Emergency Decompression Guidelines for Scuba Diving

 

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By Natalie Gibb

Scuba Diving Expert

If you plan your dive and dive your plan, there really is no reason that you should have to perform an emergency decompression stop on a recreational dive. However, everyone makes mistakes, and sometimes it’s easy to get distracted and stay down too long or stray too deep. Sometimes, exceeding your planned maximum depth or dive time happens due to forces beyond your control — staying below to help a buddy or because of an emergency situation.

As a recreational diver, you should never plan to exceed (or even dive right up to the no-decompression limits), but if you accidentally find yourself past your dive time or maximum depth and running to deco, it’s good to know what to do.

Emergency Decompression Guidelines

  • If a no-decompression limit is exceeded by 5 minutes or less: make an 8 minute stop at 15 feet and remain out of the water for 6 hours before diving again.
  • If a no-decompression limit is exceed by more than 5 minutes: make at least a 15 minute stop at 15 feet and remain out of the water for a minimum of 24 hours before diving again.

Will You Remember These Numbers on a Dive?

The emergency decompression rules are easy to memorize, but in an emergency situation, it is quite likely that a diver’s memory may not be functioning at full capacity. It is a good idea to write this information down on a slate or even on the back of your computer so that you have access to it in the unlikely event of an emergency decompression situation.

How Will You Monitor Your Emergency Decompression Stop?

Consider the series of events that leads a diver to find himself requiring emergency decompression. While a diver may simply forget to check his computer or watch, another likely situation is that he needs to perform emergency decompression because of a computer or watch failure.

Without a timing device, he may have no way to monitor the length of his emergency decompression stop. Unless his buddy is nearby, the only option left is to count out the minutes. If a diver finds himself alone and without a timing device, he may have to simply wait at the stop depth until he has used most of his breathing gas (hopefully exceeding the minimum required stop time) before surfacing slowly. Divers should be prepared for this possibility

Most regulators have an analog depth gauge, but in an absolutely worst-case scenario, a diver relying only on a computer could find himself with no idea of his depth as well as his dive time. In this situation, an observant diver may be able to visually estimate his depth, but most divers would be hard pressed to hold themselves at exactly 15 feet with no depth gauge. At this point, the diver should make his best guess and estimate. Emergency decompression imperfectly done is still better than no emergency decompression at all.

Availability of Breathing Gas

Emergency decompression can only be performed as long as the diver has air left in his tank and/or has a buddy whom he can share gas with. This is yet another reason to always dive conservatively, and to plan to surface from a dive with plenty of gas in reserve.

There Is Nothing Inherently Wrong with Decompression

This entire article is devoted to emergency decompression stops and how to avoid having to make them, but keep in mind that there is nothing inherently wrong or mysterious about decompression, it’s just that recreational dive training doesn’t teach divers to plan for and safely make decompression stops. If you are interested in learning about decompression diving, just take a course. There are many excellent courses available for reputable technical dive training organizations including stage decompression diving.

The Take Home Message About Emergency Decompression

Divers would do best to avoid an emergency decompression situation altogether. Plan for an equipment failure by carrying a back-up timing device and an analog depth gauge, and by making a dive plan based on the recreational dive tables in case of a computer failure. However, even the best divers can make mistakes, and sometimes events simply conspire against you. By understanding the rules of emergency decompression, a diver is prepared for this possibility and can remain safe and confident in even the worst of situations.

Archimedes Principle

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Learning about the physics of the underwater world can help divers to have a more complete understanding of their sport. One essential concept is Archimedes’ Principle, which states:

Any object wholly or partially immersed in a fluid will be buoyed up by a force equal to the weight of the fluid displaced.

Archimedes’ Principle in Plain English:

When an object is placed in water (or any other fluid), the water will exert an upward force on the object. The strength of the upward force is equal to the weight of the water displaced by the object.

To visualize this concept, imagine dropping a marble into a full glass of water. Some of the water will be displaced by the marble and will overflow the glass. If the displaced water is weighed, the weight of the water will be equal to the upward force.

