12 replies to this topic

[Leinster]

This may not be the best place to post however I wanted to get some expert advice.

I have been looking into fire fighting of fuel depots recently and in particular in compliance to NFPA 30. In order to design a fire fighting system for a fuel tank farm to NFPA 30 it states that the sprinkler system should be done in accordance with the relevant NFPA code which as far as I am aware is NFPA 15.

I have browsed through NFPA 15 and the water requirements are very excessive and I have never seen the amount of water requested by NFPA 15 in an actual fuel depot. One very obvious example is for system protection for vessels (I have taken an API 650 atmospheric storage tank to be a vessel as per NFPA) where it states that the volume of water on the vessel should be 0.25 gpm/ft^2 (10.2 L/min/m2) and that the distance between nozzles on the vertical should not exceed 12 ft (3.7m)... Sections 7.4.1 and 7.4.2 respectively.

In my experience with fuel depots I have never seen such enormous water requirements for a storage tank and numerous rings on a storage tank to comply to the 12ft spacing.

Is there something that I am missing to ensure that the tanks are in compliance with NFPA 30 or is the water requirement really that stringent?

I look forward to your responses.

[ankur2061]

Leinster,

NFPA 15 is not for sprinkler systems. NFPA 15 is titled as "Standard for Water Spray Fixed Systems for Fire Protection". NFPA 13 is the standard for sprinkler systems with the title "Standard for the Installation of Sprinkler Systems". The difference between sprinkler system and water spray systems is very well explained in the link below:

http://www.cheresour...y-fixed-system/

NFPA standards are developed based on industry practices for fire fighting. The NFPA 15 water spray rates are not specific to any installation but are based on unit surface area for control of burning of any equipment exposed to radiant heat from a pool fire. Different water spray rates are applicable for exposure protection as per NFPA 15 (Section 7.4). For a jet fire impinging on any equipment spraying from fire hoses would be required at very high rates. For more information on calculating surface area of equipment exposed to fire refer the link below:

http://www.cheresour...-tanks-vessels/

Table-1: Water Spray Application Rates for Exposed Surface Area in API RP-2030 (Application for Fixed Water Spray Systems for Fire Protection in the Petroleum & Petrochemical Industries) also provides the water spray rates for petroleum installations. These water spray rates are mostly identical to what is provided in NFPA 15.

Hope this helps.

Regards,
Ankur.

[Leinster]

Dear Ankur,

Many thanks for your very informative reply.

Essentially what I have seen in the fuel depots where I have worked would fall under NFPA 15 as the sprinklers are not closed sprinkler heads and are activated manually through the fire water pump. If the depots therefore do not satisfy the water requirements of NFPA 15 then they cannot be considered to comply to NFPA 30 I presume?

[AHMEDMUJTABA65]

What should be the capacity of the water tank ?

Let's suppose that we have two tanks of equal capacity (1,000 cubic meters each) of furnace oil. Then, what quantity of water tank should be built?

Is there any rule of thumb for that purpose?

[Leinster]

Dear Mr. Ankur,

In addition to my first question about compliance to NFPA 30 please could you also assist with the below;

I have obtained a copy of API RP 2030 and I have a couple of questions that I hope you can help me with;

1. It states that the maximum rundown allowed on inclined or vertical surfaces is 3.7m (section 7.3.12). Does this mean in order to comply to this you must have cooling rings spaced at intervals no greater than 3.7m down the tank? I have never seen this and normally just see the one cooling ring at the top of the tank with the rundown covering the entire tank. Please confirm.

2. I cannot see anywhere in API RP 2030 or even API RP 2001 (which is cross referenced in the 2030) where it stipulates the period of coverage for tanks and the surface area to be considered when designing the fire fighting. For example if you have 10 tanks in a bund area and you are designing the water requirements do you need to allow for the surface area of all 10 tanks to be covered at the same time and what period of time do the tanks require coverage for?

I look forward to hearing back from you.

Thanks

[kkala]

....One very obvious example is for system protection for vessels (I have taken an API 650 atmospheric storage tank to be a vessel as per NFPA) where it states that the volume of water on the vessel should be 0.25 gpm/ft^2 (10.2 L/min/m2) and that the distance between nozzles on the vertical should not exceed 12 ft (3.7m)... Sections 7.4.1 and 7.4.2 respectively.
In my experience with fuel depots I have never seen such enormous water requirements for a storage tank and numerous rings on a storage tank to comply to the 12ft spacing....

Fire fighting water rate of 10.2 L/min/m2 is normal for atmospheric tanks, look at http://www.cheresources.com/invision/topic/13256-fire-fighting-application-for-bitumen-storage-tank, especially post No 14.
I have also seen only one cooling ring close to tank top, its sprays covering the water rate as above for cooling all peripheral area of the cylinder. But look at http://www.cheresources.com/invision/topic/13437-number-of-spray-water-nozzle-rings-for-a-storage-tank. Clarifications on this point by others would be welcomed.

Edited by kkala, 11 August 2012 - 12:45 AM.

[ankur2061]

Leinster,

The spray arrangement including spacing for horizontal and vertical tanks is very clearly provided in NFPA 15. As they say, pictures speak louder than words, refer the attachment with this post where the pictorial representation for spray arrangements for both vertical and horizontal tanks per NFPA 15 is provided.

Refering to point no: 2 of your query, all tanks falling under the same fire zone need to consider simultaneous application of spray water for exposure protection even if the fire is a localized one. Defining a fire zone requires a Quantitative Risk Assessment Study (QRA) wherein risk assessement is done to satisfy ALARP (As Low As Reasonably Practical) criteria for loss prevention due to fire.

Regards,
Ankur

Attached Files

•  Water_Spray_Arrangement_Horizontal_Vertical_Tanks_NFPA_15.pdf   18.98KB   453 downloads

Edited by ankur2061, 11 August 2012 - 02:31 AM.

[Leinster]

Ankur,

Many thanks once again for your informative reply and I now understand that to comply to NFPA 15 you would need cooling rings from top to the bottom of a storage tank.

I have seen that the water requirements of API RP 2030 are a little less than NFPA 15 for an atmospheric water tank (4.1 L/min/m2) so would prefer to explore this as an option however I find the statement on section 7.3.13 Atmospheric Storage Tanks a little contradictory. I have taken extracts from this section below to seek your advice.

"...cooling water is of potential benefit only for the exposed portions of the roof and those portions of the shell that are not in contact with the liquid contents....."

"..... If spray is used, typically only the upper 12 ft to 24 ft (3.7 m to 7.4 m) of shell is sprayed; up to 12 ft (3.7m) of rundown is allowed on inclined and vertical surface. If there are wind girders at the top of the tank, spray nozzles should be placed below each girder ring....."

".... Since the exact location of the exposing fire or the amount of liquid in the exposed tank may not be known before the fire occurs, total protection would require that the entire tank be sprayed...."

It firstly states that typically only the top of the tank is sprayed and you are only allowed 3.7m of rundown and then it states that the entire surface area of the tank should be sprayed.

If the top of the tank is the most vital due to the vapours if you place cooling rings all the way down the tank the area at the bottom of the tank will receive alot more water than the top because even if you are only allowed to consider 3.7m of rundown in reality you will get rundown all the way from all of the cooling rings.

I assume that despite the statement that only the top of the tank is to be sprayed that in fact you do need sprinklers all the way down the tank at a spacing not exceeding 3.7m. Please confirm.

Thanks

[ankur2061]

Leinster,

Most of the standards I have studied and I have studied quite a few of them, have some statements which are either confusing or contradictory.

One thing I do want to emphasize is that while API 2030 is a recommended practice NFPA 15 is a standard which in my eyes makes it much more mandatory to follow then a recommended practice.

The water spray system as depicted in the figures in NFPA 15 is what I would recommend to follow.

Regards,
Ankur.

[Nomanwer]

I want to know about the expose area of tank to be cooled if adjacent tank om fire with reference. any one help me?

[eurekaignem]

Dear Nomanwer:




You asked about the exposed area of a tank to be cooled if adjancent tank is on fire.


This is a good question. NFPA 11, 15 and 30 are not explicit on this subject. The answer is... it depends.

Definitions:

1). Source tank is on fire.
2). Target tank is exposed to fire from source tank.


Exposed area to be cooled on target tank depends on the:
a). wind,
. which way the roof of the source tank rips off,
c). separation distance between tanks,
d). management,
e). and other factors not discussed here.



a). Consider wind. Flame tilt will have a dramatic impact on the need to protect the top of adjacent target tanks.

. Consider that the roof of the source tank rips along the weak seam during the initiating event, but not completely. Tanks that are shadowed from the fire by the incompletely removed roof are not in as much need for exposure cooling as tanks that are more
fully exposed to the open roof from the source tank.

c). Consider if the tanks were 2 km apart; we would not even be considering exposed area because the fire hazard to the target tank is moot. So, obviously separation distance matters.

d). Consider management. We all know that management knows even less about fire than we do. So asking management "What are your performance goals if we have a fire in one our tanks?" and "Are you Mr. Manager, willing to accept fire escalation to a second tank?" is or course going to result in an answer of "Well...uh... I....", and "No." But what management doesn't realize is, if tanks are 1/3 diameter separation and it is a windy day and the roof is completely ripped off by the initiating event, there may be very little that can be done to save the exposed tank that only 1/3 diameter away from the source tank. The option of cooling the exposed tank is further dampened if the roof which was removed from the source tank by the initiating event, lands on the neighboring tank that is only 1/3 diameter away...

Now given the above, how are we going to cool our neighboring tank? And even if our fixed cooling-system piping on the exposed tank were to survive the initiating fire event from the source tank, what about these considerations:

1. why do we cool 360 degrees around the exposed tank when at most, only 60 degrees of the tank is really being subjected to exposure? Is this not a tremendous waste of water, precisely when water may be THE critical path to extinguishing a fire in the source tank?

2. why do we accept that cooling sprinklers need to be no more than 3.5 m vertically separated, when I have seen much, much greater vertical separation achieve complete wetting down all surface area of the tank?

3. has anyone who designs these exposure tank cooling sprinkler systems gone out into the field and tested them, 10 or 15 years on? The don't work. The conditions of open sprinklers with small amounts of water left in the piping after testing is ideal for corrosion.


The answer to your question of 'to KNOW about the exposed area of tank to be cooled in event of a fire in a neighboring tank' begs that the designer consult not an engineer, and not an NFPA standard, but consult a firefighter that has successfully extinguished more than a handful of fires in tanks with diameters greater than 35 m. Without leaning on such advice, the designer may "meet the letter of the specifications and Code standards" such that the designer can go home and enjoy an nice bar-b-que and start to worry about the next project...but the design team is almost certainly wasting their client's money in inappropriate and ineffective design, and draining precious resources from accomplish the prime task: that of fire extinguishment.

Scot Deal
Excelsior Fire/Risk Engineering
eurekaignem@gmail.com

[kkala]

Radical views, deserving further thinking. So mentioned 12 ft vertical distance between two cooling (firefighting) rings can be much longer, which gives an explanation to the request of last para, post No 6 (and to posts No 1 or 8). But how could we justify this deviation from NFPA, in countries where its application is mandatory? Normally this requirement by NFPA should be replaced by a more stringent measure, thinking from legally point of view.
Indeed, standards may not be able to master the situation, even though they place minimum requirements. In the past, a documentary in local TV showed an expert team in USA extinguishing a fire of a huge fuel (diesel?) tank. They collected large water quantities and ejected them on the tank at a rate many times higher than recommended by NFPA. The fire was put out in about an hour through this (unorthodox) method. Other methods can be applicable in different cases.
Specialized firefighters can be hardly found anywhere, I remember a fire in a local fuel tank farm lasting for days until aid came from abroad (Table 6, item 1, http://xa.yimg.com/kq/groups/3862917/1523127472/name/%2525EE%252580%252580StorageTank%2525EE%252580%252581FiresStudy.pdf)

Edited by kkala, 18 November 2012 - 01:03 AM.

[ali.m.garadi@gmail.com]

since, the subject about tank fire and tank safety.
i relies in my plant we have 4 hydrogen horizontal tanks with out any sprinkler systems.
The tank pressures= 100 Kg/ cm2
atmospheric temperature = 25 -45 C
tank length = 10 m
tank diameter = 1.5 m
my question :
is sprinkler systems needed for this type of tanks?

​please provide my any document or files available please share it with us .


thanks