Greener refrigeration system issues explained.

[Dave A]

CO2 is being heavily pushed for widespread use by governments. Large subsidies are available overseas to help offset the heinous costs involved for companies who make a commitment to use it.
...

Green politics.

Got to get those carbon credits somehow

[desA]

Yep, CO2 is not combustible, it's just the gas escaping when pipework ruptures. The pressures are immense, over 100Bar (1500 psi) and there's quite an explosion when a rupture occurs.

There is also generally, compressor oil being transported around the refrigerant circuit. This oil can catch fire of an occasion with some systems. Not sure how much of an issue this may be with CO2, but at up to 150bar in some applications, the results could be interesting.

[AndyD]

There is also generally, compressor oil being transported around the refrigerant circuit. This oil can catch fire of an occasion with some systems. Not sure how much of an issue this may be with CO2, but at up to 150bar in some applications, the results could be interesting.

I'm not a refrigeration engineer but I've spent the last three months doing lots of homework.
Oil catching fire might be a problem if a larger propane system had a big leak. Oil leaks from other refrigeration systems can be very acidic which is another problem. CO2 systems tend to run in a flooded state so liquid co2 could escape in the case of a large leak or pipework failure. CO2 much prefers to be a gas (or even a solid) a room temperature and pressure so the liquid would violently boil freezing anything it came into contact with. Cold burns to a person are just as bad and possibly life threatening as heat burns.