# How Does Boyle s Law Apply to Scuba Diving?

Jul 14, 2022

## How Does Boyle’s Law Apply to Scuba Diving?

Natalie Gibb owns a dive shop in Mexico and is a PADI-certified open water scuba instructor and TDI-certified full cave diving instructor.

One of the fantastic consequences of enrolling in a recreational scuba diving course is being able to learn some basic physics concepts and apply them to the underwater environment. Boyle’s law is one of these concepts.

Boyle’s Law explains how the volume of a gas varies with the surrounding pressure. Many aspects of scuba diving physics and dive theory become clear once you understand this simple gas law.

In this equation, “P” represents pressure, “V” signifies volume and “c” represents a constant (fixed) number.

If you are not a math person, this may sound confusing. But, don’t despair. This equation states that for a given gas—such as air in a scuba diver’s buoyancy compensator device (BCD)—if you multiply the pressure surrounding gas by the volume of gas you will always end up with the same number.

Because the answer to the equation can not change (that’s why it is called a constant), we know that if we increase the pressure surrounding a gas (P), the volume of the gas (V) must get smaller. Conversely, if we decrease the pressure surrounding gas, the volume of the gas will become greater. That’s it! That’s Boyle’s entire law.

Almost. The only other aspect of Boyle’s Law that you need to know is that the law only applies at a constant temperature. If you increase or decrease the temperature of a gas, the equation doesn’t work anymore.

## Applying Boyle’s Law

Boyle’s Law describes the role of water pressure in the dive environment. It applies and affects many aspects of scuba diving. Consider the following examples:

• Descent – As a diver descends, the water pressure around him increases, causing air in his scuba equipment and body to occupy a smaller volume (compress).
• Ascent – As a diver ascends, water pressure decreases, so Boyle’s Law states that the air in his gear and body expand to occupy a greater volume.

Many of the safety rules and protocols in scuba diving were created to help a diver compensate for the compression and expansion of air due to changes in water pressure. For example, the compression and expansion of gas lead to the need to equalize your ears, adjust your BCD, and make safety stops.

## Examples of Boyle’s Law in the Dive Environment

Those who have been scuba diving have experienced Boyle’s Law first hand. For example:

• Ascent – As a diver ascends, water pressure around him decreases, and the air in his BCD expands. This is why he has to release excess air from his BCD as he ascends—otherwise, the expanding air will cause him to lose control of his buoyancy.
• Descent – As a diver descends, the water pressure around him increases, compressing the air in his ears. He must equalize the pressure in his ears to avoid pain and a possible ear injury called ear barotrauma.

## Scuba Diving Safety Rules Derived From Boyle’s Law

Boyle’s law explains some of the most important safety rules in scuba diving.

Here are two examples:

1. Don’t Hold Your Breath Underwater – According to dive training organizations, a diver should never hold his breath underwater because if he ascends (even a few feet) to an area of lesser water pressure, the air trapped in his lungs will expand according to Boyle’s Law. The expanding air can stretch the diver’s lungs and lead to pulmonary barotrauma. Of course, this only occurs if you ascend while holding your breath, and many technical diving organizations modify this rule to “Don’t hold your breath and go up.”
2. Ascend Slowly – A diver’s body absorbs compressed nitrogen gas while he dives. As he ascends to a depth with less water pressure, this nitrogen gas expands according to Boyle’s Law. If a diver does not ascend slowly enough for his body to eliminate this expanding nitrogen gas, it can form tiny bubbles in his blood and tissue and cause decompression sickness.

## Why a Constant Temperature Is Necessary to Use Boyle’s

As mentioned above, Boyle’s Law only applies to gases at a constant temperature. Heating a gas causes it to expand, and cooling a gas causes it to compress.

A diver can witness this phenomenon when they submerge a warm scuba tank into colder water. The pressure gauge reading of a warm tank will drop when the tank is submerged in cool water as the gas inside the tank compresses.

Gasses that are undergoing a temperature change, as well as a depth change, will have to have the change in gas volume due to the temperature change accounted for, and Boyle’s simple law must be modified to account for temperature.

Boyle’s law enables divers to anticipate how air will behave during a dive. This law helps divers to understand the reasons behind many of scuba diving’s safety guidelines.

## The Effects Of Diving On The Lungs

When a person dives, the air pressure around them increases. This increased pressure forces the air in their lungs to occupy a smaller space. The walls of the lungs also push against each other, making the lungs smaller. The result is that the person’s lungs shrink while diving.
The effects of this shrinkage are not usually harmful to the person, although it can be uncomfortable. It is important to remember that the lungs will return to their normal size once the person surfaces and the pressure around them decreases.

