The Buddy Pre-Dive Safety check is an important safety check that should be performed by every diver no matter what level of diving proficiency. This check is performed by a Scuba Diver with his/her buddy before descending on a dive as a final inspection of the dive equipment before diving.  The Pre-Dive safety check ensures that your equipment is working, and also familiarizes yourself with your buddies equipment should you need to assist or receive assistance from him. Most Scuba diving accidents and incidents are said to be preventable by the diver simply having properly conducted a pre-dive safety check. Despite the warnings, most divers seldom perform this crucial scuba gear check before a dive, and rush to descend. Especially with your scuba equipment being set-up by someone else, a diver should always inspect his own gear and perform a buddy check before descent.

PADI’s “BWRAF” acronym is highly popular with divers, and is an easy to remember pre-dive check. BWRAF stands for

B – BCD & Buoyancy, Check your buddies Buoyancy Compensator, check the low pressure inflator hose is connected correctly and do a quick puff to ensure the inflator button doesn’t stick. Also deflate the BCD to ensure it deflates correctly. If you are performing the check in the water, also check your own buoyancy to ensure you are weighted correctly.

W – Weights/Weight Belt : Check that your buddies weight belt is on properly with the loose end tied correctly and tucked in a manner that will allow for quick release. Make sure you are familiar with the type of weight belt or integrated weights being used by your dive buddy and you know how to release them should you need to.

R – Releases: Check that your buddies BCD is strapped correctly and all belts are tightened. Also count the number of buckles/straps tugging at each one as you become

A – Air: Check that your buddy’s air is turned all the way on and half a turn back. Make him take a couple of breaths while you watch the pressure gauge for fluctuations in the needle, or simply purge the regulator while watching the needle. Check that the tank is full and check all air connectors for leaks. You should check your buddies alternate air source by taking a couple of breaths from it and ensuring that it is clipped on the BCD and visible.

F – Final OK: Final check is a cursory visual inspection, of fins, mask, snorkel and testing dive flashlights if necessary, take a compass bearing, and check your dive computer before giving the all Ok sign to your buddy to begin descent.

PADI uses a mnemonic to help divers remember the pre-dive check BWRAF, Begin With Review And Friend. However divers have come up with several different mnemonics to help them remember, here are some of the common and not so common funny ones:

• Beans With Rice And Fish
• Bruce Willis Ruins All Films
• Breathing Water Really Ain’t Fun
• Big White Rabbits Are Fluffy
• Because We Really Are Friends
• Blonde Women Really Are Fun
• Burgers With Relish And Fries
• Bunnies Will Run Away Fast
• Bangkok Women Really Are Fellas

* photo credits: photos by Barnaby_S , Robert Scales

Whether you’re new to Scuba diving or it has just been a very long gap after your last dive, many divers experience some jitters usually from unpreparedness.

You often hear new divers say “I felt claustrophobic”, “I couldn’t breathe properly” or even experienced divers blame their dive equipment – “There was something wrong with my regulator” or stress out, “I felt a lot of pressure suddenly”. These thoughts and feelings are common because one feels out of control/practice or a lack of confidence in their equipment because they’re not familiar with it and sometimes it’s plain old nerves messing with you before a dive, either way the jitters can easily be overcome with these tips-

1. Get familiar with your equipment. If you own your own Scuba diving gear and equipment, make sure you check each piece of the gear before you leave for your dive trip. Try everything on, get the feel of things and get comfortable with them before your trip. Often when you don’t do this and then don all the gear just before a dive,the sheer amount of equipment can overwhelm you causing you to stress about what if’s and things that could possibly go wrong. If you’re renting make sure to get to the dive shop well before your dive to check and try on everything.

2. If it’s been a few months since your certification, consider a refresher course at your local dive shop or YMCA. At the very least, get permission from a local pool to test your gear out (if you have your own, or rented gear from your local shop if you don’t). Don’t wait till you’re on vacation – get comfortable with assembling and using Scuba equipment in the water now.

3. Go over hand signals and emergency scenarios with your dive buddy a day before the dive. If you and your dive buddy are on the same page and understand each other well, it’ll definitely make you more comfortable and calm some of those nerves.

