Airbells, which are small air pockets in an otherwise flooded section are relatively unusual, and from the video footage it looked like the football team had climbed up into a larger Fossil gallery overlying the current (active) flooded section. Hopefully this means they will also be well protected from any future more extreme flooding.
These little stream inlets form a source of drinking water. Even when the main cave river is a turbid mess, there's normally plenty of clean little streams coming in - some of which will be fed by percolation water (seeping through rock) and therefore effectively 'mineral' water.
Often when journalists describe caves in the press, 'one kilometer underground' would be better described as 'one kilometer into' the cave. Certainly the cave doesn't look very deep, most river caves form fairly horizontally.
For digging into or exploring from above, what matters much more is how thick the rock is above them (or above a chamber that they can reach), and what it's made out of.
Locating them on the surface (i.e. figuring out where to start digging) will also be a challenge - most caves are not surveyed with a high degree of accuracy, and doing so through a flooded, flowing, low-visibility section is extremely difficult. (One of the rescue divers, John Volanthen, has done some pretty amazing stuff with a water-proof data-logging accelerometer + flux compass in this area - the "Lazy Boy Sump Mapper".) They will probably dive a radio beacon into the cave + then use that to locate the party, combined with a (dry) survey within the cave to figure out the extent of the available space to the survivors.
Radio comms should be setup quite soon - one system which may be of general interest to the Hackernews community is the cave-link: http://www.cavelink.com/cl3x_neu/index.php/en/ It has a lot of automation + resending / checksumming of messages to enable transmission over the very low bandwidth and noisy VLF channel through hundreds of metres of rock.
Most cave systems are relatively permeable. Even if you can't see a route out, there are likely to be paths for air movement.
The immediate threat is the accumulation of carbon dioxide rather than a deficit of oxygen. Fresh air is about 0.04% CO2, but most caves have ambient CO2 levels of over 1% and some as high as 6%. You'll start feeling quite unwell above 4%, violently ill above 7% and there's a risk of seizures, unconsciousness and death above 10%. Normal air is about 21% oxygen, you can cope perfectly well on about 16% oxygen and survive on as little as 10% oxygen.
The boys seem alert and in reasonably good spirits, so I'd say that the air in their section of the cave is fairly good.
The ESA, of all groups, has a pretty good write-up on this: http://blogs.esa.int/caves/2014/11/19/the-science-of-caves-e... They use cave exploration for astronaut team-building, process/workflow training, and acculturation.
http://www.slate.com/articles/health_and_science/science/201...
Me: Just drop me a gun...I'm claustrophobic and I'd rather die once.
Was there a worldwide competition for the worst place to put these kids, or what?
Also, one detail that CNN got that I didn't see in this article: it seems the cave is one kilometer underground! [1]
EDIT 1: The CNN article partially answers my first question: "Rescuers will also pump air into the cave to improve conditions."
EDIT 2: Another important bit here [2]: "It won't be anything like diving that most people recognize. It will be diving in what is effectively muddy water, possibly fast flowing, with no sense of direction," Moret said. "You can't tell what's up, down, sideways."
[1] https://www.cnn.com/2018/07/02/asia/thai-cave-rescue-intl/in...
[2] https://www.cnn.com/2018/07/03/asia/thai-rescue-next-phase-i...