Most of us have experienced a winter that brought on warmer temperatures than expected. I for one can’t say I minded it, and above average temps certainly make the rain here much more bearable. With all of that in mind though, the water temperatures have still fallen to reasonably chilly levels.

Most of us divers have to consider that unless you are diving in the tropics along the equator, you need some sort of exposure protection. So let’s take a look at a few methods for protecting your body from the brutal cold underwater by examining some fun facts about temperatures and the difference between wetsuits and drysuits.

The human body loses heat approximately 26 times faster in water than in air of the same temperature. For this reason, when diving in water temperature less than about 90°F (32°C), you must have some means to keep your body warm to prevent hypothermia. The most popular candidate for this task amongst divers across the spectrum is the wetsuit.

Wetsuit Function

If you’ve ever been diving, you have more than likely had to don a wetsuit. My instructors used to tell me, “Remember that there are two kinds of divers: The ones that pee in their wetsuits, and the ones that lie about peeing in their wetsuits.” This adage works on the old school thought that wetsuits use a thin layer of water between the skin and the neoprene material the suit is made of to keep the body warm. The seal in the wetsuit sleeves and neck are supposed to keep new water from seeping in and chilling the body. This fun little tidbit is actually FALSE!

The wetsuit keeps your body warm by heating the air bubbles in the neoprene itself. As a result, the more water that gets into your suit, the less effective it is. So it is not uncommon to see products like Skin Seals being sewn into suits in attempt to keep cold water from getting in.

Wetsuit Fit and Myths

There’s been a strange debate as to how a wetsuit is supposed to fit. A lot of this debate has been fueled from the incorrect assumptions of the “thin layer of water principle” as well as another common myth that suits either shrink or grow over time. So let’s dispel any wetsuit myths now.

First and foremost, the whole fitting issue is simple. Based on how a wetsuit traps heat, you want to select one that fits as close to the body as possible without giving you the body squeezes. This is a simple problem to avoid. A suit should be relatively easy to get onto your body with the neck and sleeves being increasingly difficult to slide over your hands.

It was said in the old days to get a suit that fit larger but this is caused by the lack of availability of quality fabrics in the diving industry. Suits were less flexible and thus tended to squeeze in certain areas more so than today’s higher quality demand.

“Some wetsuits shrink and some wetsuits grow.” Well, if you say so. These claims are both false. The bottom line is that quality suits will not shrink or grow, but rather they will remain the same relative size for years and years. Unfortunately you can’t blame the dryer if your suit has shrunk (most suits can be machine washed). If your suit is fitting a bit snug after the holidays, a running regimen can help your suit fit a little better, I know I need it.

Now if you remember the gas laws article we put up here some time ago, then you may be familiar with Boyle’s Law. Boyle’s Law states that “given a constant temperature, the volume of a gas varies inversely as the absolute pressure.” Then you may be asking, what if I go deeper and those little gas bubbles we talked about decrease in size? You know the answer to that based on logic, the suit becomes less effective and that is why most technical divers turn to the drysuit.

Drysuits

Drysuits are a wonderful tool for those that want to take on a more adventurous or complex style of diving. Regardless of the quality of your wetsuit, eventually they simply cannot hang on to your expectations when you decide to go deeper, colder, or longer. Drysuits are much more complicated to dive with and require an actual training session to be comfortable, but the end result is a more enjoyable dive and some gawking from the other guys on the cattle boat. Let’s talk about how the drysuit works.

Plain and simple, the drysuit keeps you warm based on the clothing you decide to wear underneath it. The suit itself provides no real insulation property, but rather provides the users with a dry climate so that the user can choose appropriate garments to wear inside and a thin pocket of air between the skin and material. I’m not referencing all of the other fancy items out there like the neoprene drysuit, or the semi dry suit, I am talking about the fabric suit that you layer over cold weather garments to protect you from the elements.

This suit is generally fitted for the wearer, slightly oversized to accommodate more layers of clothing underneath. The suit consists of fabric and rubber to produce a watertight barrier with tight rubber seals at the ankles, wrists and neck as well as a waterproof zipper either across the chest or down the back. Rear entry suits require the aid of another diver to be properly donned. Once inside however, the diver is just about ready to hit the water.

Remember earlier when we referenced Boyle’s Law? This Law is a nuisance to the drysuit diver because as the gases between your body and the wall of the suit contract, they will try to suck water in through the seals. Drysuits have little plastic circles on the arms and chest that act as inflators and purge valves. This allows the diver to connect an inflator hose to his suit and force air in to keep the pressure ambient and to act as a buoyancy compensator. Upon ascent, the diver simply purges the air from the suit using any of the purge valves installed and continues a slow and steady climb to the surface.

