All divers understand the importance of the gas they carry; seasoned divers, on the other hand, understand and practice techniques that help conserve the gas in their cylinder in an effort to extend gas reserves.
There are many techniques that can have an impact on lowering gas usage; all it takes is good sense and paying attention to finer details.
Avoiding Heat Loss
Staying warm on the surface and underwater is fundamental to saving gas. When we are cold, our body’s metabolism accelerates to generate additional heat, which requires metabolic fuel in the form of oxygen and calories. As a consequence, we breathe more in an effort to meet the metabolic demand. Wearing proper thermal protection while on the surface before the dive, and while under water during the dive will help prevent heat loss by keeping our metabolism in check. This, in turn will help lower overall gas consumption.
Every person has a “comfort threshold;” the edges on either side of their comfort range at which they become uncomfortably warm or cold. However, most people do not consider the rate of heat loss as a factor in their overall comfort. For example, people generally feel comfortable until their skin temperature reaches approximately 29°C / 84°F). Though, an air temperature of 29°C / 84°F) is very comfortable; we wear light clothing, shorts and sandals. In the water, heat is absorbed 25 times faster than air at the same temperature. A water temperature of 29°C / 84°F) is also quite nice; however, a diver who stays in water at this temperature for an extended period of time will lose body heat at a dangerous rate, without realizing it. For this reason, any time a diver feels that he is cold, whether on the surface or under water, he must increase his thermal protection. Of course, it is best for divers to prevent this altogether by wearing the appropriate thermal protection to begin with.
It is vital that divers keep warm during every phase of the dive, especially during surface intervals. Cooling due to evaporation will cause body heat loss when wearing a wet exposure suit, or wet bathing suit. To prevent this from happening, and to retain as much body heat as possible while on the surface, it is recommended to change into dry clothing immediately following the dive. The ideal solution is to wear a dry suit on every dive. In warm or cold water, the proper use of a dry suit will keep you dry, and you can adjust what you wear underneath to stay comfortable in most water temperatures. Talk to your SNSI Instructor for more information about the SNSI Dry Suit Diver program.
Heat and Temperature are related, but they are not the same thing. Heat is a form of energy and is distinct from temperature. Specifically, heat affects a substance’s thermal capacity. For instance, three different substances, that each has a distinct thermal capacity, can all be at the same temperature at the same time; however, the amount of heat required to change each substance’s temperature by one degree may be different. Heat is often measured in calories, kilocalories or joules. A calorie corresponds to the amount of energy required to raise the temperature of one gram of water by one degree Celsius at one atmosphere. A kilocalorie is the amount of energy required to raise the temperature of one kilogram (1000 grams) of water by one degree Celsius at one atmosphere. One joule is equal to approximately 0.24 calories. The thermal capacity of water is far greater than that of air. Meaning that it takes much more heat (energy), to warm a given amount of water by one degree Celsius than it does to warm the same amount of air by one degree Celsius. This is essentially why water stays cooler than the air during warm summer days, and warmer than the air during the winter months.
When discussing the transfer of heat in a scientific setting, the thermal transfer coefficient, also known as the heat transfer coefficient, is used to calculate heat transfer. The heat transfer coefficient of a substance, along with many other variables, defines the substance’s ability to release heat to, or absorb heat from another substance. This value differs based on the transmission properties of the substances involved, along with a number of other properties. There are three ways that heat is transmitted by one substance to another: conduction, convection and radiation.
Heat transfer via conduction takes place when two or more objects, separate from, or within the same body, are in direct contact with one another. More precisely, conduction is when heat energy is transferred via collisions between molecules that are next to each other. The thermal transfer coefficient of a substance by conduction depends on the type of substances in contact with one another. Metals, for example, are excellent heat conductors; neoprene suits are not, which make them perfect insulators for divers.
