18 replies to this topic

[somayehn]

Hi all
i must desigh a bitumen storage tank that is insulated . for fire fighting system i have a question: beacuse insulation of tank, is it nessecary to cooling water it ?
Thanks for your reply

[ankur2061]

somayehn,

Passive protection by fire-retardant insulation may only serve to reduce the fire water and / or fire-retardant foam load, not eliminate it, although NFPA 15 does say that suitably insulated structural steel and other miscellaneous equipment may not be provided fire water system if the local authority accepts that the insulation provides enough protection.

However, in my personal opinion, any insulation which could withstand the intense radiation heat for a reasonable amount of time from a fire is highly unlikely since the nature of the fire itself being very unpredictable the calculations for radiant heat incident on a vessel surface from an external pool are at best empirical.

If I were to consider a design for fire protection I would take no credit for insulation and would provide a water spray system based on NFPA 15 guidelines which recommends a minimum water spray rate of 0.25 gpm /ft² (10.2 L/min/m²) for vessel surfaces.

Hope this helps.

Regards,
Ankur.

[somayehn]

dear ankur2061
Thank you very much for your reply and it was useful for me.
but l have another question:
if we use a good insulation application and so need no water cooling (in fire fighting design)
in the fire time for tank what is the best application? i know in the first time foam isn't useful( because the temperature of bitumen is higher than boiling point of water "180 >100) then it is necessary cooling bitumen to low temperature then using foam.
but in this condition what is the best method?

[ankur2061]

somayehn,

I would recommend that you manage to get yourself a copy of "API RP 2021 - Management of Atmospheric Storage Tank Fires". Appendix H - Fire Suppression Agents in this recommended practice provides details of both water and various types of foams for fire extinguishment for storage tanks including petroleum products storage tanks.

Regards,
Ankur.

[Qalander (Chem)]

Hello Good Evening Dear somayehn,
Although your question stands almost relied/satisfied by my friend 'Ankur'.

I only add that

• dry powder fire extinguishing agents and
• air cut-off using Inert gas blanketing etc.

are mainly the measures possible for bitumen storage tank fires initially,as envisaged by me.
However in case of a real built-up bitumen fire the loss of containment may not be ruled out

• due to very high "bitumen heating value" capable of melting even the steel structures (including the tank shell)
• final use of water based extinguishing agent as per their usual availability in-abundance may affect boil-over hazard.

A real cautions and carefully analyzed fire fighting plan is key to encounter such scenarios.
As regards sprinkler cooling ring around the shell and on roof top there are arguments/ counter arguments and practice follows similar mode that some give provisions some do away on insulated exterior reasons.

Hope this proves helpful.

[kkala]

Having read the thread, it might be useful to note local fire fighting practice (as understood at work) for API 650 tanks in refineries. I have not dealt with fire fighting design, but communicated with people that elaborated the documents for permit.
1. Non insulated tanks of liquid hydrocarbons have "cooling rings"; that is peripheral pipes with successive sprays to inject water onto the lateral tank area for cooling. It is put in operation through a manual valve in case of a nearby fire.
2. Insulated tanks of hydrocarbons are not equipped with mentioned water sprays.
3. Cone roofs do not have water sprays, evidently because existing tanks are pretty much higher than 25 ft, so their roof is not affected by a ground fire.
4. Floating roofs have the possibility to accept foam over their roofs, to face the event of a local fire. The manual valve for it is located far from the tank. Destruction of floating roof sealing ring gives an alarm for such a fire.
5. Apart from these measures, hydrants or monitors located along the underground fire water network can cover tank walls with water. Foam generators can create foam to cover the area of the tank basin (area inside dikes).
6. Fire fighting trucks approach the fire and assist fire fighting endeavor. Big tanks (dia>45 m) should be approachable through road at two diametrical points of their periphery.
7. If tank is partially insulated (near bottom), cooling ring is installed to protect the non insulated lateral walls.
8. Generally water has the role to cool the walls so that they can avoid destruction by nearby fire, while foam is mainly applied over the surface of liquid hydrocarbons (e.g. pool fire) with an intent to extinguish the fire by limiting its oxygen supply.
9. Above is also applicable for heavy black product tanks. Liquified gas storage under pressure is another cup of tea.
10. In a recent project Client required foam injection into the tank, but we had objections. I think that 97% of foam by weight (neglecting air) is water, if this water is spread into the tank, it may result in boil over during the fire. Any advice on this issue would be appreciated.
11. And of course any comments / additions on the above would be welcomed.

15 Sep 11, Correction: "4. Floating roofs have the possibility to accept foam over their surface" is corrected to "4. Floating roofs have the possibility to accept foam over their roofs".

Edited by kkala, 15 September 2011 - 01:35 AM.

[Qalander (Chem)]

Thanks Dear Kostas,
your reply is in a way seconding "non-provision" of shell cooling ring on externally insulated API 650 design tanks.
Moreover the pertinent points highlighted are useful indeed!

[kkala]

...your reply is in a way seconding "non-provision" of shell cooling ring on externally insulated API 650 design tanks...

This is their practice. I was a bit surprised to know this, because insulation is not enduring long during a strong fire. My interpretation is that hydrants, monitors and fire fighting trucks will have been mobilized before the deterioration of the insulation.

[Qalander (Chem)]

True,By all means system of main fire ring,hydrants and support D.C.P.trolleys Fire trucks etc should be there to intercept and suppress the fire.

