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.

Jellyfish Stings – Facts, Treatments, and Remedies

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By Natalie Gibb
  Scuba Diving Expert

How dangerous can a gelatinous sac of straggly tentacles be? A jellyfish’s soft, transparent body appears vulnerable to all sort of prey, and a diver may be surprised that a jellyfish can survive to grow to maturity without being eaten. Yet, a jellyfish’s delicate body is anything but unprotected. The tentacles of a jellyfish contain uncountable numbers of stinging cells, called nematocysts, which effectively protect it from many potential predators and are used to stun small prey.

Depending upon the species of jellyfish, contact with the stinging cells can injure, or even kill a human being. But how much of a threat are jellyfish to scuba divers?

Are You Likely To Be Stung by a Jellyfish While Scuba Diving?:

No. Jellyfish are not a major threat to scuba divers. The majority of jellyfish species tend to stay near the surface of the water, and are more of a threat to swimmers and beach-goers than they are to divers. In addition, a jellyfish must contact a person’s bare skin in order to sting. Generally, divers wear wetsuits or dive skins and have little exposed skin to sting.

Dive guides and local dive centers will usually alert divers if dangerous species are present. If a diver spots a jellyfish underwater, he should take care to stay at least a few meters away. Some species of jellyfish have transparent tentacles over one meter in length which may be difficult or impossible to see underwater.

Are Jellyfish Stings Dangerous?:

The effects of jellyfish stings can range from mild pain and stinging, to skin irritations and blisters, to respiratory problems, cardiac arrest, and death.

The toxicity of a jellyfish sting depends upon the species of jellyfish and the reaction of a person’s body to the jellyfish venom.

The most toxic type of jellyfish is the Box Jellyfish (Chironex fleckeri and Caruka barnesi) found in Australia and some regions of the Indo-Pacific. The venom of the Box Jellyfish has been known to kill a person in five minutes.

People react differently to jellyfish stings. Consider a jellyfish sting as a “dose” of poison. The smaller the person, the greater the effect of a jellyfish sting will be. Just as some people are highly allergic to bees and may go into anaphylactic shock from a single sting, other people may be unusually sensitive to jellyfish venom and may have a similar severe reaction.

How Should a Diver Treat a Jellyfish Sting?:

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Most diving safety organizations recommend vinegar as immediate first aide for a jellyfish sting. Vinegar, which neutralizes a jellyfish’s stinging cells, has two primary benefits – to minimize pain and discomfort, and to stop the delivery of jellyfish venom. When stung by a jellyfish with exceptionally toxic venom, such as that of the Box Jellyfish, the immediate application of vinegar to neutralize stinging cells and prevent more venom from entering a diver’s body may be the difference between life and death. Vinegar should be in every dive boat’s first aid kit. If vinegar is not available, a paste of baking soda may be used to neutralize sting cells. Salt water may be used as an additional rinsing agent if necessary.

In no circumstances should fresh water be applied to a jellyfish sting as fresh water may cause additional stinging cells to fire. Urinating on jellyfish stings is not recommended to neutralize jellyfish venom (sorry).

Jellyfish tentacles tend to stick to a diver’s skin and must be removed once the stinging cells are neutralized. Shaving affected area with a razor has proven very effective in removing tentacles. Other suggestions include using tweezers or thick gloves to pry the jellyfish tentacles away. Any abrasive material, such as sand, may be used to scour the sting area when other methods are not available.

Cold and hot packs (as long as they are completely dry) may be used to alleviate the pain of a jellyfish sting. Most doctors recommend hydrocortisone cream to be applied topically to the stung area.

The victim of a jellyfish sting should be monitored carefully for signs of shock, difficulty breathing, nausea, and other signs of severe allergic reactions. If any allergic reaction is suspected, be sure to contact a doctor immediately.

Conclusion

In most cases, an encounter with a jellyfish while scuba diving is anything but dangerous. Jellyfish are among some of the oceans most surprising and fascinating creatures, and it is enchanting to watch their pulsating movements as the drift through the water. Enjoy your jellyfish encounters, just make sure to give them plenty of space!

Tips for Effective Use of the Buddy System

Hand Signals

  1. Choose your buddies wisely.
    The ideal buddy should feel that the buddy system is important. If you are partnered with a random buddy on the boat only to find that he is a lone wolf and deserts you underwater, stick close to the divemaster and ask for a different buddy for the next dive.

    2. Discuss your dive plan with your buddy before the dive.
    Let your buddy know if you are likely to have any issues that commonly lead to buddy separation, such asear equalizationtrouble on descent (I frequently see one diver drop like a rock while the other is stuck at 15 feet attempting to equalize his ears). Discuss how you will deal with these situations should they arise.

    3. Talk about your dive objective.
    If one member of the team stops to take photographs and the other wants to race over the reef in order to cover as much ground as possible, a compromise as to the dive pace will need to be made.

    4. Pick a side.
    Choose what side of your buddy you will remain on, and then remain on that side. This might sound silly, but it is easy to become disoriented underwater and knowing where to look for your buddy is helpful.

    5. Pick a leader.
    Even if there is a dive master, decide who will make navigational decisions during the dive. One buddy swims to areas he finds interesting, and the other follows his lead. If the follower wants to check out a specific spot, he simply notifies the leader and they move together. This makes the dive more organized and more enjoyable.