The main function of exhalation is to release carbon dioxide (CO2). To eliminate CO2, a diver’s body must work harder than usual. A decrease of nearly 10% in the amount of gas that can be exhaled and inhale in one second can be seen at 33 feet and 13 feet. With a greater density, the gas viscosity also improves. At 33 feet, the maximum flow rate (peak expiratory flow rate) drops by about 13%, and at 100 feet, it drops by about 38%. During immersion, blood that normally travels to the limbs is instead moved into the chest (i.e., the middle of the chest). When the volume of the lungs shifts due to fluid shifts, this results in less total volume.

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Divers who breathe in rebreather gas must take specific precautions to avoid CO2 toxicity. The increase in CO2 levels increases the risk of oxygen toxicity to the central nervous system (CNS). These equipment, which can hold no more than 200ml, provides additional space to the conducting airways, such as the bronchi and the thora. The rapid descent causes a buildup of CO2, and there is a decreased minute volume (the amount of gas breathed in a minute). This condition can lead to hypercapnia. If the compressor intake is close to where contamination is possible, the diver can inhale CO2 at a higher concentration than he would normally. Hypocapnia in diving can be fatal if it impairs or destroys consciousness. If CO2 levels rise too high, the diver may experience headaches, or they may not feel as connected to the air as they should. There is also a risk of nitrogen narcosis, as well as oxygen toxicity in the central nervous system.

The most dangerous medical conditions, in addition to barotrauma to the lungs and decompression sickness, are convulsions and delirium. When you raise your arms or raise your hands into the air to escape the water (ascent) and breathe in gases in your lungs, you can be battered.

A pneumothorax can be fatal to a scuba diver at any depth. It is not uncommon for collapsed lungs to occur due to trauma or medical procedures close to the lungs, but diving with such lungs requires a significant amount of time to heal.

As you descend, your body’s pressure rises, and the volume of air it emits decreases. If this occurs, it can cause problems such as sinus pain or a ruptured eardrum. You lose pressure on the water as you ascend, but your lungs fill with fresh air. As a result, your lungs’ air sacs can rupture, making breathing difficult.

This exercise not only improves the lungs’ capacity, strengthens the respiratory system, and balances the nervous system, but it also increases the body’s ability to absorb oxygen. Scientists believe that increasing the body’s oxygen levels can boost energy levels, help with circulation, and aid in the maintenance of major organ function.

## What Happens To Your Lungs When Diving?

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When you dive, the air pressure around you increases. This causes the air in your lungs to compress. The air in your lungs is compressed more than the air in the diving suit or diving bell, so the air flows into your lungs. The air in your lungs expands as you descend and keeps the same pressure as the surrounding water.

A tank of air is included in scuba gear to allow a diver to breathe underwater. Pressure is increased on the human body as the depth of a scuba diver increases. As a result, the air in the tank where the diver is scuba diving will suffer. Because dissolved gasses become bubbles as soon as pressure drops suddenly, rapid ascent results in dissolved gasses becoming crystallizes. A person may develop a series of potentially serious symptoms known as the bends. Workers building underwater foundations for bridges on a riverbank first noticed this condition. Compression sickness occurs when gas bubbles in tissues cause localized damage.

When air trapped in the lungs expands during ascent to the surface, this is referred to as Pulmonary Overpressure Syndrome (PAS). Bubbles can escape if the gas is not expelled from the alveoli and passed on to it. It interferes with blood flow to critical organs, leading to death from a heart attack or stroke.

A study published in the journal PLOS One suggests that divers have larger lungs than previously predicted during their diving careers, and that FVC may increase slightly as a result of diving adaptation. When a diver ascends quickly to the surface of the ocean, the body produces an explosion of nitrogen gas, which causes bubbles to form in the blood and other tissues.

### The Risks Of Diving: What Every Recreational Diver Should Know

The risks associated with diving are not life-threatening for the average recreational diver, but they must be kept in mind and taken into account when diving. Even at moderate depths, prolonged exposure to a substance can cause serious complications such as pulmonary barotrauma and lung collapse. Divers face increased risks at extremely deep water, such as scuba diving, as well as decompression sickness, nitrogen narcosis, cardiac arrest, and even death.
It is best to avoid diving at all costs in order to protect your lungs if you are unsure of the risks. If you do decide to dive, it’s critical to make sure you don’t go to the deepest possible depths and are aware of the symptoms of demoralization, which can be fatal.

