FM Global and the allowed coverage area of a sprinkler system - any changes recently?

[SprinklerDesigner2]

I went through the most recent data sheets looking for the maximum size of a system and can't find it. Maybe I missed it so I will go back again but.....

Used to be 52k and 40k sq ft when FM followed NFPA #13 then it became unlimited but there was talk of going back to 100k when they had trouble with some alarms?

What has been your latest experience with FM in regards to total area covered by a single system?

Oh, I want to have a 70,000 sq ft system... would save a lot of money.

Thank you.

 

[TravisMack]

I do not believe there are currently any system area limitations in the FM datasheets.

Travis Mack
MFP Design, LLC

http://www.mfpdesign.com

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[SprinklerDesigner2]

Thanks again Travis.

I spent all day looking and couldn't find any area limitations but things change. Down the South, here this part of the country, we don't deal with FM Global as much as we did up north.

 

[Cidona]

While there isn't a set ft2 area limitation FM 2-0, Section 2.4.1 and 2.6.4 have wording addressing the limitations of system size. i.e. (a) hydraulically works (b) Water flow alarm initiates within 60 seconds and also (c) if local code has requirements that the local code must be followed.
If you had a large enough system that had a lot of air trapped you could exceed the 60 seconds.

 

[cdafd]

Not trying to advertise,

But this came up in a class the other day. Appears it started in the 2016

http://www.metrafire.com/metravent.html

New 2016 NFPA 13

7.1.5 Air Venting
A single air vent with a connection conforming to 8.16.6 shall be provided on each wet pipe system utilizing metallic pipe.

8.16.6 Air Venting
The vent required by 7.1.5 shall be located near a high point in the system to allow air to be removed from that portion of the system by one of the following methods:

Manual valve, minimum 1/2" size
Automatic air vent
Other approved means

 

[Cidona]

FM 2-1 (Prevention and Control of Internal Corrosion in Automatic Sprinkler Systems) Section 2.3.1 has 'recommendations' for new sprinkler systems that also mention Air Vents such as the datasheet cdafd linked to. However in FM 2-1 it looks for "... means for air release at the highest point of each branchline..".
As seems to be pretty much everything with FM Datasheets it all seems to be project specific as to which parts of their datasheet need to be complied with. It would therefore be as well to discuss the systems size and any other details the project FM Representative.
I'm not sure putting a single vent per NFPA (not my area expertise, just can't see how) on a single high point will really prevent the negative aspects to air pockets as it would seem they are only going to release air in that particular pocket. If you have systems with riser nipples and various offsets (yes, I try to avoid them but sometimes they won't build the building around me ) the single air release would seem to have limited value.

 

[cdafd]

8.16.6 Air Venting
The vent required by 7.1.5 shall be located near a high point in the system to allow air to be removed from that portion of the system by one of the following methods:

Manual valve, minimum 1/2" size
Automatic air vent
Other approved means


And if you read the appendix for this section, it says if the manual means is used, access point should not be over seven feet above the floor???

Seems like they should have just gone with automatic only, since the manual will more than likely never be used.

 

[Cidona]

I could see some benefits to the manual configuration.

For the Automatic type they would have to be located at the high point which may be inaccessible for servicing in the future. Also, if you really wanted to get all (or at least most) of the air pockets out you'd end up with multiple Auto vent locations and require piping from each for 'spitting of water'. Manual type would seem less expensive, more reliable and as likely to be used as the Auto type are to be inspected and tested (i.e. depending on owner/contractor).
I think the 7' clearance would be for a ball valve such as indicated in the FM 2-1 arrangement.

 

[Cidona]

cdafd (Specifier/Regulator)1 Feb 18 00:41
I don’t know.

If your lines are at say 20 feet and you pipe down for the valve,,

Will you really get air out??


Copied your response to the other thread here cdafd.

I would think you'd get air, then some spluttering, a somewhat steady stream of water, probably more spluttering and then a constant steady stream of water. i.e. I think the thought process is that the water will push the air out when the valve is opened. There is probably some air (quantity?) that will merge with the water and some more than will pass over the water at the top of the pipe but I think (and am of the understanding that it is FM's theory with this arrangement) that the majority will make it's way out said ball valve. However, there would seem to be limited situations where you get to have room to have a line running above the high points such as shown (maybe more feasible with ceiling only systems).