Dive Skin

When diving in waters that are warm enough to not require a suit, some divers opt for a dive skin. A skin is the diver version of what those of us in the industry refer to as under armor or base layer. It is a thin polyester material that helps reduce the likelihood of scratches, cuts, and rashes from sea life such as fish or coral. These tend to be flattering on the wearer unless you’re Daniel Craig, and provide virtually no insulating properties.

Disclaimer

ITS Tactical cannot be held responsible for any attempts at any form of diving without first seeking professional training and advice. The following article is not intended as a replacement for proper training and equipment used in any water sport activity. Diving is inherently dangerous, and introduces a unique set of risks not typically present in everyday life. We urge you to seek proper instruction from a qualified, and certified agency before attempting any sport requiring a life support system, namely: SCUBA. It is likewise very important that you contact your health care provider before attempting any training classes to ensure you are in good physical condition. Those with pre-existing medical conditions may be at a higher risk for certain complications that may become present while SCUBA Diving.

If you’ve ever been diving, chances are you’ve noticed something unique about those that have been diving for a while. You may have seen tanks lined up on dive boat and noticed those with more experience donning “NITROX” cylinders.

This isn’t just a fancy label, NITROX a mixed gas that helps divers maintain longer bottom times and reduce their risk of decompression sickness. This is generally the only other gas you’ll see when recreational diving, but there are many more out there.

In this article we’re going to go over some of the different gas mixtures, their benefits, draw backs and even ask, “What’s the point?”

Diving Concerns

There are two main concerns when diving (aside from say drowning); Nitrogen and Oxygen buildup. Wait, oxygen? That’s right. On the surface, we breathe oxygen because we need it to survive, but when you get below the surface, oxygen actually becomes toxic and begins to attack your central nervous system. This might sound a little confusing, so I’ll break it down for you.

Topside, we breathe about 21% oxygen, 78% nitrogen and roughly 1% contaminant from pollution. This is the same mixture you will breathe when you hit the water, provided you’re not diving anything other than standard “air.” A mixture of air becomes toxic to humans at about 200 ft (about 67m), whereas 100% oxygen becomes toxic at 20ft (6-7m). This depth is what we refer to as your MOD (Maximum Operating Depth) for a given gas mixture. The MOD will change as the oxygen is increased. To help simplify what we’ve just discussed we’ll cover two main advanced gasmixtures, “NITROX,” and “TRIMIX.” (pronounced “try-mix.”)

NITROX

The most common gas you will see is NITROX, which is simply air with an increased volume of oxygen. The operating range of NITROX is 21% – 40% oxygen. The ratios will change as you increase the oxygen, 21% Oxygen/79% Nitrogen; 40% Oxygen/60% Nitrogen. You might wonder why you would increase your oxygen percentage if it becomes toxic.

While it does reduce your maximum allowable depth, it provides a safety cushion against decompression sickness if dove within safe limits. It will also increase the amount of time you can stay at a given depth. The longer duration you remain close to your MOD, the more time you put on your “O2 Exposure Clock.” This clock lets you know what your overall exposure to oxygen toxicity is in a rolling 24—hour period.

Once you hit 100%, continued diving could have serious consequences such as convulsions and drowning due to CNS O2 Toxicity. The same outcome is likely if you exceed your MOD by more than a few feet/meters. As you can see there are more inherent risks in diving with more oxygen in your tank, but when dove properly, it can buy you a safer dive, longer bottom time and shorter decompression times.

If you dive air, you may have come out of the water experiencing a mild headache, this is caused by excess nitrogen, and are referred to as a “nitrogen headache.” They cause a mild headache, fatigue, and once in a while a little irritability. These headaches are virtually eliminated with the use of NITROX and often leave you with more energy than you began the dive with. Like diving air, as long as you follow your dive plan, you shouldn’t run into any problems.

Editor-in-Chief’s Note: Remember this mnemonic device that they taught us while I was diving in the Navy: Plan your dive and dive your plan!

TRIMIX

So we’ve gone through NITROX and determined that we can dive shallower for longer durations, but what if we want to go deeper? As I mentioned before, oxygen at 21% becomes toxic to humans at 200 ft (67m). The immediate logical decision would be to decrease the oxygen content in the cylinder. That’s all well and good, but there’s still that annoying dependency on oxygen to sustain human life.

Dropping the content much past 18% would surely result in suffocation and I personally can’t think of a worse way to die than suffocating underwater with plenty of air on your back. So what do we do? We know that one gas can counteract the effects of another (oxygen counteracts nitrogen buildup), and we need oxygen to survive. So we add a gas that can counteract the oxygen toxicity… we add helium to the mixture. Helium doesn’t physically counteract the oxygen on any molecular level.

It works to reduce the proportions of oxygen and nitrogen in the cylinder, thus reducing the effects of O2toxicity and the effects of nitrogen absorption. Because of its lower oxygen content(down to about 10% in common mixtures), TRIMIX cannot generally be used on shallower dives, instead a transition gas is breathed until the TRIMIX is at a safe breathable level. This gas presents some immediate dangers, like breathing it on the surface or on dives where it is not intended, it can result in death or severe injury.

