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.

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Nitrogen narcosis – The Martini Effect

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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.

The Greatest Pressure Change Is Near the Surface

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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

DEPTH CHANGE IN ATA PERCENT CHANGE
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

How to Vomit On a Scuba Trip Without Alienating Everyone

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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

What Is the Maximum Safe Ascent Rate for Scuba Diving?:

Safety StopBy Natalie Gibb – Scuba Diving Expert

How fast of an ascent is too fast? The answer varies among scuba certification organizations.

Some organizations list a maximum ascent rate of 30 feet/ 9 meters per minute, while others allow a faster ascent rate.

A safe rule of thumb, (and the most commonly published maximum ascent rate at this time) is:
Never exceed an ascent rate of 30 feet/ 9 meters per a minute.

How to Monitor Your Ascent Rate When Scuba Diving:

The easiest way for a diver to monitor his ascent rate is to use a dive computer. Almost all dive computers have ascent rate alarms which will beep or vibrate when the diver exceeds the computer’s programmed maximum ascent rate. The moment the computer alerts the diver that he is ascending too quickly, the diver should take steps to slow his ascent.

However, not all divers use dive computers. A diver without a computer may use a timing device in combination with his depth gauge to monitor the time he takes to ascend a predetermined number of feet.

For example, a diver may use his timing device to check that he doesn’t ascend more than 15 feet in 30 seconds.

Every diver should carry a timing device underwater.

However, in a worst case scenario, a diver may gauge his ascent rate by watching bubbles around him rise towards the surface.He should ascend more slowly than the smallest bubbles he can see.

One trick is to look for tiny, champagne-sized bubbles and be certain to ascend more slowly than these bubbles.

Another method of estimating an ascent rate is to ascend along a fixed anchor line or ascent line.

 

Why Is Ascending Slowly Important When Scuba Diving?:Wreck

Quick ascents can lead to decompression illness.

During a dive, a diver’s body absorbs nitrogen gas.

The nitrogen gas compresses due to water pressure following Boyle’s Law, and slowly saturates his body tissues. If a diver ascends too quickly, the nitrogen gas in his body will expand at such a rate that he is unable to eliminate it efficiently, and the nitrogen will form small bubbles in his tissues.

This is known as decompression sickness, and can be very painful, lead to tissue death, and even be life threatening.

In a worst-case scenario, a diver who ascends quite rapidly may rupture small structures in his lungs known as alveoli.

In this case, bubbles may enter his arterial circulation and travel through his body, eventually lodging in blood vessels and blocking blood flow. This sort of decompression illness is called an arterial gas embolism (AGE), and is very dangerous. A bubble may lodge in an artery feeding the spinal column, in the brain, or in a host of other areas, causing loss or impediment of function.

Maintaining a slow ascent rate greatly reduces the risk of all forms of decompression illness.

Additional Safety Precautions — Safety Stops and Deep Stops:

In addition to slow ascents, scuba diving training organizations also recommend making a safety stop at 15 feet/ 5 meters for 3-5 minutes.

A safety stop allows a diver’s body to eliminate additional nitrogen from the body before his final ascent.

When making deep dives (let’s say 70 feet or deeper for the sake of argument) studies have also shown that a diver who makes a deep stop based on his dive profile (for example a 50-foot stop on a dive with a maximum depth of 80 feet) as well as a safety stop will have significantly less nitrogen in his body upon surfacing than a diver who does not.

A Diver’s Alert Network (DAN) study, measured the amount of nitrogen remaining in a diver’s system after a series of ascent profiles. The study measured the nitrogen saturation of tissues that become quickly filled with nitrogen, such as the spinal column. DAN ran a series of tests on divers who ascended at a rate of 30 feet/minute from repetitive dives to 80 feet. The results were fascinating:

A diver who ascended at a rate of 30 feet/minute without stops surfaced with his “fast saturation tissues” 60% saturated.

  • • If the same divers made a safety stop of 5 minutes at 18 feet, these fast saturation tissues decreased to only 35% saturation.
    • If the same diver made an additional deep stop of 5 minutes at 48 feet, he surfaced with his fast saturation tissues further decreased to only 25% saturation.

Making deep stops and safety stops, even on dives within the no-decompression limits, will significantly reduce the amount of nitrogen in a diver’s body upon surfacing.

The less nitrogen in his system, the lower the risk of decompression sickness. Making deep and safety stops makes sense!

 The Final Ascent Should Be the Slowest:

The greatest pressure change per a foot of depth is near the surface.

The more shallow a diver is, the more rapidly the surrounding pressure changes as he ascends.

A diver should ascend most slowly from his safety stop to the surface, even more slowly than 30 feet per a minute.

Nitrogen in a diver’s body will expand most quickly during the final ascent, and allowing his body additional time to eliminate this nitrogen will further reduce the diver’s risk of decompression sickness.

