What is the meaning of the phrase "transitional substance" in HCFC 123 chemicals?

Question

HCFC 123 substance has an Ozone Depleting Potential but being phased out under the Montreal Protocol.

Answer 1

HCFC 123 was used to replace CFC 11. Using a HCFC refrigerant to replace a CFC refrigerant is a definite improvement but all CFC and HCFC refrigerants have got to go. So, HCFC 123 is an interim replacement for CFC 11, It is not the "fix" but is a step in the transition from all CFC anc HCFC to refrigerants containing no chlorine. That's my take on it. My take and a dollar bill will get you a cup of coffee! Maybe.

Answer 2

It is something which damages the ozone less than classic CFCs, but more than potential future substitutes.  It has the virtue that it can often be directly substituted for the classic CFCs in older devices.

So it can help transition away from really bad substances used before to much better ones to be used in improved devices in the future.