Diving to -30m (-100ft) below the water surface

Exploring the ocean has been one of the most satisfying things I’ve ever done. Imagine a world out there, with a rich ocean life, and a whole new experience waiting for you. That’s why I decided to continue my learning and go deeper in this journey.

As part of my ongoing learning, I had to do an advanced course, where you should descend to -30m below the surface (in addition to a few other things). 30 meters might sound like a normal number, but it makes sense to think of it from a pressure perspective.

Every time you go -10m below the surface, you are experiencing an extra 1 bar of pressure. As the atmospheric pressure (that’s the pressure of air) is approximately 1 bar, you’re experiencing 4 bars at 30m. That’s 4 times the pressure you’re feeling at the surface.

But still, numbers can’t do justice to this. So my instructor decided to use real-world examples to show me the immense pressure:

The empty water bottle

Before going down, we left with a small plastic bottle filled with air and tightened to our diving material with a small rope.

As you might have guessed, as you go deep, and as the extra pressure gets applied to the bottle, it will get crushed slowly.

At 30 meters deep, the bottle is completely crushed. The air inside stood no chance of counterbalancing the pressure. It was destructive, but that’s normal.

What about the next one?

The colors slate

As you know, we perceive colors by the reflection of light.

When you go as deep as 30 meters, there isn’t enough sun (and thus light) reaching that deep. So colors start to look… different.

When we were at 30 meters, my instructor gave me a color slate to note which color I saw. I noted grey/black because that’s what I was seeing. Once the instructor put some light on it (using a torch), it turned out to be red.

Red is the first color to experience this fading with deep. It starts to fade around 6m deep, followed by Orange at 15m and Yellow at 30m. The longer the wavelength for a color, the quicker it will disappear. Red having the longest wavelength, disappears first. Blue, having the shorter wavelength, disappears last (technically).

So, what does this mean in nature? If a fish is red and lives in the deep ocean, it’s technically invisible. And that’s why most of the deep ocean creatures are red(ish). It helps with the camouflage.

This was also seen in another dive. Just before doing my last dive of the day, I hurt myself in the boat and created a small wound on my finger. Not a serious one to abort the dive, so we went ahead.

Around the 15-meter mark, the instructor waved and asked to check my wound. I was bleeding green blood!

For an instant, I freaked out. How the hell am I bleeding green blood? But as I remembered what I learned before, I finally understood what was happening. The red color isn’t red anymore!

The chicken egg

This was a funny one. My instructor dived with a chicken egg. I saw it that morning, but I never understood why. Maybe to feed some fish? Probably not, but you never know!

It turns out it was for an underwater experiment.

After reaching the 30m mark, the instructor took the chicken egg and a tool we call a noise maker. It’s like a steel bar used underwater to get the attention of other divers.

Using the noise maker, he cracked the egg open. Can you guess what happened?

With the immense pressure applied from all directions, once you crack the egg, it just floats around. It stays in the same spherical shape, moving around you like a moon.

You can try pushing it around and even playing ping pong with it (that’s what we did). It will gladly accept your curiosity and stays in the same shape. You can see that in action in this video.

What a weird world and what a powerful thing to experience firsthand.

Written from a coffee shop in El Nido, Palawan. Sat, Nov 18, 2023.


Hey, I’m Ahmed, I write about productivity, business, and achieving financial independence. Get my future posts directly in your email:


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