The rescue workers use head torches to slowly progress through rocky, dimly-lit passages - but they can only get so far before full diving equipment is required.
The way out is a hard dive with many narrow passages through muddy water.
"Definitely you can feel it that it has an effect, but we're moving on".
The navy is teaching the boys the basics of diving, with a view to guiding them out through flood waters.
Volunteer diver Mikko Paasi said that the mood at the camp had changed since the rescue team learned of Kunan's death.
British caver Vernon Unsworth (C) gets out of a pick up truck near the Tham Luang cave complex, where 12 boys and their soccer coach are trapped, in the northern province of Chiang Rai, Thailand, July 5, 2018. Chiang Rai's deputy governor said authorities prefer the diving option. If the risk is minimal, we will try.
Twelve players of the Wild Boars soccer club-between the ages of 11 and 16-and their 25-year-old coach have been trapped in Tham Luang cave in Thailand's northern Chiang Rai province since June 23.
They became trapped after rain flooded the Tham Luang caves near Mae Sai and were not found for more than a week. The boys, although skinny, have been described as in good health.
Nick Vollmar, a German paramedic and firefighter said a Thai rescue organization reached out to him for help and he traveled from Europe with a Finnish cave diver to join the team.
"We are racing against the rain", the coordinator of the rescue operation said Thursday.
The governor has said the 13 may not be extracted at the same time, depending on their condition.
Mr Narongsak said the boys were still healthy and have practised wearing diving masks and breathing in preparation for the diving possibility.
It has been suggested that they may need to learn how to scuba dive in order to escape, but none of the children can swim and cave diving is a notoriously unsafe sport, as emphasised by the death of one of their rescuers, Saman Gunan, a former navy diver, in the caves on Friday.
The water is also muggy which means the visibility in the area is very low.
The boys are also being taught swimming and basic scuba inside the cave.
The navy has released videos of the boys, showing them smiling and interacting with the personnel sent into the cave to bring supplies, treat their injuries and keep them company.
Thai SEALs have praised Kunan for volunteering to help the rescue efforts and said they will continue and "won't let our colleagues die for nothing".
But Osottanakorn said divers are delivering air tanks to the chamber where the team is stuck and opening them up.
Letters that family members have written, have been delivered to the boys.
"We are trained to expect risks at anytime", Arpakorn said.
The suggestion that the trapped team might have to wait months inside until a safe way out is available - as was the case in 2010 with Chilean miners trapped underground - has met with little enthusiasm.
The military has been pumping water out of the cave but if they can not hold the water level down, they will be left with two stark options - teaching the boys to use diving equipment, or waiting months until the rainy season ends.
Asked how the boys could make it out safely if an experienced diver could not, Apakorn said they would take more precautions with the children.