• Introduction
• What do I need to learn, and how do I learn it?
• What's with all that gear?
• What are the risks?

Scuba diving inherently involves a lot of equipment. We are not designed to live in the underwater environment, and so even for a short trip we need a large amount of gear to support our lives, and enable us to see and move around easily. Given that rapid ascent to the surface is not usually advisable, and sometimes not even possible, we also need some gear, such as a dive knife to help get us out of any trouble in which we might find ourselves.

A fully-suited diver. Her lei is not standard gear!

The core of the scuba system has three components: a tank, a regulator, and a buoyancy control device (BCD; also known as a buoyancy compensator, or BC). The tank (also referred to as a "bottle" or "cylinder"), of course, contains the compressed air or other gas that you will be breathing underwater. The regulator converts the high-pressure breathing gas from the tank to low-pressure when you breathe in, delivering just the air you need. And the BCD, along with some extra lead weights you bring along, allows you to control your buoyancy; that is, it allows you to float up or sink down.

Those three pieces of equipment keep you alive while diving. Your mask, fins, and exposure protection are what make it an enjoyable experience. Your mask, of course, is your porthole into this amazing world, while your fins help you move more efficiently through the water. Even warm water is colder than our body temperature, and water will extract heat from your body much faster than air of the same temperature. So an exposure suit, such as a wetsuit, is critical to protect you from the cold and from any scrapes or scratches you may otherwise get.

Other critical pieces of gear include your pressure gauge and depth gauge, although many divers now replace one or both of these with a dive computer. There are other important and useful pieces of equipment that you will get familiar with. Read on for more information on each of the kinds of gear described above, plus lots more.

The tank is a crucial piece of gear, but is actually seldom owned by divers. They are completely impractical for the traveling diver, and even for divers that are lucky enough to be able to go diving within a short distance from their homes, they do not usual make sense. Tanks are bulky and difficult to travel with. Even if you own your own tank, you still have to get a air fills at a local dive shop. To top it off, most of the time you will be doing more than one dive in a day; each dive uses up a tank of air. So unless you are diving right near the shop (which would be very unusual), you would need to get multiple tanks and fill them all up at the shop ahead of time. It just makes more sense to rent them. Renting a full tank of air will only cost three to ten dollars most places anyway; an air fill for your own tank wouldn't cost much less! Unless you are a commercial diver doing hundreds or thousands of dives every year in your local area, the cost and maintenance involved mean that it just doesn't make sense to purchase a tank.

However, it still pays to know something about them. The typical cylinder is the aluminum 80. Aluminum tanks are popular because they are lighter and cheaper than steel tank. The aluminum 80 is the tank you will most often see on dive boats and at dive shops all over the world. It is an aluminum tank that holds as much air as fits in 80 cubic feet at atmospheric pressure, when that air is compressed to 3000psi. In other words, when full, this tank holds as much air as would fit in the bottom one foot of a eight foot by ten foot room. That might not sound like a lot of air, but it means that the air has been squeezed into less than 1/200th the amount of volume it normally takes up. This is enough air for an average diver to have a 45-60 minute dive, depending on depth and other factors.

Occasionally, you'll come across steel tanks. The great thing about steel tanks is that steel is stronger than aluminum, so you can pressurize the tank to higher pressures. For example, a 100 cubic foot steel tank is smaller than an aluminum 80, but holds 25% more air. This means 25% more bottom time. Steel tanks are heavier and more expensive than aluminum tanks, and have different buoyancy characteristics.

The invention that started it all. A regulator has two separate metal contraptions, connected by a hose. The first-stage of the regulator is attached to a valve on the tank. The first stage takes the high-pressure air in the tank and steps it down to the ambient pressure. So the air in the hose connecting the first-stage to the second-stage is at the ambient pressure. For example, when you are at the surface, the ambient pressure is one atmosphere, or about 14.7psi, so the air inside the hose is pressurized to equal the pressure in the air. At 33 feet depth in salt water, the ambient pressure is two atmospheres, and so the first stage has let more air into the hose to equalize the pressure. The second-stage, attached to this low-pressure hose is the piece that you hold in your mouth, and it delivers the air when you suck on it. Since the air is at the ambient pressure, it is comfortable to breathe.

