The Physics of Breathing Underwater
On a daily basis, most of us don't really pay attention to our breathing as we go about a number of routine tasks. However, it is a very different story when we are submerged in water. Suddenly we are all too aware of how difficult it is to breathe. Like other land mammals, humans cannot breathe underwater. When we swim, we need to hold our breath. On the other hand, fish and sea mammals have specially adapted systems that do allow them to breathe underwater or stay submerged for a long time without breathing. In the case of fish, they do need oxygen to survive, but cannot inhale the way we do. Instead, they rely on dissolved oxygen that exists in the water. Water flows in through the mouth and over the gills. The gills absorb any available oxygen from the water and filter the rest out. Those who keep pet fish may observe that they often tend to open and close their mouths as they swim to aid in the respiratory process. Larger fish that require higher oxygen levels may leave their mouths open for a longer time to allow more water to enter. Many marine mammals, like whales, seals, and dolphins need to surface for air. Even so, they respiratory systems are adapted in a way that allows them to retain oxygen for a long time, enabling them to dive deep without ill effects.
In the earliest days of undersea exploration for humans, they had to simply hold their breath and resist from diving too deep. Prototypes of the modern day snorkel allowed divers to keep their faces submerged near the surface, while observing underwater. The next significant advance was diving bells. It was a bell-shaped chamber that was lowered into the water with the open side facing down. The diver could then go in and out of the chamber for a breath of air as they required. While this system was certainly an improvement over any existing methods, the real mark of progress was the invention of the scuba system. Scuba divers are equipped with a large metal tank that typically contains a diluted mixture of helium and oxygen. A hose running from the tank to the breathing apparatus, known as the regulator, allows oxygen to pass into the diver's mouth. This system is now in common use among professional and leisure divers, since it allows them a high degree of flexibility. Of course, there are still risks associated with humans breathing underwater. As we move deeper below, water pressure increases and compresses the lungs. This means that the air inside the lungs is also compressed. When the diver beings to ascend, they must do so very slowly to give their lungs time to expand gradually and naturally. Ascending too fast would cause the air inside the body to expand faster than the lungs can. This could lead to traumatic internal injury or even death. While the ability to breathe underwater is exciting and convenient, we must also take necessary precautions to stay safe.
How Sea Creatures Breathe Underwater
How Humans Breathe Underwater