3 replies to this topic

[GarethSteval]

Hello everyone

 

I've just joined this forum after seeing how helpful the members are. I could really use some help from the community.

 

I've been scanning through:

NFPA 11, 13, 14, 15, 19, 20, 22, 24 and 30 and cannot seem to find 2 things:

 

For how many hours of full firewater use should the tank be sized for (it seems industry standard is 2 hours, but cannot find this in NFPA - does someone know where it is?)

I've also noticed in a report that the firewater is designed to only spray adjacent tanks on half of the shell (half of the height). Why is this? Is this in NFPA, and if so, where?

 

Thanks so much! I've spent a few hours trying to research this and I just can't find these answers.

 

Gareth

[Brocklesnar]

Gareth,

 

NFPA 850, provides guidane for fire protection system in power plants. The fire water tank should be sized to suffice minimum 2 hours of maximum fire water demand.

This is also a typical industry practise but I came across few high rise building & infra projects where even 1 hour of maximum fire water demand storage is acceptable.

[ankur2061]

Gareth,

 

Some company guidelines for firewater storage are as follows:

 

1. Exxon recommends storage capacity for minimum 6 hours at full design flow of firewater.

 

2. In a Samsung standard, it is mentioned that when fire water pumps take suction from a storage tank, BP provides guidelines that the storage tank be sized for 10 hours storage at a rate of 820 m3/h.

 

3. Chevron provides very detailed guidelines depending on the type of installation for firewater storage capacities. These are as follows:

 

a. 1-hour supply at 500-1000 gpm for offices, shops, warehouses, single-berth dock

b. 2-hour supply at 1000-2000 gpm for Sulfur plant, H2S recovery plant, Small processing plants, Tankfarm areas, Pipeline terminals, Marketing terminals, Refinery tankfarms

c. 4-hour supply at 2000-4000 gpm for Midsize, 0–500 psi process plants, Gas plants, Multi-berth docks, Offshore platforms

d. 4-hour supply at 4000-6000 gpm for integrated, high value, 0–500 psi plants; Midsize, 500–1000 psi process plants

e. 6-hour supply at 6000-8000 gpm for Integrated, high-value plants, large quantities of fuel at pressures above 1000 psi

 

From the above you can see, that different companies have adopted different guidelines based on their own experience and engineering judgement.

 

Hopefully you may now be able to make some judgement on what basis you want to size your firewater storage tank.

 

Regards,

Ankur.

[GarethSteval]

 

Thanks so much for your replies Brocklesnar and Ankur, it has helped a lot! This is a tank farm so both of your answers seem to agree with each other - 2 hours seems to be the norm.

 

Have you heard of spraying only half the height of the adjacent tank's shells? I still can't seem to find any documentation about this though IP 19 uses half the height in a calculation. Thanks again!