Learning Depth and Pressure When Scuba Diving

"Learn the Basics of Pressure when scuba diving in Cozumel and the Consequences"

Pressure & Scuba Diving in

Cozumel Island

At Promos Cozumel we are dedicated to helping Cozumel tourists, Cozumel cruise passengers and Cozumel locals learn everything there is to know about Cozumel as well as exciting and interesting guides, articles, and do it yourself guides. Our goal is to help our visitors experience Cozumel Mexico like never before and not get stuck at the tourist traps and pay the high price tour prices from cruise lines and tour salesman.

So let’s continue to learn about Scuba diving about how pressure changes underwater. How does pressure change underwater and how does the pressure change effect capabilities when scuba diving in Cozumel. So it changes the equalization, buoyancy, bottom time, and the risk of decompression sickness? Review the fundamentals of pressure when scuba diving in Cozumel, and discover a theory no one else knows when scuba diving in Cozumel Mexico, and the pressure changes more rapidly the closer a diver is to the surface.

The Basics

• Does Air Have Weight?
Yes, air actually has weight. The weight of air applies pressure on your body which is about 14.7 psi (pounds per a square inch). This amount of pressure is called one atmosphere of pressure because it is the amount of pressure the earth's atmosphere exerts. Most pressure measurements in scuba diving are given in units of atmospheres or ATA.
• Pressure Increases with Depth
The weight of the water above a diver employs pressure on his body. The deeper a diver descends into the Caribbean Ocean of Cozumel, the more water there is above and the more pressure it applies on the body. The pressure a diver experiences at a certain depth is the amount of all the pressures above them, both from the water and the air.

• every 33 feet of salt water = 1 ATA of pressure

pressure a diver experiences = water pressure + 1 ATA (from the atmosphere)

Total Pressure at Standard Depths*

Depth / Atmospheric Pressure + Water Pressure / Total Pressure
0 feet / 1 ATA + 0 ATA / 1 ATA
15 feet / 1 ATA + 0.45 ATA / 1 .45 ATA
33 feet / 1 ATA + 1 ATA / 2 ATA
40 feet / 1 ATA + 1.21 ATA / 2.2 ATA
66 feet / 1 ATA + 2 ATA / 3 ATA
99 feet / 1 ATA + 3 ATA / 4 ATA
*this is only for salt water at sea level

• Water Pressure Compresses Air
Air in a diver's body are air spaces and the dive gear will compress as pressure increases (and expand as pressure decreases). Air compresses according to Boyle's Law.

• Boyle's Law: Air Volume = 1/ Pressure
This means that the deeper you go, the more air compresses. To find out how much, make a fraction of 1 over the pressure. If the pressure is 2 ATA, then the volume of the compressed air is ½ of its original size at the surface.

Pressure Effects Many Aspects of Diving

We have now explained the basics, so let's look at how pressure affects four basic aspects when diving in Isla Cozumel.

1. Equalization
When you begin to descend during your dive in Cozumel, the pressure increase causes the air in the body, the air spaces to compress. The air spaces in the ears, mask, and lungs become like vacuums as the compressing air creates a negative pressure. The delicate membranes, such as the ear drum, to be sucked into theses air spaces causing pain and injury.

When ascending after your dive, the reverse happens. Decreasing pressure causes the air in a diver's air spaces to expand. The air spaces in the ears and lungs experience a positive pressure as they become overfull of air. In a worst case scenario this could burst a diver's lungs or eardrums! This is the reason that a diver should never hold his breath underwater because if they do hold their breath during ascending, just even a tiny bit, it could over-expand the lungs.

To avoid a pressure related injury (such as an ear barotrauma) a Cozumel diver must equalize the pressure in his body's air spaces with the pressure around them.

• To equalize his air spaces on descent a diver adds air to his body airspaces to counteract the "vacuum" effect by

- breathing normally, this adds air to his lungs every time he inhales
- adding air to his mask by breathing out his nose
- adding air to his ears and sinuses by using one of several ear equalization techniques

• To equalize his air spaces on ascent a diver releases air from his body air spaces so that they do not become overfull by

- breathing normally, this releases extra air from his lungs every time he exhales
- ascending slowly and allowing the extra air in his ears, sinuses and mask to bubble out on its own

2. Buoyancy
Cozumel Divers control their buoyancy (whether they sink, float up, or remain neutrally buoyant without floating or sinking) by adjusting the lung volume and buoyancy compensator (BCD).

