I have never dived with a closed circuit, I understand the
principle fully, just never done it but I read a transcript
from the Apollo 13 moon mission (from launch to splash
down in real time, 5 days in total of transmitted talk) and
obviously the part where they had to convert the lunar
landers C02 cartridge to accept the Command modules
Cartridge was very interesting.
Anyway I digress, in the comments from space ship to Earth
the changing of the cartridge is mentioned quite a lot and
the cartridge only needed changing about every 12 hours.
So if the Command modules cartridge could clean the atmosphere
for 3 men for 12 hours why can't a similar smaller version be used
for 1 diver for 12 hours?