hose stream for combined system (standpipe) 3

[pipesnpumps]

What are the requirements for design flow for a combined system standpipe?

Let's say I am designing for NFPA 13 Ordinary 2, I read that the inside hose would be 100 gpm and outside would be 150 gpm (total 250 gpm inside/outside).. But the purpose of a 100 gpm hose (1-1/2") would be for first-aid fire fighting and clean up, not fighting a fire..

Then NFPA 14 requires four 2-1/2" hoses (1000 gpm total), but without any sprinklers flowing.

So does NFPA 13 or NFPA 14 not address the situation of design sprinklers flowing at the same time as 2-1/2" attack hoses?

I don't understand the logic of designing either for
a) sprinklers + a clean-up hose, or
b) four 2-1/2" attack hoses, but no sprinklers operating..

Am I just imagining that firefighers would want to leave the sprinklers operating and still hook-up to hoses? If so, the system would not be designed to accomodate both the hoses and a design fire area.

If anyone can shed some light, I would appreciate it!

 

[chicopee]

The insurance industry that provided fire insurance considers one hose stream (2-1/2") equivalent to 250 GPM.

 

[firepe]

Perhaps you should consider hiring a qualified fire protection engineer to do the "designing".

 

[chicopee]

Or if this is for a project under construction, talk to an insurance fire inspector to discuss some of the fuzzy points since soon or later the insurance company (whicever it may be will want to review your sprinkler plan with all associated calculation for ISO approval.

 

[pipesnpumps]

firepe, there is a "qualified" fpe.. But a title means nothing to me, so I check their work before it goes to bid. Numerous code errors.

Right now the answers I have are "that's just the way it is". Or "they will boost the flow and pressure with an engine". It may also have something to do with statistics, and that very few fires grow past a few heads, so there would be flow available for an attack hose.

Either way, the NFPA 13 and 24 flow requirements are not additive.

 

[firepe]

pipesnpumps,

ok, I'll bite..

If it's wrong and there are code errors then they're not qualified, are they?

As for NFPA 13 and 14 (not 24), and flow requirements...These are 2 separate and distinct standards, and are not intended to be intermixed. You simply either have a sprinkler system design demand including a hose stream allowance (which should be further divided into inside and outside hose), or you have a standpipe system with a specified flow requirement, which does NOT have to be simultaneously available with the sprinkler demand.

I think you need to look at it as sprinklers first, standpipes after. the standpipes are there for the FD to use, that's all, to assist the application of additional fire water when they arrive (if needed).

Now to really confuse things, let's use the standpipe system to feed the sprinkler system, that ought to stir things up.

But it does not have to. Keep it simple, 2 different standards, DO NOT MIX THEM.

 

[pipesnpumps]

firepe,

I understand the 13 and 24 codes are not additive, not mixed, separate codes, etc. all that.. That was clear from the beginning.

The code jockey answer is take the highest of either 13 or 24 requirements. In my example, NFPA 24 would govern for the water supply design and requires 1000 gpm @ 100 psig.

My question was about a realistic scenario, not wording of the code. With a combined system standpipe (sprinklers fed by the same pipe as the attack hoses) why do the codes not allow for leaving the sprinklers on while the fire department is flowing simultaneous through attack hoses?

In other words what is the logic behind designing for either sprinklers or hoses when clearly both may/could be used at the same time.

I've explained some reasoning behind this. The idea is that the pumper truck will take the gpm allotted for outside hose stream and deliver this through the standpipe to the attack hoses. All this would be in parallel with the water coming from the fire pump feeding the sprinklers.. The hangup I have with that is the standpipe will be designed for ~1/2 the flow that would be needed in that situation. So the pressure drop would be alot greater and the fire fighters might need to shutoff the sprinkler flow to get enough flow/pressure for attack hose(s).

You've not furthered the discussion other than to a) question my abilities, and b) prove that you can read a code book and emphasize that I should not be thinking. just put my brain on a shelf, keep it simple, and read the code..

 

[pipesnpumps]

I meant to say NFPA 14 (standpipes), not 24 (private service fire mains).

 

[firepe]

pipesnpumps,

correct me if I'm wrong here, but you asked an initial question that appeared to indicate some confusion on the application of two related standards, NFPA 13 and NFPA 14.

At that time I suggested you may want to find a "qualified" fpe to help you.

You reponded by stating that there already was a "qualified" fpe, and that "a title means nothing to me, so I check their work before it goes to bid. Numerous code errors."

So pardon me for thinking that you did not trust your "qualified" fpe's information and were back checking, and on a fishing expedition.