4. Get to know the site you are diving. Ask the dive master in charge about the dive site. When you know what to expect like the depth, currents and so on it makes focusing on other dive aspects easier which will make you feel more comfortable. Comfort underwater is the key to a good dive it even influences other scuba diving skills like buoyancy control and air consumption etc.

5. Ask questions. Never be shy, intimidated or too proud to ask questions about anything that you are uncertain of. Scuba instructors and dive masters will always be ready to help no matter how ‘dumb’ you feel your queries are. If it’ll help you feel better prepared, don’t even think twice before asking.

At the end of the day, the better prepared you feel, the less nervous you’ll be during the dive. So eliminate those nerves by familiarizing yourself with the equipment, dive site and your buddy. The rest will vanish when you hit the water and see that first fish swim by.

*Photo credits: Photos by unwritten, Aenneken, Philippe Guillaume on flickr

A question that gets asked a lot by beginner and intermediate divers alike is, what is the best way to enter the water from a dive boat or platform? The truth is, that there is no one good method, and the method one should choose is usually determined by a combination of the type of platform you are diving from, the what you’re most comfortable using, and the safest  way determined by the conditions.

There are four basic types of water entry procedure for Scuba Divers that we will cover today: wading/shore entry, giant stride method, seated entry and back roll entry.

Wading Entry Method

The wading entry procedure is performed from a beach or the shore. It involves wading out to your dive site by walking backwards while shuffling your feet to avoid stepping on sharp rocks and to scare away bottom dwelling creatures like rays. While it may sound like an easy method of entry, wading through the surf backward while wearing heavy scuba diving equipment is no easy feat. Divers should wade with their BCD’s partially inflated and regular in their mouths and wade till the water gets around waist high after which one can swim. Avoid using the shore wading entry when conditions are rough, and surface is muddy, or you could end up losing a fin.

The Giant-Stride Entry Method

One of the more common methods of entering the water, and also one of the easiest methods is the giant-stride entry. Most commonly used while diving off a dive boat, but can also be used to step off a pier or jetty where the water is deep enough. The giant stride entry method can be used while diving into deep water or where the platform is steady. This method involves getting your scuba gear on in the boat itself, and standing on the edge of the dive platform will the ball of your fins on the edge. Then holding your mask and regulator with the heel of your palm on the regulator and fingers holding your mask in place, step off the platform with a giant stride forward. Once in the water bring your legs together to return to the surface, recheck your gear and signal the boat that you’re OK and your buddy to begin decent. The giant-stride method of entry is best used where all divers assemble at the surface of the water before descending together all at once. When currents are strong or surface conditions poor, this entry method should not be used.

Seated Entry Method

The controlled seated entry method is best used where the water is too shallow for a giant stride off the boat or where your boat/platform is low to the surface of the water or the platform is unsteady. Seated entry involves kitting up in the dive boat itself and while seated at the edge of the boat/platform, using your hands on each side of you, lifting yourself up and outward with your hands and lowering yourself into the water. This method of entry is great when you are diving near shallow reefs, where jumping in could cause the diver injury. Care should be taken while pushing yourself off the boat that your clear both yourself and your tanks from hitting the side of the dive boat.

Back Roll Method

The back roll or rear roll is the preferred method for entering the water from a small boat as fully kitted divers standing up in a small craft could easily upset the balance of the boat. To execute the back roll, the divers should be fully outfitted and seated at the edge of the gunwale of the boat facing inwards with his tank facing the water. Then with the chin tucked in and one hand holding the mask and regulator in place, the diver rolls backward moving through a full somersault into the water. While this method looks difficult, it is quite easy to perform and great for immediate descents with a group of divers off a small craft.

Apart from the four basic water entry methods shown above, there are several other such as feet first step off, while diving off high platforms, or donning the BCD once in the water, ladder entry etc. which are essentially variations of the basic entry methods. Once again the method you chose should always consider safety first, and the situation/platform you diving from. Over time water entry method selection becomes almost automatic to a diver.

* photos by: maplebed, Orang Asli, jeshua.nace, Barnaby_S

Henry’s Law

William Henry was an English physician and chemist who in 1803 proposed what is now called Henry’s law, which states that “At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. “

The Law essentially has two parts; one states that as pressure increases, solubility of gasses in liquids increases. The Second part states that as temperature increases, solubility of gasses in liquids decreases.

