Understanding Nitrogen Absorption in Scuba Diving : Sponge Analogy
You sure know those fancy sponge that is green on one side and yellow on the other. This analogy may sound silly, but sponges absorb water similar to the way Scuba divers absorb nitrogen. The sponge comparison will help you understand the fundamentals of nitrogen absorption while diving.
The sponge has two different layers that absorb water at different rates. For example, the loosely-woven rough side becomes saturated with water more quickly than the yellow, dense side if the sponge. When drying, the reverse is true. The green side dries quickly, while the yellow puffy part takes a bit longer to dry. Just has the layers of the sponge absorb and release water at different speeds, various part of the diver’s body absorbs and releases nitrogen at separate rates. Simply put, while some areas of a diver’s body can “dry” nitrogen immediately, other parts remain “wet” with soaked up nitrogen for hours or even days.
How does this occur? When a sponge is submerged in water in slow, steady motion. Water penetrates the sponge to the point that it can’t hold a drop anymore. At this point, the sponge is thoroughly soaked with water. During a dive, a diver’s body takes in nitrogen and has the diver descends, the nitrogen in the body and that in the tank air is compressed by the increasing water pressure. As a result, the increasing water pressure forces the nitrogen molecules to close together to the point that they occupy less space. The diver’s body fills the space by absorbing more nitrogen, and this continues until it can hold no more, just like the sponge absorbing water till it’s saturated.
The result? The nitrogen will form bubbles in the diver’s blood and tissues. These bubbles may move through his arteries and stop blood flow from various parts of the body or remain in his tissues and cause damages.
Prevention of decompression sickness.
If a sponge has absorbed too much water, it may be impossible to remove it from the water slowly enough to avoid drips. In this situation, the sponge must be squeezed while it is still underwater. Squeezing the sponge can force enough water out that the sponge will not drip on the surface.
Similarly, to avoid the damaging effect of excess nitrogen, a diver must allow his body added time to eliminate the high quantity of nitrogen in his system by making a safety stop or decompression stop i.e. a pause during the ascent at a certain depth for a specific amount of time. In skilled diving, some divers breathe gas mixtures with a higher than normal ratio of oxygen to nitrogen. This process helps the body to eliminate nitrogen more quickly than normal and shortens the length of required decompression stops. This is similar to squeezing the sponge