One way you can get out of a one-piece harness is to use a loop with a safety buckle. This will simply not slip nor break, nor accidentally open, thus fits the "one piece only" DIR mantra.
When open, it releases 9" more strap lenght so you can get your arm out of the harness. It's easy to put back together in the water and you use a snoopy loop to keep the harness flat. Installed on the LHS, it gives you that additional slack to get it over your shoulder dump.
Used this for a while when diving off a RIB. Back on the surface you can easily get out of your harness without half drowning (unless you're just amazing and have such contortional abilities, you can flick a one-piece harness off in 3 seconds flat -- if you're that person, look away now, nothing for you to see here).
Also have this installed on my rebreather harness as it makes getting out of it on the boat much easier.
The two tri-glides, top and bottom, mean the loop doesn't slip. Knitting it is straightforward enough the second time. It just works.
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