Is Pipe Schedule Extra Hazard Equivalent to EH1?

11/2/2021

If an existing building has a pipe schedule system that is determined to be "extra-hazard", without any design information, would that system be equivalent to an Extra Hazard Group 1 hydraulically-calculated design curve of 0.30 at 2,500 sqft?

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6 Comments

Alex

11/2/2021 05:32:50 am

Hi,

Yes, if the sign only reads “Extra Hazard”, I would say you can only assume it protects Extra Hazard Group 1 (0.3 over 2,500 as stated).

Although, I would say that if you are modifying the system in any way that you should calc the system to ensure adequate protection.

Alex

Anthony

11/2/2021 08:24:07 am

Depends what equivalent means in this case.

NFPA 13-2016 Explicitly says extra hazard systems shall be hydro calc'd

11.2.2.2 Pressure and flow requirements for extra hazard occupancies shall be based on the hydraulic calculation methods of 11.2.3.

Without any design (water flow data) information no. Even LH and OH pipe scheduled systems require some minor calculations namely can the available flow/pressure over come the losses due to elevation and back flow preventer.

I have seen several scheduled systems in my time that are code compliant but are not able to satisfy a hydraulic demand curve when calculated.

With all that said I have seen several scheduled systems in my time that are code compliant but are not able to satisfy a hydraulic demand curve when calculated.

Run a calc.

Jesse

11/2/2021 08:34:38 am

Great question. The short answer is probably "yes". The EHPS was intended to provide an EH1 density. Now of course, if using 2016 NFPA 13, we can't even modify an EHPS system without calculating it per 23.7. So, my recommendation is take the extra time and steps to calc the system to be sure it is hydraulically adequate to do what you expect to do.

Dan Wilder

11/2/2021 08:37:26 am

This one I'm going to disagree with. This is two separate design approaches and while they accomplish the same end result for allowable design, I would not interchange the two.

Pipe schedule systems were base on providing a minimum PSI at the base of riser, calculated via a required minimum at the remote sprinkler + elevation loss without account for friction loss through the pipe or over discharge. Then a maximum # of sprinklers allowed on a branch line was enforced (6 in this case).

While the EH minimum PSI were left up to the AHJ (Per the 1978 version of NFPA I could find), both OH1 & OH2 had the same starting pressure or 15PSI. Even using a 5.8K sprinkler, max spacing of OH is 130 this would cover an OH1 (19.5 GPM) but fall short of the OH2 (24 GPM)...this gets worse with as the K-Factor decreases. Note that this minimum has been revised up to a 20 PSI in current editions (not sure when this occurred).

The system would be equivalent to a pipe schedule system for EH (possibly EH1 or EH2 assuming # of sprinklers on the line, pipe sizing, sprinkler coverage of 90FT², system area no greater than 25,000 FT² are all followed), as for what density, that would be proven via hydraulic calculations.

franck

11/2/2021 10:05:55 am

Not necessarily.
Pipe schedule is no longer applicable for extra hazard occupancies.
Note that in the "good old time", the required densities were not the same (there even used to be an OH Gr 3 occupancy).
For example, in 1978, EH gr 1 was 0.29/2500 and EH Gr 2 was 0.37:2500 (now respectovely 0.3 and 0.4).

Thios being said, for a small room, the answer is probably yes as you pipes would be large enougfh for a large density relivered by your sprinklers.
For a large area, this is more problematic as your demand point (if calculated) could exceed your water supply (in flow and/or pressure).
The only way to determine if your water supply is able to fulfill your demand is to make an hydraulic caculation, as stated by all other peers above.

Then, my conservative approach : if you are really dealing with an extra hazard occupancy which is greater than just a small room (io.e. more than 6 sprinklers), don't gamble... make an hydraulic calculation to be sure you are able to control a fire in that area!

Joshua Freedman

11/2/2021 10:18:00 am

I would say although it is possible, most often times it is not. I am an inspector and have seen many pipe schedule systems over the years that have been hydraulically calculated later to determine it's actual design, and as a previous commenter stated, it is highly dependent on pressures available, as well as pipe diameter installed. Most Extra Hazard pipe schedule systems I have seen calculated, or have calculated myself, usually come up around 0.15 - 0.20 / 3000, around an OH2 output. An option you might look at that I see sometimes is installing a fire pump on the system to boost the pressures up - with fire pump installation I have seen pipe schedule systems get into the 0.33 - 0.45 range.

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Is Pipe Schedule Extra Hazard Equivalent to EH1?

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