Fire Fighting in Atmospheric Storage Tank Farm

[Clamont]

I do not know if double posting is frowned upon and I apologise if it is however I am desperate to get some advice from people regarding fire protection in a storage tank farm and compliance to international standards (I had posted similar content in NFPA forum). Is there anyone who can offer some advice on the below relating to NFPA standards in relation to a fire protection system for a tank farm;

1. It is my understanding that to comply to this standard it more or less comes down to the type of fire protection you have in place compared to the proximity of your tank(s) to outside surroundings. In some instances if your tank(s) is far enough away from property lines or public ways then you may not require ANY fire fighting to be compliant to the standard if you are storing Class II or III products (and Class I if under 190m3 volume). I know this seems very clearly spelt out in the standard and may be incredibly obvious but I am struggling to get my head around the fact that you can have no fire fighting capability and still be compliant to an NFPA standard.

2. If you do want to comply with NFPA 30 and you require a fire fighting system the design must be in accordance with the appropriate NFPA standard which for fixed spray system is NFPA 15. In this standard it stipulates for an atmospheric storage tank that the amount of water to allow for is 10.2 L/m2/min and the maximum height between horizontal cooling rings is limited to 3.7m. If designing to this standard it often work out that the volume of the water tank is equal or larger to the volume of the product tank dependent on the duration of spray that you design to. I have never seen an atmospheric storage tank with cooling rings spaced at 3.7m from one another and also never seen a tank farm with such large water reserves. All of the tanks I have seen generally just have the one cooling ring at the top of the tank. Are these tanks basically non-compliant to NFPA or am I missing something?

3. This brings me to my 3rd question. It states in the standard the water volume requirement per m2/min however if you have multiple tanks in a tank farm must you consider the water requirement for every single tank at the same time? This would require massive amounts of water however cannot see anything to imply otherwise.

4. It also does not stipulate the length of time that the water must be applied to the shell at this rate for. I have often heard a 2 hour coverage is required however cannot find it anywhere in the standard.

Any advice would be greatly appreciated.

 

[IFRs]

The deluge system is intended to cool the tank shells of those tanks exposed to the tank on fire. Using a plot plan, circle one tank and determine the surface area of adjacent tanks that would be lit up by the circled tank if it would be on fire. think light bulb and where the light shines. No need to water cool surface area in shadows or not directly lit by the tank on fire. Do this for the whole tank farm and find the worst case - the largest surface area of any single tank burning. That is your surface area, I don't usually figure more than one tank is burning at a time. Many tank farms use underground piping and aboveground monitors that will fire water on tank shells to cool them. I usually see cooling rings on smaller tanks.

If the tank is all alone in a large field, who cares if it is on fire? You will lose that tank but adjacent structures and threats to the population is nil. Either let it burn out which for a largest tank may be your only real option anyway or pump foam on it to put it out.

The length of time you need deluge water streams? Until the fire is out would be my answer.

My opinions only !

 

[Clamont]

Many thanks for your reply IFRs....

Firstly, what design standards when it comes to fire fighting have you worked to or designed to?

On the smaller tanks that you have come across with cooling rings do they have cooling rings at 3.7m intervals all the way down the shell or just the one at the top of the tank and then rely on rundown to cool the remaining portions of the shell? This is clearly stated as not acceptable in NFPA 15 however I have only ever seen the single ring at the top.

What you say about the surface area of the adjacent tanks makes perfect sense however is this outlined in any particular standard?

Your mail states that the deluge system should have enough water until the fire is out, however when it comes to designing the capacity of water storage tank how much coverage should be considered?

Look forward to your opinions on the subject.