Heat transfer via convection is most commonly seen in fluids and gases. Convection occurs when a heated substance’s molecules move away from the source of the heat, the molecules become less dense and rise. As they cool, they become denser and sink towards the source of the heat. This cycle forms a circular motion as the molecules warm and cool. This is one of the mechanisms by which heat is removed from the unprotected diver. Water touches the divers skin where it is warmed, becomes less dense and rises, only to be replaced by denser, cooler molecules. While diving in a current, the molecules are pulled away from the diver after they rise, so the diver’s body is constantly heating colder water. As this takes place, the diver’s body uses energy via metabolism, in order to stay warm. This happens faster in water than in air because water’s thermal transfer coefficient by convection is much greater than air’s. Wearing a wet suit helps prevent this from happening; though, it is important to understand that heat transfer through convection often occurs simultaneously with conduction. Preventing, or slowing one form of heat transfer does not always mean that another form will be prevented.
Heat transfer via radiation is very different than that of conduction and convection. Radiation heat transfer takes place as energy emitted as electromagnetic waves, mostly in the infrared wavelength spectrum and does not involve the interaction of matter. All substances that have a measurable temperature radiate heat; however, there is little to no application for divers beyond that of the sun’s thermal radiation on the Earth.
When the diver loses an excessive amount of heat and the body temperature decreases from the normal 37°C / 98.6°F to below 35°C / 95°F), the beginning stages of hypothermia have set in. Hypothermia and other temperature related conditions are examined further in the SNSI Rescue Diver course.
Buoyancy Control
Good buoyancy control helps you look and feel like an advanced diver. It helps diving become more comfortable and enjoyable for you and your buddy, and boosts your confidence. But, most importantly, as it relates to this section, it helps you decrease your overall gas consumption.
For these reasons, throughout your SNSI Advanced Open Water Diver practical sessions, your instructor will make sure that you are maintaining your buoyancy by demonstrating good buoyancy control skills.
Moving Calmly Underwater
Whenever possible, swimming with fins in the water should be calm and tranquil. This will help you save energy and make your dives more enjoyable. Referring back to the discussion on hydrodynamics, you will recall that water is 700 to 800 times denser than air. As divers, we must expend a significant amount of energy to propel our body and equipment through it. Simply doubling our speed while underwater requires four times the amount of energy. Additionally, when we kick harder and faster, our fin’s efficiency decreases, and we must significantly increase our gas intake, which means that our regulator resistance increases. The faster we try to go, the more we realize that it is a losing battle over the long term. It is best to maintain a slow and wide kicking style, which will help you to save gas and enjoy the dive.
Hydrodynamic and Streamlining
Ensuring your body and equipment are streamlined before entering the water is one of the simplest ways to reduce gas consumption. As cave divers are well aware, dangling and disorganized equipment increases their gas consumption because of the additional drag it creates, not to mention that it is an invitation for snags and trouble. In order to save gas, and their equipment, cave divers streamline themselves to become more hydrodynamic.
The first step towards becoming more hydrodynamic is to secure all dangling instruments and hoses. These create significant resistance in the water, which requires more energy output from the diver to overcome. Dangling equipment damages the environment when it touches a reef, or when it is dragged along the bottom. In turn, this causes damage to your life support equipment. The best way to avoid this is to secure your instruments, hoses and alternate air source to your BCD in such a way that they are still easily accessible, but secure and out of the way. Your SNSI Instructor will help you arrange your equipment so that you are more hydrodynamic.
REDUCING Gas Consuming Actions
When you think about it, it is surprising to see how much gas is used with no apparent reason.
It is highly recommended that you evaluate your habits and actions before and during a dive to help identify the actions that result in gas consumption.
For example, while you are waiting for your buddy to join you at the descent line, are you breathing from your second-stage regulator? Or, do you have your snorkel in your mouth?
Underwater Awareness
Getting lost while under water will result in higher gas consumption for many reasons. When you are lost, you are not using your gas for the purpose of the dive. It can be stressful, which results in a higher breathing rate, which will also affect your buoyancy control.
