Maximum and Minimum Pressures for FDC Sign?

3/18/2022

We have been asked to supply FDC signage for an existing building with combined sprinkler/standpipe system.

The AHJ has requested that both minimum and maximum operating pressure be included on the sign.

Can we use existing hydraulic data information or should it be recalculated including friction loss from the fire hose to pumper truck?

Also, what would constitute the maximum pressure in a combined sprinkler / Class III system?

Would it be max 175 psi at all 2-1/2” hose connections if there are pressure regulations devices on the 1-1/2” hose valves?

Thanks in advance in helping us sort this out.

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14 Comments

Derek

3/18/2022 08:06:34 am

I have never heard of an AHJ requesting this....FFs are taught across the board to pump into FDC's at 150psi. I imagine using the existing hydraulic information would be sufficient. Good luck!

Anthony

3/18/2022 08:19:10 am

If its a manual system the minimum should be 150 psi at 1000 gpm per NFPA 14 - 2016 A.7.10.1.2

With out extensive examination the the components attached to the system I'd keep the maximum to 175 psi as that is the most common maximum psi rating for fire protection system parts. Its also the maximum static allowable on hose valves without pressure regulating/reducing devices.

The AHJ (local fire marshal) would know better what the local response teams can handle and train with. They may want a lower pressure as high pressure hoses can get dangerous.

If its automatic I'd look at the fire pump test report and match the rated combined flow for the minimum with a maximum at the churn+city water supply would be.

Alex

3/18/2022 08:23:31 am

Hi,

Rerunning the calculations depend on what you have modeled/calculated currently. If you have a standpipe calc with your FDC located adjacent to the pump, then I would say you're okay without running an additional calc. Although, if you have a longer run from your FDC, I would highly recommend running another. In the end, running a calculation does not hurt and is always the best approach.

NFPA 14 (2016) 7.8.1.2 states "manual standpipe systems shall be designed to provide 100 psi at the topmost outlet with the calculations terminating at the fire department connection". This will be used to help determine your minimum pressure. Note: you do not calculate the pressure loss from the FDC to the pumper.

For your maximum pressure, NFPA 14 (2016) 7.2.1 states "the maximum pressure at any point in the system at any time shall not exceed 350 PSI". You can use this value at the base of your standpipe to calculate the maximum pressure allowed by the fire department.

Thanks,
Alex

Alex

3/18/2022 08:25:06 am

Clarification on the 350 PSI. This value requires PRVs off of the standpipe contingent on elevation loss. Ensure you review the entire system before providing the maximum pressure.

Alex

Dan Wilder

3/18/2022 08:28:45 am

The signage should be the requirement at the FDC inlet only. Let the Truck Engineer do the math on losses for the connections between the truck and the FDC (could be a run 2-2.5"x50' hoses or 1-4"x50' to a wye and 2-2.5"x50' hoses depending on how far away they park or available hoses). They have the potential of pumping far greater than 175PSI into a system.

The minimum pressure (required pressure) should be based on calculations for the standpipe system (most cases the more demanding)...as for a maximum, that is subjective in my eyes. Are there any other examples in the jurisdiction you can reference? I would stay clear of providing a maximum, this is an operations training item with the crews and is subject to interpretation across installation companies.

Alex

3/18/2022 08:43:24 am

Hi Dan,

I've never seen a maximum either but the idea of one sounds useful. For instance, in my small town I have a few small (under 3 story) buildings equipped with a sprinkler system. It could be "easy" for our truck to exceed 175 psi and begin to risk damaging the system.

To me, providing the maximum pressure is a way for the engineers to provide more guidance on the system. Curious on where this question arose!

Alex

3/18/2022 08:45:08 am

I believe the AHJ is after the sign required by NFPA 13 2016 8.17.2.4.7.2. However it is probable that they are mistaken on the need, and proper use of the sign like our local AHJ's who often require this. The sign is required on systems that have a demand greater than 150 PSI. If the original calculation data is available, I would say that is safe to use, since the system was designed to that data, and the original sign (if needed) would have been off of that information also. Essentially when our AHJ's require this they are looking for what the inlet pressure should be at the FDC when the pressure is greater then the normal 150 psi starting pressure. I'm not sure what the minimum operating pressure they are looking for could be, and it is the fire department responsibility to calculate friction loss to the FDC. With the various types of FDC's, size fire hoses, and lengths of hose, it would be difficult to calculate the friction loss from the pumper to the FDC unless the fire department was very involved in the process.

Jesse

3/18/2022 08:52:26 am

We do this a lot.

The standpipes are calc'd at 250-gpm @ 100-psi with the number of outlets flowing (calc'd) determined in 14.

Most of our AHJs have an SOP for the pump operator to set the discharge pressure at 155-psi. The agency I was at did 160. For anything above that, they require signage.

For example my last one, the standpipe test showed we had to set the pump pressure at 170. They required a sign at the FDC saying "PUMP TO 175 PSI"

Franck

3/18/2022 09:14:41 am

- Personnel opinion -
To my point of view (but maybe asking what the AHJ has in mind would be better - communication is a key element to avoid mistakes and misunderstandings).
- the minimum requirements to be indicated is the sprinkler demand of the most demanding area (flow and pressure)
- The maximum to be indicated is 175 psi as sprinkler systems should not operate above that pressure. No need to indicate a flow as the 175 psi is the maximum value, with or without flow.

Emil Ohler

3/18/2022 10:01:27 am

Maybe the signs they are looking for are as per NFPA 14 6.8 Hydraulic design info

Original Poster

3/18/2022 02:58:58 pm

Wow! Thanks for all the great replies. I agree the AHJ in this case might not be aware of the 150 psi clause as per NFPA 14.

I did the calc’ and came up with minimum 110 psi at 500 gpm as per the local building code for this area. (65psi at most remote FHC). Then used 175 psi as the max for sprinkler components and 2 1/2” Hose Valves.

After that I thought why not check out the surrounding area? The building next door had signage indicating Minimum 90 psi / Maximum 175 psi, so I believe we are on the right track.

Thanks for all the great posts! 👍

Pete D.

3/18/2022 04:53:31 pm

It completely depends on the situation. What if your building is 50 stories 15 ft. elevation each? If the fire is in the penthouse, 175 psi will get the water a little more than halfway there.

Original Poster

3/18/2022 04:58:38 pm

Agree. If it was a high building there would likely be pressure reducing valves on the sprinkler zones and pressure restricting hose valves on the lower floors to accommodate a higher maximum pressure. In this case we had a 5 story building.

4/13/2022 10:39:44 pm

From a firefighter's perspective, we want to be prepared for the unexpected while maintaining simple, consistent procedures throughout the membership. Before I explain, a few bullet points:

Task: Supply the fire attack with more than enough pressure.
- Nozzle 185gpm @ 50 psi
- 200' of 1.75" hose (FL = 30 psi per 100')
- Minimum 110 psi
- Fire Attack controls the discharge pressure at the standpipe connection with a 2.5" gate valve that we put on.
- 5 psi per floor for the total number of floors in the building.

FDC Pump Discharge Pressure:
1-5 Floors = 175 psi
6-10 Floors = 200 psi
11-15 Floors = 225 psi
>16 Floors = 175 psi + 5 psi for every floor
Add supply hose FL to get final pressure.

Example #1
7 Story Apartment = 210 psi
200 psi + 10 psi for supply FL

Example #2
23 Story High Rise = 300 psi
175 psi + 115 psi for Elevation + 10 psi Supply

Love to hear what you guys think.
Any questions please ask.

Maximum and Minimum Pressures for FDC Sign?

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