NFPA 30 Diking capacity

[carletes]

Dear all!

I am dealing with the sizing of the required capacity of the impoundment (diked) area around two crude oil storage tanks. I know that according to NFPA 30 it must be as a minimum equal to the largest tank volume. My question regards to the fire fighting water storage. I thought that during a ground fire the diking drain valves must be closed, so I think that impoundment capacity should be able to store not only crude oil from the tank but this fire fighting water as well. Why NFPA do not consider a bigger required capacity to consider the fire fighting water collection? Perhaps the drain valves of the diking must be open during a fire in order to drain water+hydrocarbons and in this way minimize the risk of fire extending to other tanks?

Thank you for any help.

 

[pleckner]

NFPA 30, ANNEX A, paragraph A.4.3.2.3.2(B) indicates that desiging for fire water collection is sometimes done but is a function of local conditions. So the short answer is, NFPA gives you the bare minimum, for anything extra, consult with the local requirements.

 

[stookeyfpe]

Two other things to consider when considering dike volumes:

A) API at one time had proposed a standard for the required fire flow for petroleum terminals. The standard was never published because calculating the fire flow for terminals is dependant on tank designs, stored product, and if intermediate diking is provided.

B) If your tanks are located in the US, the fire code official can require that the containment dike be constructed in accordance with NFPA 30 and provide sufficent volume to also accomodate a 24 hour/25 year storm.