In simplistic terms:

• Under more pressure, a greater quantity of gas can be absorbed by a liquid
• Secondly, the cooler the liquid, more gas can be absorbed by it, as a liquid warms up, the gas escapes from it.

Mathematically the Law is expressed as:

P=KC     Where

P = the partial pressure of the gas

C = Concentration of the gas

K= Henry’s Law Constant

When trying to understand Henry’s Law, it helps to draw parallels to a bottle of Soda. Before the bottle is opened, its contents are under pressure, which causes the carbon dioxide in it to be soluble in the soda. As soon as you open the cap, you release the pressure causing the carbon dioxide gas to lose its solubility and escape in the form of bubbles or fizz.

In the same manner, as a diver descends, nitrogen inhaled has nowhere to escape and under pressure gets soluble in the bloodstream, muscles and tissues. This is no problem, until the diver begins his ascent.  As a diver ascends, the pressure is released and like the soda bottle, the nitrogen in the body tries to escape and may form bubbles if the diver ascends too quickly causing DCS or Decompression Sickness also known as the bends. This is the reason why divers ascend gradually, to allow the nitrogen to dissipate rather than form bubbles.

Henry’s Law also explains the reasons why divers are asked to not to take hot baths after a dive, or asked to abstain from doing strenuous activities or exercise. Based on the second portion of Henry’s Law, the increase in temperature caused by the exercise or hot bath may cause the nitrogen to become less soluble and increase the off-gassing possibly cause DCS or Decompression Sickness.

In the same manner, while diving in colder water, the on-gassing/absorption of nitrogen is greater, which should be taken into consideration, as it will allow the diver shorter dive times, and shallower dives.

Also Read: An Introduction to Scuba Gas Laws – Part 1 : Boyle’s Law
An Introduction to Scuba Gas Laws – Part 2: Charles’ Law

Photos Gaetan Lee, azteca90

In order to successfully complete any Scuba Diving training, a student receives what is called a C-Card or a Certification Card. This card acts like a license to dive and all dive shops are required to  ask to see this card before renting out any dive gear and equipment. As a sport recreational scuba diving doesn’t have any one centralized certifying or regulatory agency, but is mostly self regulated. There are, however, several large diving organizations that train and certify divers and dive instructors and have become recognized certification agencies of the sport the world over, which most dive outlets and dive shops consider proof of proper scuba training.

These agencies work by training and certifying instructors in their syllabus and teaching methods, and then allowing those instructors to certify individual divers. In addition to providing all levels of diver training, the agencies also regulate the sport as a whole and represent diving professionals such as dive masters, dive instructors and dive operators. They widely participate in researching dive medicine, promoting marine conservation as well as marketing diving as a sport.

At a beginner level, the certification agency doesn’t play too much of an importance as the courses they offer as more or less similar courses and any main agency will be recognized by dive operators anywhere in the world. Right up to the professional level training the agencies recognize each others qualifications for recreational diving. However, when it comes to diving professionally they may not recognize each others qualifications.

When you first start off diving, you need to consider the instructors experience and the dive center offering up the course rather than letting the agency dictate your choice.

Here are the most recognized Scuba Certification agencies around the world today. Of these, PADI and NAUI are the most prevalent in the United States.

PADI- Professional Association of Diving Instructors
Based in the United States and by far by the biggest and most recognized dive certification agency in the world, PADI was started in 1966 to improve the training into a variety of different courses rather than just the one single universal course. prevalent at the time. PADI courses are very performance based dive programs. The introductory level emphasizes practical knowledge, safety and motor skills along with the foundations of diving physics, physiology and chemistry.

PADI centers are the most widely spread out across the world and you can find one in almost any dive destination. More beginner divers are certified by PADI than all other agencies combined. It has certified approximately 70% of divers in the United States and approximately 55% of divers worldwide.They are very active in promoting the sport and also in marine conservation through their Project AWARE operation.
Website: www.padi.com

NAUI- National Association of Underwater Instructors
Again a United States based agency, NAUI started in 1959 is the oldest recreational scuba certification agency. NAUI is a non-profit association which was started for the promotion of dive safety through education. Its diver courses are very similar to that conducted by PADI and SSI and it enjoys a status of being the second largest scuba certification agency after PADI.

