Boil over and AST foam protection. I need coments.

[DavidCR]

Dear everybody

In NFPA 30-96,99 (Definitions 1.6) they define the fenomenom of boil-over. They say that "most crude oils" present this risk.

I thought that boil-over could be developed in any oil (less dense than water) when the conditions associated with boil-over are met to complicate a fire. (I´m thinking of above ground storage tanks vertical 10 to 28 m diam. with fixed cone roof, capacities aprox. from 1850m3 to 5000 m3 (12000 to 30000 bbl)).

Query 1.
I´d like to know if heavy fuel oil (HFO) or fuel oil #6 and diesel (fuel oil #2) can be considered as a typical boil-over oil.

Query 2.
We are buying some fire protection equipment and they say that foam chambers are no recomended for fuel oil #6 (HFO) since it is less volatile and it has boil-over characteristics. Can somebody tell me a comment on if this is true and what are the bases for this? Is boil-over an aspect that must be considered on indicating foam chamber protection or not?.

(They are including foam chambers for diesel tanks, but not for the HFO tank).

Query 3.
NFPA 11 (Foam) requires that for foam protection for tanks (chambers) must include foam protection for diked area. Can somebody give info about the type of hidrants, nozzles or monitors recomended for this dike foam protection?.

Any comment will help. Thanks, luck & blessings to everybody.

 

[MJCronin]

David,

I believe the accident scenario you are interested in is called a BLEVE or "Boiling Liquid Expanding Vapor Explosion" ( Check the referenced website :

http://www.nfpa.org/Research/FireInvestigation/AlertBulletins/BLEVE/bleve.asp)

This phenomenon can occur in an atmospheric storage tank (flat bottomed)when the burning mass on top of the liquid suddenly sinks to the bottom of the tank. The mass "boils away" water commonly found on the bottom, generating steam and forcing a large mass of burning liquid upward. The BLEVE is so deadly because it is an unexpected occurence for many untrained firefighters and because it occurs when the fire seems to be under control.

The BLEVE can also occur during a propane tank fire, however the phenomenon is somwhat different.

I question if any of your Number 2 and number 6 fuel oil tanks require foam protection. Get yourself a complete copy of NFPA-30 and review the categories of combustable and flammable liquids. This categorization is based on the flash-point of the liquid. Unless the rules have changed rather recently, under NFPA-30, neither N0.2 or No 6 oils require foam protection.....

Now, of course you local fire authority, or local rules and statures could require foam protection ( above and beyond the rules of NFPA-30.....

Suggest you use GOOGLE (THE BEST THING ON THE INTERNET) and search for BLEVE, NFPA-11, Fuel oil and Fire fighting foam

Good Luck

MJC

 

[DavidCR]

Thanks a lot for the BLEVE point. The info you ref. is quite good for understanding this on gas accidents.

Well, the boil-over can lead to a bleeve, and I´m still courious on boil-over on AST as per my original questions.

As little as I´ve understood on NPFA (30 and 11) the distances, type of tank and type of fuel are associated with the type of protection (table 2-1, 2-7 and p. 2-9). For our application we are thinking of a water cooling system and foam chamber protection for our particular interest and not for NFPA code requirement since it is not very strict on this.

 

[frgb]

Boil over happens when there are considerable amount of water in any hydrocarbon liquid tanks and the temperature was not controlled enough below the water boiling point. We have seen this happen to Heavy Vaccum Gas Oil Intermidiate tank where the rundown coolers fail and we have enough water in the receiving tanks which resulted to boil over,

Thus your question of boilover on diesel tanks and fuel oil tanks are possible if ther are possibilities of getting high temp such AFC fails and in case of fire continegency.

Hope this helps