Why is everybody squeaking?

How SeaLab's legacy inspired my sci-fi underwater adventure

As soon as I knew I wanted to write a novel set at a futuristic underwater resort, I started rummaging around the internet, looking for what we’ve learned so far about living at 200 meters deep here on Earth.

Which is how I found myself watching old US Navy films about SeaLab—and listening to an “aquanaut” sing “Good Night, Irene,” in a chirpy Donald Duck vibrato. What the heck? [see video clip]

Turns out, the air mixture that deep-sea divers and the people who stayed in SeaLab breathe carries a lot of helium. This mixture turns their voices chirpy for the same reason inhaling the gas from a helium balloon does.

Helium is much less dense than either oxygen or nitrogen, which make up most of the air we breathe topside. When a person inhales an air mixture containing a high percentage of helium, the vibrations of that air passing through their vocal cords as they talk change because sound travels 3 times faster through helium than it does through nitrogen. So we squeak!

Why breathe this mix? When you dive really deep, the atmospheric pressure pushes harder on your chest, making it difficult to breathe regular air because it's too dense. Even at only 60 meters down, where SeaLab 1 sat, the pressure was 6 times that at sea level.

Adding helium to the mix makes the air less dense and easier on your heart and lungs. Plus it’s a smaller molecule (smaller bubbles), so it can pass through body tissue and blood faster and easier than other gases, which helps to lower the risk of getting the bends (decompression sickness) when it’s time to go back up-top.

Reducing the usual balance of nitrogen and oxygen by adding helium to the mix also can reduce the chances a diver could develop nitrogen narcosis or oxygen toxicity (hyperoxia), both of which can be dangerous or even fatal. “Trimix” helps prevent these risks by adjusting the gas mixture to suit each high-pressure environment.

The SeaLab projects, started by the Navy in the 1960s, were missions to prove that people—well, men—well, white men—could actually live and work underwater for extended periods. Turned out they could, which opened up a world of possibilities for undersea exploration.

The aquanauts/guinea pigs who stayed in these mobile-home-sized submersibles faced many challenges: dealing with the effects on the body of prolonged exposure to high pressure, and the effects on the mind of isolation (or crowding, in SeaLab’s case) in an alien environment.

Manipulating the air mix was one of the key ideas that made SeaLab possible at that time. The SeaLabbers called their first mix “heliox” because it was 96% helium, 4% oxygen. But very soon during the first experiment, SeaLab 1, they altered the mix to 76% helium, 20% nitrogen, 4% oxygen. We still call the mixes today trimix.

The mix we breathe on land is roughly 78% nitrogen, 21% oxygen, .9% argon, .04% carbon dioxide, and traces of other gases. The 78-21 proportion is pretty stable around the world; the trace elements vary by location, altitude, and local weather.

Because Navy, the SeaLab engineers also developed an early form of voice modulation that somewhat alleviated the quack. [see clip]

In my new novel, Frankie Takes a Dive, I take the SeaLab concept to the next level by imagining a futuristic resort located 200 meters beneath the surface of an alien ocean. To survive in this high-pressure environment, the staff and guests must breathe a special air mixture of helium, nitrogen, and oxygen. So they squeak!

My story is a mystery-adventure, with the emphasis on adventure. Adding this goofy detail helps keep the tone lighter—it’s certainly not a noir detail. Plus, it keeps pretty true to the science, which I always try to do.

I also included references to recent developments in materials science, such as the creation of ultra-strong, lightweight alloys and super-strong transparent materials for the resort’s domes. Biotech breakthroughs such as genetic engineering and synthetic biology also help some of the underwater staff handle the pressure.

Of course I’m guesstimating—and also leaving stuff out that doesn’t fit the needs of the story. For example, one of the characters gets a little pressure-sick at the start, but feels better almost immediately. It usually takes longer than that. And even though it is a common effect of living under high-pressure, no one in my story has lost bone density or muscle mass—there are a couple of real bruisers on staff!

One detail I wish I could have included was a dolphin who delivered supplies, the way Tuffy the dolphin did during the SeaLab II mission. My dolphin-standins have a different role to play.

As you dive into the pages of my book, I invite you to embrace the sense of wonder and possibility at the heart of both scientific discovery and speculative fiction.

What will we discover next?