But i'm curious, at a site like hin daeng/muang, if you are guiding 4 people, and one person goes out of air 20/30mins in, what would you do?
First of all I think that the briefing for certified divers before
any dive should include a variety of options for them to choose from. Diving with a buddy, diving with more than one buddy, following the DM (guide) for the whole dive, following the DM (guide) for part of the dive and solo diving should
all be possibilities to choose from for the divers.
Simply putting a bunch of divers in a group and telling them they
must follow the DM (guide) throughout the dive,
must end their dive when the first person runs low on air and
must dive with a buddy is imo just not right.
If I were guiding some divers and someone would get
out of air (not: low on air), I would put that diver on my alternate airsource, slowly ascent, make a prolonged safety stop (air permitting) and surface with the diver.
Other divers from my group could either stay down and continue with their dive or (if they felt uncomfortable with not being with the DM) ascent with me.
If someone in my group would run
low on air (not: out of air) I would let that person ascent to safety stop depths on his/her own (or with his/her buddy if he/she had one and if they preferred that) and continue guiding the other divers from my group.
This may all sound a bit radical to you but personally I believe in giving
all divers on the boat a
choice that fits to each and every diver's experience and comfort level while diving.