The European Union now allows flammable refrigerants per
STANDARD EN378.
In short, A3 class refrigerants (such as R290) are limited to 1000g if any component is below ground, and 1500g if all components are above ground. This applies to comfort cooling and heatpumps too. Allowable amounts are further restricted by a "practical limit" based on the room size a component is in, the distance above floor, and the lower flammability limit of the refrigerant in question. A split system with a ceiling cassette in a 530 square foot room could use 650g of R290 without a flammable gas detector.
We haven't seen news reports of fires/explosions, even though there are millions of vending machines, cold cases, and other devices with flammable refrigerant in the EU.
Efforts are ongoing to standardize US regulations to these, which already allow charge amounts up to 150g.