When you breathe air from a regulator at depth, you are filling your lungs with much more air than you would be at the surface. For example, at 33ft, you are holding twice as much air in your lungs than you would be at the surface. Of course, it just feels normal, because you are holding the same volume of air as at the surface. However, you have to be very careful to never hold your breath when scuba diving. If you are holding your breath as you ascend from 33ft toward the surface, the air inside your lungs will expand as the ambient pressure decreases, resulting in an embolism and possibly death.

While it sounds scary, with proper training and care, it can be very safe. This is one of the reasons why diving requires special training and certification.

There is another part of the regulator, affectionately called an octopus, or more formally an "alternate second stage". This is just another second-stage, for backup in the event that the primary second-stage malfunctions, or more commonly for buddy-breathing when your buddy foolishly runs out of air. Since they are rarely used, alternate second stages are usually less expensive models. In addition, they often come in bright yellow or orange. This allows a desperate out-of-air diver the best chance of seeing the octopus, instead of ripping your primary second-stage out your mouth!

Most people naturally have positive buoyancy, meaning they float. Even with all of the scuba gear, most people are still positively buoyant. So, in order to get under the water, we need to carry extra, negatively buoyant weights. Usually, this is done with lead weights strung on a nylon or canvas belt that is worn around the waist.

The goal here is not to be negatively buoyant, so you sink, but rather to have neutral buoyancy. This gives you maximum control over your descent and ascent rate, and allows you to hover without sinking or rising. Slow ascents are important for safety, as is the ability to prevent yourself from sinking to the bottom! In addition, many dives are done in areas with coral reefs and other fragile marine life; divers with poor buoyancy skills can cause damage by colliding with the reef and other creatures.

Unfortunately, it's not quite as easy as just figuring out how much weight to carry. As you descend, your buoyancy changes. Air spaces in your body are compressed, so the you actually take up a little less space, which makes you a little more negatively buoyant. More of an effect is felt however, from the compression of your wetsuit. Neoprene, which most wetsuits are made of, contains many small air bubbles. Just like the spaces in your body, these are compressed, creating more negative buoyancy. Other factors, such as the air you use from your tank and the fullness of your breaths also affect buoyancy.

A jacket-style buoyancy compensator.

This is where the BCD comes in. The primary purpose of the BCD, as the name implies, is to help you control your buoyancy. It is a device, usually a sort of jacket or vest, with air bladders. Modern BCs are attached directly to the first-stage of your regulator, on the low-pressure side, allowing you to use the air from the tank to automatically inflate the bladders. By making small adjustments, a skilled diver can balance the loss of buoyancy from the descent with a little air in the BC's bladder.

Another type of BC that is growing more common is a "back inflation" BC. While the typical jacket-style BC has its largest air bladders on the front sides of the BC, a back inflation BC has its air bladders along the back. Many divers find this more comfortable, and feel it offers them better control.

Many BCs nowadays have "integrated weights". This means that there are removable pouches in which you can put your weights. The pouches are then inserted in special pockets in the BC. The advantage is better weight distribution than with a traditional weight belt. However, because weights must be able to be quickly released in the event of certain kinds of emergencies, manufacturers have had to come up with clever ways to make these pouches quickly removable, without being complicated to insert and without accidentally falling out. More than one diver has put too much weight in the pocket of an integrated-weight BC, only to have the pouch fall out and have to struggle to swim down and retrieve it (remember we need the weight to go down!).

When purchasing a BC, it is important to take into consideration not only jacket-style vs. back inflation and weight-integration, but also lift capacity and fit. Different BCs can hold different amounts of air in their bladders; this results in the ability to create different amounts of positive buoyancy, or lift. And of course BCs come in different sizes, and in different shapes for men and women. It's best to work with a dive retailer when selecting a BC, so that you can have specific advice for your size, shape, skill level, and comfort considerations.

A diving mask. Note the soft silicon contour for access to your nose, but that the nose and eyes are all in one air space.

It is surprising to many newcomers, but the mask is one of the most important and personal pieces of gear. Underwater, smell and taste are not available, and sound is distorted, so you are only left with sight and touch to sense the world. And there are many things underwater which you either don't want to touch, or shouldn't in order to protect and preserve the marine life. So sight is your primary sense underwater, even more so than on land.