## How Do Free Divers Lungs Not Collapse?

When free divers take a breath, their lungs fill with air just like ours. The difference is that free divers exhale completely before diving, so their lungs are empty when they start their descent. This is why their lungs don’t collapse. The air pressure outside is greater than the pressure inside their lungs, so the air inside their lungs doesn’t try to escape.

## How Do You Breathe Less When Diving?

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When diving, it is critical to learn how to breathe properly underwater in order to conserve air. If you can increase your breathing rhythm and take longer, deeper breaths, your body will be able to absorb more oxygen. As a result, the volume of dead air is reduced and the amount of carbon dioxide is eliminated.

Diver who emerges with the most air in his tank is the best at it. Despite the fact that diving keeps you fit, unless you drift against the current on a regular basis, you will not lose weight. The most important thing you can do while scuba diving is be fit. If you know you’re diving into a large body of water, don’t be afraid to wear safety goggles. Thermal protection is an important part of air consumption. If you are overweight, inflate and deflate your diving vest on a regular basis. As a result, water becomes more humid, making it more difficult for you to move beneath water.

During PADI level 1, you should always snorkel with your instructor. To reduce air consumption, the best way is to increase your buoyancy. If you want to inflate your BCD while scuba diving and feel completely comfortable underwater, fill your mouth with air to save air. It is very common for recreational diving accidents to be avoided underwater. Keep your breathing in check and observe what is around you by focusing on your lower lungs, such as yoga. Stress is the primary cause of increased heart rate, as well as an increase in physical activity and cramps. The more prepared you are, the less anxious you will become and the less air you will consume.

It is important to have a dive computer in order to be as confident about your diving depth and to keep up with how quickly you are diving. If you have to be the first to empty your dive tank, it is always best to keep it a little bit deeper. As a result, you will consume less air per person than everyone else in the group.

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## How Deep Can You Dive Before Your Lungs Collapse?

Gas exchange via the alveolar capillary interface will not stop at depths greater than 200 m [5], causing nitrogen to diffuse along the alveolar–tissue pressure gradient during the lung collapse process, resulting in nitrogen dissolving

A square inch of human bone crushes to approximately 11159 kg. Humans are usually found 30 feet below the surface of the water. When you dive deep into the ocean, nitrogen can accumulate in your brain so deeply that you may appear drunk or confused. Breathing control is one of the health benefits of scuba diving. Breathing slowly and deeply, both for health and for the lungs, is a common way of doing so. A nuclear submarine can dive to depths of approximately 300 meters. In submarines, crush depths are classified, but it is widely assumed to be more than 400 meters.

Inflammation of the upper and lower respiratory tracts is common in vaping, according to literature. Divers who engage in deep breath-hold diving have a significant risk of serious neurological injury as their depth increases. Free divers can go to depths of up to 214 meters (the current record is 21 meters). In women, nine minutes is the world record for holding your breath, while men can hold their breath for 11 minutes. The British navy mistook three whales for enemy submarines during the Falklands War and fired torpedoes at them, killing them. retired naval officer Victor Vescovo spent four hours piloting his submarine to a depth of 10,927 meters (35,849 feet) in the Mariana Trench during a four-hour exploration. A great white shark attacked the boat in which Jaws was shot in the film ‘Jaws.’

After drifting for 15 weeks in the Pacific Ocean, a police officer told how a shark helped him to a rescue boat. Water vapor will not produce the thick clouds that people are used to vaping for, as they are made of glycerine (VG) and propylene glycol (PG). Smoking and diving pose few long-term health risks, in part because smoking causes chronic lung disease over time. It is not a good idea to smoke while scuba diving.

### Can Your Lungs Collapse From Diving?

When exposed to moderate to excessive amounts of oxygen, the lungs can collapse, the lung can fall, there is pulmonary barotrauma during ascent or descent, alveolar haemorrhage, cardiac arrest, nitrogen narcosis, and even death.

#### The Dangers Of Diving Without Good Lung Function

Divers descend in response to decreased ambient pressure, while their lungs’ ability to exchange gases decreases. Atmospheric pressure (P) and water pressure (W) have both decreased during this time. As the diver enters the cave, the oxygen exchange capacity of his lungs decreases, as gas exchange requires P-W 1.3 to function effectively. Furthermore, the decrease in atmospheric pressure reduces blood flow through the lungs’ blood vessels. This results in a reduction in the amount of oxygen carried by the lungs and a reduction in the amount of oxygen used by the body. This decrease in oxygen availability is the most noticeable at depths greater than 100 m, with the greatest decrease occurring at depths greater than 100 m. As a result, keeping your lungs healthy is essential if you want to dive competitively and safely. With diving, you can increase your lung capacity, strengthen your respiratory system, and balance your nervous system.

