Fire Water Systems design

[khomotso]

hi guys

i am working on a fire water system and i found a few guidelines on NFPA20. What is the maximum pressure that the fire water header can be designed at?

 

[gr2vessels]

khomotso,
If you try protecting your chicken farm, 1000 kPa(g) will do. If you try protecting the Burj Khalifa in Dubai, you have to pump water in top of the skyscraper, so you will get 1000 kPa(g) in top. That is, 1000 + 8300 = 9300 kPa(g). Hey, that's the minimum pressure, not the maximum. The maximum for Burj should be 9300 + 10% margin, that is 10,230 kPa(g). For your application, use the above principle.
Cheers,
gr2vessels

 

[KiwiMace]

Your limitation is the piping material and rated capacities.

 

[MJCronin]

Do you have a fire monitor in your system ?

How high must it spray ?

 

[khomotso]

@ MJCronin: the pressure at the tip of the most remote fire hose must be atleast 11 bar when the hose is fully extended. i guess what im really trying to ask is that will my system be able to handle any pressure above 12bar which is what the fire water system is kept at. i recently had to change my source of water and it is coming at 5bar more than the previous source. so discharge pressure on my pumps is now 17bar and there are no PSVs on my system.

 

[rconner]

You may want to check the pressure listings (per appropriate underwriting organizations) for all the materials exposed in your system. After all, "a chain is no stronger than its weakest link". For many years the minimum allowable pressure rating for some piping materials, joints and joint restraints etc., per what some might argue is the most conservative organization (Factory Mutual) was 175 psi. This listing required some very high pressure structural testing of the components and joints, where the manufacture is required to demonstrate for the witnessing inspector(s) among other type performance tests that the components and joints do not burst or separate while holding five minutes at a pressure of 4X that listing pressure.
Fire fighting and fire flow testing can involve some very high flow velocities, as well as opening and closing valves and hydrants in quite pressure-packed (so-to-speak!) emergency/rear-ends-and-elbows circumstances, along with concomitant shocks to all components of the systems exposed due to water hammer etc.
Some pipe materials, joints and manufacturers have demonstrated very high FM ratings of products, e.g. for some ductile iron pipe manufacturers and joints that rate up to twice that minimum, i.e. 350 psi or more, whereas some plastic pipes e.g. might rate far lower. [I think I may have seen a lower minimum rating than 175 psi now allowed by FM for some plastics, but am not really sure why.]

 

[khomotso]

thanks!