I am currently in the process of building a cascade for my PC. The cascade will run with R507 using a Tecumseh CAJ2464Z 1.5ph R404a LBP compressor for the high stage, and with ethylene (R1150) using a Danfoss SC21B LBP R502 compressor for the low stage.

Thus, the low stage is going to run using 'feared hydrocarbons', and one which is capable of developing extreme pressures when all active and passive safety measures fail (over 50 bar is possible).

Now, I was wondering what the official requirements (preferrably Dutch/European) are for the low stage. High side test pressure, low side test pressure, special precautions, etcetera.

Ethylene scares me, so everything will be built to survive an atomic war. Therefore I guess that it takes little effort to have the system adhere to the standards, so I would prefer to do so.