As a PADI Dive Master; I enjoy taking people diving and showing them around the dive site and where all the critters hide out. I also enjoy talking and teaching the ins and outs of diving because I believe the better we understand the fundamentals the better our decisions are in the water.
In this article, I'm going to focus on a beginner explanation of how scuba works and why it works the way it does.
The fact that we have the ability to spend extended amounts of time underwater is a huge feat for mankind. We owe much of our gratitude to the pioneers of underwater exploration. People like Jacques Cousteau, inventor of scuba-diving apparatus and film-maker is a pioneer that is well known in the sport of diving.
The incredible history of some of our most iconic ships below the surface would most likely still be a mystery to us today, along with the thousands of species of life we have discovered and still discover would be unheard of.
The best part here is with just a couple of hours of training you can find yourself enjoying this beautiful underwater world.
How Scuba Works
As land roving mammals we face two major problems underwater. I will attempt to outline these problems as best I possibly can.
1. Breathing - although free divers have the ability to stay underwater for as long as a few minutes at a time, it's not enough for those that desire uninterrupted lengthy visits to the depths, and because we are land mammals, we require some type of device to assist our breathing for extended periods of time underwater.
2. Buoyancy - is one of the most fundamental aspects of diving behind the ability to breathe underwater. Buoyancy is the upward force exerted by a fluid that opposes the weight of an object. For instance, if you go into the water and the weight and mass of your body are lighter than that of the water you are trying to displace your body will float. Take that same amount of weight in a smaller object which will displace less water and it will sink.
In short, the problem here is our bodies are too light for the amount of water we are displacing so we need a device to both sink our bodies and float our bodies in the water, this is called neutral buoyancy, we will get into this more later.
There are a few factors at play here which are saltwater vs freshwater. Saltwater is much heavier than freshwater because it contains a higher amount of minerals which explains why we are much more buoyant in saltwater. It takes more weight to displace that amount of water.
Muscle mass is another factor that determines our buoyance, as muscle is denser than fat so it displaces less water and sinks more readily.
Scuba Equipment
In short, scuba is the acronym for Self Contained Breathing Apparatus. Essentially it is an apparatus that allows you to stay and breathe underwater. This apparatus has many parts and features that work in unison to make that happen.
Let's break down the equipment and its key features. There are many different types and designs for each part we are going to be discussing, but to keep things simple I will not be getting too technical in this post.
When diving we need some protection from the cooler temperatures underwater so in this section we will discuss how we do that and how it affects the problems we face underwater.
Wetsuit - Also called exposure suit; this piece of equipment keeps you warm and comfortable underwater. As you descend below the surface the temperature drops so you need an extra layer of insulation. This comes in the form of a neoprene suit in various thicknesses and lengths, from 3mm to as much as 8mm in thickness, and a half suit designed to protect your upper body and vital organs from the chilly water to full piece protection with a hood and boots.
A wetsuit works, not only by creating an insulated barrier between your skin and the water but also by creating a layer of water between the shin and the suit. Your body heats up this layer of water and it eventually equalizes with the temperature of the skin. Because water takes longer to heat and cool, the sudden temperature changes below the surface aren't experienced as drastically as they would be without that layer of protection.
Drysuit - A drysuit on the other hand is as it says; a drysuit. They are worn in frigid waters or below the ice. They are commonly made of stockinette fabric coated with vulcanized rubber, laminated layers of nylon, and butyl rubber with an inner layer of polyurethane. This is the outer layer, the diver also wears an inner garment that is comfortable and insulated.
The drysuit is normally fitted with latex seals around the hands and neck. They usually come with a pair of attached boots and a hood.
There is also a low-pressure connection that allows the diver to add extra air to the suit for buoyance or thermal protection. The diver must also be able to dump that air so it will also have at least one dump valve.
Section Conclusion
While an exposure suit solves the problem of thermal protection, it does not solve either of the two main problems discussed above, in fact, it adds to the buoyance problem as the wet and drysuit both add a lot of buoyance and very little weight. As a result, the diver is most likely going to struggle to get below the surface, never mind 20 or 40 feet. The good news is there is a way to counteract that problem so stay with me and we will find out what that is.
Breathing
The equipment involved that gives the diver the ability to breathe underwater is the most important part of the dive kit. It consists of the compressed air cylinder, the first stage regulator, and a second stage regulator along with a second stage called the octopus which is for emergency use.
In this section, we are going to look at the equipment and its important features, that allows the diver to breathe underwater.
Cylinder - There are many different types of cylinders in the dive industry and each has its own application, but the most common is the 12litre aluminum body. It holds 80 cubic feet of air or nitrox that is compressed to around 3000psi. Since the air is compressed we need a device to reduce the pressure to a breathable pressure. This is done via two regulators.
1. First Stage Regulator - The first stage regulator attaches to the cylinder and reduces the pressure from 3000psi to an intermediate pressure around 140psi. This is still far too much pressure to breathe so we need a second stage.
2. Second Stage Regulator - The second stage regulator is attached to the first stage via a high-pressure hose and has a mouthpiece that the diver puts into their mouth and breathes the compressed air from the cylinder. The diver can breathe fairly normally from this regulator by drawing air in and the exhaled air is released into the surrounding water.
Section Conclusion
With cylinders and 2 regulators, we have solved the number one problem we face underwater. There are many different regulator types and designs but they fundamentally work the same to solve the same problem.
Buoyance
When it comes to buoyancy, neutral buoyancy is what we are trying to achieve. That allows us to control our positioning in the water. In this section, we are going to have a look at the equipment that helps the diver accomplish that.
