That is table 22.4.2.1 in the 2008 edition. I don't have an earlier edition to refer to so you would have to specify size and type of tank and class of liquids. The first line in case it is relevant:

All tanks < 150' = 1/6xsum of adjacent tanks but not less than 3' for floating roof, fixed, or horizontal tanks. It get's more specific with larger tanks.

I am somewhat befuddled with the 3' requirement. Why 3' and not another distance other than possibly for egress. It's hardly a distance that would allow for a service vehicle let alone pipe runs, etc..

Regards
Dave  

Thank you very much, lightecho.
I have to verify spacing between two aboveground storage tanks for methanol service, both 138' diameter, 69' height. According to NFPA 30 - 2000 edition, if diking is provided, minimum spacing shall be 1/4 sum of adjacent tank diameters.

If correctly recalled the minimum spacing was 15 ft previously.That sounded somewhat safer/ might have been in a way conservative.

Since now-a-days every one is getting cramped for space; probably the downward revision has come.

But undoubtedly this 3 ft seems somewhat dangerously too small and may yield catastrophe outcome since ample Firewater resources (to counteract against possible radiant heat from close vicinity) are also drying-up,I believe.

Any forum Giants e.g.stookeyfpe,cdafd,DavidCR,JLSeagull& FFP1 may guide us better!

Best Regards
Qalander(Chem)

Comparing shell to shell spacing table 22.4.2.1 of the 2008 ed. to table 2.7 of the 1999(96) ed. there is no change. I don´t have the 2000 ed.

Apart from this, some personal thoughts.
Yep, the 3´ looks to me quite small.

Thinking of the oil industry, API documents (recommended practices) related to fire protection (doc API RC 2001) refer the distances to NFPA 30 and of course free room for other criteria due to especial risk considerations.

API fire reports don´t give much information about the importance of shell to shell distances. If I remember well  they mention that in actual fires, cooling exposed tank walls with spray systems have not been a very important issue related to losses on adjacent tanks. (Although API has a RP 2030 doc.  where they recommend exposure protection with fixed water spray).

So it gave me the impression that it is not very well defined how important is the shell to shell distance based on actual fires; when I see photos of actual fires in the oil industry I think that it is difficult to generalize a criteria about when shell to shell spacing is important. There are people doing fire exposure modeling with advanced calculation tools, but I haven´t heard if they are giving us valuable data to revise the prescriptive NFPA rules. With the actual oil industry situation and the terrorism risk, I was expecting that some aspects were going to change.

Other industrial standards I´ve seen require bigger distances but they look to me that they are not well updated.

If your are working with methanol, a volatile one, maybe it would be better to think of complementing the NFPA with other criteria, and consider the expected fire fighting practices.

I am laying out a large tank farm and need to know the spacing recommendations of NFPA.  Specifically I need tangent to tangent dimensional requirements, and tangent to burm redcommendations.

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