Unlimited area sprinkler system sizes for Factory Mutual

I had heard rumors that they cut the system size back down to 60k sq ft. But, if you read the current data sheets, the system size is not limited. I bet you will be limited by branch line size and not really be able to put it all on 1 system. If you branch lines are 250' long, you will be having a lot of friction loss in those lines. You will likely need 2-4 systems to keep the branch line sizes reasonable.

But, the last FM project I did, we went about 65k sq ft per system and didn't have any issues.

Travis Mack
MFP Design, LLC

Do not forget compliance with the IFC. The IFC adopts NFPA 13, which doesn't have such a provision. IFC Section 102.8 allows the use of other standards as prima facia evidence of compliance. The issue is that FM loss prevention data sheets aren't standards.

You should talk with the local fire code official about your proposed designs. I would accept it, but I would require compliance with all of the FM requirements. Mixing NFPA 13 and FM LPDSs doesn't meet the intent of the IFC.

Stookey,

Correct as always. Thanks.

Yeah, for the particular project I had, it was full FM. There was no mixing of NFPA 13/FM.

Another "nice" part of the FM standards is that you are no longer required to add the flow of ESFR sprinklers located under an obstruction. You just pipe to it with piping the same size as your branch line. In the past, and per current NFPA 13, you are required to include up to 2 additional sprinklers in the calcs. That could be a huge impact to your system.

If the project is per FM data sheets, but sure to read through all of the pages, and the referenced data sheets as you are held to all of them. Also, you will want to speak with the FM reviewer prior to starting the project to see if there is anything additional that may be required. FM projects are pretty simple from a technician point of view as virtually everything is spelled out in black/white for you. You just have to get the correct data sheet and speak with the FM rep. Follow all of those, and the design/approval process usually goes pretty smooth.

Travis Mack
MFP Design, LLC

Has anyone ever dealt with running 10in. aerial pipe in a warehouse? What are the required hanging methods to support this pipe? Clevis hangers seem like the option, but do we need to trapeze? What about seismic?

Thanks
Manny

Congratulations!

I have done FM ESFR jobs but also had to comply with the local AHJ. As such NFPA 13 was the ruling document but we used FM's design criteria. We were limited to the 40K sq.ft. maximum. Also FM required a 0.8 coefficient on flow tests.

As for the 10" pipe, we have used clevis hangers for it and kept the length to a minimum by way of hydraulic calculations. If I recall correctly we were unable to locate 10" band type hangers. You do need to carefully read the structural drawings, for these we also needed a hanger attached to the center of the top chord of the bar joist.

Just got back from a week long CEU seminar where the FM system size was discussed. Appears they are all over with 60,000 being in style for the moment.

As told to me the problem they have experienced is actuating the alarms (flow switch) with super large systems.

Ah, makes sense. Perhaps automatic air vents would fix the problem of the flowswitch delay.

Be careful with 10" pipe on bar joists. 10" is heavy enough that its load may have to be spread across two joists with a structural member, depending on the spacing of the hangers (which is obviously proportional to the load per hanger). Always check with the structural engineer.





Real world knowledge doesn't fall out of the sky on a parachute, but rather is gained in small increments during moments of panic or curiosity.

Coming in a little late, as far as 10" pipe goes, I have only used it where required for large fire pumps. Split that flow, it will likely be cheaper to run 2 6" mains and the fitters will thank you.

As far as the 10in pipe run goes , its about 100 ft total after my hydraulics were done. Thanks for the feedback folks.

I've just completed 2 FM ESFR projects, one of which has a system size of 90,000 ft². My approach to the waterflow switch is replacing it with a Potter pressure switches. One switch supervises high / low pressures, the other triggers an alarm at a specific set pressure. Thus eliminating time delay from a flow switch from such a large system.