BCD - Is the acronym for the device known as Buoyancy Compensator Device. The BCD is a jacket-style device with pockets and D-rings to attach to and keep things streamlined and in an orderly fashion. It has two important features.
1. Integrated Weights System- Remember in the exposure protection section above that the wet and drysuit adds buoyance that doesn't allow the diver to descend; most new BCD's are equipped with an Integrated Weight System that allows the diver to strategically place the right amount of lead weights in specifically designed pockets or clip-on pouches to counteract the existing or added buoyance. For BCD's that don't have a Weight Integrated System, the diver wears the weights on a belt known simply as a weight belt. The diver usually adds enough weight to be slightly overweight with all the gear on. This means that they would readily descend upon entering the water.
2. Bladder - This is the area where things get tricky. The BCD is also equipped with an inflatable bladder that is either on the back of the jacket known as a back wing style or on either side, extending from the hips to the underarm area, this is known as the jacket BCD.
We know that when a diver has the proper amount of weight they are negatively buoyant, as mentioned above they would most likely descend upon entering the water. However, adding a little bit of air to the bladder again counteracts the extra weight which will keep the diver afloat. The BCD is equipped with a deflator allowing the diver to deflate the bladder whenever they are ready to descend.
Divers always preplan every dive. This means that they know how deep they are going to be diving, so when the diver gets to the desired depth they can add or subtract air from the bladder to neutralize themselves in the water. This is called neutral buoyancy, meaning the diver is not descending nor ascending they are simply bobbing at a certain depth. This is why it's tricky as it takes practice to master buoyancy and maintain good control underwater. The act of breathing adds complication to this, as an in-breath adds buoyancy and the diver would naturally ascend a little bit, but this effect can be minimized by a combination of having just the right amount of air in the bladder and a swimming technique.
Section Conclusion
The BCD and its features give us the ability to control our positioning underwater and this solves one of the problems we face. Although there are many different types and styles of BCD devices they fundamentally all work the same way.
Additional Dive Equipment
Diving requires more than regulators and BCD. We need to know how much air we have consumed and how much we have remaining. We need to keep track of our time underwater as well as manage the hazards that compressed air and dive physics have on our bodies. So in this section we will discuss some of the most important dive equipment, accessories and their features.
SPG & Compas - Is the acronym for submersible pressure gauge. It is a simple pressure gauge that shows the pressure in the air cylinder. This is a safety device so the the diver has a visually representation of the remaining air and make a safe return to the surface.
A compass is also essential for diving. The diver would use it to navigate underwater.
Dive Computer - When the diver descends in the water they are subjecting the body to higher pressure due to the water column above them. This is considered atmospheric pressure. Atmospheric pressure increases by 1 every 33 feet or 10 meters. This means that the pressure the body experiences on the surface doubles at 33feet, tripples at 66 feet and so on. This has a tremendous effect on a few things in our bodies. The first being the air pockets like the eardrum and that sinus cavity. The diver would experience extreme discomfort called squeeze. That can be overcome by equalizing the air pocket.
Another, and probably the most important, of is the compression of gas molecules in our system. The air we breathe is a mixture of mostly nitrogen (78 percent) and some oxygen (21 percent). When you inhale air, your body consumes oxygen, replaces some of it with carbon dioxide and does nothing with the nitrogen. At normal atmospheric pressure, some nitrogen and oxygen is dissolved in the fluid portions of your blood and tissues. As you descend under the water, the pressure on your body increases, so more nitrogen and oxygen dissolve in your blood. Most of the oxygen gets consumed by your tissues, but the nitrogen remains dissolved. Increased nitrogen pressure has two problematic effects on your body: nitrogen narcosis and residual nitrogen.
These problematic effects can be life-threatening to the diver so we need a piece of equipment to mediate that risk. This is where the drive computer comes in. Although it cannot save the diver from these life threatening situations, the dive computer can certainly warn the diver when they are approaching the limits that can be life threatening, by tracking the divers depth and calculating the intake of nitrogen and visually displaying the current depth and allowed bottom time at that depth.
Mask & Fins - We cant forget mask and fins as you can't go very far without seeing, or a piece of equipment that can aid movement while conserving as much energy as possible underwater.
Section Conclusion
It's important to remember that this additional safety equipment will not save a diver, they are just aids that sound alarms and give the diver a visual reference so they can make life saving decisions underwater.
Accessories
Nothing nowadays comes without bells and whistles anymore and diving is not an acception. there is some equipment that falls into the accessory category because they are not necessary for diving. However, most of this equipment would be considered part of the standard kit. In this section we will be looking at some of these accessories.
SMB - Calle a submersible marker buoye. This device is a sausage-like tube with the standard scuba marker (red with a white diagonal stripe) on it. It is deployed to the surface to provide visual reference to boats on the positioning of the divers below the surface. It is deployed by adding air to the open end of the SMB, it then floats to the surface. It is attached to the diver via a line.
Light - Dive light is required in low visibility situations. These lights are waterproof and come in various powers and sizes. They are an essential piece of equipment for night diving.
Dive Knife - A knife is more of a safety device. With so much fishing activity there are bound to be abandoned fishing nets and lines. A diving knife can be a life saver should the diver get entangled in this line or net. It also serves as a general tool for prying and and other applications.
DPV - A DPV (dive perpulsion vehicle) is an underwater scooter. It is used for traveling long distances and in most cases for physically impaired divers.
Section Conclusion
Although these tools are considered essential in diving, they can be extremely helpful in providing extra safety underwater. They should be part of every divers kit.
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