Helium

Helium is the key ingredient used to make the gas safer, but is not without its drawbacks. Helium conducts heat about six times faster than air and is not generally a good gas to use when inflating your drysuit (due to the exposure to lower temperatures found at deeper depths, diving a wetsuit is impractical and can be dangerous). We’ll cover diving a drysuit in another article, but what you need to know right now is that it uses air from your cylinder to work properly.

Aside from the heat conductivity, Helium absorbs into tissues much faster than nitrogen and can cause what is known as “Hyperbaric Arthralgia” upon decent. This is basically arthritic joint pain caused by descending too rapidly. Fortunately, it off-gasses much faster than Nitrogen and has very little narcotic effect. If you have ever been on a dive deeper than about 100 ft (34m) then you have more than likely experienced Nitrogen Narcosis. This isn’t necessarily dangerous other than the fact that it produces a narcotic effect which can result in bad decisions.

While it is possible to develop a tolerance to this narcosis, it can be increasingly dangerous as you descend. The Helium acts to counteract these effects as well, making your dive safer and more enjoyable. besides, is there anything more entertaining than hearing all of your dive buddies talking like chipmunks underwater? Of course the obvious advantages of diving with TRIMIX are that of a deeper MOD (something like 500ft (167m), longer bottom times and lower risk of decompression illness. This is all contingent on the assumption that you are sticking to the pre-dive plan. With diving deeper comes more responsibility and attention to detail.

You must stop at designated depths to fulfill your decompression obligation. As with any decompression dive, TRIMIX divers will leave full cylinders secured to a line at their predetermined deco depths to minimize the amount of weight carried through the dive. As they ascend from their dive and stop to decompress, they will “pick up” their bottles (cylinders) and continue the ascent. Generally speaking, these bottles will have progressively higher oxygen content (NITROX) to speed up the decompression process.

Notes

I don’t want to get too technical with TRIMIX diving, I merely wanted to point out some of the pros and cons on diving with different gases. There is awhole world out there waiting to be explored and if you have the proper motivation, you can find the people to get you into deeper waters and more technical diving.

While there are more dangers present and significantly more math involved, you’ll find the effort is definitely rewarding. Feel free to post any comments or questions. I do my best to share the knowledge I have of diving with the community, but I’m still relatively new to TRIMIX and may have missed something (exact mixtures of TRIMIX are intentionally left out). As always, be safe and have fun!

Whether you are recreation diving, combat diving, technical diving, or just goofing around in the pool, there are some things to keep in mind.

In all of my years of diving, I didn’t hear the words “tighten up your rig” until I started tech diving. I spent a lot of time diving off of cattle boats, but looking back, I wish someone had mentioned what I am about to cover just a little bit sooner.

I want to give you some pointers and lay out the benefits of the pony/bailout bottle as well as a review of some “safe second” devices. This article is going to be very informative for those that have not been around a diving community much. We have some ground to cover, so I’ll jump right in.

Controversy

There is often the controversy of “shears vs. knives” in the diving world. People tend to get very heated bout the subject, as with nearly anything in diving. For some reason or another, people believe there is only one right way to dive, and similar to dog trainers, there way is best.

I’m not going to instruct you on how your dives should be completed, but instead I will present you with the facts and my personal opinions, allowing you to draw your own conclusions. So, instead of fighting over knives and scissors, which is a remedy for potential bad situation, why not take some preventative measures instead?

Pressure

Your standard SCUBA diving 1st stage regulator consists of (generally) 1-2 high pressure ports, and 2-4 low pressure ports. High pressure ports support the much higher pressure of the cylinder to display your remaining air supply on your pressure gauge.

Low pressure ports supply your 2nd stage equipment with a much lower, intermediate working pressure (around 130 psi/9 bar). Your second stage equipment consists (again, generally) of 2 working regulators (one primary, one secondary) and your inflator for your BC (Buoyancy Compensator).

Some diving in the colder waters will generally have an extra hose for the inflator on their drysuits, but if you don’t know about this, you probably don’t need to yet.

Snags

So now we have all of these hoses running every which way, and they are very good at getting snagged on things. Trust me, your 2nd stage regulators pop off of their hoses with little more than a gentle tug underwater. I feel certain most of divers reading this article have seen the guy with his octopus and his pressure gauge hanging freely from his gear. Most of the time, these hoses drag the ground and do a great job of destroying the coral reefs. This is more than just obnoxious, this is flat out dangerous. How can a rubber hose be dangerous?

Let’s put this same “hose dragger” on a wreck dive for a minute. He and his buddy decide to go inside. Being the irresponsible divers that they are, one of them whacks the yoke of his regulator really hard on the overhead ceiling. The regulator pops off, damaged, and the diver loses his air. So he grabs his buddy to let him know he is in trouble. But he can’t find his octopus. I don’t have to go into detail, and I am sure you have formulated your own “well I would…” by now. Hopefully you wouldn’t dive with this person in the first place.

