There is an undeniable allure to the deep. When you are hovering at 60 feet and you look down over the edge of a coral wall into the dark, indigo abyss, human curiosity kicks in. You want to know what’s down there.

For many divers, 100 feet (30 meters) is the ultimate goal. It is the gateway to exploring intact shipwrecks, massive sponge formations, and cruising alongside sharks and manta rays. But the deep ocean is an unforgiving environment. You can’t just kick downward and expect the dive to feel the same as a shallow reef tour.

At 100 feet, you are under four atmospheres of pressure (four times the pressure you feel on the surface). That invisible weight fundamentally alters how your gear functions, how your lungs work, and even how your brain processes information. Here is the breakdown of what is actually happening to you in the deep.

The Air Guzzler: Your Lungs at Depth

If you take nothing else away from this, remember this rule of physics: as pressure increases, gas compresses.

When you take a breath from your regulator at 100 feet, the air is four times denser than it is on the surface. That means with every single breath you take, you are consuming four times as much air from your tank as you would be on the dive deck.

This is why deep dives are notoriously short. Even if you have the lungs of a marathon runner, you will watch your air pressure gauge drop surprisingly fast. Deep diving requires meticulous gas management and a constant awareness of your “turn pressure”—the exact moment you need to start heading up.

The Shrinking Wetsuit: Buoyancy and Cold

Just like the air in your tank compresses, so do the tiny gas bubbles trapped inside your neoprene wetsuit.

By the time you hit 100 feet, a thick 7mm wetsuit is crushed down to the thickness of a windbreaker. This causes two immediate problems:

• You lose your insulation: Deep water is already colder because sunlight can’t penetrate it. Combine that with a compressed wetsuit, and you can get chilled to the bone very quickly.
• You become heavy: Because your wetsuit shrinks, you displace less water, making you significantly negatively buoyant. If you aren’t actively adding short bursts of air to your BCD on The “Martini Effect”: Nitrogen Narcosis

This is the most fascinating—and potentially dangerous—aspect of deep diving. As you breathe compressed air at depth, the high partial pressure of nitrogen begins to act as an anesthetic on your central nervous system.

We call it Nitrogen Narcosis. The old scuba wives’ tale says that every 50 feet of depth feels like drinking one dry martini on an empty stomach.

How does it feel? It’s different for everyone. Some divers feel incredibly euphoric and relaxed. Others feel a sudden wave of dark anxiety or paranoia. Most commonly, it manifests as a slowing of your reaction time and poor decision-making. You might stare at your dive computer and suddenly forget what the numbers mean, or you might find something incredibly funny that isn’t a joke at all.

The good news? Narcosis is completely temporary and leaves no hangover. If you or your buddy start acting strange, all you have to do is ascend a few feet. The pressure drops, the nitrogen leaves your nervous system, and your head instantly clears.

Unlocking the Deep Safely

Reading about the physics of deep diving is one thing; experiencing it safely is another. You should never attempt to dive past 60 feet without an instructor to guide you through your first encounters with narcosis and rapid air consumption.

The SSI Deep Diving Specialty is designed specifically to take the anxiety out of the abyss. We teach you how to properly plan your gas, how to manage your decompression limits, and how to safely execute a simulated emergency at depth.

Ready to see what is hiding down below? Drop by 72 Aquatics or check out our calendar to sign up for the Deep Diving course. Let’s expand your limits and unlock the other half of the ocean!