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? But before we really dive into this, we’d
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or click on the link in the description and snap yourself up some free entertainment! 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! Watch this and tons of other brain boggling
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