NAUI boasts of a no. of celebrities and industry pioneers certified by them like Kevin Costner, Tiger Woods (NAUI divemaster member), Cameron Diaz, Jacques-Yves Cousteau (inventor of the aqualung) and many more. Many of whom have popularized the activity for NAUI. As of 1997 NAUI published standards for teaching technical diving as well.
Websites: www.naui.org

BSAC- British Sub Aqua Club
Founded in 1953 and based in the United Kingdom, BSAC is the largest dive club in the world. With over 50,000 members it has being recognized as the official governing body of recreational diving in the United Kingdom. BSAC operates through 1600 local independent dive clubs and over 400 diving schools world wide. Given that UK waters are relatively cold and have restricted visibility, BSAC training emphasis on rescue training very early in the programme.
Website: www.bsac.com

CMAS- Confédération Mondiale des Activités Subaquatiques/ The World Underwater Federation
CMAS is the international umbrella organization for diver training organizations. Founded in 1958, CMAS is based in France. The organization offers the international framework for diver and instructor qualifications and members of the CMAS Council are representatives of the other recognized dive agencies.

The training philosophy of CMAS members originates from professional or military diving backgrounds and tends to reflect the full range of European and world diving standards.The difference in the philosophy for diving between CMAS and US-originated dive education is very distinct as their ideology is entirely about quality education over profit, which accounts for its courses being taught worldwide in more dive schools than dive shops.
Website: www.cmas2000.org

SSI- Scuba Schools International
With 35 Regional Centers and Area Offices around the globe, the 1970 established SSI is based in the United States. It has well over 2,200 authorized dealers and supports Dive Businesses and Dive Resorts. A major difference between SSI and other diver education organizations like PADI, NAUI, CMAS and others is that SSI is a Retail based organization, intended to ensure the quality of training worldwide.
Website: www.divessi.com

Other Agencies
IDEA- The International Diving Educators Association (www.idea-scubadiving.com)
ACUC- The American Canadian Underwater Certifications (www.acuc.es)
PDIC- The Professional Diving Instructors Corporation ( www.pdic-intl.com)
SDI/TDI- The Scuba Divers International/Technical Divers International (www.tdisdi.com)

To Shop for Scuba Diving Equipment and Gear visit LeisurePro.com – The Diver’s Emporium

You’ve heard about Scuba Diving, probably have friend or two who have gone diving before or you just seen divers on TV and thought you would like to give it a try, but you’re unsure about how to go about it.

SCUBA which stands for Self Contained Underwater Breathing Apparatus is a very popular recreational sport which does however require a specialized training to get started. The requirements to complete undertake training are very basic, like you need to be in good health, not have any ear, sinus or heart conditions, you should be able to swim, feel comfortable in water and so forth. Close to 1 million people take up and become certified Scuba divers each year around the world.

Here are 3 steps to help getting you to take that first plunge underwater. Once under and before you know it you’ll be hooked and just wanted to keep diving.

STEP 1: Talk to a Diver
A good way to know what you’re getting into is talking to someone who has been diving before. It’s better if you can find a dive instructor or a dive master to talk to, but even some one with a little dive experience should be able to help you out. Use them as a guide to help decide if that’s what you want to experience and if it’s right for you. You usually will be met by the diver gushing about the joys and experiences he/she has had on numerous dives and what makes it the best activity they have tried. But before getting completely roped in, ask about any concerns you have, maybe about sharks, jelly fish, risks, a worry about panicking or any other concerns you may have. Also, remember to ask them the organization they were certified by and how their course was.

STEP 2: Research Certification Courses
There are a number of international organizations and associations that specialize in Scuba training and certification of divers. Local dive shops, resorts, dive operators, YMCAs, colleges, and community centers, where you can sign up for a course are often affiliated with such associations such as PADI (Professional Association of Diving Instructors), NAUI (National Association of Underwater Instructors), CMAS (Confédération Mondiale des Activités Subaquatiques/The World Underwater Federation), SSI (Scuba Schools International) and a few other groups. However, in the United States, PADI and NAUI are the two biggest certification agencies as well as the most recognizable.Their sites provide plenty of information about certification courses close to you.