Tighten up your rig

With that behind us, let’s move on to tightening up your rig. In tech diving the instructors like to go over your gear very thoroughly with you before you even consider getting in the pool. The first thing I was taught about assembling my rig was to turn my first stage regulators on their side, and allow the hoses to head straight down the length of the tanks.

Most always you will see rental gear, and regular open water divers that have hoses spanning out to either side of their bodies. In my humble opinion, this makes you look like you are from another planet, and is absolutely ridiculous.

Following the steps below will get your hoses out of the space around you, and into your gear so that you will be streamlined and much safer in the water. Keep in mind that this is not to “DIR” standards and is not to be used as a reference to tech diving. This is a reference for recreational SCUBA ONLY.

• Begin by removing all hoses and plugs (those things with the hex key openings) from your first stage regulator.
• Turn the regulator so that it will allow the hoses to travel downward, as if they are to be run right alongside your tank.
• Now plug the holes on the top of the regulator. The idea here is to (again) get your hoses running down your rig, and not up or out.
• Begin attaching the hoses one by one, loosely, so that they sort of cradle your body instead of fanning out.
• Attach clips, snaps, or bungees to your octo and gauge console. Be careful not to clip anything across your body as this could prevent a quick escape from your gear if necessary.
• Ensure you don’t try to shorten the length of your hoses by tucking them under the 1st stage regulator, you want as much length as possible for a diver in an out-of-air scenario.
• Avoid any extreme bends or creases in your hoses as you begin to set everything in place. When the rig becomes pressurized, creases can rupture, or (most likely) the fit will change compared to what you had planned as the air straightens the hoses.

If you are diving a pony or a bailout bottle, it may be ok to remove one regulator from your dive setup as your entire system has become redundant. An extra inflator hose is a good idea for the overly cautious, but you can always inflate your BC manually underwater with little effort.

Pony/Bailout Bottle

A growing trend in SCUBA is the bailout bottle. This is a bottle ranging in size from 3-40 cubic feet. I don’t know what this translates to in the metric system, but maybe half a liter to something like 5 liters. Anyway, these bottles are carried in a number of ways.

The smallest bottles are usually put into a custom bag with a hook and loop closure on top and then strapped to the leg. The medium sized bottles can be tucked underneath the dive wing or bladder. The larger ones are either mounted on the side of the primary tank, or hung off of the front of the diver like a stage bottle.

Editor’s note: A HEED Bottle (Helicopter Emergency Egress Device) is shown on the right and is commonly used for helicopter water emergencies, but has found its way into service as a bailout bottle in SCUBA/Combat Diving applications.

The use of a pony bottle or a bailout bottle provides a very large safety cushion for the diver, but also poses a new set of obstacles. In most cases, the bottles have to be offset with counter weight. The diver must take several things into account like the negative weight of the bottle in the water, the weight of the regulator, how far is the bottle from your center of gravity, and so forth. Most ponies are of aluminum construction and tend to get positively buoyant as they are drained, so counter weight must be readily moveable to prevent instability.

On the flip side of hassling with weight, there is the added safety as mentioned before. When diving with “doubles,” you are required to dive with a completely independent regulator on each tank. Each regulator consists of a 2nd stage regulator, an inflator hose, and a pressure gauge.

The primary tanks can be isolated from one another in the event of a catastrophic failure by closing the manifold. There is no need for a backup 2nd stage regulator on either side since you have two complete breathing systems. This is the same concept with the pony bottle. It’s there for emergencies like a system failure or an accidental deco hit.

Safe Second

If you’re not one to add another bottle to your array of gear, you can always add an integrated regulator/inflator to your BC. I don’t recommend these for technical diving, but again, you are welcome to do as you wish. The point of this device is to basically streamline your gear by removing a hose that would be used for your back up regulator.

It’s also a great piece of equipment for that diver who can’t get his stray hoses under control since you won’t have to flail about while you look for your other octo so your buddy doesn’t drown. You simply pull your primary reg. out of your mouth and pass it off to your buddy, and grab your inflator system to begin breathing.

I don’t personally use one of these devices on my technical rig because they often require special hoses, and carrying extra bottles in an emergency situation makes operating your inflator cumbersome. I do, however, use one on my other BC that I use for diving warm water reefs and shallower wrecks. This sort of thing simply boils down to preference.

Notes

There is nothing dangerous about this equipment, so don’t let divers scare you out of what’s comfortable for you, regardless of experience level. Remember, you’re the one that has to dive your rig, so don’t let someone else decide what’s best for you. Take your time, get it right, and have fun.

There is a little running joke amongst our dive circle that says “Divers and dog trainers are just alike. The only thing they can agree on is that everyone else is wrong.” It doesn’t take long to see that everyone has their own flavor of diving and gear. You must have your own style as well. Remember to check out Intro to Diving if you are a little confused about getting into diving.

