Students are often fascinated by extreme sports such together SCUBA (Self-Contained Underwater breathing Apparatus) diving. This interest can be harnessed come teach an exciting lesson ~ above gas laws and also their importance to SCUBA diving. Note: SCUBA diving is a sports filled with plenty of inherent dangers and requires dedicated training and also equipment. Perform not attempt any kind of diving task without appropriate training and certification.

You are watching: Why do scuba divers exhale air when they ascend to the surface after a dive?

© J. Robert Patrick

SCUBA diving basics

The dried air us breathe every job is composed of 21% oxygen, 78% nitrogen, and

Boyle"s law: P1V1 = P2V2

A fundamental rule that SCUBA diving is come "never host your breath." A look in ~ Boyle"s law explains why this dominion exists. Once a diver inhales waiting from a SCUBA tank, the air that enters the diver"s lung is in ~ ambient pressure. If a diver inhales indigenous the tank on the surface, the press in she lungs will be in ~ 1 atm. If she inhales air from her tank in ~ a depth the 30 m (~99 ft), the push in her lungs will be 4 atm (30 m / 10 m/atm = 3 atm indigenous the water plus 1 atm indigenous the air in ~ the surface = 4 atm). Suspect the diver"s lung volume is 1 L, us can complete the left side of the equation because that Boyle"s law. If a diver in ~ 30 m has 1 l (V1) of air at a push of 4 atm (P1) in her lungs and ascends to the surface ar (P2) when holding she breath, the adhering to equation applies:

4 atm × 1 together = 1 atm × V2

Solving for V2, we watch that the diver"s lung volume would rise to 4 times its typical volume. This rise will an outcome in severe damage to the lungs, which deserve to be fatal. The boost of volume through a diminish in pressure can likewise be seen in the gas balloon exhaled by a diver as she rises to the surface. The exhaled air balloon are tiny at depth and increase in dimension as castle travel in the direction of the surface. See the photo.

© man Simone

After working through this example, students often ask why free divers space able to dive to such extreme depths. Complimentary divers fill their lung at the surface ar with air in ~ ambient pressure (P1) climate descend when holding their breath. The pressure adjust has the opposite impact on the volume of their lungs. A complimentary diver diving come a depth of 30 m would have actually his lung shrink come ¼ of your initial volume, which have the right to be established using the adhering to equation:

1 atm × 1 l = 4 atm × V2

SCUBA instructors sometimes demonstrate this rule to their students by bringing a foam cup follow me on a dive. As the pressure rises with depth, the gas balloon trapped in the foam decrease in volume, shrinking the cup.

Boyle"s law likewise has effects on the lot of air used from the tank through each breath. At 10 m (2 atm) double as plenty of oxygen and nitrogen molecules room inhaled with each breath. Depths dives call for closer security of a diver"s waiting supply since the diver uses his supply an ext rapidly. An additional question students frequently ask in this discussion is, "How is the SCUBA tank influenced by these changes in pressure?" because the tank is a strict container, the volume is not altered with the adjust in exterior pressure no one is the gas it has affected.

Gay-Lussac"s law: P1 / T1 = P2 / T2

In SCUBA diving, Gay-Lussac"s regulation (sometimes referred to as Amontons" regulation of pressure-temperature) is most crucial in relationship to the quantity of breathable wait in a tank. The pressure of one "empty" tank is short (around 500 psi), and the temperature is equal to the ambient temperature. SCUBA tanks made the end of aluminum commonly have a rated fill press of 3,000 psi.

A SCUBA tank is a strict container, thus its volume is hosted constant. When a tank is filled, added oxygen and also nitrogen molecules are included to the tank and also the pressure and also temperature increase. If a tank is filled promptly to 3,000 psi (P1), that is temperature can rise come as lot as 150° F (65.6° C). Since all gas laws use absolute temperatures, this temperature needs to it is in converted.

