The Thai cave complex where 12 boys and their football coach became trapped is a snaking system of caverns and crevices which pose a range of problems for rescuers.
Some stretches of the Tham Luang cave are more than 10m (33ft) high, while others are a tight squeeze through water-filled passages.
The death on 6 July of an experienced former Thai navy diver, who was part of a team trying to supply the boys’ cave with oxygen tanks, emphasised the dangers of the mission.
The group of boys and their coach were exploring the caves when a sudden storm caused the passageways to flood, trapping them inside. They had spent nine days in the cave with little food or light when they were discovered on Monday 2 July.
Rescuers initially wanted to keep the group supplied underground until the end of the rainy season – which would have taken months.
But with heavy rains expected in the days and weeks to come, and water levels expected to rise, an operation is now under way to bring them out.
How will the boys escape?
Rescue divers with specialist breathing equipment reached the group through a series of water-filled passages.
The boys will have to be taken out the same way.
The Thai government has released a graphic showing how they plan to rescue the boys.
Two divers will accompany each boy, and will guide them through the dark using ropes.
In narrow sections, rescuers will have to take off their air tanks and squeeze the boys and the tanks through.
Each boy will be given a full face mask – thought to be easier to use for novice divers.
The diving option is considered extremely dangerous by some, but British dive experts say the priority is to get the boys out before the rains bring more flooding and debris into the cave system.
Martin Grass, Chairman of the Cave Diving Group, says the rescuers will probably instruct the boys not to hold their breath, to use their fins slowly and breathe gently.
Mr Grass notes that the boys will have two divers each chaperoning them, “to make sure they don’t panic”.
The boys will also be tethered to a diver so there is 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.
The pumping continues to try to reduce the flooding, and Chiang Rai provincial governor Narongsak Osottanakorn, who has been leading the operation, said that water levels inside were now at their lowest levels so far.
Divers have been taking hundreds of compressed air tanks into the cave, and have established a base camp inside a chamber.
Waiting and pumping
There has been a round-the-clock pumping operation to try to clear the caves.
But however much is pumped out, the water is being fed by sinkholes and streams in the hills above, and the risks from the imminent monsoon rains are high.
Mr Narongsak said the mission was “a race against the water”.
“Our biggest concern is the weather. We are calculating how much time we have if it rains, how many hours and days,” he told reporters.
Drilling down
The authorities have tried to drill holes in the cave walls to help drain some of the flood water – although the thick rock hampered efforts.
There were also suggestions that drilling could be another way to get to the boys and lift them out.
But to even begin the process, new roads would need to be built up above the caves to accommodate the heavy drilling equipment needed to break through the rock.
A detailed survey of the area would also be needed – otherwise there would be little chance of digging a hole in the right place to reach the boys and their coach.
What are the dangers down there?
The boys, aged between 11 and 17, and their 25-year-old coach have been huddled on a small rock ledge. The environment is wet, so they must keep warm and dry or risk hypothermia.
There are concerns about the level of oxygen in the air in the space where the boys are trapped. Officials said at one point that the level of oxygen in the air had fallen to 15%. The usual level is 21%.
Rescuers have transferred about 100 oxygen tanks to the cave to help improve the air supply.
Thai diver PO Saman had been helping transfer the tanks when he got into difficulties on the way back and did not have enough air himself. He died after losing consciousness in one of the passageways and his colleagues could not revive him.
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What help have they received?
Much-needed food and medical supplies, including fresh water and paracetamol, reached the boys and their coach on Tuesday. Rescuers transferred supplies to the boys to build up their nutrient levels.
Rear Admiral Apagorn Youkonggaew, head of the Thai navy’s special forces, told reporters they were given “easy-to-digest, high-energy food with vitamins and minerals, under the supervision of a doctor”.
Officials said most of the group were unhurt, although some were weak or had minor injuries.
How have they dealt with mental strain?
The boys may have had torches or lights on mobile phones, but they had potentially been sitting in the dark for hours.
So rescue teams have been taking lighting into the chamber, and keeping the group company.
Divers have also brought letters from the boy’s parents to help them handle the strain.
“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.”
Source: BBC news
