Getting trapped people out of a flooded cave can be one of the easiest — or one of the most challenging — types of cave rescue. It is one that an international team is facing with the discovery of a group of 12 boys and their soccer coach — missing for nine days — alive, and basically well, in a cave in Thailand. They had gone into the cave after soccer practice and rising flood waters prevented them from leaving.

How to get them out?

I’ve been an active caver and cave rescuer for more than 30 years, having studied both extensively. I chair the board of regional coordinators (there are 10 regions in the United States) of the National Cave Rescue Commission, which has been developing and teaching cave rescue techniques since 1978.

This rescue in Thailand is one of the toughest I’ve seen.

But there are some essential guideposts in even a rescue of this colossal difficulty.

To begin, the basic tenet of cave flooding rescue is this: WAIT. Either the people are alive and safe somewhere inside, in which case taking risks only serves to place rescuers in danger, or they have already perished, in which case there is zero reason to place rescuers in danger.

A few things to understand about caves: Most are formed by water, and are dissolved out of (usually) limestone rock over millennia. There are a few exceptions, such as ice and lava tube caves, but even in these, water can run through them.

Not all caves continue to flood, but some still serve as natural “storm drains.” In most caves in the United States, and many places around the world, a cave that has some water in it can flood further. This is usually in response to rain, and the water will drain fairly quickly. Only a few caving areas, such as in southeast Asia area, have continuous, monsoon-style rains that can cause a cave to remain flooded for several months.

Among organized cavers, caves that can easily flood, or stay flooded for long periods of time, are avoided if rain is a possibility. Often the general public is not allowed in such caves, but as with this cave, there are exceptions.

Usually when rain traps people in a cave, once the rain event subsides, a few hours to a few days later, the water lowers and rescuers can go in, or the trapped people come out on their own.

Meanwhile, on the surface, there are a few things that can be done to determine whether there is anyone trapped inside and how they might be faring.

Rescuers can monitor the water for depth and temperature, for debris, or for evidence of the trapped people. And the same with weather, which is predictable now to a high degree of accuracy. Efforts can be made to lower water levels through diversion or removing obstructions, or by pumping. Responders can search for other entrances, or can attempt to make new ones. In a few situations, cave divers may be used to make contact or ferry supplies. Mostly, though, it’s a waiting game.

And this is very hard for rescuers who are used to doing, not waiting. There can be enormous pressure from family, from officials, and from the media to take action. This pressure can cause rescuers to take ill-considered risks. In most flooding situations, though, the water subsides soon and the question is answered: are they alive or are they not?

In the Thailand case, though, the waiting may well not be enough. The soccer team was found alive 1.2 miles into the Tham Luang Nang Non cave, and the water may not go down for months. Nine days had passed before the first contact was made, something that is highly unusual in cave flooding situations. Also unusual is the cave temperature, in the mid-70s — higher than most caves in the world, as caves tend to be the average temperature of the area they are in.

In much of the United States and Europe, cave temperatures are between the mid 30s and mid 60s. This means hypothermia: something that would likely have killed people who were unprepared and who were trapped for that length of time. From that standpoint, the trapped Thais are very fortunate.

What is not fortunate is nine days with no food. In a twist of irony, the soccer players and their coach have plenty of water, though if the water had made them sick before Navy Seal rescuers (including a doctor and a nurse) reached them, as they now have, it could have hastened their deaths.

With water, humans can survive for 3-4 weeks without food. After nine days, though, they are weak. Their gastrointestinal system begins to shut down. Their metabolic processes have changed. A full meal right now could kill them. Rescuers are reportedly reintroducing food gradually and carefully. It could take weeks to rebuild the boys’ strength; right now they can barely stand, let alone do the rigorous activity likely required to get out.

As to that, there are three primary options.

The most dangerous is trying to teach them enough diving skills to dive them out. It’s physically strenuous: in water, through blackout conditions, through tight squeezes for hundreds of meters. It’s something that skilled cave divers spend hundreds of hours training for after they have already been open water divers for quite some time. A moment of panic or loss of the breathing regulator can be fatal for the novice diver, and may also put the cave diver escorting him in danger.

Drill an entrance? This requires heavy equipment that has to be brought to the site where a full-sized road has been made, and requires highly detailed mapping or specialized radiolocation from inside the cave. Even then, it’s like hitting that needle in the haystack. Find a new entrance to the cave? They have been looking for 10 days now, and the odds go down with each passing day.

Wait for the water to go down? It’s monsoon season. Even with pumping, it could be weeks — even if the weather cooperates. Longer if it does not.

Finding this group at all certainly gives hope. And if where they are in the cave is safe from further flooding and the divers can supply them with food and care, they can live in the cave as long as necessary. If they cannot be safe from further flooding, then the only option may be the first and riskiest: diving them out.

Meanwhile, the world watches and judges. The rescuers are in a tough spot. Unless all people are safely out eventually, the rescuers will be blamed by the “you should haves” and by the self-doubt of “what if we’d only…”