R454B Refrigerant:

This is the new refrigerant that carrier and a few others are going to to replace R410a. Phase out for R410a equipment is 2025.

R454B is an A2L refrigerant that is made up of 2 components; R32 and R1234yf. So pressure wise not really all that different R410a. This refrigerant is a super low temperature glide refrigerant so we don't have to worry about fractionation. Though you should charge a a liquid like R410a, since it is a blend.

This refrigerant is considered an A2L refrigerant (has some flammability). This is scary for some but it's not bad. First of all to even be able to have ignition you have to have a pretty high concentration, the good news is that the refrigerant disperses in the air rather quickly. Plus it cannot stay on fire by itself, it needs a constant ignition source. So based just on those two things you will have to work at getting this stuff lit. Let's not forget that R410a is also flammable.... Burn velocity for this refrigerant is 10 cm per second... So it's a slow spread and only about 8.5 BTUs per pound of refrigerant, so again, not a lot of heat energy at all. 

Tips:
Use common sense.... Don't try to arc capacitors or do anything like that with wiring around this refrigerant. 
Standard gauges can be used. The tanks will come with left handed thread port. You just need an adapter and you are good to go. I would suggest a sperate set for this refrigerant or just make sure you are cleaning out your gauges after every use. 

Equipment will be coming with mitigation boards and sensors, this will allow the units to shut off heat or cool call and run the fan till dilution is down under 20% concentration then unit will resume operation if after minutes the sensor is clear the unit restarts. Sensors, at least on the Carrier/ICP side, will be designed for full life expectancy of the equipment. 
So don't overthink it, it's not  really a big deal.