Some objects, such as ping pong balls, will float partially above the water. In this case the upward force is equal to the weight of the water displaced by the submerged portion of the object.

How Does Archimedes’ Principle Help to Determine an Object’s Buoyancy?

Archimedes’ Principle describes the upward forces acting on an object immersed in water. However, an object’s weight (a downward force) also affects its buoyancy. To understand an object’s buoyancy, it is necessary to consider both the downward and upward forces present, and to determine if they are equal or whether one is greater than the other.

If the downward force on an object is stronger than the upward force, it will sink and is said to be negatively buoyant. If the upward force on an object is stronger than the downward force, the object will float and is said to be positively buoyant. Finally, if the two forces are equal, the object will remain suspended in the water and is said to be neutrally buoyant.

In the case of the marble dropped into the water glass, the marble will sink because the weight of the marble (the downward force) is greater than the weight of the water it displaces (the upward force). A ping-pong ball, on the other hand, will float when placed in water.

Archimedes’ Principle reveals why the ping pong ball and other air-filled objects tend to float. An air-filled object weighs little but displaces a relatively large amount of water. One example is a boat, which is basically an air-filled shell. Even a metal boat can float, provided that the water it displaces weighs more than it does.

What Does Archimedes’ Principle Have to Do With Scuba Diving?:

Archimedes’ Principle explains how various factors including a diver’s size, weight, and dive gear affect his buoyancy. Here are a few examples of Archimedes’ Principle in action:

Buoyancy Compensators (BCs):

In its simplest form, a BC is an inflatable air cell that a diver carries with him underwater. He inflates and deflates the air cell during the dive to adjust his buoyancy. When the diver inflates his BC, the air cell expands, displacing a greater volume of water, and increasing the upward force on the diver. When the diver deflates his BC, the air cell loses volume, displaces less water, and weakens the upward force on the diver. Underwater, a diver uses his BC to maintain neutral buoyancy. On the surface, a diver inflates his BC almost completely to allow him to float on the surface.

Weights:

The use of lead weights in scuba diving is also justified by Archimedes’ Principle. When fully geared up, most divers are positively buoyant on the surface. A scuba diver displaces quite a bit of water! To counteract the upward force, a diver wears lead weights, which are small and heavy; they increase the diver’s weight but barely increase his water displacement.

Wetsuits:

A wetsuit increases a diver’s water displacement without significantly increasing his weight, which makes the diver more buoyant. Even a thin wetsuit will increase a diver’s buoyancy. The thicker his wetsuit, the greater a diver’s water displacement, and the greater the upward force on his body will be. Dry suits are bulkier and much more positively buoyant than wetsuits

Tanks:

Aluminium tanks also have an interesting affect on a diver’s buoyancy. When full, a standard 80-cubic-foot aluminium tank (Al 80) is negatively buoyant. However, the shape and volume of an Al 80 is such that when the tank is empty, its water displacement is greater than its weight (aluminium is very lightweight). As compressed air is breathed from a full tank, the tank becomes lighter and lighter, until it eventually becomes positively buoyant. A diver must weight himself to counteract the buoyancy of the aluminium tank at the end of a dive, which means he will begin the dive slightly overweighed. He must inflate his BC to compensate for this negative buoyancy when he starts the dive, and then gradually release air from the BC throughout the dive to maintain neutral buoyancy.

Mastering the Command Chain

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In any kind of diving, the ability to react to problems with the right skills is paramount. Of course, a diver’s main focus should be on anticipating and avoiding problems in a first place, but when problems do occur, the diver should focus on diving basics (such as buoyancy) first.

Doing so will lead to a safer and more controlled solution.

What are the steps leading to a correct and controlled response?

The following protocol will help you achieve a deliberate, controlled, and safe reaction in a difficult situation.

  1. Check Your Breathing Rate

Breathing on land feels natural, and most of the time, we don’t think about it. However, underwater, the surrounding pressure and breathing resistance from the equipment will cause a diver to think again about something that is usually automatic.

