Emergency Decompression Guidelines for Scuba Diving



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

Scuba 3

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.


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.


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


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.

Nitrogen narcosis – The Martini Effect


The Martini Effect is a slang term used in scuba diving to refer to nitrogen narcosis, the physical and mental impairment experienced by scuba divers on deeper dives.

The high partial pressures of nitrogen experienced by divers on deeper dives has an anaesthetic affect on the brain, it can cause a sense of euphoria, impair motor abilities and coordination, lead to poor judgement and reasoning, and in extreme cases, prevent the diver from remembering much of the dive.

Why the Funny Name?

Nitrogen narcosis has been compared to being drunk, and with good reason!  Many of the effects are the same. Clearly, nitrogen narcosis can be dangerous to divers, and has been implicated in many incidents and accidents. You wouldn’t drink and drive, and you shouldn’t get narced and dive either.

The name is cute, and the experience of being “narced” on a dive may even be pleasant, but make no mistake. Nitrogen narcosis is seriously dangerous.

At What Depth Will I Experience the Martini Effect?

The deeper a diver descends, the stronger his narcosis will be. This is how the term The Martini Rule originated.

Divers have said that every 30 feet/10 meters of depth will have the effect on a diver of drinking one martini.

Most divers won’t feel the effects of narcosis at 30, or even at 60 feet. However, the analogy holds true. Some divers feel nitrogen narcosis at shallower depths than others, much as some people get drunk more easily than others.

Research has shown that all divers are at least partially impaired at 100 feet/ 33 meters and below. Even if a diver doesn’t notice the effects of narcosis, he will experience impairment of judgement and reasoning in novel situations.

How Can I Avoid Narcosis?

This is indeed the question to be asking!

The simplest way to avoid narcosis is to limit your depth. A diver who descends no deeper than 60 feet (the recommended depth limit for open water certified divers) is extremely unlikely to ever feel the effects of narcosis.

During the Advanced Open Water Course, divers experience their first deep dive under the supervision on an instructor, and this is an excellent way to test yourself and your susceptibility to narcosis in a safe and controlled manner.


Keep in mind that many additional risks are associated with deep diving, and recreational divers who plan to dive deeper than 100 feet/30 meters would do well to take a Deep Diving Specialty Course.


Technical divers, however, regularly descend well below 100 feet. They do so safely by reducing the percentage of nitrogen in their breathing gas mixture by substituting a less narcotic gas, helium, for some of the nitrogen. This type of gas mixture is known as trimix, and requires technical diving gear and training to use safely.

Divers who want to go beyond the recreation depth limits of 130 feet/ 40 meters can do so safely by enrolling in a technical diving course.

Jellyfish Stings – Facts, Treatments, and Remedies

Article by: 
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?:


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.


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!

The Greatest Pressure Change Is Near the Surface


For the sake of simplicity, let’s consider just one of the reasons that a fast ascent during any part of a dive is dangerous. Increased pressure underwater causes a diver’s body tissues to absorb more nitrogen gas than they would normally contain at the surface. If a diver ascends slowly, this nitrogen gas expands bit by bit and the excess nitrogen is safely metabolised and released.

However, the body can only metabolise nitrogen so quickly. The faster a diver ascends, the faster nitrogen expands and must be removed from his tissues. If a diver goes through too great of pressure change too quickly, his body can not metabolise all of the expanding nitrogen and the excess nitrogen forms bubbles in his tissues and blood.

These nitrogen bubbles can cause decompression sickness (DCS) by blocking blood flow to various parts of the body, causing strokes, paralysis, and other life threatening problems. Rapid pressure changes are one of the most common causes of DCS.

What many divers do not realize is that the greatest pressure change during ascents and descents occurs close to the surface. If a diver descends from the surface (1 atmosphere of pressure, or ATA) to 33 feet (2 ATA) the pressure doubles.

If he descends from 33 feet (2 ATA) to 66 feet (3 ATA), the pressure only increases by half. The closer a diver is to the surface, the more rapidly the pressure is changing.

Most divers are familiar with the effects of the increased rate of pressure change near the surface. For example, divers must equalize their ears and adjust their buoyancy more frequently the closer they are to the surface.

This data suggests that divers should be vigilant about their ascent rates near the surface and ascend most slowly through the last fifteen feet of the dive to reduce the risk of decompression sickness.

While a safety stop allows divers to gain control of their ascent and eliminate as much extra nitrogen as possible from their tissues, it is not the end of the dive.

The most critical part of a diver’s ascent is after his safety stop.

Table: Percentage of Pressure Change During Ascent

40-35 ft 2.21-2.06 ATA – 7%
35-30 ft 2.06-1.91 ATA – 8%
30-25 ft 1.91-1.76 ATA – 9%
25-20 ft 1.76-1.61 ATA – 9%
20-15 ft 1.61-1.45 ATA – 11%
15-10 ft 1.45-1.30 ATA – 12%
10-5 ft 1.30-1.15 ATA – 13%
5-0 ft 1.10-1.15 – 15%

Article by: Natalie Gibb Scuba Diving Expert

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!

How to Vomit On a Scuba Trip Without Alienating Everyone


The feeling of seasickness starts as an uncomfortable lurching in the stomach, a slight dizziness, and a heightened sensitivity to any nasty boat fumes wafting through the air. Despite a truly heroic effort to force his stomach contents to remain in their rightful place, the victim soon finds himself leaning over the railing trying to be as inconspicuous as possible as he donates his last meal to the sea.

Seasickness is terrible, but it happens to the best of us. Here are tips on how to avoid alienating the rest of the dive group when the inevitable arises.

Vomiting Politely on the Dive Boat:

If you happen to be on the boat when seasickness strikes . . .

  1. Acknowledge That You Are, Indeed, Seasick:

The moment you start to feel nauseated, take action! Move to an appropriate position on the boat and prepare for the worst. Don’t try to act tough — the only thing worse than vomiting during a dive trip is vomiting on the deck or in the cabin.

  1. Stop, Think, and Barf:

If the boat is moving, take a moment to position your head so that you are vomiting with – not into – the wind. If you release your breakfast into the wind, chances are that it will blow right back at you and you will get to experience it not only for a second, but a third time.

  1. Location, Location, Location:

If you acknowledge seasickness early and note the direction of the wind, you will have time to position yourself so as to avoid spewing all over the deck and other divers. Move as far back on the dive boat as possible, and onto the lower deck if there are multiple outdoor levels on the boat Beware the dreaded cross breeze and try to position yourself so that your spewage moves away from the boat.

  1. Take Aim!:

If the dive boat is picking up or approaching divers, take note of their position. If divers are coming up a ladder or waiting to board the boat, stagger to the opposite side of the boat before liberating your stomach contents. Similarly, if divers are boarding the boat from the back, try to note the current and aim your projectiles so that they float with the current away from the other divers (not into them) It’s no fun to surface from a dive to find a floating present drifting towards you as you wait for your turn to board the dive boat.

  1. Assure Everyone that You Are Okay – If You Are:

Judging from your greyish colour and the fact that you are wobbling around the dive boat in rather unpredictable patterns, other divers may begin to wonder if you are about to die. Assure the divers around you that you are simply seasick and miserable — and that you are not experiencing decompression sickness, sunstroke etc. If you do have symptoms of aliments other than seasickness, be sure to alert the boat crew or dive guide, so that they can take appropriate steps.

The Take-Home Message about Vomiting on a Dive Boat:

Most divers will be sympathetic to a seasick diver who feels the need to vomit on the dive boat. Following these few simple guidelines will ensure that a diver’s seasickness does not become a problem to the other divers (and boat crew) on the dive trip