Keeping in mind the problems and concerns of boil over highlighted in my previous post.

However I have physically observed effectiveness of dry chemical powder to suppress a bitumen storage tank fire with little material in it.

Hope this is helpful.

Edited by Qalander (Chem), 07 September 2011 - 10:02 AM.

[kkala]

...Keeping in mind the problems and concerns of boil over highlighted in my previous post.
However I have physically observed effectiveness of dry chemical powder to suppress a bitumen storage tank fire with little material in it....

Mentioned foam in previous posts is a mixer of water (say 97% b.w., excluding air) and foam agent, to produce air bubbles after mixing and injection. This is the main fire fighting medium for liquid hydrocarbons here, according to information, while dry chemical powder is used for LPG fires.

Edited by kkala, 07 September 2011 - 11:00 AM.

[somayehn]

Thanks for replies and these are useful surely.
As discussed frothing or slopover is a serious problem. and when it calm water spray will be useful.
maybe dry powder fire extinguishing agents or gas blanketing are the good choice. but what is rate application and time? tnx

[Qalander (Chem)]

• Application rates Information may be found at many fire fighting equipment suppliers websites.
• As regards LPG I doubt if the D.C.P. is at all effective, except for a very small fire at very initial stage.
• LPG Fire is more effectively intercepted through high pressure very fine water mist or fog to fully cover and cool such fires cutting from atmospheric air.

Hopefully it is guiding to correct direction.

[Qalander (Chem)]

Dears,

Hope the attachment proves useful!

Attached Files

•  API_RP_2001-_Fire_Protection_in_Refineries.pdf   402.63KB   261 downloads

[kkala]

Having checked local refinery practice, following is my understanding on some aspects:
1. Cooling rate to protect wall of API 650 tanks against overheating in case of fire: water at 10.2 l/min/m2.
2. Foam rate on applicable area (e.g, inside dikes): 4.1 l/min/m2 for 30 min (*), which is verified by attached pdf file (Foam Fire Fighting Guide). The latter gives 0.1 GPM/ft2 ~ 4.1.0 l/min/m2 for at least 15 min (p. 11) for gasoline, diesel, and similar fires, according to NFPA.
3. Dry powder can be applied to specific natural gas fires (http://www.cheresour...ransfer-system/). It is true that it cannot suppress a big LPG fire, but could prevent it, see http://lpg.nv.gov/Sa...LPG%20Fires.pdf, as well as http://www.torbay.go...eum_gas-lpg.pdf.
4. According to information, high expansion foam can be used in cryogenic (also LPG?) tank fires, but your advice on it would be appreciated.

(*) For permanent foam supply. In case of mobile foam generators (250 gpm each), number depends on max tank diameter d in the dikes (1 generator for d<19.5 m, 2 for d<36 m, 3 for higher d). Time of foam supply also depends on d (10 min for d<10.5 m, 20 min for d<28.5 m, 30 min for higher d).

Attached Files

•  Foam Fire Fighting Guide.pdf   1.16MB   221 downloads

Edited by kkala, 15 September 2011 - 02:43 AM.

[Qalander (Chem)]

Dear, I still maintain that

• Dry Chemical Powder trolleys are very effective fire fighting resource in many gas and liquid fire fighting situation Having higher rate of dischare) and
• not the common DCP portable Fire extiguishers. with respect to practical application effectiveness.
• Hiving said that I still maintain that high pressure fog or mist is the best cooling or smothering media to principally fght LPG/gas fires, Equally good results for most Class "B" and built-up bitumen fire

Thanks and best regards(Actually I personally encountered many such suppression activities with satisfactory prompt success.

[kkala]

"Industrial Fire Protection Engineering" by Robert G Zolosh (Wiley, 1993) http://books.google....20fires&f=false supports water mist as an effective fire extinguishing medium (complying with above post on the point), among with other Fire fighting matters.
For low flash point liquids (para 7.6.3, p 227): Fire suppression is more effective with small drops, tending to vaporize more rapidly upon passing through flame. The drops reaching the liquid do not provide any benefit for this category of liquids (comment: they may cause harm by coming into the liquid).
Extinguishement time decreased from 100 s to 10 s, when water mass median dropplet size decreased from 0.48 mm to 0.28 mm, at water application rate of 16.6 l/m2/min. It is generally not possible to suppress gasoline fires with water drops larger than 0.50 mm.
Liquid LPG (flash point between -60oC & -104 oC) can be considered as a low flash point liquid, so water mist has advantages as above in case of fire.
For medium expansion foam (para 7.7.2, p 234): It can be used against liquified gas fires.
Sincere thanks to Qalander (Chem) for the useful info on firefighting.

[Qalander (Chem)]

Thanks,

However I will further revert back soon

• after Current NFPA 30&NFPA 11review,
• considering stored material, storage tank roof type and envisaged minimum application time.
• accordingly the foam application rate values may slightly vary

Hoping this proves useful.

Edited by Qalander (Chem), 16 September 2011 - 06:58 AM.

[Qalander (Chem)]

Dears

As committed above some info(May prove useful!) is shared through "Hall Fame" downloads section;Subject to acceptability/permission by the Forum admin

Best of Luck to all.

[papilon]

Can somebody email some P&ID for the fire protection of Bitumen Storage Tank, I appreciate