Nitrox diving is becoming increasingly popular in Scuba diving recently. So much so, that you can almost always spot one or two of those telltale green and yellow tanks that announce the presence of nitrox or oxygen-enriched air in dive boats across the world. Often confused for jargon related to technical diving, nitrox has actually been used in recreational diving for nearly over 25 years. For anyone unfamiliar with Nitrox and why you want to dive nitrox we’ve put together a practical guide to Nitrox diving for the everyday diver.

What is Nitrox and Enriched Air Nitrox (EAN)?
Nitrox simply means a mix of nitrogen and oxygen. In diving terminology however, enriched air nitrox (EAN) sometimes referred to as just Nitrox is a special nitrogen/oxygen gas mixture with an oxygen concentration higher than the 21 percent found in normal air. While the gas mixture can come in a variety of ratios including less than the normal 21% oxygen, a mixture containing more than 21% oxygen is used in recreational and sport diving and is called hyperoxic nitrox. It’s also called SafeAir or Enriched Air Nitrox (EAN or EANx). The ‘x’ in EANx stands for the percentage of oxygen in the mix and is clearly marked with a nitrox tank band on the scuba tank and states the mix percentage, for eg. EAN40 (40% oxygen in the mix).

There are two general types of diving nitrox: Nitrox I also called Nitrox 32, which is comprised of 32% oxygen and 68% nitrogen (EAN32); and Nitrox II, also called Nitrox 36, which is comprises of 36% oxygen and 64% nitrogen (EAN36). The 32 percent oxygen concentration is the most common in Nitrox diving.

How does Nitrox/EAN diving differ from diving with regular air?
As we all learn when we first start diving in the Open Water Certification, water pressure causes the nitrogen from the air you breathe to dissolve in your bloodstream. The longer and deeper a diver is underwater, the more nitrogen is absorbed by his system. As the nitrogen builds up, a diver can only be underwater for a limited time depending on depth as the pressure is more deeper and then must ascend slowly, make decompression stops consequent surface interval times before diving again.

The diving time allowed when using enriched air nitrox changes as the “enriched” air used has more oxygen and less nitrogen. This means, when diving nitrox a divers body absorbs less nitrogen during the dive than a diver that uses regular air. It’s important to note however, that although enriched air nitrox allows a longer no-decompression limit, it does not eliminate the risk of decompression sickness or nitrogen narcosis but simply lowers it.

Another common misconception about Nitrox is that it allows you to dive deeper, well this is not the case. According to the percentage of oxygen in a nitrox mix, the maximum operating depth becomes is shallower with the increase in oxygen. A Nitrox mix is good for mid deep dives ranging from 20-40 meters (60-130 feet).

Risks of Nitrox Diving
While Nitrox diving may increase bottom time for no decompression dives and lowers the risk of nitrogen narcosis it comes with it’s own concerns that air diving doesn’t have. For one, the increased levels of oxygen too can be narcotic and hazardous in high concentrations. It is called oxygen toxicity, which can lead to visual distortions or even convulsions. The major problem with oxygen toxicity is that you may get little or no warning of an attack making them harder to survive.

As nitrox contains a larger percentage of the highly flammable oxygen, the handling and cleaning of Nitrox tanks and valves must be done properly with care to avoid unintended explosions.

In short nitrox diving is not any less dangerous than air. Like conventional diving when done right with the proper training (special nitrox certification is a must) and when the guidelines are adhered there is no increased risk and it can be a safe activity to pursue.

*Photo Credits: photos by bananeman, nsyll, c.lathe and CasaDeQueso on flickr.

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

There’s always a fascination and illusion that Scuba diving means to dive deep. The belief doing rounds is that there’s better stuff to see, but this in fact is one of the most common mistakes of many new divers, as we’ve seen in Myth Buster: More Scuba Diving Misconceptions Dispelled.

Recreational Scuba divers breath compressed air and are limited by physical laws to a certain amount of time underwater at a certain depth. The standard rule of thumb however is the deeper you dive, the less time you can spend underwater. That leads us to one of the most common questions asked about diving: “How deep can you scuba dive?”.  While there’s no fixed answer to the question as you can potentially dive as deep as you like, there are consequences and risks of diving beyond certain depths with standard scuba diving equipment.

To put it in perspective, when you get your first certification to dive (Open Water Diver) the dept limit to dive is 60 feet (18 meters) whereas an Advanced Open Water diver is certified to dive to 100 feet (30 meters). Different Scuba certification agencies permit different depth after the various training levels are complete. However, PADI recommends that the absolute maximum depth for any recreational diver is 40m (130ft), while BSAC says a maximum depth of 50m (165ft) is ok with proper training.

