What fire zone are you referring to? There is no reference for 25 or any meters in particular, if you think of some diameter... there is a reference for 25 ft, for the expected height of a poolfire. Do you have a copy of the API 521? I could not locate anything of what you have mentioned, in my copy of API 521. Can you re-phrase your question?
cheers,
gr2vessels
Like gr2vessels, I suspect you are referring to height. API 521 uses 25 ft, NFPA 30 uses 30 ft which is also the value that API 2000 suggests.
If your question regarding fire zone is related to a system that follows API 521, then also review the section in API 521 covering "Vapor From Fire Heat Input". That's section 3.19.2.2 in my 4th edition, I believe the section number but not the title has changed in the more recent 5th edition. The dicussion indicates considering a fire zone to include 2,500 ft2 (232 m2) of plot area but you should read the full discussion.