When a diver is stressed or task loaded, the first thing that usually happens is that he either increases his breathing rate or holds his breath – and he usually does not notice that he is doing it! Not only does this affect his buoyancy, but it creates stress as his body builds up carbon dioxide. In the event of any task or problem management, first check your breathing and focus on long, slow exhalations. This will allow your body to get rid off carbon dioxide, allowing better mental focus, lower gas consumption, and reduced anxiety.

  1. Confirm That You Are Neutrally Buoyant

Before a diver takes any action, he should confirm that he is neutrally buoyant.

Neutral buoyancy requires the use of your BCD or wing and your breathing. As stated above, a diver who is hyperventilating or holding his breath will find himself ascending even with the proper amount of air in his BCD.

To check your buoyancy, the first thing you should do is nothing at all . . . just wait! There is always a delay between exhalation and sinking, and between inhalation and rising. Playing with this delay will allow you to find the buoyancy sweet spot – the pattern of breathing at which you rise and fall approximately the same amount with each breath, and return to the same depth with each breathing cycle.

The goal is to have the correct amount of air in your BCD so that you can breathe in a relaxed and consistent pattern while maintaining your depth. If you are exaggerating your exhalations or inhalations, adjust your BCD so that you may breathe normally. The incorrect amount of air in your BCD may affect your breathing rate, leading to stress! The worst part is that experienced divers often make these type of compensations unconsciously, so it is worth the small amount of time it takes to check your buoyancy and breathing rate before taking any action.

  1. Assess Your Trim

Trim refers to a diver’s body position. Many times, proper trim is horizontal but not always; it depends upon the environment. A diver’s body should be parallel to the bottom or the floor. This is very important in cave diving and wreck diving, where a silty bottom may not be horizontal!

Proper trim will help to reduce drag and the work of propulsion, as well as limit silt outs and damage to the environment.

Proper trim also gives a diver better control by offering greater contact with the surrounding fluid.

A diver in good trim will feel controlled and stable in the water – a diver out of trim will feel sloppy.

Achieving proper trim requires a bit of practice and equipment adjustments at first, as well as an awareness of the environment. Before taking any action underwater, check your trim to be sure that you are not struggling with an inappropriate body position. Doing so will allow you to focus on the task at hand, instead of struggling to maintain position.

  1. If Necessary, Consciously Choose Your Propulsion Technique

If the task at hand requires swimming, such as reaching a wreck or exiting a cave, choosing the most appropriate propulsion technique will help you to get to where you are going in an efficient manner.

Some good options include:

The Frog Kick

The frog kick propels water behind the diver (as opposed to downwards or upwards) creating a almost purely forward movement that prevents silting and damage to the environment. This kick is easy to match with your breathing, and it is the best technique for long swims and diving with bulky rigs.

The Reverse Kick

Trying to position yourself without a good reverse kick is like trying to parallel park a car without a reverse gear – it’s not possible. The reverse kick is used to manoeuvre in small places, reposition yourself without losing sight of your surroundings, or just to stop on a dime.

Flat Turns

Also known as helicopter turns, a flat turn in useful in positioning, allowing the diver to rotate around his center of gravity while keeping proper trim. Mastering flat turns will help to prevent dropping your feet (and all the problems associated with it) and allows you to manoeuvre in very tight spots.

  1. Consider Your Position

The next step to consider before taking action to solve a problem or complete a task is to choose your position relative to your dive team and the environment.

Be sure that you are not your partner(s)’ blind spot: your entire team should be aware of your presence thanks to your positioning.

In cave, wreck, and deep diving, this can also be achieved with your light beam position.

Choosing the proper position may involve more than just your placement relative to your team.

Considerations may include your position relative to a guideline or the current. Positioning is an art anticipating others’ movements and vice versa. Diving in a properly positioned dive team feels like being part of a team of jet fighters, and can be pure bliss once you master it.

  1. Finally, Take Action!

Once everything else is under control, analyze the situation and take deliberate action.