As for "furthering the discussion", well, again, I never questioned your abilities, I was simply trying to help you focus on the 2 standards as separate standards. Since you claim you understand this concept, yet still have questions about a "realistic scenario", does make me now wonder.

The standpipes are there to simply provide the fire department a convenient means to deliver fire fighting water for hose streams/mop up operations.

When designing combination systems, it is typical that the sprinkler system demand including the NFPA 13 hose allowance is NOT the most demanding system, the standpipe system IS, so there is an over design, a cushion if you will.

As an example, let's say you have a light hazard sprinkler system with a theoretical water demand of 150-gpm (.10/1500) and a hose alowance of 100-gpm, for a total of 250-gpm. A building with even just 1 standpipe would have a standpipe system design/demand of 500-gpm, which exceeds the sprinkler system demand by 250-gpm (not to mention the 100-gpm allowance in the sprinkler demand).

If you had a building with multiple standpipes and had a system "maxed" ou at a 1000-gpm standpipe system demand, there would be at least 750-gpm left over for the hose streams, in addition to the sprinklers.

So the point is that there already is some overlap built into the designs of these systems within the 2 standards. The fire department will have enough water to apply their hose streams from a properly designed standpipe system, and still leave the sprinklers in service, or they may decide to shut the sprinklers off. either way, this is already unstated, yet built into the standpipe system stadard's design criteria.

 

[pipesnpumps]

Your example is for NFPA 13 light hazard. This particular design exceeds NFPA requirements (highly protected risk), for 0.2 @ 3000. By the time one accounts for pressure overage (~30% in this case), the sprinkler and standpipe demands are roughly equal.

Sprinkler Demand: 0.2@3000 = 600 gpm x 1.3 overage = 780 gpm.
Standpipe req't for two standpipes = 750 gpm

So there is no "overlap", no "cushion, if you will" to allow for even ONE hose.. There is nothing "already unstated, yet built into the standpipe system stadard's design criteria" for the higher hazards.

Since you claim you understand this concept, yet still can't understand my point, that does make me now wonder.

 

[DavidCR]

Pipenpums, yep, if I was in your shoes, I´ll appreciate the thoughts of experts if you are thinking of the 1350gpm(780+750) demand.

I´ve come across with similar situations but for industrial installations where the cost does not change much among the different hose demand scenario alternatives.

True, an expert designer is required and there is no room for amateurs for such a decision. But I agree with pipesnpumps. I´ve asked similar question to NFPA people and never got a decent response on what the NFPA really wants with respect to combined systems.

I reckon that NFPA 13 intention, according to NFPA101, is to state that sprinklers are enough, and that is useful to sell the idea that sprinklers are not expensive, this if when we are dealing, with a "flat line" of hose demand on the design curve (with no pressure requirement for this hose demand or no big diameters or big pump for other design scenarios).

But with combined systems, the design deals with lots of issues for the designer such as hose demand, pressure reducing devices, interconnection of risers rules, bigger diameter and pumps, etc. that leave place to bad interpretations sometimes.

I think that NFPA 13 or 14 should clarify more or give an appendix with guidelines for combined system, to avoid misunderstandings or bad interpretations.

So going back to the point, I hope more experts can give us their thoughts about combined systems.

 

[MGXFP]

Personally in every combined system I've designed the standpipe is the most demanding by far in comparison to a sprinkler system.

Given a Class I standpipe and an extra hazard I occupancy the sprinkler piping should be sized according to hydraulic calculations, even though that sounds strange to have an extra hazard I in a combined system. One thing to remember is the standpipe also has the 100 PSI requirement (at the top for Class I) this has in every case pushed the standpipe demand well above that of sprinklers in my experience.

 

[SprinklerDesigner2]

I'm certainly no expert but seems to me the confusion comes up with having two separate systems joined with the word "combined".

You're trying to read to much into it.

With few exceptions standpipes and sprinklers have little to do with each other.

The most common exception is reducing standpipe demand to 1,250 gpm in a fully sprinklered building or perhaps a reduction in the required pressure at the top outlet if the building is equipped throughout with sprinklers.

Two completely unrelated hydraulic calculation sets are required. One for just the standpipe the other just for sprinkler as if the standpipe didn't exist. Hose stream for sprinkler would be 100 or 250 which I suppose could be added at the nearest fire hydrant or city connection. I've always been a little unclear about exactly where to add sprinkler hose stream so I always added it at the standpipe. If the standpipe is capable of deslivering 500 gpm to the two top outlets it should be able to easily handle sprinkler plus 100 gpm (most standpipes are in buildings of light hazard) at the nearest hose outlet.