Mankind is the upright ape, evolved perfectly for walking and running on land.
But we also have some evolutionary features that allow us to enjoy a dip in the ocean
- and as we’ve advanced as a species, we’ve invented complex technology to take us deep
into the oceans.
But take away all this and how far can we go without a big submersible to protect us?
What’s the lowest depth humans can survive?
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Deep sea diving has many dangers - and I don’t just mean sharks and harpoon-wielding Bond
villains.
The effects of water pressure are the biggest challenge to the human body.
Sitting on your boat at sea level, the air pressure is 1 ATMOSPHERE (1 BAR), to which
your body is comfortably adapted.
But just 33 FEET / 10 METERS underwater, the pressure is 2 ATMOSPHERES (2 BARS).
With only this one additional atmosphere (bar) of pressure, your lungs will collapse by half
- and the pressure increases by 1 ATMOSPHERE (1 BAR) for every additional 33 feet (10 meters)
you dive.
This increased pressure can lead to several problems in the human body, which is not well
adapted to underwater conditions, regardless of the gear you’re wearing.
You might suffer BAROTRAUMA, as the water pressure squeezes the air pockets inside you
and ruptures your eardrums or bursts the air sacs in your lungs.
If air bubbles get into your blood, you might suffer an EMBOLISM, causing a heart attack
or stroke.
Bad enough on land - even worse when you're a hundred feet underwater.
Alternatively, you might experience “the rapture of the deep” - or, less poetically,
NITROGEN NARCOSIS.
This happens because higher pressures allow your body to absorb more nitrogen, which makes
up 78% of the air we breathe.
If you breathe too much nitrogen, you’ll feel a little drunk.
At 328 FEET (100 METERS) deep, you could pass out.
At shallower depths, you might then do stupid things like try to breathe without your regulator
and drown, or rise to the surface too quickly, which can lead to DECOMPRESSION SICKNESS - also
known as THE BENDS.
Rising at the right rate allows your lungs to safely expel all that extra nitrogen your
body absorbs at higher pressure.
If you rise too fast, the gases will expand suddenly - like opening a fizzy drink.
These bubbles can cause joint pains, nerve damage, paralysis or, if the bubbles get in
your brain, death.
To mitigate these dangers...
...scuba divers must be properly trained and scuba tanks often contain a special mix of
compressed air that is up to 36% oxygen.
And just to be sure, the recommended safe limit for diving is no more than 130 FEET
(39 METERS) deep.
Scuba gear and careful diving can help you avoid these nasty conditions.
But what if you don’t have any gear?
How deep can you dive just by holding your breath?
Diving this way is called FREEDIVING, and humans can do pretty well without an oxygen
tank thanks to a perk of evolution called the MAMMALIAN DIVING REFLEX.
This is triggered by holding your breath and wetting receptors in your nostrils.
Basically, when you submerge your face in cold water, your body goes into ‘diving’
mode.
This reflex triggers several physiological changes.
The first, BRADYCARDIA, reduces the rate at which your body consumes oxygen by slowing
your heartbeat by 10 to 25%.
Some professional freedivers can slow their hearts to only 14 beats per minute.
That’s three times slower than a person in a coma!
The Mammalian Diving Reflex also lowers your blood pressure, which allows for PERIPHERAL
VASOCONSTRICTION - the constriction of blood vessels in your limbs.
This moves oxygenated blood towards important organs like the heart, the brain and in particular,
BLOOD SHIFTS to the lungs, to expand the vessels and balance out the pressure from the water.
Despite our Mammalian Diving Reflex superpower, freediving is one of the most dangerous sports
on Earth, with a long list of fatalities to back this up.
And No Limits Freediving is widely considered the most dangerous form of freediving.
This sees you strapped to a weighted diving sled attached to a rope, before you’re plummeted
to record-breaking depths within a couple of minutes.
In 1949 scientists claimed that it would be impossible to dive deeper than 100 to 130
feet (30 to 40 meters) without your lungs fatally collapsing.
During the 19th century, this is the depth pearl hunters would dive on a single breath
to gather oysters and mussels to extract pearls.