Take Home-Message about Ascent Rates and Scuba Diving:

Divers should slowly ascend from all dives to avoid decompression sickness and AGE.

Mastering a slow ascent requires good buoyancy control and a method of monitoring the ascent rate.

In addition, making a safety stop at 15 feet for a minimum of 3 minutes during every ascent, and deep stops when appropriate, will further reduce the amount of nitrogen in a diver’s body upon ascent, which reduces his risk of decompression sickness.

(Further reading and source: Diver’s Alert Network (DAN) Article, “Haldane Revisited: DAN Looks at Safe Ascents” by Dr. Peter Bennett, Alert Diver Magazine, 2002.) Read article.

Ways to Keep Your Hair Out of Your Face When Scuba Diving – From Natalie Gibb

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Controlling long hair when diving is important for two reasons. The first is that long hair floats in front of a diver’s field of vision (and gets horribly tangled in the process). The second is that loose hair tends to slide around under the mask strap, which causes the mask to move during a dive. Here are some tricks to control long hair that I have learned after years of diving.

Ponytails

A ponytail will hold your hair back during a dive, but it is probably the worst of all solutions. If your hair is long enough, position your ponytail on the top of your head. If not, place the ponytail at the nape of your neck. Either of these placements will avoiding disturbing the position of your mask strap.

I dislike ponytails when diving for two reasons. The first is that they tend to loosen during a dive, causing the diver’s mask strap to slip around and lose position as the hair moves. If ponytail loosens to the point that it becomes undone, the elastic band is lost and turns into underwater pollution. The second reason I dislike ponytails for diving is that they allow your hair to tangle. The loose end of the ponytail becomes knotted (especially in sticky salt water) and the elastic band tends to get knotted into the hair. Wavy hair becomes so tangled after diving in a ponytail, that you  sometimes have to cut the elastic band out.

French Braids

A single French braid beginning at the crown of the head works well to hold hair in place during a dive. The hair strands are interwoven, and are less likely to come free during a dive than in a ponytail. A French braid also helps to keep the hair from sliding around and disturbing the position of the mask strap. French braids are great for divers with layered hair, or hair that is too short to efficiently pull back in a pony tail.

The only drawback of French braids is the post-dive tangle. I would strongly urge divers who have French braided their hair to leave it braided until showering. Salt water causes the interwoven strands of the braid to stick to each other, creating a tangled mess if the braid is undone before rinsing with fresh water. In a pinch, use a dollop of conditioner at the bottom tip of the braid, and then carefully brush or comb the braid out starting at the bottom and working inch by inch to the top. Spread the conditioner along the hair shafts as you go.

Pigtails / Two Braids

One hairstyle that works very well for diving is pigtails. Part your hair down the middle and braid it into two equal braids. Pigtails keep a diver’s hair from sliding around but do not tangle it as much as a French braid does. Care must still be taken when combing out the hair post dive.

Head Scarves

In many diving destinations, local shops sell head scarves made for scuba diving. These scarves are usually made of a bandana-type material, and look like modified headbands. They have a wide strip of fabric that runs over the top of a diver’s head and down behind the nape of the neck, where the fabric is gathered with elastic to hold tension.

These head scarves seem like a great idea, but I have rarely seen them work. Most divers remove them after one dive because the scarves tend to slip around (or off) underwater.

Hoods

By far the most effective method for hair control when scuba diving is to use a neoprene diving hood. A variety of hood styles are available, from beanie-style hoods that fasten underneath a diver’s chin, to full hoods that cover the head and neck, to hooded vests that fit under a diver’s wetsuit.

Hoods work with all lengths of hair. For divers with short or medium length hair, it may be easiest to first wet your hair to keep it back, and then to slide the hood over your head. An easy way to do this is to enter the water with the hood down around your neck, lean back in the water to wet your hair and slick it back, and then carefully slide the hood on.

For long hair, it works well to twist your hair tightly into a bun on the top of your head. Hold your hair in place and slide the hood over it. No hair elastic of other method of securing the hair is necessary! The hood will hold your hair in place.

Hair elastics and other accessories are not necessary when using a hood, so hair is less likely to get tangled.

Danielle's Dives Blog

I have been reading some rather interesting articles lately about dehydration and the effects on a diver.  With lobster season almost upon us and the Florida shore dive season in full swing, I thought we should visit the topic of dehydration and diving.  I was noticing after long shore dive days, I was parched and would occasionally get headaches.  After a few years, doing multiple shore dives in a day, I now hydrate fully the day before slowly, loading up on H2O and making sure I have my vitamins in me.  For those of you who have never shore dove before, it is fabulous and having steel tanks gives me the opportunity to get 2-2 1/2 hour dives enjoying everything I come across.  Well, times this by 2 or 3 and you are talking a serious workout during the day!

Also a scuba diver can lose fluids through sweat or…

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