Just because you can go a certain depth does certainly not mean it is safe to dive at to that depth. At depths between 30-60m, while not dangerous in itself, divers are likely to experience the intoxicating condition of nitrogen narcosis which can have a severe impact on a diver’s decision making, leading to stupid and sometimes dangerous actions. After a certain depth, at partial pressures greater than 1.44bar, the oxygen in a divers air supply becomes toxic, so going further or experiencing this toxicity for too long could prove fatal.

Due to increased pressure at greater depths the chances of decompression sickness are also increased. Diver’s are required to take longer decompression stops, to avoid the formation of gas bubbles in the body. By releasing the water pressure on the body slowly at the end of the dive and allowing gases trapped in the bloodstream to gradually break solution and leave the body, a diver minimizes their chances of getting ‘the bends’. Another concern when diving deep is air consumption. Under  water pressure the air in a diver’s tank too gets compressed further, providing fewer “breaths” which in turn runs out a lot quicker than if you were diving at a shallower depth. This means either carrying an additional small cylinder of air called a pony bottle or having a drop tank available is advisable.

In technical diving, 60 metres / 200 feet may be a “deep dive”. These divers use specialized pieces of scuba diving equipment or special gas mixtures other than normal atmospheric air to overcome depth issues like nitrogen narcosis, oxygen toxicity and the tremendous pressure. It is possible to technical divers to go deeper than 200m (700ft) with closed circuit rebreathers. This sort of ultra-deep diving requires extraordinarily high levels of training, experience, fitness and surface support in the form of decompression chambers.

FUN FACT: The Holy Grail of deep SCUBA diving was the 1,000 ft (300 m) mark, first achieved by John Bennett in 2001 and has only been achieved twice since. Only eight (or possibly nine) persons are known to have ever dived below a depth of 800 feet (240 m) on self contained breathing apparatus recreationally. That is fewer than the number of people who have walked on the surface of the moon!

*Photo credits: photos by Ilse Reijs en Jan-Noud Hutten, Dude Crush, star5112,  Rafael Robayna – ecocentrik.com on flickr

The simple and most commonly heard answer to this question is yes, it is true; you don’t have to be especially good at swimming to Scuba dive.

I’ve heard this said a little too often and surprisingly by some experienced Scuba Instructors which is a little worrying to say in the least especially when the statement isn’t backed up by a longer explanation. What is even more shocking is when you hear somebody say, “You don’t need to know how to swim to Scuba Dive, your BCD acts as a life vest”. The truth is that you need to be able to swim if you want to learn to Scuba dive, and not just one swimming lesson either,  to get by your certification requirements, but well enough to be able to save yourself should the worst occur. Certification agencies like NAUI and PADI require the diver to be able to swim at least 200m unaided to certify, and to be able to tread water (stay afloat) for at least 10 minutes and be comfortable in the water. This is the bare minimum requirement to be able to Scuba Dive.

So when an instructor tells you that you need to be especially good at swimming, it means that you may not need to be a champion swimmer, but for your own safety and to those around you, you should at least be able to comfortably swim back to a dive boat, stay afloat unaided while waiting for a dive boat to come pick you up, and be able to swim underwater without constantly bumping into your dive buddy or in to every coral outcrop. Knowing how to swim well will improve your confidence in the water, and will prevent you from panicking should you need to do a surface swim with a deflated Buoyancy Compensator.

What if on the way to your dive site you get knocked into the water when the dive boat hits a particularly rough wave? You would need to swim or tread water until the dive boat returned to pick you up. . Just one of the many reasons why knowing how to swim properly is necessary to learn Scuba Diving.

Knowing swimming techniques is especially useful when diving in currents, by being able to avoid objects when currents change or to simply find your way around underwater.  Learning how to streamline your movements underwater and minimize ineffective movements that consume energy and precious air, are all things that you can learn by being good at swimming. Divers who haven’t learnt how to propel the water around them using minimal hand and fin movements often end up stirring the sea bed, or have trouble controlling buoyancy and maneuvering underwater.

So if you spend that extra time in the pool fine tuning those swimming techniques, you’ll be pleasantly surprised at how much the spent will help you in your Scuba diving.

Photos by Camp ASCCA, Magnera, David Clow – Maryland

If you want to try Scuba diving and are looking to take up the Sport, getting an Open Water Certification is one of the the first steps to doing so as we’ve previously mentioned in the post- “3 Steps to Becoming a Certified Scuba Diver “. There are a number of Scuba Certification Agencies that offer this basic course that teaches you scuba diving skills required to dive safely and independently without a dive professional.

