Safe distances from oil tank fire 6

[DavidCR]

I´m looking for information on safe distances from aboveground oil storage tanks in order to know where to locate valves, monitors, hydrants.

I´ve been told some recomendations about it, some say that 2.5D (D: diameter of tank) is a safe distance, also I´ve seen a standard from Colombia that requires al least 1D from the tank wall, but I´d like to have more criteria on the point.

In order to have a formula to calculate in an aproximate basis the heat received from an oil tank in fire at different distances, I´ve seen some general ecuations on the text by Drysdale "Introduction to Fire Dynamics", but I wonder if in actual safe distances estimation these methods are really used or if there is a formula for the specific case of oil tanks.

I´d appreciate your comments on this.

 

[IFRs]

NFPA (National Fire Prevention Association) in the USA may cover that in NFPA-30. I know it has distances betwen tanks, from tanks to property lines, etc.

 

[JoeTank]

I doubt that it is in a code, but a safe distance would be at last two zip codes away.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[MJCronin]

david,

The "two zip codes" suggestion is not too far from the truth.....!!!

What you should investigate is a phenomenon known by the acronym "BLEVE" or Boiling Liquid Expanding Vapor Explosion. This type of explosion can and has occured in oil tank farms.

Try these:

http://www.cmi.k12.il.us/Urbana/projects/apple/service/department/types/type.html

http://www.csb.gov/completed_investigations/docs/CSB_HerrigFinaldigest.pdf

Oil tanks can also exhibit a behavior where a top layer of burning combustion products/solids suddenly sinks within the tank and causes any water ( which has collected in the tank bottom) to suddenly boil. This can occur when the oil fire seems to be extingusihed.

NFPA books describe one oil tank fire (at a power plant in South america...I think )where an oil storage tank was located somewhat uphill from a crowd of on-lookers. After some time (hours) had passed fighting the fire, a hot top layer sank to the tank bottom, caused a steam explosion and killed many in the crowd.

One or two zip codes......yup, I agree.

Have you read through NFPA-30 ?

Suggest that you "GOOGLE" BLEVE and "oil storage tank" fire

Anybody else out there got info ?


MJC

 

[DavidCR]

Thanks for your comments. I´ll try to be more clear with my question.

What I´m looking for is criteria to define distances to locate fixed fire figthing equipment, hidrants, valves, foam proportioning equipment, monitors, etc., as well as oil handling equipment, away from the ASTs.

Yes, I´ve read the NFPA 30, as far I understand, it indicates distances from tanks to buildings, neighbor´s building streets or limits and to other tanks, etc. And I´m not sure if the distances indicated there, can be used to locate fixed fire fighting equipment.

For these distances I´ve been told some criteria (distances I mentioned before) and calculations that try to model in a simple way a safe distance based on radiant heat calculations or on experience. But I don´t want to use them with no further information to base them.

We have Diesel (Fuel oil 2) ASTs of 5000m3. Fixed cone roof API 650, 28m diam, 9m height.

Of course, if you are thinking of a BLEVE or a boil-over no NFPA 30 or similar criteria distances would be reasonable to consider, and you would have to think on quantitative risk analalisys tols on such a disaster.

As far as I know boil-overs is not spected to happen on diesel, and a BLEVE woud not be a good criteria to define a safe distance to locate equiptment for fire fighting activities.

So, the "post" is still alive and more comments will be wellcome.

PS.
About the zip code distance criteria, I´m not in USA so I´d appreciate and equivalent to zip code distance to Costa Rica (just a silly joke).

 

[Slowzuki]

Hello, I've worked on a project similar. API have some good standards as well.

We use

Managment of Atmospheric Storage Tank Fires

and

Interim Study-Prevention and Suppression of Fire in Large Aboveground Atmospheric Storage Tanks

They are available in PDF form on the API website.

 

[farshi]

hi

the place of fire fightining equipment is a safe place ,it should be putted in maximum distance of equal to two times of storage diameter.in nfpa-30 or releated nfpa ,the safe distance have been given.
from explosion anlysis we could find the safe distance ,that monitor could be operated safely.

 

[peebee]

I'm not familiar with your specific question, but I'm rather familiar with the related problem with oil-filled transformers.

NFPA has little in the way of specific detail on this, only vaguely mentioning things like "adequate protection" and "sufficient distance" and the like.

HOWEVER, Factory Mutual (FM) has LOADS to say on this. You might want to check for an FM standard, or if your actual insurance company has any specific recommendations. FM is often referenced as they are one of the most detailed and stringent out there -- beware that you might find them "excessively" stringent in some applications (but better safe than sorry, right?).

When the insurance company is happy, everybody's happy. When the insurance company is not happy, nobody's happy.

 

[DavidCR]

Peebee
Could you help me to find the specific standard or recomendations of FM?

 

[peebee]

FM Global:

http://www.fmglobal.com

FM Global Loss Prevention Data Sheets:

http://www.fmglobal.com/scripts/store/item_details.asp?catid=13&prodID=5

-- looks like you can order a single data sheet for $25. The big sets get pricey, though. . .