There is a threat at the heart of diving, an opponent so deft that we may not have a chance to fight back until it is too late.

This factor is present in nearly everything we do, but underwater it could mean your life. This unnoticed opponent is simply, complacency. I have been working here and there on a series of articles for ITS in regards to diving, but after a personal experience, I want to bring this one to the forefront.

A couple of weeks ago I fell victim to a dive computer malfunction. I’d used my computer on over 50 dives without a second thought on its reliability, and nearly paid the price. You see, over the course of the last year, I’ve become rather complacent.

While using my computer without incident, I began to omit things that I deemed unnecessary for the dive. Unfortunately, this dive I had opted out of my dive watch and my dive tables. I guess in a manner of sorts I am lucky because I was able to notice that I had fallen 12 minutes into decompression dive before my computer went on the fritz. Using what I know from past limited-decompression dives, I headed for the ascent line and made additional safety stops.

Equipment and Procedures

Most dive charters use their own scuba tanks for the customers, as well as provide gear for a minimal cost. This can pose some minor problems for divers that typically use their own scuba gear due to the unfamiliarity with the rental equipment. Hopefully, prior to getting on the boat, you’ll have time to go over your rental gear with your buddy.

At the very least, discuss your out of air scenario thoroughly before entering the water. Make sure your dive is properly planned, and please, be realistic with yourself. Diving outside of one’s abilities often leads to unnecessary deaths. Editor’s note: A great mnemonic device for diving is “plan your dive and dive your plan.” Make sure you also carry some form of surface signaling device and make sure to ask when the batteries were last changed in the rental lights and computers.

I want you to think about a moment in your life when you may have skipped something you thought was unnecessary, only to come out alive. Certainly you’ve been in a situation that you looked back on and said, “man, that could have gone terribly wrong.” Think about what you would have done differently if that situation did end up a disaster.

I’d also like to add some friendly advice to those diving in foreign countries. I understand the UK and the US primarily hold the same standards for diving. Some of the more remote or far off countries may not though. I know for certain that there are PADI five star dive centers all over the world, but unfortunately, I cannot speak to any of the other diving agencies.

If you plan to dive with a charter that is not sponsored by such an agency and you plan on diving with their rental gear, here are some friendly tips:

• Inspect rental gear thoroughly before diving, check for corrosion or rust anywhere on the gear.
• Be sure to turn the tank on and make sure the air contains no smell or odor of any kind, as this may mean contamination.
• Face your dive buddy with all of your gear on and go over your emergency scenarios.
• Ask the dive charter when the batteries were changed in their computers and lights, if necessary, buy your own new batteries. It’s a shame to “waste” the money, but is your life not worth $10?
• After your gear is set up and ready to go, test all inflators, purge buttons, and regulators prior to entering the water.
• Most importantly, have fun and be safe. Diving is an adventure that should be shared by everyone.

Closing Notes

Make sure you divers don’t turn my mishap into your nightmare. I have been diving for 11 years and have been in many bad scenarios, but this is the first time I have been wholly responsible for my own endangerment.

I urge everyone here to get their gear serviced regularly, and change the batteries in your computers and lights often. Diving is a great experience, but don’t let complacency prevent you from enjoying it.

Disclaimer

ITS Tactical cannot be held responsible for any attempts at any form of diving without first seeking professional training and advice. The following article is not intended as a replacement for proper training and equipment used in any water sport activity. Diving is inherently dangerous, and introduces a unique set of risks not typically present in everyday life. We urge you to seek proper instruction from a qualified, and certified agency before attempting any sport requiring a life support system, namely: SCUBA. It is likewise very important that you contact your health care provider before attempting any training classes to ensure you are in good physical condition. Those with pre-existing medical conditions may be at a higher risk for certain complications that may become present while SCUBA Diving.

So now that we’ve got the diving introduction out of the way, let’s jump right into what we feel is a major issue. When it comes to SCUBA Diving, it is important to know your Gas Laws. In Dive Physics, during the Second Phase of BUD/s, they teach you that these laws are very important to a diver. A diver must be aware of the physics affecting him underwater. Without the knowledge of what happens to the human body underwater, circumstances could easily become disastrous.

In this article, we’re going to cover six important diving laws and principles that every diver needs to be aware of. We urge you to study this article and develop a full understanding of how these laws work and to draw your own opinions about why they’re important. The definitions are taken from documents provided in BUD/s training, and we can’t think of anyone better to talk to about the water than the SEALs.

Boyle’s Law

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Boyle’s Law states that “given a constant temperature, the volume of a gas varies inversely as the absolute pressure.”

This law can be interpreted any way you like, but we should stress that this law is dependent on the absolute pressure. That means that as the pressure increases, the volume decreases. It would be silly to think that you could decrease the absolute pressure simply by increasing the volume of a gas, so it is fair to say that as pressure decreases, the volume will increase.