Most students know they can transform a Celsius temperature come an absolute temperature the Kelvin by including 273. However, they space not most likely to be mindful that castle can add 460 come a Fahrenheit temperature to transform it come a Rankine temperature, i beg your pardon is based upon the Fahrenheit scale however with zero representing absolute zero. As the tank cools to ambient temperature (T2) after the quick fill, the gas pressure in the tank will also decrease. Suspect the approximately temperature is 70° F (21° C), the complying with equations can be provided to determine the push at the lower temperature:

Using the Kelvin scale:T1 = 65.6 + 273 = 338.6 KT2 = 21 + 273 = 294 K3,000 psi / 338.6 K = P2 / 294 KP2 = 2,604 psiUsing the Rankine scale:T1 = 150 + 460 = 610 RT2 = 70 + 460 = 530 R3,000 psi / 610 R = P2 / 530 RP2 = 2,606 psi

Charles"s law: V1 / T1 = V2 / T2

Charles"s law is hardly ever relevant to diver safety; however, the ramifications of this law are responsible because that an exciting phenomenon for divers using dry suits. A dry fit is a watertight garment worn by divers (typically over warm clothing) the serves to keep the diver heat by trapping a class of air in between the diver and also the suit. Dried suits are usually worn in cold air and/or water temperatures.

During the dive, divers can add and remove air from their dry suits v their regulators. This permits them to readjust for changes in their suits" gas volumes as result of pressure changes during assent and descent. If the waiting temperature is chillier than the water temperature as soon as the divers arise at the finish of the dive, lock can come to be "vacuum sealed" in their suits because of the to decrease in their suits" gas volumes. Divers can add air to the suits from your tanks, or unzip your suits, to relax the "squeeze."

Dalton"s law: PTotal = P1 + P2 + P3 . . .

Also well-known as Dalton"s legislation of partial pressures, this regulation states the the total pressure that a gas mixture is equal to the sum of the partial pressures of its ingredient gases. As stated earlier, dried air is a mixture created of 21% oxygen and 78% nitrogen. Both of these gases deserve to have an unfavorable impacts top top a diver in ~ high pressures. Short partial pressures of oxygen are likewise dangerous but are only an worry for technological diving, i m sorry is beyond the limit of this discussion.

Oxygen can come to be toxic to a diver as soon as the partial press of the oxygen breathed is above 1.6 atm. Symptoms of oxygen toxicity have the right to include alters in vision, dizziness/vertigo, and seizures, all of which deserve to be problematic because that a diver and also can lead to death. To calculate at what depth a diver might start to experience symptoms the oxygen toxicity when diving v compressed air, we need to very first calculate at what air press would the partial pressure of oxygen be equal to 1.6 atm or greater.

At 1 atm of total pressure for air, oxygen would have actually a partial press of 0.21 atm. Therefore, the complete pressure of the air would certainly be 7.6 atm (1.6/0.21 atm) for the partial pressure of oxygen come be in ~ 1.6 atm or greater. Remember that for each 10 m that depth the pressure boosts by 1 atm, however the push at the surface ar is 1 atm, therefore the partial pressure of oxygen in air would certainly be 1.6 atm at 66 m (216 ft).

Nitrogen narcosis can result from a diver"s exposure come high partial pressure of nitrogen throughout her dive. Symptoms of nitrogen narcosis most carefully resemble those the alcohol intoxication. These symptoms appear an ext gradually than those the oxygen toxicity but likewise increase with depth.

Henry"s law

Henry"s law states the the concentration the a gas liquified in a liquid at a provided temperature is straight proportional come the partial pressure of the gas over the liquid. The implicit of this law for SCUBA diving is that as depth increases (and as such pressure) the quantity of a gas dissolved in the diver"s blood will additionally increase. Oxygen is consumed by the body"s physiological processes, yet nitrogen is physiologically inert. The longer that a diver remains at depth, the an ext nitrogen is liquified in his blood.

During long dives a considerable amount of nitrogen can be liquified in the diver"s bloodstream. Once the diver ascends the partial push of nitrogen drops, and also due come Henry"s law the liquified nitrogen starts to come out of solution. Nitrogen bubbles kind in the diver"s bloodstream, which can lead come decompression sickness (DCS).

See more: The Study Of Heat Flow And Heat Measurement Is Called, How Do You Measure Calorimetry

The symptoms of DCS and also their severity rely on wherein in the diver"s body the bubbles migrate and can range from soreness in the joints or blisters under the skin come death. Treatment for DCS commonly involves number of sessions in a hyperbaric oxygen chamber. In your training, divers room taught to stay within dive time and depth boundaries to minimize their risk of DCS and also to ascend gradually from every dive.

Related products

For further expedition of the gas laws, we recommend the following products: