Containment of fire water from fire sprinklers

[SprinklerDesigner2]

We have a 100,000 sq ft building equipped with a dry pipe system designed to a density of .30 over 3,900 sq ft plus 500 gpm hose stream allowance. This design was a recommendation from FM Global about 12 years ago but the company is no longer an FM Global risk.

Product stored is chemicals.

The owner asked me about "containment" which we have all dealt with on foam systems but it is something I have yet to run into on a standard wet or dry sprinkler system.

Specifically how much water would need to be contained in the event of a fire?

The minimum theoretical discharge would be 0.30*3,900=1,170 gpm but seeing how FM Global required a maximum velocity of 20 fps and the water available was 160 psi static, 152 psi residual @ 3,000 gpm the actual discharge from 39 open sprinklers would be considerably more. A sprinkler discharge of 1,700 gpm seems more realistic.

1,700 gpm for 120 minutes? That's twenty swimming pools.

The owner asked me what would be "realistic" in the event of a fire and I don't know how to answer that. I doubt the question is coming from the insurance company because they would know the answer.

Anyone ever run into something like this?

 

[cdafd]

Scott knows the correct answer.

Is the business being required to retro fit???

 

[cdafd]

FYI

The IFC states in 5004.2.2.3 for indoor design, “Secondary containment for indoor storage areas shall be designed to contain a spill from the largest vessel plus the design flow volume of fire protection water calculated to discharge from the fire-extinguishing system over the minimum required system design area or area of the room or area in which the storage is located, whichever is smaller. The containment capacity shall be designed to contain the flow for a period of 20 minutes.”

 

[LCREP]

Storage of “ chemicals” is a pretty broad term can you get more specific?

From an insurance point of view we really got concerned if the chemicals were flammable or a combustible liquid. If so see NFPA 30 they have very specific requirements for containment. Most times for existing warehouses it was cheaper to convert to a foam system than start to add trenches and outside of the building storage of run off water from a fire. You add the environmental requirements to anything leaving the building and it got real crazy. Most of my work experience was in New Jersey were we have a lot of environmental requirements.

 

[UFT12]

SprinklerDesigner2 you may have already but see important information in NFPA 15, A.4.4.7 where some durations are recommended depending on various considerations. It seems these can vary from less than 30 min up to an hour depending on responsiveness of manual FF means.

In addition, although the occupancy may not be the same, NFPA 33 suggests a duration of 20 min containment. See chapter 9.

The containment should include the maximum anticipated number of containers spilled plus water discharge.

Last, some type of liquids do not require containment at all so check first NFPA 30 or IFC or the code pertinent to your case and compare with the MSDS.

Hope that helps.

 

[stookeyfpe]

[(0.3 GPM/Ft.^2)(3,900 Ft.^2)] (20 minutes) = 23,400 Gallons required for secondary containment + the volume of the largest single liquid or solid product container. Gases do not require secondary containment.

There are some factors that can raise or lower this number but given the information, my answer is good for how you described it. For example, is all 100K Ft^2 of building a chemical warehouse or is it a small room whose area is < 3,900 Ft.^2? If the area of the room is less than the design area, you only calculate the room area for the purpose of determining secondary containment volume. I don't know the volume of a typical swimming pool but I've designed or reviewed 200-300 indoor and outdoor containment designs. Inside of buildings, it can commonly done with depressed foundations or sloped floors to an exterior containment basin.

This methodology was first adopted in 1988 when ICBO updated the 1988 Uniform Fire Code and Uniform Building Code. I remember the discussions with industry and the fire service. By the early 1990s the BOCA and Southern Fire Codes also adopted this methodology and it's currently specified in NFPA 400, Hazardous Materials Code.

Now if you want an explanation of why 20 minutes was selected I'll be happy to answer the question.

Finally, you shouldn't even answer the question. That's up to someone who has reviewed the chemical inventory, the scope of this project's work, is it storage, use or both?

 

[UFT12]

Also, in case where lowering floors or draining may be impractical, containment can be also achieved by utilizing special kinds of closures at doors. Typically such containment barriers are designed of appropriate high and installed on floors at or near doors to achieve the required containment.