To illustrate this law, we take a bottle full of air down to a depth of about 100ft (30m), or 3 ATA (atmospheres). As the bottle descends, the absolute pressure around the bottle forces the gas (Air) inside the bottle to compress therefore allowing for less volume. This happens because as you go deeper into water, the pressure increases at a rate of one ATA every 33ft (10m). This is the pressure that decreases the volume of gas inside your bottle.

Lets say we take that bottle up into the air 36,000 ft. (10,970m), cruising altitude for a standard commercial jet liner. The air in the atmosphere actually has a lower absolute pressure than we do here on the surface. You may have heard a little rumor about how space is a vacuum, well this is that transitional point from our perfect living conditions. Now, using Boyle’s Law we can conclude that the bottle will actually grow as the absolute pressure around it decreases. The difference here is that the pressure changes are not as drastic in the atmosphere of planet Earth as they are in the water.

Charles’s Law / Gay-Lussac’s Law

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Charle’s law states that given a constant pressure, the volume of a gas varies directly as the absolute temperature. This law is sometimes referred to as Gay-Lussac’s Law.

This is probably one of the simpler laws. The same principles are in play most often in your daily life. Most of you know that as metal gets hot or cold, it expands and contracts (more notably than other things like plastic). Well gases do the same thing.

What Charles’s Law says is that if you take a volume of air, and keep it at a constant pressure, you can increase your volume simply by heating it up. You could also effectively reduce the volume by putting it in a deep freeze, or setting it outside if you live up north. So to illustrate this law, we use a SCUBA tank.

When a SCUBA cylinder is filled, the friction of the air entering the cylinder heats things up from the inside out. This makes the surface of the cylinder warm to the touch. Just about all of your shops will overfill cylinders by about 10%, which is the maximum allowed by the DOT. There is a reason for this.

Every cylinder model has a different “working pressure,” which means that they can handle being filled to lets say 3000 psi (206 bar), plus 10% of that pressure. So then we have a cylinder that gets filled to 3300 psi (227 bar). This is not a safe working pressure for the cylinder (theoretically), so why do we fill a cylinder to more than its safe working pressure? They are overfilled because of Charle’s Law. Friction heats the cylinder and that cylinder will eventually cool off, thus, decreasing the volume of air inside. So to counter this effect, dive shops put more air in the cylinder than would be necessary for a typical dive.

Dalton’s Law

Dalton’s Law states that the total pressure exerted by a mixture of gases is the sum of the pressures exerted by each of the gases.

This is pretty straight forward. It becomes most useful for anyone qualified to fill a scuba cylinder. Lets say your target working pressure is 3000 psi (206 bar) for a typical SCUBA cylinder fill. Normally, you would take the air from the room you are standing in, compress it down, and pump it into a cylinder. Some people prefer the use of different breathing gases. For simplicity’s sake, we’ll use the breathing gas “NITROX.” There will be an article on the different gases, so don’t panic if you are a little confused by this. The air we breath is an average 21% Oxygen 79% Nitrogen. Nitrox is a gas with an oxygen content of 22%-40%. The benefits of breathing oxygen rich gas are numerous, but we’ll cover that as well at a later date.

So, to reach a higher oxygen content, there are formulas that need to be followed. Many factors go into consideration, such as working pressure, cylinder volume, percent of O2 desired, etc. The basic formula says this: start with Xpsi of 100% O2, and then fill to 3000 psi (206 bar) with air. This gives the desired percentage of oxygen in your nitrox gas. So we have a hypothetical 400 psi (27 bar) of pure oxygen, and we will top off the cylinder with 2600 psi (179 bar) with air, leaving 3000 psi (206 bar) of pressure in the cylinder. 400 + 2600= 3000psi (27+179=206 bar). The total pressure is equal to the sum of the pressure of each part of the mixture.

Henry’s Law

Henry’s Law states that the amount of gas that will dissolve in a liquid is directly proportional to the partial pressure of that gas.

Here is a law that goes much deeper than mixing gases and heating SCUBA cylinders. This is the mother of dive laws in our opinion, but we believe others would agree. This law does not reference any of what has been discussed previously. We could think of ways to get gases to dissolve into fluids, but this law should be presented in the manner it was intended.

If you’ve taken a diving class, you know that nitrogen is your biggest opponent underwater. Nitrogen happens to be a gas, but we’re not so worried about the nitrogen absorbing into the water at higher pressures. Not hardly. You see, while you’re on the surface, nitrogen absorbs into your skin. This is not a real issue while you’re walking around, driving your cars, etc. Take that body down to 100 ft (30 m) of water and you change the circumstances dramatically.