Consider what needs to be done, and plan your movements step-by-step before executing a task.

You have time (you are already in control) and thinking through a task step-by-step will help to avoid mistakes and the need to fix them or to start over.

The Command Chain in Practice

Putting these six steps together will lead to more controlled, less stressful diving.

For example, if a moment of stress leads to hyperventilation or over-breathing, your buoyancy, trim, and all that follows will be negatively affected.

Stop, and go back to the basics starting at the beginning of the list.

Calm your breathing, check your buoyancy, check your trim, etc.

Whatever action you wish to accomplish, be it swimming, laying a line, or inflating a surface marker buoy, will become easier and smoother.

Putting the command chain into practice helps to avoid additional problems, and increases your overall control and enjoyment of a dive.

One Final Tip – This Works for All Divers, Regardless of Level!

The command chain works equally well for recreational and technical divers. Divers who use the command chain will become more confident, relaxed and controlled. They are able to manage complex tasks, and generally proceed much more quickly through training.

Train yourself from now on that THE mantra to repeat to yourself in any circumstance is:

Breathing, buoyancy, trim, propulsion, position, action!

You will be a better diver for it!

Vincent Rouquette-Cathala is a technical diving instructor at Phocea Dive Center, Mexico

Underweighting can be just as dangerous as overweighting.

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Equipment and the Environment Will Both Affect Your Buoyancy

Wetsuits, tanks, and even accessories and tools will affect your buoyancy. Whenever you change one of these items, it is necessary to complete a buoyancy check to determine the effect of the new item on your buoyancy. The salinity of the water will also affect a divers buoyancy. The obvious example is buoyancy in fresh water vs salt water, but keep in mind that the salinity of the ocean may also vary in different regions of the world, and you may need slightly more or less weight depending upon your dive location.

Conducting a weight test before a dive can make the difference between a miserable dive and an enjoyable one.

 

Conduct a Buoyancy Check Before DivingScuba 2

Test your buoyancy in a new location or whenever diving with a new piece of gear. Most of the time, diver’s have a limited number of dives on vacation, and it is worth the effort to make every dive comfortable and safe.

In fact, most dive operators will be thrilled if you ask to wade into the ocean or hop of the pier before your first dive to double check your weighting.

 

The general rule of thumb for proper weighting is that with all of his gear in place, with a nearly empty tank, a diver who completely empties his BCD and holds a normal breath should float at eye level. When he exhales he should sink.

 

Remember!! As the tank empties, it will become positively buoyant.

If you can empty your BCD, hold a normal breath, and float at eye level at the beginning of the dive, you will not have enough weight to comfortably maintain neutral buoyancy at the end of the dive.

The problem here is that most dive shops are not in the practice of providing nearly empty tanks for buoyancy tests. There are two solutions to this:

 

  1. Conduct the buoyancy test with a full tank as outlined above, and then add the appropriate amount of weight to offset the buoyancy swing of your tank as it empties.
  2. Conduct the buoyancy test as outlined above with a full tank, but instead of checking that you float at eye level, check to see that you sink slowly while holding a normal breath.

 

Double Check Your Buoyancy at the End of a Dive

Once you have successfully completed a dive with enough weight to keep you comfortably below water the entire time, it is a good idea to double check your weighting at the end of the dive.

To do this, purge your regulator gently until you are down to about 500 psi or 30 bar. Then, on the surface, conduct a buoyancy check before exiting the water. Do you float at eye level and sink when you exhale?Scuba 3

Do you have to swim to get down? Float like a balloon on the surface? Add a little weight on your next dive.

Do you still sink while holding your breath? Remove a few pounds and try again on the next dive.

 

Adding a Small Amount of Air to Your BCD During Descent Is Good

Many divers seem pleased that they can descend and arrive at the planned depth without adding air to the BCD.

Again, this is not a desirable situation. Because most tanks become more positively buoyant throughout a dive, divers who do not need to add air to their BCDs during descent to establish neutral buoyancy are likely to be underweighted.

