LPG Sphere - cone deflector 1

[israeljrr]

Hello everyone,

Does anyone knows if the NFPA prohibits the use of deflector cone on top of a LPG sphere? and if it's true, in which standard is mentioned.

The doubt is coming because the client want use cone deflector instead a fire protection ring with sprinkler

As a reference parameter the average wind velocity it's around 1.5 m/s.

Thanks
Israel

 

[DavidCR]

I think NFPA does not address such systems. I´m not sure since I´m not very familiar with LPG and spheres.

API´s point of view from "API 2030 Application of Fixed Water Spray Systems for Fire Protection in the Petroleum and Petrochemical Industries" says...

"Alternative designs for protection of LPG storage spheres are in common use and are generally acceptable. As discussed in API 2510/2510A, these designs can involve one or more very large discharge nozzles at the top of the sphere, along wit some type of distribution system such as a weir. The design objective is to create a uniform film of water that covers the critical portions of the sphere´s surface."

On the following lines, it clarifies that spray nozzles or monitor protection are needed for the lower part of the sphere and for the dry spots near the supporting structure.

In my opinion, I would not use them for the following reasons:

- I thin layer of clear water is not good to cool from radiant heat. So your are using water to cool, but not in the best way.
- It is difficult to control the water distribution uniform.
- They are less efficient (I would add more water as a flow safety factor).
- Since the spray NFPA 15 is needed for the other areas. I´d follow a standard practice and avoid a "special" costly performance based design.
- In case of fire I´m not sure on what the insurance company would about a special deluge systems.
- I´m not sure if this systems would enter in the NFPA´s "performance based option" design category, I´d try to avoid this.

I´ve seen this old central application of water on cylindrical tanks with cone roofs, they are not recommended now, since it is known that the heat percentage that receives the roof is not very significant and the water distribution on the tank vertical walls is very inefficient.