During your time underwater, the pressure around your body forces nitrogen into your blood stream. This can (but not always) lead to a rather pleasant narcotic feeling at depth we refer to as “nitrogen narcosis.” Nitrogen has a narcotic effect on the brain which can be alleviated by ascending to a shallower depth until symptoms pass. The longer you stay, and the deeper you go, the more nitrogen will be forced into your blood stream. If you don’t get narcosis easily, then you will most likely not notice the build up of excess nitrogen in your blood. We know this gas is present because of very extensive research conducted by Navies around the world, more notably the US Navy which releases nearly a thousand page manual on diving to certain jobs.

The nitrogen at depth is not the issue, but rather when you complete your dive and begin your ascent to the surface. As you ascend, the nitrogen gas that has dissolved into your blood stream will begin to form bubbles as the gas expands. If you were to acquire an excess of nitrogen and immediately get out of the water, within about 15 minutes you would begin showing symptoms of DCS (decompression sickness) which can be fatal if not treated. This sickness has been dubbed “the bends,” or “Cassien’s disease” by divers in the past. This build up of nitrogen is removed from the body by ascending to a shallower depth and allowing the nitrogen to pass through your blood stream, and into your lungs. Once in your lungs, the nitrogen returns to its undissolved, gas state and passes from your body as you exhale. The depth and amount of time required for “off-gassing” is directly related to the amount of time, and depth of your dive.

Dive Tables

To prevent death or nerve damage, the US Navy released what is a called a “dive table.” If you are a certified diver, you will have been required to dive from a table to acquire your certification. For those who may be unfamiliar, a standard air diving table basically lets you know how much nitrogen you will build up at any depth for any amount of time. This basic table is a “no-decompression dive table,” which means that at any depth (to 130 ft or 40m) for any time allotted on the table, you will not be required to stop and off-gas nitrogen since you have not acquired any excess in your bloodstream. Tables can be quite confusing if you have never used one before so I will break it down for you.

In a nutshell, you select the depth at which you plan on diving. Always use the deepest point of the dive, even if it’s only for a minute unless you are using a planning wheel which will be covered at a later date. The depths are typically listed in both feet and meters so everyone can safely understand them. Next, move down the row to the corresponding number of minutes you plan on staying. You may notice that the deeper you plan on going, the less time you have available for the actual dive. The numbers represent the maximum amount of dive time allowed per dopplar no-decompression diving limits. Any longer, and you are in a decompression dive, which is not necessarily a dangerous situation, but you must be prepared for decompression stops. Some dive tables have mild decompression diving information on them used generally for emergency situations.

The tables help you understand how much nitrogen has been absorbed into your bloodstream, and what precautions must be taken to prevent serious illness that may prevent you from diving in the future. Going beyond the dopplar limits without proper training could prove to be fatal.

Archimedes Principle

Archimedes Principle states that and object wholly or partially immersed in a liquid is buoyed up by the force equal to the weight of the liquid displaced.

This one is very simple to understand. Lets say we fill a cup with water until it’s about to spill over the edge. Then we take a rock, and drop it in that cup, the water would begin to flow over onto the table. Now to find the value referenced by Archimedes Principle, we would simple take the water that spilled, and weigh it. Lets say for the sake of argument the displacement of the water weighs eight grams. That means, according to the principle in discussion, that the rock is being pushed back up with a force of 8 grams.

This law is similar to Newton’s law of relative motion which states: for every action, there is an equal and opposite reaction. This is basically the same theory, we are just talking about objects being immersed in fluid, rather than friction and motion.

We use this law for many different things while in the water. It is mostly used to calculate the specific buoyancy of an object. This will be important for anyone that spends time underwater. For instance, if your Buoyancy Compensation Device does not have the lift capacity to bring up your steel SCUBA cylinders, you will surely be stuck on the bottom. We can set values to plan these things because of Archimedes Principle.

This law doesn’t only apply to the underwater community. Naval Architects will use this principal to calculate many different requirements of a ship’s hull. An aircraft carrier is made mostly out of steel, but because of the way she’s designed, she floats. If you were to place any discrepancy in the hull of a carrier below the water line, the consequences could be dire. The same goes for the laws of density. If you have two pieces of bread, and you throw one in the water like it is, then it will float, but if you crush the other into a ball and toss it, it will surely sink. This is the issue with ships as well, if we use Archimedes Principle along with other amazingly simple laws, we have enormous metal structures floating and moving under their own power.

Notes

We’d like to thank Derek Gill for his help in getting these gas laws rounded up into an article for ITS, and appreciate all his help. Please let us know if you have any further questions regarding any of these gas laws, and be sure to throw up a comment. We look forward to bringing you more information in the future regarding diving, and would like to hear what you’re interested in!

Disclaimer

ITS Tactical cannot be held responsible for any attempts at any form of diving without first seeking professional training and advice. The following article is not intended as a replacement for proper training and equipment used in any water sport activity. Diving is inherently dangerous, and introduces a unique set of risks not typically present in everyday life. We urge you to seek proper instruction from a qualified, and certified agency before attempting any sport requiring a life support system, namely: SCUBA. It is likewise very important that you contact your health care provider before attempting any training classes to ensure you are in good physical condition. Those with pre-existing medical conditions may be at a higher risk for certain complications that may become present while SCUBA Diving.