 

I Don’t Need to Add Air During Descent. I Am Fine at the End of the Dive!

These are the people who have exceptionally low air consumption rates, and surface with at least half of their air remaining. Yes, they can be perfectly neutral during their safety stops, and they don’t go flying to the surface like awkward buoys at the end of the dive. Their tanks have not become positively buoyant because they haven’t breathed enough gas to cause a buoyancy swing.

 

The problem with this habit is that it does not prepare divers for an emergency situation, when they are low on gas because they over-breathed a tank due to a stressful situation, surface with less gas than normal due to an unforeseen occurrence, or are forced to share air with another diver.

In these situations, such a diver will have trouble staying down, and of course, these are the situations when having enough weight can make a big difference between an annoying situation and an uncontrolled ascent to the surface.

Plan for the worst case scenario: a low tank and increased breathing rates due to stress.

 

Diving with less weight does not make you a better diver.

Diving with the correct amount of weight does.

Slight overweighting is correctable: just add a little air to the BCD.

To be safe on dives, proper weighting is key.

Take the time to get your weighting right and you can avoid many potentially dangerous situations and dive more comfortably.

Buoyancy Basics – Seven Ideas for Adjusting Trim Without Adding Weight

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Before making any adjustments to his gear, a diver must first check his trim. He should enter the water with all of his diver gear and attempt to hover in a horizontal position without moving his fins or arms. He can then note whether he has a tendency to hover head or feet up, or to roll to one side.

1. Move Weights Around

Changing the position of a diver’s weights may help to adjust his trim. Many buoyancy compensators (BCs) have trim weight pockets just below the diver’s shoulders. A diver who tends to float head-up may use the pockets to redistribute his weights, placing a few pounds in each pocket. For example, a diver who uses ten pounds of weight may want to carry six pounds on his weight belt and four pounds (two on each shoulder) in his trim weight pockets. If a diver’s BC does not have trim weight pockets, some divers will place a weight on the BC’s tank band for a similar effect.

Redistributing weights is not always possible, as in the case of a diver who uses very little or no weight, or a diver who uses a BC without trim weight pockets. Some divers simply find that redistributing weight does not correct their trim. Fortunately, it is possible to manipulate other pieces of dive gear to perfect a diver’s trim.

2. Tank Position

A diver’s tank position affects his trim. A tank can be lowered or raised in relation to a diver’s BC by changing the position of the BC strap on the tank. A diver who attaches his BC strap near the top of his tank will find that the tank sits low on his body. This may help to correct for a foot-up position by shifting the weight of the tank towards the diver’s feet. Attaching the BC to a lower part to the tank will have the opposite effect.

3. Reposition the Buoyancy Cell

Some equipment configurations, such as a backplate/ wing system, allow a diver to move his buoyancy cell (the part that inflates and deflates) upwards or downwards in relation to his harness. A diver can move the buoyancy cell towards his head to compensate for a foot-up position, or towards his lower body to correct a head-up position.

4. Change Your Neoprene

The thickness and distribution of a diver’s neoprene garments can have a huge effect on his trim. Thick, full-length wetsuits, especially wetsuits that have 5 mm or 7 mm legs, have a tendency to cause a diver to float feet-up. Switching to a wetsuit that has a 7 mm torso and thinner legs can remedy this situation. Similarly, thick wetsuit booties can cause a diver’s feet to float. Simply switching to thinner booties may solve a foot-up position. Finally, warm-water divers who find themselves floating foot-up may consider switching to a short wetsuit, as long as the suit still provides adequate thermal protection.

Adding neoprene layers to the torso may also have a slight effect on a diver’s trim. Thick vests and hoods add buoyancy to a diver’s upper body, and may be useful in compensating for a foot-up position.

5. Change Your Fins

Changing your fins may sound like a drastic step, but switching your fins can often be a helpful method of correcting trim. Different brands and styles of fins have astonishingly different buoyancy characteristics. For instance, SCUBAPRO Jet Fins are some on of the most negatively buoyant fins on the market. Other fins may be neutral or even positively buoyant. Heavier fins can compensate for a foot-up position, while lighter fins can compensate for a head-up position.