The mask is a personal piece of gear because it needs to fit properly. It is frustrating and wasteful of precious air to need to constantly clear the water from a poor-fitting mask. The best method for testing fit is easy to do right in the shop:

1. First, look up.
2. Place the mask over your face as you normally would, except do not pull the strap on.
3. Make sure no hair is caught between your face and the mask, and inhale gently with your nose.
4. Look forward. The mask should stay in place on your face. If it does, it's a good fit.

Don't be afraid to try a number of different masks out in this way; you want to make sure you have a good fit.

Not all masks are appropriate for diving; it is best to get one at a dive shop. Two main things to avoid are swim goggles, and masks that do not have a soft nose covering. Any diving mask must include the nose in the same air space as the eyes, because as you descend you need to exhale air from your nose to prevent the increasing water pressure from pressing the mask into your face too hard. This eliminates swim goggles. Some inexpensive masks do not give the wearer access to the sides of the nose. This can be a problem because many divers need to gently hold their nose in order to properly equalize the pressure in their ears.

Adjustable-strap fins.

Without fins, divers would have no chance of fighting even a mild current. Even if you are a great swimmer on the surface, when you are underwater, with a limited air supply and a lot of extra weight and drag from your gear, swimming without fins is extremely difficult. Fins make us much more dexterous underwater, although no human can approach the speed and dexterity of pretty much any fish or marine mammal.

Full-foot fins.

One of the major decisions in purchasing fins is whether to get an adjustable-strap fin, or a full-foot fin. Adjustable-strap fins have a strap that goes around your heel that can be made looser or tighter as needed. This is useful if you will dive with different kinds of exposure protection for your feet, such as if you dive in both cold and warm water environments. One disadvantage is that they require some sort of booty, since most adjustable-strap fins are very uncomfortable with bare feet.

Full-foot fins are the kind most non-divers have been exposed to. They are molded all of one piece of material, and snugly hold the foot. The big disadvantage is that they are sized very specifically. Since you cannot where booties with them, they are not very good for colder water.

Split fins.

In the last couple years, split fins have become popular. These have been shown to be much more efficient than traditional fins, and their use is growing rapidly. These work by pushing less water up and down, really channeling the energy of your leg movements into pushing the water back instead. Since it is pushing the water back that moves you forward, this results in less work and more forward movement. Less works means less air used and more bottom time!

You should be sure to get fins with an appropriately-sized blade. Fins with too long or large of a blade can be tiring for divers who do not exercise those leg muscles often enough.

Exposure protection includes exposure suits, such as dive skins, wetsuits, and drysuits, as well as gloves, hoods and booties. It serves both to protect you from the cold, and to protect you from stinging corals and bumps and scrapes from sharp edges on wrecks.

Dive Skins

Dive skins provide some thermal protection, as well as protection from stings, scratches, and scrapes. They have the great advantage of being easy to pack, without taking up a lot of space, and of not adding a lot of buoyancy like a wetsuit. Most dive skins provide as much thermal protection as a 2mm wetsuit, but are very thin.

Full-length wetsuit.

Wetsuits

Wetsuits are the most common exposure protection. They are usually made of neoprene and come in a variety of thicknesses, from 0.5mm to 7mm, allowing use in waters ranging from 45° F on up. There are also several different styles, like shorties, farmer johns, and full-length. Wetsuits work by trapping water between the suit and your skin. This water is then warmed by your body, providing extra insulation against the cold. The thickness of the wetsuit determines how quickly the trapped water is cooled, with thicker suits of course slowing the cooling process, and thus keeping you warmer.

It is critical that a wetsuit fits snugly, especially around the openings for your hands, feet, and neck. If the suit is not snug, the trapped water will escape, allowing cold water to replace it, and losing much of the thermal protection.

Dry Suits

Dry suits work differently from wetsuits; they actually keep the water off your skin. This results in much better thermal protection, but they are much bulkier, more expensive, and require special training due to their buoyancy characteristics.

A wetsuit hood.

Accessories

Typical exposure protection accessories are hoods, gloves, and booties. Of these, the hood is the most critical for thermal protection. A large amount of your heat is lost through your head, so by putting on a hood you can greatly increase your warmth underwater. Even just a small beanie or dive cap can make a big difference in your comfort.

Very warm gloves for drysuit diving.

For cold water diving, gloves are also very important to keep your hands comfortable. Booties are more common than hoods or gloves, though, since most people wear booties with their adjustable-strap fins.