### At What Depth Does Lung Squeeze Generally Occur?

Boyle’s law estimates the squeeze depth by dividing the diver’s total lung capacity (TLC) by his or her RV. According to this calculation, lung squeezes would occur at a depth of *34 m.

#### Dangers Of Scuba Diving

If the diver does not ascend immediately, the bubbles will burst, resulting in severe pain and, in some cases, death. Air embolisms can cause a variety of symptoms, including head pain, seizures, and comas.

## Lung Overexpansion Scuba Diving Symptoms

Chest pain, blood congestion, and painful breathing are all symptoms. ruptured lungs can cause mucus to form in the center of the chest on the top of the heart. fainting or shortness of breath as a result of the pressure on the heart is possible.

Overexpansion injuries in the lungs are caused by a variety of factors. The most serious form of scuba diving injury is an overexpansion of the lungs. Breathing normally through scuba keeps your airways open, allowing for any expanding air to escape while keeping the volume of your lungs constant. If you held your breath while climbing, your lungs would likely expand and cause a rupture of your lung tissue.

### Most Lung Overexpansion Injuries Are Preventable

Almost all injuries to the lungs are preventable with proper diving safety guidelines. To ensure the safety of both the diver and the diving equipment, the diver must receive proper training and supervision.

## Gas Laws of Scuba Diving – The Science Behind Scuba Diving

There is a whole science behind SCUBA (Self-Contained Underwater Breathing Apparatus), diving. These laws are what protect a SCUBA Diver from the pressure that the water exerts on the human body as well as safety standards for your air tank and other factors.

For every 33 feet of water, the pressure increases by 14.7 psi, so pressure builds up very fast. So for example at the surface (1 atm), the pressure is 14.7 psi and then at 33 feet (2 atm), the pressure is 29.4 psi, then at 66 feet the pressure is 44.1 psi (3 atm), and so on …

IMPORTANT: SCUBA diving is a sport filled with many dangers and requires specialized training and equipment. Do not attempt any diving activity without proper training and always have a buddy diver or someone topside with you.

### Some Scuba Basics

The atmosphere that we breathe every day is composed of 78% Nitrogen, 21% Oxygen, and 1% of other gases.

SCUBA Divers use a scuba tank (air tank), of compressed air to breath with underwater and they are made out of steel or aluminum. The air is fed from a valve at the top of the tank, via a hose and a regulator that takes the high pressure (≈ 3000 psi) of the tank and drops it down to safe levels for the diver to breath off of.

### Gas Laws

#### Gay-Lussac’s Law

P1 / T1 = P2 / T2

In SCUBA diving, Gay-Lussac’s law impacts the amount of breathable air you have in your tank. It has to do with the heating and cooling of the air in the tank during filling. An empty tank has a pressure of around 500 psi. You must always keep some pressure in the tank to help preserve and always make sure that you are filling it with dry air.

As you fill a tank the pressure and heat go up. A tank can reach temperatures around 150° F and when it cools the pressure will drop too. So for our example let’s assume the ambient temperature is 70° F. Now that we got these values we can apply Gay-Lussac’s formula by converting to the temperatures to the Rankine scale as follows:

T1 = 150 + 460 = 610 R

T2 = 70 + 460 = 530 R

P1 = 3000 psi

3000 psi / 610 R = P2 / 530 R

P2 = 2606 psi

So based on the above calculation we can see that after filling up from empty we are not quite full yet. So we could now that is has cooled down we can top up the tank.

#### Boyle’s Law

P1V1 = P2V2

A fundamental rule of SCUBA diving is to never hold your breath. Boyle’s law explains why this rule exists. When a diver breathes in air from a tank, the air is at ambient pressure. This is the pressure that is surrounding the diver at the time they take a breath. So a regulator adjusts the pressure to the ambient pressure surrounding it.

When a diver breathes in the air at the surface, then their lungs would be at 1 atm. Now say that diver dives down to 99 feet, which is 4 atm. By knowing this and assuming that the diver’s lungs hold 1 L of air we can complete the left side of Boyle’s law.

