Fire Protection Spray Rings 4

[sshep]

My Friends,

I was advised to repost my question in this forum.

We are building some new plants in the USA Gulf Coast which will require many tanks of all sizes. I am asked to get some information to use as guidence on the use of external spray fixed fire protection. In some newer plants I have worked on elsewhere, the local site standard required sectional or full fire protection spray rings on all tanks containing flammable and combustable liquids. It seems like a good idea, but this site particular does not have such a standard, and has not built many new units recently.

Consider these larger tanks as references, although there will be duplication, and many other services:
Product Dia(m) Ht(m) Vol(m3) Vol(bbl)
Diesel 70 12 46181 290943
Naphtha 70 12 46181 290943
Methanol/Ethanol 20 12 3770 23750
Paraffins (decane) 40 12 15080 95002

Any advice, reference, or opinion will be helpful.

best wishes,
sshep

 

[Duwe6]

External spray is not a bad idea, but a much more useful protective means would be a Foam Riser*, with a distribution header to allow an 'easy' way to get a fast blanket of firefighting foam onto the liquid in the tank. Spray would be more for cooling of the tank while other tanks burn, fail catastrophically, and cause a 'pool fire' that envelops the tank with the spray system.

*Foam Riser is a firefighting connection at the edge of the berm that gives the firetruck a connection to send firefighting foam 'AFF' over to, and into a burning tank.

 

[IFRs]

Installation of monitors is also customary to deluge tanks near to the one burning.

 

[stookeyfpe]

As a regulatory official who has dealt with fire protection of large petroleum terminals, I recommend you start with a review of API RP 2021:

http://www.techstreet.com/products/913794

I don't know how many times I've been asked to intervene on the issue of the necessity of fire protection systems for field erected tanks. At one time in my career I was responsible for hazardous materials enforcement in the 5th largest city in the US and I've been employed in the US fire service for about 27 years. I can safely conclude that few fire departments have little to no understanding of field erected petroleum storage tanks and have probably not contemplated the three highest probability fire scenarios.

If the installation of a water-based fire protection system is being driven based on corporate standards or insurance requirements, aqueous film forming form is one solution. You do need to be careful in its selection, because AFFF formulations are selected based on the tank contents, with alcohol being the great influencing variable. You also need to have a sufficient foam supply to not only extinguish the fire but to also safely perform tank overhaul. I've had incidents where the fire was extinguished in 2-3 hours but we needed to remain on scene to ensure the tank contents are safely removed after a floating roof was compromised. These can easily become 20-40 hour incidents and additional foam is needed in the event re-ignition occurs. Second is that I generally double the discharge density for the purpose of determining the required amount of AFFF because it's application is rarely practiced due to costs and environmental concerns.

My research on loss history based on data from Lee's Handbook of Process Safety and API leads me to conclude that if the storage terminal is located in a jurisdiction that has little or no understanding or resources to deal with a fire event a better use of the funds is on IFRs, overfill protection systems, and consider providing extra tank capacity so in the event of a fire, the product can be safely pumped out of the burning tank to reduce the incident duration, which I term a passive strategy.

 

[Duwe6]

and this is why these Fora are so valuable . . . information + experience not in the testbooks.

 

[Clamont]

Does anyone have any clear water flow rates for cooling water systems in storage depots? I have long tried to find something a little more lenient than NFPA 15 which demands a cooling ring every 3.4m and 10.2Lpm/m2 however every depot I have worked in have only ever seen the one ring at the top with the rest of the shell reliant on rundown.

I have found a design document where they use IP Model Code of Safe Practice Part 19 and NFPA 15 and they have used 2 Lpm/m2. When I search this standard all I can see is that the tank which is not on fire can use this flow rate and for the tank which is on fire should use the same 10Lpm/m2.

When designing to this 10Lpm/m2 the water storage requirements are enormous and I would like to find a suitable standard to design to with more lenient water requirements such as 2 Lpm/m2 with just the one ring at the top as opposed to multiple rings down the tank.

Any assistance would be hugely appreciated.

 

[sshep]

Check out API 2030, section 7.3.13 which advises that spray on only the unwetted upper section has value- this was the result of my research anyway.

best wishes,
sshep

 

[MJCronin]

sshep....

Was NFPA 30 consulted in the layout/spacing of the tanks AS WELL AS the location of the fire protection system ?

What are the NFPA 30 flammability designation for all of the liquids stored ?

There must be an overall layout study developed for possible tank fires, fire fighting equipment locations, and the safe location of fire fighters.

Usually, this is required by the regulating authority.....

MJCronin
Sr. Process Engineer

 

[sshep]

Thanks MJCronin,

Everything is fine with the spacing, and we have our insurer's blessing for the design at this stage. All the fire system layout is fine, and the plan for foam pourers, etc. A project standard was written which proscribes spray rings, even though I consider them to be a luxury in most cases, but I will take them.

best wishes,
sshep

 

[Clamont]

Dear Sshep,

I find this statement in API RP2030 a little confusing as it first states that only the upper portion is to be sprayed then it goes on to state that the entire tank is to be sprayed as the exposure is unknown.

It also only seems to state the occurrence if another tank is on fire and does not give water flow rates to combat the actual tank on fire which IP Part 19 does. IP Part 19 gives 10 Lpm/m2 for the tank on fire and 2 Lpm/m2 for tanks adjacent to it.

Any ideas?

 

[Clamont]

Anyone else have any ideas how to reduce the water requirements to a more reasonable level?

As mentioned when using IP Part 19 everything is explicitly mentioned however the fact that you must cater for a 10L/min/m2 for each tank results in huge fire water lines and also an enormous water storage tank (adjacent tanks 2L/min/m2 however pipelines must allow for a scenario where any tank may catch fire). As mentioned I stumbled across a document catering for 2 L/min/m2 however cannot find anywhere to back this argument up.

Thanks

 

[Tyal51]

With several years of fire suppression system design under the belt a good suggestion is to start with NFPA 15 - Water Spray Fixed systems for fire protection.
As the type of tank is not given - i.e. cone roof with internal pontoons, floating roof etc. the most economical (recommended) system cannot be given. You will need to select the system based on several things - is the intention to stop the tank from carbonizing in the event of a fire - this can be achieved by using a well designed deluge water or fixed spray system. If the intention is fire suppression then water sprays or roof foam pourers work best, and do not forget to install foam pourers in the dyke to prevent ground fires. An additional suggestion is to provide some convenient fire hydrants fitted an adjustable fog monitor to spray the tank or adjacent tanks.

Hope this helps