Each of these agencies have different philosophies and methods of training. They sometimes use different dive tables,offer the course for different prices, lengths and class sizes.It’s not easy or right to say one is better than the other as they are all very well reputed and specialized training agencies for Scuba Diving.

You are essentially looking to sign up for the Open Water/ SCUBA diver course which is the first level of diver certification, your ticket to an exciting adventure in the underwater world.

STEP 3: Signing up with a Good Dive Center & Instructor
What’s more important than the agency is that the dive center’s instructor you choose is well qualified and that they have not only experience but the ability to teach that knowledge correctly to you. He is your teacher and essentially the translator of the agency he represents, teaching with their material and pre-requisites.

Ask that the dive center show you their license to teach diving, this usually means the dive instructor’s C-card which should be valid and not expired at the time. Ask about class size and length that is offered by the dive center. Smaller classes mean more time spent with individual students, which is better for learning and leads to safer diving. The instructor-student ratio should ideally be no more than 1:4. Also, the length of the training ideally should be a minimum 4-5 days. While there are weekend classes or 3 day crash courses offered at cheaper price, ask yourself if you will you be able to absorb all there is to learn in such a short time and how many practice sessions can they cram into such a short span of time?

Choose a dive center and course that offers you a good number of practice dive time and pool or training sessions as well as classroom sessions. The key to diving is practice and if they aren’t putting you in the water enough and just focusing on theoretical knowledge it’s not a good choice to go with them. Don’t forget to get information on the study material they provide with the course, text books, log book, c- card (on certification), dive tables and so on. Also, inquire about the dive equipment you may be expected to have (usually just the dive mask, snorkel and fins) and what scuba equipment they would provide as part of the course or with a rental charge and boat fees.

1-2-3 and you are on your way to becoming a Scuba diver!
Once you’ve got these 3 steps sorted and follow them through, you’ll be a certified Scuba Diver in no time and I bet top dollar that you’ll be looking to do your next level of training soon, or planning your next vacation as a dive trip!

*Above images by Dan Hershman, Ed Bierman, highlander411, frerieke & * Lisa * on flickr

I can distinctly remember my first day at my open water dive class, when our dive instructor asked us all to spit into our dive masks and put them on. Eyebrows went up in disbelief everywhere, and not to mention a few chuckles as well. When we asked our instructor why, his reply was simply “to prevent your masks from fogging up underwater.” We accepted this and proceeded with our class and found out quickly that the spit really did work well.

But have you ever stopped to wonder why spit? What makes ordinary saliva so effective against fogging of masks? Why do masks fog up in the first place? Why won’t simple water do the trick? To answer this, we have to get a little technical.

A Scuba mask fogs up when the inside of the lens is at a temperature below the dew point of the air inside the mask. So water condenses on the inside of the lens. But the explanation doesn’t stop there. The surface of the glass in your mask is potholed with microscopic depressions. Moisture is attracted to this uneven surface and adheres to the front causing the fogging. Decreasing the surface tension and creating a moisture film prevents fogging.

So how does Spit help? Saliva acts as a surfactant. Surfactants are wetting agents that lower the surface tension of a liquid, allowing easier spreading. The term surfactant is a blend of the words surface acting agent. As a surfactant; saliva decreases the surface tension of the droplets. The water from the condensation does not mound up as beads or droplets but, instead breaks to form bigger droplets that just roll away into the mask.

Ok so why use Spit? Well simply because it’s the most conveniently available surfactant and it works really well too. You could just as easily use shampoo, detergents, toothpastes, soaps, alcohols, or glycerin all used by divers as a spit alternative used to the same effect. You could also purchase manufactured defogging solutions. But spit is free, plentiful and doesn’t require a wetsuit with pockets to carry around!

Photographs by Many Cats 4 Me and rainspoo

Just as man took to the skies like a bird with the airplane, Scuba gear is man’s way of taking the plunge to explore the blue world underwater. Scuba Diving is an amazing way to discover what nature has in store for us with 70% of our planet covered in water. For those unfamiliar with the sport the equipment a diver uses may seem complicated and a little daunting to try, but this guide aims at pointing out the basic Scuba gear a diver uses and how it works. If you choose to take up diving, a part of your Scuba diving certification training is dedicated to the diving equipment, how to assemble it and how to use it safely and responsibly.

