SCUBA Gas Laws

Earth's atmosphere is composed of a mixture of gasses that obey the famous chemistry "Gas Laws." Some of these laws become matters of life and death when using a Self Contained Underwater Breathing Apparatus (SCUBA) device. Understanding just four of these laws will help you stay alive and out of trouble while SCUBA diving.

Boyle's Law

For SCUBA divers, the most important of the gas laws--and the most deadly one to ignore--is Boyle's law. Boyle's law says that as long as temperature is constant, pressure and volume are inversely proportional--when one goes up the other goes down and vice versa. If you have an inflatable container--such as your lungs-- decreasing the pressure increases the volume. So if you take a deep breath and then move toward the surface while holding your breath, your lungs expand. If you hold it too long your lungs will explode. This is why you should never hold your breath while SCUBA diving--not even briefly. If you breathe consistently the volume of air in your lungs will constantly adjust to the changing pressure.

Amonton's Law

Amonton's law says that if the volume of a gas is constant--as it is in a SCUBA tank--the pressure and temperature are directly proportional. If one increases so does the other, and vice versa. If you fill up your tank on a summer day and then jump in water that's 40 degrees cooler, you are going to have less pressure than you might think. Therefore, the tank will not last as long. If you fill up a tank and then put it in the trunk of the car where it is 60 degrees hotter, the pressure might rise to dangerous levels and damage your equipment.

Henry's Law

Henry's law describes how pressure determines a liquid's ability to absorb gasses. As pressure increases, more of a gas will dissolve in a liquid. When a diver dives, the pressure increases and more gasses dissolve in the diver's tissues. Most of Earth's atmosphere is nitrogen, which is relatively inert so it does no real harm. If the diver ascends slowly the nitrogen comes out of the tissues as the pressure decreases. If the diver with nitrogen-saturated tissues (too deep, too long) ascends too quickly, the nitrogen comes out too fast--in bubbles. This causes a very dangerous condition known as the "bends," which can cause permanent damage or even death.

Dalton's Law

Dalton's law says that if a gas is a mixture, the pressure of each component depends on the percentage of that component in the mixture. Earth's atmosphere is about 78% nitrogen, 21% oxygen, and one or two percent other gasses--depending on where you live. If your tank is filled using faulty equipment, you might be getting a lethal dose of something that is relatively safe at low pressures. Even oxygen can be toxic at high pressures. Nitrogen at high pressures can have a narcotic effect (known as "rapture of the deep") that can cause a deadly loss of judgement.

By Carlos Mano, eHow Contributor

Kathy Dowsett
www.kirkscubagear.com

Salt Water Aspiration and Scuba Diving

Thanks Natalie Gibb

As a scuba instructor, I tend to err on the side of over-caution. The dive equipment set-up and revision which I teach my students is very meticulous, and I insist that they perform these checks on every dive. One piece of equipment that I see many divers (and scuba instructors) overlook during their equipment set-up and inspection is the regulator mouthpiece. A mouthpiece's bite tabs may wear down or break off after many uses. Mouthpieces also tend to develop holes where the plastic tie-wrap holds them in to the regulator second stage. This is dangerous! Any mouthpiece developing holes must be replaced before diving. Holes in the mouthpiece can lead to salt water aspiration - a little-recognized syndrome that divers should know about.


Accidents happen. I observed an incidence of salt water aspiration (thankfully not on my dive!) at the beginning of my dive career. A diver ran low on air at the safety stop, and the instructor handed the diver his alternate air source regulator to allow the diver to breathe from his tank. All appeared well when the two surfaced and boarded the dive boat. The instructor had just launched into a lecture about the importance of carefully monitoring one's air supply underwater when the diver began to have difficulty breathing. He coughed, gasped for air, and felt weak. Suspecting decompression sickness, the instructor administered oxygen to the diver. When the boat reached the dock, and ambulance rushed the diver to the hyperbaric chamber.

The diver was not bent. He had inhaled a fine mist of salt water through a hole in the mouthpiece of the instructor's alternate air source regulator. The droplets of salt water were so fine that the diver didn't notice that he was inhaling anything other than air. When the dive gear was inspected, the hole discovered was so small that it was not visible unless the mouthpiece was pulled on and twisted. The diver, stressed from the low air situation, had pulled the hole open by looking around during the safety stop, and inhaled enough vaporized salt water to cause salt water aspiration syndrome. After treatment, the diver recovered and was perfectly fine.

