When phasing out R-22, which of the following gases does NOT cause serious damage?

R-417A is a refrigerant that was developed as a retrofit option for R-22 systems and is designed to have a lower environmental impact compared to R-22. It is categorized as a hydrofluorocarbon (HFC) blend and is less harmful to the ozone layer, which makes it a preferable choice during the transition away from ozone-depleting substances like R-22.

HFC-134a, while also a hydrofluorocarbon, has a higher global warming potential when compared to R-417A. R-12 is a chlorofluorocarbon (CFC) that is known to be very harmful to the ozone layer and has been largely phased out due to its environmental impact.

The choice of R-417A as the option that does not cause serious damage is based on its better sustainability regarding ozone depletion and lower environmental risks compared to the other listed refrigerants. This choice reflects the ongoing efforts in the HVAC industry to move towards more environmentally friendly refrigerants while phasing out those that deplete the ozone layer.