### Theory:

Pressure in liquids and gases

Important!
The pressure in a liquid or gas depends on the density and depth of the liquid or gas or the height of the gas column.
$\phantom{\rule{0.147em}{0ex}}p=\mathrm{\rho }\mathit{gh},\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}\phantom{\rule{0.147em}{0ex}}\mathit{where}\phantom{\rule{0.147em}{0ex}}g=9,81m/{s}^{2}$ - acceleration of free fall.
Water in the seas and oceans puts a lot of pressure. At a depth of ten meters, the water pressure is approximately 100 kPa, and at a depth of one kilometer, 10,000 kPa, which corresponds to a mass of 100 kg applied per square centimetre.

The permissible water pressure on the human body is 300 kPa.

Example:
To what depth can a person dive without accessories?
 $\begin{array}{l}p=300\phantom{\rule{0.147em}{0ex}}000\mathit{Pa}\\ {\mathrm{\rho }}_{\begin{array}{l}ū\\ \end{array}}=1000\mathit{kg}/{m}^{3}\\ g\approx 10m/{s}^{2}\end{array}$_______________h-? $\begin{array}{l}\phantom{\rule{0.147em}{0ex}}p=\mathrm{\rho }\mathit{gh}\\ \\ h=\frac{p}{\mathrm{\rho }g}\end{array}$ $h=\frac{p}{\mathrm{\rho }g}=\frac{300\phantom{\rule{0.147em}{0ex}}000}{1000\cdot 10}=30\phantom{\rule{0.147em}{0ex}}\left(m\right)$
Answer: A person without equipment can dive to a depth of 30 meters.

Some interesting facts:

If a person has dived to a depth of 100 m, without proper suits, to survive he must spend some time in a decompression chamber.

Deep-sea fish, accustomed to enormous pressure, lifted out of the water, explode. To view them, they must be placed in special cameras.

Deep-sea fish

Reference:
Fizika 9. klasei/Ilgonis Vilks. - Rīga: ZvaigzneABC, 2008.-192lpp.:il.-izmantotā literatūra: 47. lpp.
Fizika 8. klasei/Gundaris Gailītis, Vija Rasmane - Rīga: ZvaigzneABC, 1997.-192lpp.:il.-izmantotā literatūra: 138. lpp.
http://www.silverspringscommunity.com/utilities/water/underdrain-system/
http://lv.wikipedia.org/wiki/Panamas_kan%C4%81ls
https://commons.wikimedia.org/w/index.php?search=scuba+divign&title=Special%3ASearch&go=Go&ns0=1&ns6=1&ns12=1&ns14=1&ns100=1&ns106=1#/media/File:Discover_Scuba_Diving_--_St._Croix,_US_Virgin_Islands.jpg