Most scuba certification agencies differ in their teaching styles, courses and syllabus but they all more or less cover the same basic skills in the open water certification. Here’s what you learn to become an Open Water Diver-

Practical Skills and Training:

• Preparation and assembly of all your Scuba equipment and gear for a dive. Disassembly of equipment post-dive.
• Pre-Dive Buddy safety check. Making sure that you and your buddy’s equipment is in place and working properly before the dive.
• Hand signals used underwater to signal your dive buddy in case of an emergency. Other standard hand signals.
• Water entry methods – wading/shore entry, giant stride method, seated entry and back roll entry. (Read: Scuba Diving Water Entry Methods)
• Regulator clearing and recovery. Techniques to recover your regulator in the event that it is knocked out of your mouth.(Read: Scuba Regulator Recovery and Clearing techniques)
• Mask clearing. Learning to clear a partially/ fully flooded mask comfortably underwater. Completely removing and replacing your mask underwater while breathing.
• Use of Buddy’s alternate air source. Role play scenarios of being out of air, signaling to your buddy, securing their alternate air source and ascending safely with them.
• Buddy breathing. Sharing one air source between buddies to simulate an emergency situation and learning to ascend safely while buddy breathing.
• Buoyancy control. Learning how to hover and regulate your buoyancy underwater.
• BCD Oral Inflation. Practicing how to orally inflate your buoyancy compensator/ buoyancy control device in case the inflator is not functioning properly.
• Proper descent and ascent. Following safe descending and ascending methods.

Theoretical Knowledge:

• Scuba Gas Laws – Charles Law, Henry’s Law &  Boyle’s Law
• Reading Dive tables.
• Dive Planning. Calculating dive times and decompression stops.
• Risks of Scuba Diving
• Decompression Sickness
• Scuba diving safety

Some certification agencies may include some more advanced skills like underwater navigation and no mask swimming,  scuba unit removal and replacement and so on. But making sure you properly learn and practice the above skills in your open water course, you should be just fine underwater to confidently scuba dive with a buddy.

* Photo Credits: photos by Nemo’s great uncle, Philip Morton, frerieke, @kevinv033 on Flickr.

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

Even though Regulator recovery and clearing is one of the most basic things taught to a diver during his open water certification course, it is still a crucial skill that several  divers are reluctant to learn or practice after their certification courses.  Regulator mouthpieces get knocked out of divers’ mouths all the time, and can easily get snagged on BCD’s. In our certification courses we learn to recover our scuba regulators while kneeling on a steady platform such as the sea bed or the bottom of a swimming pool, which is why it is important to practice recovery where you may not be able to steady yourself.

The important things to remember while recovering your regulator is :

Don’t Panic – calmly try and locate your regulator mouthpiece using the practiced methods

Exhale continuously when you lose your second stage, to prevent lung over expansion injuries. Avoid holding your breath.

Sweep Method
The sweep method is the most commonly used technique to recover a second stage regulator. It involves  the diver leaning towards the right to let gravity move the second stage away from you and then stretching out your right hand in front of you and  making a sweeping arc,  back and right towards the bottom of your scuba tank so that the regulator hose should now be in front of you, and then bringing your arm forward catching the rouge regulator.  You then bring the regulator to your mouth purging the piece first before resuming normal breathing. The whole process takes less than a few seconds and can be repeated a couple of time if you are unsuccessful at first. Always remember to continuously breathe out through the process to prevent your lungs from over expansion, should you be unconsciously ascending while looking for your dive regulator.

Over-The-Shoulder Reach Technique
The Over-the-shoulder reach technique is one of the more effective techniques for lost scuba regulator recovery. Lean towards the right turning your neck to the right while reaching  back with your right hand until you feel the first stage of your regulator while at the same time lifting the bottom of your tank with your left hand so you can see the first stage. Then following the hose from the first stage with your right hands thumb and forefinger bring it forward so you can find the second stage and retrieve it. Many find this technique a little tricky and prefer the sweep method, however with a little bit of practice, the over-the-shoulder retrieval is more reliable.

Secondary Regulator
What if you cannot retrieve your regulator using both the sweep method or over the shoulder reach? Don’t panic, use your spare secondary regulator that should be clipped onto the front of your BCD, unclip it and begin breathing normally. Then calmly try to locate your main second stage once again.

Get your Buddy to Assist
Sometimes it helps to signal your buddy to help you spot your missing regulator, as it could be snagged in your BCD belts.  Use your spare regulator while your dive buddy assists you with retrieval. Some divers comfortable with removing their BCD’s while maintaining buoyancy, do so to free their tangled hoses. Always remember to have your buddy standing by to perform buddy breathing if you ever attempt to try this.