Visit Scuba gear on Polyvore.com for details on the gear pictured above or visit www.leisurepro.com

Mask & Snorkel: Needless to say Dive Masks are your windows to the underwater world. Keeping water out of your eyes and making your view of coral, fish, sea mammals and other life that much more clearer. Masks prove very important as they are have an air pocket in front of your face which allows you to equalize your ears while descending.  The snorkel on the other hand is not really considered a necessity but proves useful when breathing at the surface before descending, without having to use the air in your tank.

Dive Booties and Fins: Fins are to a diver exactly what a tail and fins are to a fish, a means for movement and propulsion underwater. Diving fins are important in terms of helping a diver move with ease, navigate and work again currents. When a diver moves easily and effortlessly underwater using good Scuba fins they in turn conserve more energy, thus using up less of their air supply.  Dive booties are neoprene boots worn with fins for a snug fit. (See How good dive fins can make a difference.)

Wetsuit: Wetsuits are more than just dive apparel. Their primary function is for warmth. Made from neoprene, wetsuits preserve body heat by trapping a layer of water against the skin through the material. This water warms up because of body heat and acts as an insulator. Wetsuits unlike dry suits are not good insulators against very cold water but are decent protection from minor thermo clines (changes in water temperature at different depths) and are available in different thicknesses making them suitable for diving in different water temperatures.

Tank: A Scuba tank is where the air a diver breathes is stored. A common misconception about diving is that a diving tank is filled with oxygen, which is not true. For Scuba diving, the regular air we breathe is compressed at about 3,000 psi and filled in the tank/cylinder divers use. It has the same composition of regular air which is around 78% Nitrogen, 21% Oxygen and the remaining other gases.

Buoyancy Compensator (BC)/ Buoyancy Control Device (BCD): A BCD or Buoyancy Compensator is a vest like fitted jacket to which the tank is strapped on and worn by a diver. The BC is connected via a hose to the tank and has air pockets which can be inflated and deflated with a push of a button allowing you to control your depth in the water and also compensating the weight of all the equipment including the tank used by a diver. Another way of inflating a BCD is manually as they have a mouth piece you can blow into.

Weight Belt: People are positively buoyant and therefore need weights to help them descend and stay underwater while diving. Typically weights are added to a belt that goes around your waist or in some cases weights can be put into your BCD pockets. The amount of weight needed differs from person to person depending on body fat and a person’s natural buoyancy.

Regulator: A Scuba regulator is what allows you to breathe underwater. The regulator attaches to the top of the tank and then has a hose connecting it to a mouthpiece allowing you to inhale air underwater. The main function of the diving regulator is that is reduces the pressure of the air that is stored in the tank from 3,000 psi to a safer level and more breathable 140 psi. (See How a Scuba diving regulator works.)

Alternate air source: Your alternate air source is a spare regulator used incase your primary regulator for some reason fails or if you need to share air with your dive buddy if he/she runs out.

Pressure Gauge: Also connected to your tank your pressure gauge indicates how much are is left in your tank during a dive. This gauge is also normally accompanied with a depth gauge on the same console. Sometimes a compass and dive computer can be added to the console.

Dive Computer: All dive computers tell you 4 basic things- Your current depth, your maximum depth during the dive, length of time underwater and how much longer you can stay safely underwater at any particular depth. Depending on the model of computer, it can also tell you much more information and have a lot of different features.

Charles’ Law

If you have read my first article in this series, An Introduction to Scuba Gas Laws – Part I: Boyle’s Law, you will already be familiar with Boyle’s Law which studies the relation between pressure and volume of a gas while temperature remains constant.  Charles’ law also studies volume of gas however taking into consideration the effects of temperature on the volume and Pressure of the gas.

Jacques Alexander Charles was a French scientist, mathematician, inventor and a balloonist who first studied the effects of temperature on the volumes of a gas and formulated Charles’ Law in 1787. The law states that “At constant pressure, the volume of a given mass is of an ideal gas increases or decreases by the same factor as its temperature increases or decreases.”

Mathematically Charles’ Law is expressed as:

P1 x V1     P2 x V2
______ = ________
T1               T2

Where’ T’ is temperature,’ P’ is pressure and ‘V’ volume.  ‘1’ indicates the initial temperature and volume while the’ 2’ indicates the final temperature and volume.

