The boys could also be tethered to a diver so there was no risk of them getting lost in the fast flowing, murky water.
"It could be a bonus that the boys are young. When you're young, you feel invincible and they'd see it as a bit of an adventure," he said.
The boys could spend 10 to 15 minutes under water at a time, depending how much of the passageways are flooded. But the journey back to the entrance, which also involved walking and scrambling through narrow spaces, could take a while.
It has taken rescuers 11 hours to complete a round trip of to the group and back - six hours there and five back.
How risky is the Thai boys rescue?
"They're mentally stable which is actually pretty good," Ben Reymenants, a Belgian diver helping with the rescue operation, told AFP news agency.
"Luckily the coach had the sanity of mind to keep them all together, huddled together to conserve their energy, that basically saved them."