There’s a sport, both recreational and professional, that goes unnoticed by many people every day. When a plane goes down in the Hudson River, when a ship meets disaster and sinks, when oil rigs needs to be built, and when SEALs need to get somewhere undetected, they turn to a skill that has continuously been in development since it’s very inception.

SCUBA diving has evolved from the aqualung, to the Closed-Circuit Rebreather (CCR) through many years of trial-and-error, and extensive research. Originally developed as a stunt, SCUBA (Self Contained Underwater Breathing Apparatus) has brought a new twist to both civilian, and military operations.

So, I’ve gotten together with ITS Tactical to bring you a more in depth look at what SCUBA Diving is, and why it’s important to every productive member of society.

Rescue Diving

There are styles of diving available for people from all walks of life, but the popular opinion here says the most important style is rescue diving. There are varying degrees of rescue diving that go beyond saving someone in an out-of-air situation. This particular flavor takes you into emergency first responder, dive rescue, and even search and recovery, depending on your class schedule.

You don’t have to be an EMT, or a commercial diver to get that phone call requesting an immediate response to the trapped divers in the shipwreck off the coast of Key Largo. You do, however, have a certain path you must follow to get there.

The focus of this article is to help encourage everyone to get involved with their local diving community. There are a series of articles on diving getting fired up, and I personally want to make sure no one is lost when they start appearing on the homepage.

While it would be nice to list the ins and outs of diving, I’m not here to teach, nor am I licensed to teach. Instead, I want to give a few pointers on finding the right dive shop or certification agency for you.

Getting Certified

The first step you must take in SCUBA is “Open Water Diver” certification. A few of the more popular agencies are PADI, NAUI, SSI, and PDIC. Many people are particular to PADI since they will often make dive shops follow certain standards to maintain their insurance and licenses by labeling them “PADI 5 Star Certified.” This DOES NOT mean that the other agencies are less strict. I personally chose the SSI route, and hold certifications in all four agencies listed as well as others.

Nowadays, most agencies offer online, and distance learning for most of your certification, leaving only the pool work and check-out dives to be completed in person. This certification teaches you the basic knowledge, skills, and habits to be a SCUBA Diver.

So now you’re excited about getting started, right? Here are some things you should keep in mind while looking for a dive shop. Many instructors unfortunately use their training classes as a sales pitch. They will take the opportunity to lock you down and sell you the most expensive gear they stock because anything less is just blatant suicide.

I assure you, there is not one piece of diving equipment commercially available in the world that is unsafe or prone to failure, especially not for an open water diver. Bottom line is this, if it was unsafe, they would not sell it. Don’t feel like you must have all of the latest and greatest gear. In fact, I don’t even recommend the investment in a dive computer until you move to Advanced Open Water Diver. Fancy, expensive gear doesn’t make you a better diver, it just gives you more to worry about while you’re down there.

Next, ask around. If you work in an office, there is a good chance that someone working around you is secretly an avid diver. This will be your best bet for finding a shop that will not try to cut corners with your education. If you don’t know anyone, a quick google search will show the shops in your area. Pay them a visit, but don’t commit to anything unless you feel very good about the establishment.

The shop should be clean and well maintained, as well as have a friendly and knowledgeable staff. Make sure to ask what their safety record is. They should say 100%. If they don’t, think very carefully about what you’re getting into with that particular shop.

Don’t stress the agency so much, since they generally all teach exactly the same things. The only real concern here is that you stick to one of the certifying agencies that have proven results, and a generally high satisfaction rate. Remember that dive instructors by their very nature are strange individuals. Don’t let them scare you off before you finish your class.

Here is a list of the previously mentioned agencies and their website links:

• PADI www.padi.com
• PDIC www.pdic-intl.com
• NAUI www.naui.org
• SSI www.divessi.com

Have a look at some of these sites, and feel free to post some others that you may be partial to. My experience with SCUBA certification does not extend beyond the borders of America. Keep your eyes peeled here for some upcoming discussions on old school diving and how you can learn sure fire ways to stay out of trouble on multi-level dives.

Disclaimer

ITS Tactical cannot be held responsible for any attempts at any form of diving without first seeking professional training and advice. The following article is not intended as a replacement for proper training and equipment used in any water sport activity. Diving is inherently dangerous, and introduces a unique set of risks not typically present in everyday life. We urge you to seek proper instruction from a qualified, and certified agency before attempting any sport requiring a life support system, namely: SCUBA. It is likewise very important that you contact your health care provider before attempting any training classes to ensure you are in good physical condition. Those with pre-existing medical conditions may be at a higher risk for certain complications that may become present while SCUBA Diving.