRI or FM wanted to see any sprinkler drawings. Government authorities weren't involved one bit and for inspections they, local AHJ'S, never even looked at sprinklers much less reviewed drawings.

In today's world imagine turning someone with eight or nine months experience loose in laying out a Wal-Mart.

RE: Dilemma- sprinkler addition on a gridded dry system.

Pure, simple curiosity: do you feel that today's systems give better fire suppression, or better reliability than those systems -designed in the 70s and 80s?
(or should I have started a different thread? I'm not looking to start any trouble here)


(Me,,,wrong? ...aw, just fine-tuning my sarcasm!)

RE: Dilemma- sprinkler addition on a gridded dry system.

Flash, there is no comparison data for your question.
What is being protected now is far different than what was protected then.
How things are stacked and protected, way different.

I would like to think that the systems are better, however, they used to make steel pipe out of metal back then..


RE: Dilemma- sprinkler addition on a gridded dry system.

It's plastics, it's all plastics.

I grew up in the late 1950's and 60's and we simply did not have the plastics we have today. All of our clothes were cotton, ketchup and mayonnaise came in glass bottles and I had a Schwinn bike that didn't have a single ounce of plastic on it.

My cap guns, my "Made in Occupied Japan" toy road grader and Lionel train set was 100% metal. Yes, for me 70 is just around the corner.

Even in the mid 70's when I started my sprinkler career we had rubber products but I don't remember all that much plastic like we have today.

Go into a toy store today, look around and try to find anything not made of plastic.

I remember Stookey commented on a Carhart jacket he purchased that was nearly all plastic... nothing like this existed in the 60's. If it did it sure was kept a secret from me.

Today when I run into a warehouse project I just assume it's all Group A plastics until someone tells me in writing and most of the time I am right. I just purchased a new printer and it's all plastic wrapped in a expanded plastic cocoon placed in a box.

The Class I, II and III categories are near a joke anymore.

I don't know if this is allowed but here's a one minute scene from the 1967 movie "The Graduate" describing our future.

RE: Dilemma- sprinkler addition on a gridded dry system.

Nice topic.

For my family we bought old antique furniture because it is far less combustible than newer, petroleum based fabrics and plastic furniture.

On topic today's systems are superior in regard to our understanding of how fire works, the suppression modes, special sprinklers and myriad other factors. Egress, visibility, smoke control, notification is all much improved over previous decades but as others have noted the heat release rates of modern materials is much greater than in years past so in a sense it is more dangerous.

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