P1 = 4 atm

V1 = 1 L

P2 = 1 atm

4 atm × 1 L = 1 atm × V2

V2 = 4 atm

This means that if the diver is at 99 feet and takes a breath of air then rises to the surface holding their breath, their lungs would expand to 4 times the limit thus rupturing the lungs and probably killing the diver. So NEVER hold your breath while SCUBA diving!!

By Boyle’s law we can now also see that a diver at 99 feet would require 4 times as much air per breath than on the surface so keeping a close eye on your air supply is critical, don’t you think?

Because a Freediver takes a breath of air on the surface, 1 atm, and holds it, they do not have to worry about the effects of Boyle’s law on them. Their lungs actually get crushed in size, so a diver at 99 feet would have lungs a quarter of the normal size.

#### Charles’s Law

V1 / T1 = V2 / T2

Ok, I am going to explain this law using the example of what happens with a dry suit.

Dry suits are worn for extreme cold waters, like ice diving where you actually go and dive under the ice. You wear a pair of wool long- johns and some other warm clothing under the dry suit and the suit keeps a layer of air between you and the suit.

When a diver has been down for a long period of time the air in the suit can become colder, and thus less dense, than the air outside. So when they get out of the water the suit gets squeezed around them and they either have to put air into the suit to alleviate the squeeze or unzip their zippers.

And that shows the effect of Charles’s Law on a diver.

#### Dalton’s Law

PTotal = P1 + P2 + P3 . . .

Dalton’s Law states that the total pressure of a gas mixture is equal to the sum of the partial pressures of its component gases.

Oxygen poisoning can occur when the partial pressure being breathed is above 1.6 atm. It will cause seizures, dizziness, vertigo, and changes in vision. Any of these can be fatal to the diver. Imagine being at 99 feet and having a seizure or you start to vomit because of dizziness or vertigo. It would be a really bad situation don’t you think?

So to calculate at what depth this may occur we can use Dalton’s law. As mentioned earlier dry air is made up of mainly 78% Nitrogen and 21% Oxygen. Thus at 1 atm, the partial pressure of Oxygen would be 0.21 atm. So to get the partial pressure of Oxygen to 1.6 atm we would need a total air pressure of 7.6 atm (1.6/0.21 atm). So, therefore, you would need to be at around 216 feet to begin to be in the danger zone.

Remember the 78% Nitrogen in the air? Well, a diver can get Nitrogen Narcosis whose effects are very similar to being drunk. The deeper you go the more the effect intensifies. Nitrogen Narcosis can start occurring as shallow as 45 feet and deeper.

You will get head spins, nausea, and fumble around trying to use your equipment just as if you were drunk or start doing stupid stuff like feeding the fish your air.

#### Henry’s Law

Henry’s law states that the solubility of a liquid is directly proportional to the partial pressure of the gas above the liquid. To a diver, this means that as you go deeper the pressure will increase. Because of this, the air is forced into your bloodstream at a faster and faster rate the deeper you go.

So when ascending to the surface you need to “bleed” off all that air in the bloodstream. This is why there are decompression stops after long deep dives. This is to get all that air/gas back out of the bloodstream SLOWLY. If you ascend too fast then the air/gas comes out too fast in the form of tiny air bubbles (like Champagne), that stay in the bloodstream and get distributed throughout the body.

These tiny bubbles tend to collect in the joints and under the skin. This causes extreme pain, convulsions, blisters and even death. This is called DCS, Decompression Sickness or more commonly called “The Bends”.

This is why using your Dive Tables is so important. If you would like to know how to read your Dive Tables then take a look at the article on how to use your Dive Tables .

You have to be treated in a Hyperbaric Chamber to be cured of DCS and they are very expensive and are few and far between (not readily available around the world).

#### Archimedes’s Law

Even though this is not a gas law it still applies to the SCUBA diver. Archimedes’s Law states that any body completely or partially submerged in a fluid (gas or liquid) at rest is acted upon by an upward, or buoyant, force the magnitude of which is equal to the weight of the fluid displaced by the body.

Well, that wraps up the science behind SCUBA Diving, I hope that you found it interesting and informative.

#### Combined Gas Law

Ok, when we take Boyle’s law, Gay-Lussac’s law, and Charles’s law and combine them we get the Combined Gas Law which states:

Pressure is inversely proportional to volume, or higher volume equals lower pressure. Pressure is directly proportional to temperature, or higher temperature equals higher pressure.

Source https://www.tripsavvy.com/boyles-law-and-scuba-diving-2962935

Source https://www.desertdivers.com/the-effects-of-diving-on-the-lungs/