If you do not know where you are, or where you are going, it is likely that you will surface, following the correct ascent procedures, to gain your bearings, resulting in wasted gas.
Diving in currents can be an enjoyment or a frustration depending on how you have planned the dive.
To help you save energy and your breathing gas, it is highly recommended to plan a dive so that it progresses in the direction of the current rather than against it.
A properly planned drift dive will allow you and your buddy to simply “go with the flow” of the current and relax until it is time to exit the water. Most drift diving is conducted from a boat, so it is a good idea to be familiar with boat diving etiquette. The next chapter of this manual will discuss boat diving techniques.
When drift diving is not an option, it is a good idea to dive in an area that has little to no current.
Consult a tide table and find out what time high and low tide are expected in the area you plan to dive. If diving in current is unavoidable, always start your dive swimming into the current. You will have more energy at the beginning of the dive and will be able to use the current to help you back when it is time to return.
Preventing Gas Leaks
There are very few things in scuba diving that are as irritating as a gas leak. You may have seen, or possibly may have experienced this: a consistent, small pearl-like string of bubbles, streaming away unused. While these small leaks may seem irrelevant, they add up, especially at depth when the escaping gas is significantly more than what escapes at the surface.
When checking for leaks, pay attention to hose connections points, particularly at the high and low-pressure ports on the first stage, and the junction where the hoses connect to your gauges and second-stages.
To find out if there is a leak in your system, assemble your scuba unit and open the cylinder valve enough to pressurize the entire unit. Note the cylinder pressure indicated on your pressure gauge. Close the cylinder valve, but do not relive the pressure. Wait a few minutes and check the pressure gauge again. If the pressure has gone down from the initial reading, there is a leak somewhere in the system.
If you cannot find the leak while the scuba unit is dry, submerge it in water and look for a consistent stream of bubbles. If the bubbles originate at a connection point, disconnect the hose, inspect the o-ring, and remove any visible debris. Reconnect the hose, pressurize the system and check for leaks again. Often, this is sufficient to correct the problem; however, if the leak remains, you will need to have it inspected and repaired by a professional equipment technician.
Your mask is an important piece of equipment. It may also be a point of significant gas loss. Every time you clear your mask, you are using gas. If you have to clear your mask often, due to leaks or fogging, you are using more gas than you need to be.
Before every dive, check your mask’s seals, and apply commercial defog to the lenses. If your seals are in good condition, and you still experience leaks, take off your mask and put it on again. Make sure that there are no obstructions between the mask seal and your face. Common culprits include hair, hoods and aesthetic accessories.
Mental State
An individual’s mental state can have a significant affect on respiratory rate and overall performance. These are compounded under water. A diver who is nervous, anxious, or stressed will have an increased respiratory rate, their heart will beat faster, and they may become tense. In contrast, a relaxed diver will breathe normally, have a normal heart rate and feel comfortable in the water.
There are a variety of ways to reduce stress and tension under water. However, the best ways to become more comfortable under water are by diving frequently and continuing with more advanced training. The SNSI Rescue Diver course is highly recommended for all divers to participate in as it provides practical information and hands-on training regarding stress prevention and management.
Maintain Static, Upward Trending Depth Profiles
Every diver rises and sinks during a dive; but, a dive in which there are multiple or erratic profile changes, has a significant effect on gas usage. Each time you sink, you deflate your BCD, and every time you rise, you inflate the BCD.
At depth, this can amount to a large amount of gas that is essentially wasted. In order to help prevent this, plan your dives accurately so that you have a relatively static depth profile. Start your dive at the deepest point and work towards the surface.
If you find that there is something at a deeper depth that you want to explore, include it in the plan for the next dive.
Reducing gas consumption allows you to extend your dive time, increase your comfort and helps to make you a more confident diver.
You are able to increase your gas reserve, which is valuable in the event of an emergency, or if you need to assist another diver.