Clearing
Clearing your regulator is as simple as exhaling sharply into it. All the water will be expelled from the regulators exhaust valve. The other method to clear your mouthpiece is to use the purge valve. A quick two bursts of the purge valve immediately before putting it into your mouth should remove any water or debris from the chamber.  Or alternately depress the purge valve while it is in your mouth blocking the mouth piece with your tongue to prevent the burst of air into your mouth. Be careful to release the purge valve once you resume inhaling to prevent over filling of the lungs.

Scuba Divers should practice all of these methods in a controlled environment on a regular basis, so that they remain calm when the situation may occur. Use the method you are most comfortable with using and ensure you practice more than just one.

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

Navigating your way underwater where there are no roads, no signs, no prominent landmarks so to speak is not an easy Scuba diving skill to master. Coupled with other factors playing on a divers mind like buoyancy control, keeping time, depth, conserving air and of course co-coordinating with your buddy, underwater navigation is all the more difficult to keep a track off. Dive sites don’t come with maps and the terrain underwater appears random, irregular and often unpredictable unless you’ve dived the site before a number of times, so this diving skill takes more than a little practice to acquire. When you do learn underwater navigation and know exactly where you’re going, where you’ve been and where you are at any given time underwater, it definitely makes diving a lot more enjoyable and stress free.

Here are 10 tips for improving your underwater navigation skills:

1. Plan Ahead - An important part of underwater navigation is gathering as much information about the location before hand. Collect information about the expected scenario like large coral formations, rocks, drop offs, sandy patches, wreck size, and so on from experienced divers or dive operators in the area.

2. Draw a Map – Map out the dive site on dive slate before you go and maybe chalk out an intended dive plan in the direction you want to go in for reference underwater. Sometimes just doing that helps you visualize the map in your head and you may not need to use the map. A good idea is once you’re diving the site you can note certain landmarks on your map to find your way back easily.

3. Know where your dive boat is - Just like a car in a parking lot you need to make a note of where your dive begins, so as to return to the right spot. Make a mental note of the surroundings, any particular rock or coral formations where you first descend. Pay attention to the direction you can see the sun and remember what your dive boat looks like from under especially if there are more than one in the vicinity.

4. Carry a compass - As a minimum, a diver must carry an underwater compass for navigation. Buy a simple compass and learn the correct way to use it. Take it on guided dives to get the hang of using it before heading off on your own.

5. Setting the bezel - Before beginning a dive you should set the bezel of your compass to point you to the direction dive boat and in case of shore diving to the shore. In this case once the bearing is set it shouldn’t be changed during the dive and to return, one simply rotates himself in the opposite direction.

6. Measuring distance - A rookie mistake when it comes to underwater navigation is noting down the direction but completely losing track or not measuring distance. It’s important to know exactly how far you have swum out and in what direction in order to return. One way of doing this if you are a consistent swimmer is by time or even air consumption. It may not be as accurate as counting fin strokes as you are thought in your course but it sure beats spending most of your dive concentrating on counting rather than the surroundings.

7. Use natural directional indicators – When diving in good clear water conditions and in the day, the sun is a great natural compass. For example during a morning dive you know the sun will be in eastern direction while for afternoon dives the sun indicates west.Sand ripples caused by currents too are good directional indicators as they always run parallel to the shore. The deeper imprint of the ripple, the nearer to the shore you are.

8. Don’t use currents as indicators - Don’t rely on currents to tell you in which direction you are heading. Currents can twist and turn around undersea objects thereby leading you astray.

9. Trust your instruments - If there is a discrepancy between what you feel and what your dive compass is telling you, go with the compass. Be sure that it is working properly before the dive and that there is no interference from undersea objects like shipwrecks or anything that can be magnetic however.

10. Practice, practice, practice – Practice using your compass on land. Do squares, rectangles, set headings and reciprocals, note bearings, in short…perfect your compass skills on land. Then on guided dives, practice your own navigation rather than blindly following the dive master, it’s a great feeling to successfully hit your mark when you try. Make it a habit to jot down things like bearings, landmarks, directions, times on your dive slate throughout your dive. With time and practice you’ll be a pro at navigating during a dive and even the fish will be seeking your instructions.

* Photos by Brianz and Jorge del Valle on flickr

** Products pictured above – Aqua Glow Slate Medium 4″ X 6″ , Oceanic Optional SWIV Compass and Suunto SK7 Add-On Compass. All available from LeisurePro.com

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