An index of "FM Global Loss Prevention Data Sheets":

http://www2.mapfre.com/documentacion/scc/documentos/publicix.pdf

-- #7-88 might be of interest.

Maybe a couple phone calls to vessel vendors, your insurance company, etc., would save you the $25. Or maybe you can Google around to find out what the #7-88 requirements are. . . .

Good luck.

 

[peebee]

Another thought after reading "What I´m looking for is criteria to define distances to locate fixed fire figthing equipment, hidrants, valves, foam proportioning equipment, monitors, etc., as well as oil handling equipment, away from the ASTs." --

Maybe you should ask your local Fire Chief. If he's not happy, nobody's happy, including your insurance company.

 

[advidana]

Try checking the Fire Protection Manual From NFPA,the chapter called "Special Systems And Extinguishing Techniques". also try NPFA 11 standard For Foam Extinguishing Systems and NFPA 11B Synthnetic Foam Extinguishing Systems and NFPA 15 Water Spray Fixed Systems.

 

[JamesCG]

Hi,
I'm a Chartered Fire Engineer from the UK. I have come across this in the past related to diesel storage tanks (about 15m diameter)for power stations and we located foam system operation valves at a safe distance based on radiation calculations, however the software we used to do this (PHAST by DNV Technica) is quite costly - as specialist software usually is. If you are really concerned, you may be able to source someone to carry the calculation out for you.

The distances were quite large (can't remember the exact details, but needed to get down to a thermal radiation level of under 4.7 kW/m2 which we took as a level where fire fighting personnel could safely access - API RP 510)

Hope this helps.

James

 

[DavidCR]

Thanks a lot JamesCG. I don´t have anybody in mind that can help me with such a software. Our case is diesel tanks, fixed cone roof, 28 m diameter, 9 m high.
I´m not aware of API RP 510 so I`d appreciate if you can tell me how this aspect is mentioned there.

 

[JoeTank]

API-510 is the Pressure Vessel Inspection Code. I think the poster gave an erroneous reference.

Steve Braune
Tank Industry Consultants

http://www.tankindustry.com

 

[JamesCG]

The only part of the API Code I know is through use of a book by F P Lees called "Loss Prevention in the Process Industries" where a set of tables of incident radiation vs levels of damage are given. 4.7 is given as the intensity where emergency actions lasting up to several minutes may be required without shielding, but with protective clothing.

This also ties in closely with the criteria given in a British standard (5908) which quotes 4.5 kW/m2 as the intensity sufficient to cause pain in personnel unable to reach cover in 20 seconds, though blistering of skin (first degree burns) is unlikely.

I have used this when assessing escaping personnel moving away from a fire affected area.

If you can get hold of The SFPE handbook of Fire Protection Engineering (3rd Ed) there is a section on Fire Hazard Calculations for Large Open Hydrocarbon Fires that may be useful. The book is available via the SFPE website and costs $230.00 for the CD Rom version.

This section has various calculations from simplified screening calculations to more complex ones which may be of use (make sure you take note of any limitations or safety factors that are recommended).

 

[CaptGunner]

Some references to use:
NFPA-11, NFPA-30, Fire Protection Handbook (NFPA), API-2021 (Fighting Fires in and around Flammable and Combustible Liquid Atmospheric Storage Tanks) (long title, but good concise guide). API-2025 (Emergency Planning and Mutual Aid for Products Terminals and Bulk Plants).
A note for you: BLEVE is only a concern in a pressure vessel, or a seriously malfunctioning cone roof tank (with plugged vents, etc.) Floating roof tanks do not BLEVE. Also, boilover is a serious concern, but, again, only with products that have multiple boiling points (i.e. crude oil). #2 F.O. (diesel) is a refined product, and does not have boilover potential. (After it burns for a while, and you apply water and/or foam, it is hot enough to boil that water at the burning surface, and it may "froth" over a little, but not a boilover. By the way, with a crude tank, if you were to suspect boilover to occur soon - the recommended evacuation distance is 10 tank diameters - and that is a MINIMUM recommendation.
Good luck to you!

 

[MAFS]

Hi
I had a similar problem in a project I finished recently. In the absence of specialized thermal radiation software, I used the method described in Spanish Standard "NTP 326: Radiación térmica en incendios de líquidos y gases", which you can find at

http://www.mtas.es/insht/ntp/ntp_326.htm

(if you can understand spanish). This method uses a view factor approach and is of immediate applicability. It also mentions the 4,7 kW/m2 limit. We assumed 140 kW/m2 average flame emissivity, 100 g/m2 fuel mass fuel consumption rate per second. Bibliography used for this method is mentioned in the bottom of the website.
On our particular study we also considered flame tilting effect by wind action (which alters the view factors to be used and the safety distances signifficantly). I think the SFPE handbook also contains view factors for tilted cylinders.
I hope this helps.