But in 2007 Herbert Nitsch smashed through this limit seven-fold by plunging all the
way down to over 700 FEET (214 METERS)!
This is deeper than some WWII U-boats could go before they collapsed.
The water would press down with a force of around 308 pounds per square inch, compressing
your lungs to the size of tennis balls.
In 2012, Herbert Nitsch improved his record to 831 FEET (253 METERS) but he suffered serious
decompression sickness afterwards.
He went through months of rehabilitation and several brain strokes before recovering.
Incredibly though, this may not be the limit.
Author and Journalist James Nester and bio-physician John Fitz-Clarke, believe that this is still
a way off the maximum depth.
Clarke’s laboratory simulations suggest that the ultimate limit is actually close
to 1,000 feet (984 FEET / 300 METERS) deep - that’s more than 3 American Football Fields
and the equivalent to climbing to the top of the Eiffel Tower, underwater.
Even if you throw your scuba gear back on it’ll be tough to beat this predicted 1,000
feet limit with the deepest ever recorded scuba dive coming in at 1,090 FEET (332 METERS)
by Ahmed Gabr in the Red Sea in 2014.
To help him reach this depth, he breathed a mixture of nitrogen, oxygen and helium,
to avoid the problems of nitrogen narcosis.
However, breathing helium at high pressures has its own risks, including HIGH-PRESSURE
NEUROLOGICAL SYNDROME, which can cause NAUSEA, SLEEPINESS and INVOLUNTARY MUSCLES JERKS.
Not wanting to lose control of his limbs, Ahmed returned to the surface when symptoms
of this syndrome started to show.
The dive itself lasted just 12 minutes, but the dangers of decompression meant it took
him 15 hours to safely reach the surface.
The sheer length of time it takes to decompress is a problem for commercial divers, who need
to spend hours working at great depths.
In order to get around this, they use a technique called SATURATION DIVING.
Often used by gas and oil industries, this is where the diver adjusts their body to deep
water pressures in a high pressure chamber,
and uses it - or a pressurised diving bell - to travel to and from the ocean floor.
With divers never actually leaving the pressurized environment they don’t need to spend days
decompressing each time they need to return to the surface.
They just return in the pod and continue living under the same pressure of the deep sea.
And with decompression from saturation diving taking more than a day per 100ft you’d otherwise
be looking at a lot of lost work hours.
As such, saturation divers will live in a pressure chamber for up to 28 days at a time.
That’s a long time to risk sickness from breathing nitrogen at high pressure - so saturation
divers breathe a mix of just oxygen and helium.
Not only does the helium help you pass the time with funny voices, but it also comes
in useful as it’s rather good at conducting heat- and that’s pretty important with the
cold depths of the ocean hitting an average temperature of 3.8 DEGREES CELSIUS (39 DEGREES
FAHRENHEIT).
But that’s not enough to prevent them suffering hypothermia, so saturation divers also usually
have warm water pumped into the outer layer of their suits via an umbilical connected
to the surface, keeping them nice and toasty at the bottom of the ocean.
Divers can then simply swim around at depths that would otherwise crush them into oblivion.
In fact, in 1988 the deepest dive ever recorded saw a team of French commercial divers spend
six days working at a depth over 1,700 feet / 534 meters - about 1.3 times the height
of the Empire State Building and deeper than the maximum diving depth of a blue whale!
The water pressure was so high that their lungs were almost at zero capacity and could
barely function.
So they breathed a special mixture mostly comprised of the lightest gas known to man
- hydrogen - and containing just 1% of that annoyingly heavy gas, oxygen.
Whilst this is the deepest actual open water dive ever recorded, Comex followed this up
in 1992 with an experiment in a hyperbaric research chamber, which proved humans can
survive even deeper still with one diver reaching a synthesised depth of 2,300 ft or 701 meters!
This record breaking experiment required 24 days of decompression and a further 2 and
a half months of monitoring!
If you’d like to know more about the limits of human survival then let us know in the
comments!
But in the meantime, would you like to learn about the critical development stage that
the teenage brain goes through and how it is key to the survival of the human species?
Then we’d highly recommend watching Surviving The Teenage Brain, a great documentary where
you’ll discover all this from a scientific and evolutionary point of view!
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