6. Change Your Regulator First Stages

Regulator first stages can be very heavy or relatively light. A heavy regulator first stage can help to fix a head-up position, and a lighter regulator first stage can help to compensate for a foot up-position. Of course, regulators should be selected first and foremost for their breathing characteristics, but given the choice between several similar first stages, a diver may want to make his final decision based on weight. The weight of the first stages is of particular interest to technical divers, who use at least two first stages on every dive.

7. Consider Your Accessories

Finally, a diver may want to take a look at his accessories and consider their effect on his trim. A diver who carries a heavy dive light may have a tendency to list to one side — in this case he may want to place other accessories (or counterweight in a worst-case scenario) on the side opposite side of his light. Divers who carry huge, heavy reels on their rear d-rings may notice that they float head-up. Switching to a lighter reel may fix this problem without any other adjustments.

In most cases, a diver’s trim can be adjusted without adding weight. Before making any adjustments, a diver should attempt to hover in horizontal trim with all of his dive gear in place (even accessories) to diagnose any trim problems. He can then begin repositioning or changing dive gear to improve his trim. It is advisable to change or reposition only one piece of gear at a time, and to get into the water after each adjustment to evaluate its effect. It is difficult to determine the result of an individual alteration when several adjustments are made at once.

 Take your time and make methodical adjustments to your equipment, one change at a time, until you are happy with your trim.

The Art of Equipment Configuration

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1. Accessibility:

The single most important concept in scuba equipment configuration is accessibility. A diver should be able to deploy, use, and stow dive gear easily and efficiently. Any configuration that makes accessing a piece of dive gear difficult or complicated should be re-thought, even if it fulfils all the other tenets of optimized equipment placement. Whenever possible, configure all dive gear so that it may be deployed and operated with one hand. This ensures that a diver can use his other hand for emergency management, such as maintaining physical contact with an out-of-air buddy.

2. Durability:

The manner in which a diver configures his gear should ensure that it will stay in place for an entire dive. A common equipment configuration failure is the alternate air source regulator coming free of its quick release.  The first time a piece of gear comes loose, the diver should reconfigure his gear to prevent the problem from reoccurring.

If it happened once, it will happen again!

3. Streamlining:

All dive gear, including accessories and hoses should be streamlined. In no circumstance should a piece of dive gear dangle more than a few inches below a diver’s horizontal body line . Hoses should be adjusted so that they do not loop above or beside the diver. Keep in mind that regulator hoses are available in a variety of lengths. Proper streamlining reduces the chance of entanglement, damage to the environment, and drag.

A common failure of streamlining in standard recreational scuba diving is the octopus-style alternate air source, which necessarily must be attached to a longer hose to facilitate donation to an out-of-air diver. The hoses on octopus-style regulators typically loop out to the side of the diver, presenting an entanglement hazard and creating drag. As far as streamlining goes, integrated alternate air sources and long hose/necklace regulator configurations are both preferable.

All types of diving require some level of redundancy in the gear. Recreational open water diving requires that a diver carry at least one redundant second stage for his buddy to use in an emergency. More advanced or technical types of diving may require additional redundant gear for safety. A diver should carry the minimum amount of accessories and gear that allows him to dive safely. At a certain point, additional gear no longer increases dive safety. The trick is to balance redundancy and simplicity when configuring dive gear.

5. Trim and Comfort:

Once a diver has optimized his equipment configuration, he should test it in a forgiving environment such as a pool or shallow water dive site. When evaluating changes to his gear configuration, a diver should notice whether the changes upset or improve his trim and whether or not position of the gear is comfortable. No matter how fantastic it seems on the surface, the final test of an equipment configuration is whether or not it is comfortable and functional underwater.

Evaluating and adjusting your scuba diving equipment configuration can make diving easier, safer, and more comfortable.