Belzelbub
Contributor
I did a checkout dive for working at an aquarium last year. The gear used in the aquarium is setup with primary donate, though in reality, an actual air sharing would be unlikely. Depths are relatively shallow, and each diver also carries a Spare Air.Since Covid do they actually really share air during OW cert? When I did mine the training BCD had an air2 so not much different but that was a long time ago.
Nevertheless, the checkout dive covered both air sharing and using the spare. The air sharing was simulated. Primary was offered, donor switched to secondary, OOA diver acted like they would breathe off the donated reg, but in reality, just removed their primary, then replaced primary, purged and breathed off their own during ascent.