Emergency Pressure Relief.

[conners]

Please could someone advise me on the following issue.
I am currently in the process of installating a solvent storage tank. The volume of the tank is 30 cubic meters and it is to contain Tetrahydrofuran. I have calculated that the maximum discharge requirement for the emergency relief device is 8870 NMCH/Air. I have used the method of calculation as outlined in the American Petroleum Institute (API)standard (Venting Atmospheric and Low Pressure Storage Tanks)
In this standard it states that certain environmental factors such as tank insulation can be input into the calculation to reduce the maximum required discharge rate.
However it also states that water spray systems should not be considered as environmental factors and therefore cannot be used to reduce the max discharge required.

I have been speaking to a supplier today who has told me that it is common practice to multiply the max discharge requirement of the emergency venting device by 0.3 if the tank is surrounded by a suitably approved fire protection system.

The tank I am installing will have a foam suppresion system covering the tanks entire surface area. The system will comply with NFPA 11a and NFPA 15 requirements.

Is it common practice to reduce the max discharge required from a emergency vent if the tank has a suitable water system around it?

Also is 0.3 the correct value to use as the environmental factor?

Advice on this matter would be greatly appreciated!

 

[SeanB]

API 2000 states what environmental factors you can use. If your tank is insulated - 1" thick then you can use 0.3 as your factor - this is where that value comes from. API 2000 also clearly states that you cannot take any credit for fire water protection.

 

[johngerhart]

It is not allowed to take credit for insulation unless you have a solid PM program to enure its integrity . I also agree with Sean B about not taking credit for the fire protection systems . In a fire they often run out of resources

 

[shahyar]

...and that 1" insulation should be "fire resistant",not conventional silicate types.

 

[PAN]

shahyar,
Please advise more about "fire resistant" of insulation material. Normally, I always use rock wool and calcium silicate as insulation material. Can I use the factor 0.3 for this case?

conners,
You should ask for the reference from the supplier. He may give you some supporting documents.