Use Existing Fire Pump for Higher Foam Demand?

9/17/2020

We have scenario where we are using foam system under NFPA 11 for a floating roof tank with Crude Oil.

Based on our previous calculation for a prior tank the fire water demand is 1,926 gpm so we have existing 2,000 gpm pump to be able to supply the required flow. But an additional Crude Oil tank has been added and we have run our new hydraulic calculations and we come up with 4,496 gpm new flow requirement.

Is there a way we can still use the existing fire pump?

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7 Comments

Dan Wilder

9/17/2020 10:52:38 am

The only way I see this working is if you setup the pumps in parallel. As the old pump works for the original remote area it's a matter of setting the second pump up for the correct "PSI ON" for sequencing along with the correct proportioner requirements

The bigger issue is going to be the suction/discharge/testing/bypass piping of the pumps to take on the additional volume (again, the assumption that the current setup is 10", the new setup would require 16" incoming and 14" discharging for example) per NFPA 20.

I am also assuming this is a municipal/site supply capable of handling the flow demand. If it's pulling from a tank/pond/reservoir those calculations will also need to be reviewed.

Brad K

9/17/2020 12:42:45 pm

I agree with the above. The suction sizing was my first concern for parallel pumps. Please consider the ID of suction pipe if HDPE pipe in play. This is a common issue.
Also, recommend extensive support from the pump supplier to assure sequencing and piping requirements.

Jon Dimanlig

9/17/2020 08:02:54 pm

Water source is coming from a Fire water storage tank. We are using a balance pressure pump proportioning foam system.

anthony brown

9/17/2020 01:39:37 pm

Some questions and some assumptions: I am assuming that this is a Wet System and that it is using low expansion foam. Is the Bladder Tank able to hold capacity, I'm assuming that it is sized for the existing system, and if I am reading your question correctly a new oil storage tank was added and that created the additional loading. final assumption is that you are supplying the system from a Municipal source i.e. "City Water".

Running two pumps drawing form one source will require a 16" supply and a 14" system as already mentioned. Can the supply in the street cover that size pipe and can you buy a 16" BFD? In addition it is likely that you will have to get a new Bladder and hopefully you will have space to place it.

I'm thinking your best bet would to be get the new pump and supply it with new street supplied service. Run your calculations to size the required service. I think when all is said and one it will be a safer, cheaper, and efficient way to go.

Brett

9/17/2020 02:51:39 pm

What is the reason for simultaneous foam application on the two tanks? What is the separation distance between tanks? Most multi-tank farms are not designed for simultaneous foam application across all tanks. I would recommend speaking with the local AHJ to determine what their requirements will be before proceeding. The local fire departments operational procedures for response to the facility should be taken into account in the design.

9/17/2020 04:40:04 pm

Certainly your new demand (4496 gpm) can not be met by existing Pump (2000 gpm) if scenario established to needing water/foam in both tanks together. The way I see with limited information which you provided, foam system for both tanks together probably not required in any scenario and other tank may need only water spray. It depends where you are applying foam whether it's for Seal RIM fire (external floating room) or for Dike protection. Please note that foam is ONLY meant to protect from pool fire scenario whether it's on roof or at ground. For Exposure/Cooling protection water spray system is required for adjacent tank (s) if these tanks are located downwind and affected by thermal radiation from "Tank on Fire". So in either the case, if foam applying for one tank, other will need water spray only. Water Spray can be limited to unwetted surface only for nearby tanks. Another scenario for crude tank fire is "Roof Lost Fully Involved Tank Fire" where you can not do anything for the "Tank on Fire" except watching helpless, you need to let that burn but your focus should be shifting to protect other adjacent tank(s) from heat exposure to avoid escalation. It is worth noting that "Roof Lost Fully Involved Tank Fire" is not credible scenario and failure frequencies for such scenario are very rare if tanks are complying API/ANSI requirement. However before I address your concerns more appropriately; appreciate following information;

1. Tanks Sizes (ID and Height)
2. Type of Tanks (whether it's Dome Roof with IFR or External floating Roof, If it's Dome roof, what is the slope angle for roof.
3. Are both tanks placed in same dike or not (this will change your protection philosophy.
4. Prevailing wind direction/Or confirm tanks is affected if there is fire on other tank either on top of roof or in dike.
5 Are these semifixed or fixed foam system Automatically operated.
6. How you getting 4496 gpm, I means what is being expected to operate.

Regards
Sunil

Mike

9/17/2020 04:42:50 pm

I agree with Brett. Scenarios are based on one fire event. In my experience, if tanks are closer than 1 diameter cooling water is used on adjacent tanks. API 2030 and NFPA 15 are good references along with NFPA 30. Maybe a radiation study would be more revealing in actual risks.

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