What Is Salt Water Aspiration?:


Salt water aspiration may occur when a diver inhales tiny droplets of salt water due to an equipment malfunction or poor diving technique. Salt water aspiration may also occur in near drownings, or in any other scenario in which salt water is inhaled.

Salt water does all sorts of nasty things to a diver's lungs. One of the effects of inhaled salt water (without getting too technical) is that the high saltiness of the salt water in comparison to the relatively lower saltiness of the fluid in a diver's lung and body tissues causes body fluids to move through the walls of the divers' lungs (specifically the alveoli) and into his breathing spaces, making breathing difficult, if not impossible.

Symptoms of Salt Water Aspiration:


Salt water aspiration may be difficult to diagnose, because it mimics many of the symptoms of decompression illness. Some divers may have severe reactions to salt water aspiration (such as those with a history of asthma or hay fever) while others may have a much milder reaction. Symptoms are usually delayed from one to fifteen hours and may include the following:

difficulty breathing and chest pain
a cough that produces phlegm
flu-like symptoms including body aches, exhaustion, fever, nausea and headache
pale skin
shivering


What Is the Treatment for Salt Water Aspiration:

Most cases of salt water aspiration are mild, go undiagnosed, and resolve within a few hours. If a diver feels sick enough to suspect salt water aspiration, he should seek immediate emergency medical care. The symptoms of salt water aspiration mimic those of decompression sickness, and decompression sickness must be ruled out before salt water aspiration is diagnosed. Some of the treatments include administration of oxygen, rest, and administration of bronchial dilators. Treatment may also be required for infections caused by bacteria in the inhaled salt water. With treatment, even severe cases of salt water aspiration have a high chance of resolution.

How to Avoid Salt Water Aspiration When Scuba Diving:


Correct gear maintenance and diving procedures should prevent most cases of salt water aspiration. Check to make sure that your regulator mouthpieces have no holes. Be sure to stretch and pull the mouthpieces to ensure there are no hidden holes and check carefully around the margin of the mouthpiece where the tie-wrap holds it in place. Do this to both your primary and alternate air source.

More tips for safer diving:

• Why You Should Never Use the "Up" Button
• 8 Tips for Being a Safer, Better Buddy
• What Are No-Decompression Limits and Why Are They Important?

Check to make sure that the regulator's exhaust valves seal properly before diving. With the first stage dust cap in place, place the regulator in your mouth and inhale. If any air leaks in, the exhaust valve is not sealing properly, and will breathe "wet" when diving. Any regulator that leaks through the exhaust valve or breathes wet underwater requires maintenance.

Follow diving protocols that minimize the chance of water entering your mouth. Seal your lips well around the regulator mouthpiece, and be certain to block water from entering your mouth when using the regulator purge button. Exhale, or block the opening of the mouthpiece with your tongue when pushing the purge. Avoid removing the regulator underwater whenever possible, and refrain from flipping upside down or into unusual positions when diving. Most regulators will breathe a little wet when inverted.

The Take Home Message About Salt Water Aspiration and Scuba Diving:

Salt water aspiration is fairly uncommon in scuba divers, but it does occur. The condition may be difficult to diagnose because the symptoms mimic those of decompression illness. With this in mind, be sure to check your gear carefully before a dive (especially rental regulator mouthpieces), and follow procedures to prevent salt water from entering your regulator second stage.


Thanks to Natalie and About.com

Kathy Dowsett

www.kirkscubagear.com

Diving Barotrauma

Image via Wikipedia

Barotrauma is physical damage to body tissues caused by a difference in pressure between an air space inside or beside the body and the surrounding fluid. In addition to humans, and in contrast with Avian lungs, bats suffer fatal barotrauma around wind farms.

Barotrauma typically occurs to air spaces within a body when that body moves to or from a higher pressure environment, such as when a SCUBA diver, a free-diving diver or an airplane passenger ascends or descends, or during uncontrolled decompression of a pressure vessel. Boyle's law defines the relationship between the volume of the air space and the ambient pressure.

