4 replies to this topic

[Diederik Zwart]

John,

The refrigeration company is correct in that the classification is an electrical one and the chance of flammable vapors being present is not a reason to consider a fire relief case. However if in your plant flammable liquids can spill (either from the refrigeration unit, or from another source), and a pool fire under a vessel/heat exchanger/piping of the refrigeration unit can occur, then you're absolutely right in specifying a relief valve sized for a fire case.

In my experience you don't let a vendor size such a relief valve, but you specify the size based on your own sizing practices. If the vendor supplies you with dimensions of the unit and with the physical properties of the refrigerant, then sizing for a fire case is fairly straightforward. Afterwards you have to discuss with the vendor as to the best location on the unit. If it is an 'off-the-shelf' unit, then I can imagine that it will take some time and extra cost to add a nozzle of the right size, so a re-estimation might be required.

I hope this helps,
Diederik Zwart

[ShaunHill]

On the chiller I have typically seen the PSV being sized for the tube rupture case which is normally higher than the fire case. However, my experience with refrigeration is specific to chilling high pressure gas, and I don't know if you are using this in the same application. If you are chilling something at low (or atmospheric) pressure then tube rupture may not be the limiting case, in which case I would see fire as the next criteria to consider.

If we are talking about the PSV on the discharge of the compressor, then the blocked flow case is usually more restrictive than fire case.

The only places in the referation system I can think of where you should have a fire case PSV would be the refrigerant accumulator.