    6. Discuss a way to attract each other’s attention.
    This could include underwater noisemakers, rapping on the tank with a metal ring or clip, or even shouting into the regulator. If you and your buddy know what to listen for, you are more likely to be able to get each other’s attention underwater.

    7. Familiarize yourself with your buddy’s gear and refresh emergency procedures together.
    This doesn’t have to take a long time, a simple “my weights are released here and my alternate air source is here” and a brief review of the gear you are using usually covers the equipment. A quick discussion of emergency air sharing procedures takes about 30 seconds.

    8. Communicate during the dive.
    Discuss hand signal communications and then use them. Ask your buddy if he is okay periodically, point out interesting aquatic life to your partner, and communicate your tank pressure. Divers who are in constant communication tend to stay closer together and more aware of their partners.

Scuba instructors teach the buddy system for a reason: a diver using the standard single-tank equipment configuration cannot solve all emergencies himself. Stay close to your buddy and stay safe!

Underweighting can be just as dangerous as overweighting.

scuba diver in lotus position

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.

“Save a Dive” Kit

SaveaDiveKit

 

Save a dive kits may be a small as a zip-lock bag or as big as a tool box, a diver’s save a dive kit will differ depending upon his needs and type of diving.

Suggested parts for the Basic Save a Dive Kit:

Spare mask strap
Mask straps are one of the most common items to break before a dive. Be sure to select a spare mask strap that fits your mask.

Spare fin strap and buckle
Fin straps break less frequently than mask straps, but they do break.  Be sure to choose the correct strap for you fins.

Spare regulator mouthpiece and zip tie/cable tie to secure it.

A spare regulator mouthpiece is an absolute essential.

Basic o-ring kit
This should include o-rings for low pressure and high pressure hoses, as well as o-rings for yoke tank valves or o-rings for DIN regulators (depending upon which you use).

High pressure and low pressure port plugs for the regulator first stage.

When a diver removes a hose from his regulator first stage, he must plug the hole with a port plug. Bring along both a high pressure and low pressure port plug that fits your first stage (apex first stages have unusually large port plugs).

Small adjustable crescent wrench
This is used to remove hoses from the regulator to replace o-rings.

Hex wrenches/ allen keys
Hex wrenches are used to remove port plugs, as well as for a variety of other applications.

Cutting device/knife
At a minimum, your cutting tool should be able to cleanly slice off zip ties and snip strings and bungee.

Needle nose pliers
Needle nose pliers are great for just about everything that needs to be pulled or tightened.

Small pot of silicon lubricant

This is used for greasing o-rings in dive gear, dive lights, etc.

A lighter

Zip ties and duct tape

Nail clippers

Nail clippers are useful for nipping of zip ties and clipping small items.

White trash bag.
Use a white plastic trash bag as a work surface on dirty or wet areas. This makes seeing o-rings and parts easier, and keeps them clean and dry.

Dry suit zipper wax.

Essential if you use a dry suit.

A DIN-to-yoke or yoke-to-DIN adaptor

This allows you to dive with both DIN and yoke tanks.

• Bungee/ Shock Cord

Bungee can be used to secure lights, create necklaces for back-up regs (long hose configuration), manufacture watch/computer straps, and create octopus/alternate air source holders.

 

 

 

Do I Need to Be a Good Swimmer to Scuba Dive?

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Participation in a high school swim team is not a prerequisite for scuba certification. Scuba certification swim tests are not timed, and participants can use whatever swimming stroke they desire to pass the test – even goofy ones.

Should All Scuba Divers Be Able to Swim?

This is certainly an interesting question.

People enrol in scuba courses for a variety of reasons. Some state that they want to learn to dive in order to overcome a fear of the water or to learn to swim. I would urge such people to become comfortable in the water by enrolling in swimming courses before ever considering a scuba experience program or entry-level certification.

Diver Confidence:Swim1

While the technique of swimming underwater in scuba gear is very different from the technique of swimming on the surface without equipment, confidence in oneself and one’s abilities in the water does translate to diving.

In many cases, this confidence and ability appear to be directly correlated with a student’s comfort level when scuba diving. Students who are completely certain that they would be able to survive in the water with out scuba gear are certainly much more comfortable using it.

• Basic Diving Skills:

Consider that even a scuba program that does not include a swim test will still require the student to put water in his mask and to remove a regulator underwater.

Students who are afraid of having water in their faces will not enjoy these skills, and would do better to increase their comfort level in the water before attempting to dive.

• Problem Solving:

Scuba diving is an equipment dependent activity, and the reliability of the equipment is extremely high.

However, the remote possibility exists that a diver will need to deal with an equipment-related issue by using emergency management skills such as switching to another regulator, even during an initial dive experience.

Scuba divers do not need to be expert swimmers, but a basic ability to handle oneself in the water without fear or stress is an absolute requirement in my opinion.

Knowing how to swim and float are a huge step in acquiring that confidence. Prospective divers who do not have the ability to stay calm on the surface without a floatation device or who cannot swim (however sloppily) for a short distance should first learn these skills with a professional swimming coach.

A diver who is not confident without his gear is one uncomfortable situation away from panic, and panic, as all scuba divers know, endangers both the person panicking and those around him.

Although knowing how to swim is not required for basic scuba experience programs, it is advisable.