According to Charles’ Law, if we were to take a balloon filled with air and increase the temperature of the air inside, the volume of air would increase causing the balloon to expand.  This is caused by the heating of the molecules of air inside the balloon causing them to move rapidly. In the same manner if we cooled the balloon in a freezer, the volume of air decrease, making the balloon look partially deflated.

In the same manner a Scuba tank filled to 3000 PSI if heated, would increase the pressure in the tank as the volume of the air inside the tank is at a constant.

So how is this applicable to Scuba Diving? For starters, Charles’ law helps divers understand the hazards of leaving scuba tanks out in the hot sun, or why we should never leave tanks in the trunk of a hot car. The gas under pressure subjected to heat can cause the tank to explode. A scuba tank filled to capacity with compressed air at 3000 psi could just as easily go up to 3400-3500 psi if heated. Proper storage of air tanks on the dive boat too is crucial to ensure the tanks aren’t left to bake in the sun.

The law explains why the pressure in a scuba tank recently filled may appear to drop or increase slightly depending on whether the tanks were filled outdoors, or indoors. The law also explains why scuba tanks when being filled with compressed air, get hot.

I’ll admit knowledge of Charles’ Law isn’t as useful to us as perhaps Boyle’s Law, nevertheless it helps us understand everyday phenomenon and helps us better understand the remaining gas laws as well.

The reason for writing an article on Gas Laws is simply because I, like so many other divers, constantly forget the Scuba Gas laws taught to us in our Open Water course. We all tend to understand the concepts and application while diving, but when asked why bleed air from your BCD while ascending, I know that the volume of gas is expanding as pressure decreases, but what was the name of that law again?  Was it Charles’, Boyle’s, Dalton’s or Fred’s? Hopefully this series will help us better understand  and remember these scuba gas laws.

Boyle’s Law

Robert Boyle was a chemist and a physicist who published this law in 1662. The law describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system. In simple English: If you increase pressure, the volume of the gas decreases, and if you increase the volume of the gas, the pressure decreases.

Mathematically Boyle’s Law is expressed as

P1V1=P2V2, where

P1 = Starting Pressure (expressed in absolute pressure, i.e. atmospheres)

V1 = Starting Volume (liters)

P2 = Ending Pressure (expressed in absolute pressure, i.e. atmospheres)

V2 = Ending Volume (liters)

Let’s try and understand Boyle’s law using a simple example. At the surface we are subjected to 1 ATM (atmosphere) of pressure. At 33ft underwater, we are subjected to 2 ATM; i.e. 1 ATM of Air pressure and 1 ATM  of water pressure.

So if we take a 1 liter Coke bottle filled with air faced down with no cap on, to 33ft (10m) underwater, we would see that the volume of air decreases to around ½ a liter of air, and water would begin filling into the bottle without any of the air escaping. Because at 33ft the pressure has increased of 2 ATM or has doubled, thereby halving the volume of the air.  If we take the bottle down to 66ft (20m), we would be at 3 atmospheres of pressure and the air in the bottle would be 1/3 of a liter and so on.

Now assume we add air into the coke bottle from our scuba tanks at the depth of 33ft (10m) topping off the half full bottle, cap the bottle tightly, then begin to ascend.(remember the air in our scuba tank is also being subjected to Boyle’s law ) As we rise, the pressure decreases, causing the already compressed air to expand. At the surface the volume of the air in the 1 liter bottle would have doubled to 2 liters probably causing the bottle to burst on the way up.

This is the reason why we bleed out air from our BCD’s as we ascend to prevent us from rising too fast as the air present inside the BCD expands with decrease in pressure.

Boyle’s Law helps us understand the importance of compensating and balancing air in our BCD’s, masks, lungs, ears, and wherever air is contained. Mask squeeze as we descend, or the need to blip a little air into our BCD’s as we descend deeper to maintain neutral buoyancy is also attributed to this law.

The need to equalize is also attributed to the small air spaces inside our ears, which causes our ear drums to bend as the air behind the ear drums decreases in volume.

The law also explains the reason why we are instructed to exhale deeply and continuously while ascending, and also why we are told never to hold your breath while ascending, as the air inside your lungs can over expand, causing severe internal injury.

photos by riandreu and Mik Canavan