As a Cozumel diver descends, the increased pressure causes the air in the BCD and wetsuit (there are small bubble trapped in neoprene) to compress. The Cozumel diver will become negatively buoyant (sinks). As the diver sinks, the air in his dive gear compresses more and he sinks more quickly. If the Cozumel diver does not add air to his BCD to compensate for his increasingly negative buoyancy, the diver can quickly find themselves fighting an uncontrolled descent into the Caribbean.

In the reverse situation, as a Cozumel diver ascends, the air in his BCD and wetsuit expands. The expanding air makes the diver positively buoyant, and begins to float up. As the diver floats towards the Caribbean surface of Cozumel, the ambient pressure decreases and the air in the dive gear continues to expand. The Cozumel diver must continuously vent air from the BCD during ascent or they risk an uncontrolled, rapid ascent (one of the most dangerous things a diver can do).

A Cozumel diver must add air to his BCD as they descend and release air from the BCD when ascending. This may seem counterintuitive until a beginning Cozumel diver understands how pressure changes effect buoyancy.

3. Bottom Times
Bottom time refers to the amount of time a Cozumel diver can stay underwater before beginning his ascent. Ambient pressure effects bottom time in two important ways.

• Increased Air Consumption Reduces Bottom Times

The air that a Cozumel diver breathes is compressed by the surrounding pressure. If the diver descends to 33 feet, or 2 ATA of pressure, the air the diver breathes is compressed to half of its original volume. Each time the diver inhales, it takes twice as much air to fill the lungs than it does at the surface. The Cozumel diver will use the air up twice as quickly (or in half the time in half the time) as they would at the surface. The diver will use up his available air more quickly the deeper they go.

• Increased Nitrogen Absorption Reduces Bottom Times

The greater the ambient pressure, the more rapidly a Cozumel divers body tissues will absorb nitrogen. Without getting into specifics, the diver can only allow the tissues a certain amount of nitrogen absorption before they begin their ascent, or the Cozumel diver can run an unacceptable risk of decompression illness without mandatory decompression stops. The deeper the diver goes, the less time before the tissues absorb the maximum allowable amount of nitrogen.

Because pressure becomes greater with depth, both air consumption rates and nitrogen absorption increases the deeper a diver goes. One of these two factors will limit a diver's bottom time.

4. Rapid Pressure Changes Can Cause Decompression Sickness (the Bends)
Increased pressure underwater causes a Cozumel divers body tissue to absorb more nitrogen gas than they would normally contain at the surface. When the diver ascends slowly, this nitrogen gas expands bit by bit and the excess nitrogen is safely metabolized and released.

However, the body can only metabolize nitrogen so quickly. The faster the Cozumel diver ascends, the faster nitrogen expands and must be removed from the tissues. If the diver goes through too great of pressure change too quickly, the body cannot metabolize all of the expanding nitrogen and the excess nitrogen forms bubbles in the tissues and blood.

These nitrogen bubbles can cause decompression sickness (DCS) by blocking blood flow to various parts of the body, causing strokes, paralysis, and other life threatening problems. Rapid pressure changes are one of the most common causes of DCS.

The Greatest Pressure Changes Are Closest to the Surface.

The closer a Cozumel diver is to the surface, the more rapidly the pressure changes.

Depth Change / Pressure Change / Pressure Increase
66 to 99 feet /    3 ATA to 4 ATA /               x 1.33   
33 to 66 feet /    2 ATA to 3 ATA /               x 1.5      
0 to 33 feet /      1 ATA to 2 ATA /               x 2.0      

Look at what happens really close to the surface:

10 to 15 feet /    1.30 ATA to 1.45 ATA / x 1.12      
5 to 10 feet /      1.15 ATA to 1.30 ATA / x 1.13
0 to 5 feet /        1.00 ATA to 1.15 ATA /   x 1.15

A Cozumel diver must compensate for the changing pressure more frequently the closer to the surface. The more shallow the depth:

• The more frequently a diver must manually equalize his ears and mask.

• The more frequently a diver must adjust his buoyancy to avoid uncontrolled ascents and descents

Divers must take special care during the last portion of the ascent. A Cozumel diver should never rush straight to the surface after a safety stop. The last 15 feet are the greatest pressure change and need to be taken more slowly than the rest of the ascent.

Most beginner dives in Cozumel are conducted in the first 40 feet of water for safety purposes and to minimize nitrogen absorption and the risk of DCS. This is as it should be. However, keep in mind that it is more difficult for a Cozumel diver to control their buoyancy and equalize in shallow water than in deeper water because the pressure changes are more extreme.






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