You pressure gauge lets you know another vital statistic while you are underwater: how much air you have left. When beginning a dive, your pressure gauge will usually read around 3000psi (assuming you're using an aluminum 80 tank). When you reach 1500 psi, you know you are a little over halfway through the dive. You will want to reach the surface with around 500-700psi left in your tank. The excess is there in case you have any trouble during your ascent, and need to stay down longer.

Needless to say, if you do not carefully monitor your pressure gauge, you can run out of air. This creates an extremely dangerous situation, and is one good reason that the diving community has stuck with the buddy system. You will learn air-sharing techniques in your certification classes, and your training will include ways to help keep calm in an out-of-air situation. Of course, the best thing to do is simply monitor your air and avoid the problem altogether.

An analog pressure gauge (bottom) and an analog depth gauge, in a convenient console.

The depth gauge is another critical piece of gear. While it is not directly involved in your life-support system, without it you could easily cause serious injury or even kill yourself. A large component to safe diving is to carefully monitor your depth and make sure you understand how depth relates to decompression sickness ("the bends"), nitrogen narcosis, air use, oxygen toxicity, and other factors.

Depth gauges come in both analog and digital forms. In addition, all dive computers integrate the depth gauge, as depth is essential to calculating nitrogen loading.

An air-integrated dive computer.

Dive computers have greatly simplified diving, and have provided divers with extended bottom time. When diving without a computer, you use various tables to calculate your nitrogen-loading, which is the amount of dissolved nitrogen in your body tissues. This limits how deep and how long each of your dives can be. With tables, you use the deepest depth you plan to dive to, and calculate how long you can stay submerged based upon that. The dive tables are based on a simple descent to a particular depth, a stay at that depth, and then an ascent. But this does not match with most real dives. Usually, you will ascend and descend some throughout the dive. And often in reef diving environments, you can follow the reef up from deeper depths, slowly ascending with the geography. This makes the tables overestimate the amount of nitrogen build up, resulting in less bottom time for table divers.

A dive computer, on the other hand, continuously monitors how long you have been at various depths, and adjusts your remaining bottom time accordingly. This leads to much more accurate calculations of nitrogen loading, and thus more bottom time.

Many newer dive computers are air-integrated meaning they serve not only to replace the depth gauge and dive tables, but also the pressure gauge. This is handy because they can actually monitor your breathing rate, and give you an indication of how much time you have left, taking into account both nitrogen loading and remaining air.

For just a little more money, you can usually get a version of the computer that handles both normal air and nitrox. Nitrox is another commonly used breathing gas; it is just regular air with additional oxygen added. By adding oxygen, you reduce the amount of nitrogen build up, allowing for longer stays under the surface. Of course, this requires a different technique for calculating nitrogen loading, and thus a different computer. Nitrox diving has other special considerations, and should not be undertaken without special training, regardless of whether your computer can perform nitrox calculations.

A dive knife. Notice the steel knob on the bottom of the hilt. This can be used to tap on the side of your tank to get other divers' attention.

When we said above that the dive knife is used to get you out of trouble, we did not mean that it would be used for defense. In fact, some people prefer to call it a "dive tool" rather than a "knife", since it is not intended as a weapon. Your dive knife is used in case of certain emergencies, such as becoming entangled in fishing line or kelp. It can also be stuck in a sandy bottom to give you a handhold in a stiff current. Generally the knife is used for prying, digging, hacking and chiseling, not for attacking the marine life!

Like other dive gear, you should pick this up at a dive shop. Knives that may be available at sporting goods or other stores will be quickly destroyed by salty sea water. In addition, most dive knives have a line-cutting notch and a serrated edge in addition to the straight-edge. Many dive knives that are not intended for use while spearfishing have a blunt tip, to avoid accidental injury and to improve prying ability.

There are dozens, if not hundreds, of other accessories available to scuba divers. Most divers have a snorkel for long surface swims where you do not want to waste the air in your tank. There are dive lights for night diving and for seeing in dark holes in reefs and wrecks. And a slew of other small accessories, like dive slates for writing under water, whistles and other attention-getting devices for use both on the surface and underwater, and compasses to help you find your way back to the dive boat. Some of these are very important to improve your safety, while others are just useful to have while diving. As you start diving you'll learn which of these little items make sense for the diving you do. So get out there and learn to dive!