Robert Laird: The one thing that kills divers more than anything else is panic. It can start with a small thing, like suddenly you see bubbles coming off a hose. That seems so trivial and minor but that can immediately put doubt in a mind because you’re in a cave. There’s no escape. There’s no quick way up. It tends to cascade.

When you’re panicked, there’s absolutely no logic. There’s no reasoning. There’s no logical method of thinking. I’ve seen panicked people underwater, and they do not behave normally. You can even point the way out to them and they look at you like you’re crazy, and they’ve convinced themselves another way is the correct way. They may swim into the cave, rather out of the cave to safety.

Zhang: What do you have to do differently when diving in a cave?

Laird: I would say the most important thing is being able to maintain absolute neutral buoyancy, so you don’t drift up into the cave ceiling and you don’t drift down into a very, very silty bottom. If you hit the silt, you can end up in a “silt out,” which means that silt fills the room that you’re in. You put your head underwater and you look and you can’t see anything. You can put your light against your mask and you can see your light, and that’s about it.

Typically in a large cave with known visibility that’s fairly good, the chances of a complete silt out that you can’t wait out are fairly small. The area that’s really bad is sump diving, which is where you have a dry cave that has tunnels that sometimes go underwater and sometimes come up and through air again.

Zhang: Like the cave in Thailand?

Laird: Which is much like the Thailand case. Those sumps are typically very, very silty. You have to have some specialized experience to traverse these silts successfully—with the idea you’re not going to be able to see, you’re not going to be able to communicate.

Zhang: What mistakes can experienced open-water divers make when they start diving in caves?

Laird: Experienced open-water divers, unfortunately, think that they are qualified to dive into caves, but they’re not. There have been lots of extremely experienced open-water divers that have died in caves. The main one is the rule of thirds, which is reserving the amount of air that you have left, so that you always have two-thirds of your tank available at your furthest penetration. There are lots of examples of open-water divers that dive into a cave and they dive into the halfway point of their air. Cave divers look at the situation and go, “They’re already dead and they don’t know because they’re probably not going to make it out.”

That’s because you may not be able to go out with exactly the same amount of air you went in with. All you need is 30 seconds of no air and you essentially can’t go up to the surface. Chances are you’re not going to make it.

Zhang: Have you ever had a close call?