Damage occurs in the tissues around the body's air spaces because gases are compressible and the tissues are not. During increases in ambient pressure, the internal air space provides the surrounding tissues with little support to resist the higher external pressure. During decreases in ambient pressure, the higher pressure of the gas inside the air spaces causes damage to the surrounding tissues if that gas becomes trapped.

Ear barotrauma

Barotrauma can affect the external, middle, or inner ear. Middle ear barotrauma (MEBT) is the most common being experienced by between 10% and 30% of divers and is due to insufficient equilibration of the middle ear. External ear barotrauma may occur on ascent if high pressure air is trapped in the external auditory canal either by tight fitting SCUBA equipment or ear wax. Inner ear barotrauma (IEBT) though much less common than MEBT shares a similar mechanism. Mechanical trauma to the inner ear can lead to varying degrees of conductive and sensorineural hearing loss as well as vertigo.

Barosinusitis

The sinuses similar to other air filled cavities are susceptible to barotrauma if their openings become obstructed. This can result in pain as well as epistaxis.

Mask squeeze

If a diver's mask is not equalized during descent the relative negative pressure can produce petechial hemorrhages in the area covered by the mask along with subconjunctival hemorrhages.


Pulmonary barotrauma

Pulmonary (lung) pressure damage in scuba divers is usually caused by breath-holding on ascent. The compressed gas in the lungs expands as the ambient pressure decreases causing the lungs to over expand and rupture unless the diver breathes out. The lungs do not sense pain when over-expanded giving the diver little warning to prevent the injury. This does not affect breath-hold skin divers as they bring a lungfull of air with them from the surface, which merely re-expands safely to near its original volume on ascent. The problem only arises if a breath of compressed gas is taken at depth, which will then expand on ascent to more than the lung volume. Pulmonary barotrauma may also be caused by explosive decompression of a pressurised aircraft.

Causes

When diving, the pressure differences needed to cause the barotrauma come from two sources:

* descending and ascending in water. There are two components to the surrounding pressure acting on the diver: the atmospheric pressure and the water pressure. A descent of 10 metres (33 feet) in water increases the ambient pressure by approximately the pressure of the atmosphere at sea level. So, a descent from the surface to 10 metres (33 feet) underwater results in a doubling of the pressure on the diver.

* breathing gas at depth from SCUBA equipment results in the lungs containing gas at a higher pressure than atmospheric pressure. So a free-diving diver can dive to 10 metres (33 feet) and safely ascend without exhaling, because the gas in the lungs had been inhaled at atmospheric pressure, whereas a SCUBA diver who breathes at 10 metres and ascends without exhaling has lungs containing gas at twice atmospheric pressure and is very likely to suffer life-threatening lung damage.


Avoidance and treatment

Diving barotrauma can be avoided by eliminating any pressure differences acting on the tissue or organ by equalizing the pressure. There are a variety of techniques:

* The air spaces in the ears, and the sinuses. The risk is burst eardrum. Here, the diver can use the Valsalva manoeuvre, to let air into the middle ears via the Eustachian tubes. Sometimes swallowing will open the Eustachian tubes and equalise the ears. See ear clearing.

* The lungs. The risk is pneumothorax. which is commonly called burst lung by divers. To equalise, always breathe normally and never hold the breath. This risk does not arise when snorkel diving from the surface, unless the snorkeller breathes from a high pressure gas source underwater, or from submerged air pockets.

* The air inside the usual eyes-and-nose diving mask. The main risk is bleeding around the eyes from the negative pressure[10] or orbital emphysema from higher pressures. Here, let air into the mask through the nose. Do not dive in eyes-only goggles as sometimes seen on land with industrial breathing sets.

* Air spaces inside a dry suit. The main risk is folds of skin getting pinched inside folds of the drysuit. Most modern drysuits have a tube connection to feed air in from the cylinder. Air must be injected on the descent and vented on the ascent.

Following barotrauma of the ears or lungs from diving the diver should not dive again until thoroughly cleared by a doctor, which can take many months.

Thanks to Wikipedia, the free encyclopedia

Kathy Dowsett

www.kirkscubagear.com

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