Sunday, March 3, 2013

Responses to Heat and Cold Underwater


Divers need to be more concerned about heat before and after a dive than during a dive. Even in warm water the body gets cool, so than the primary concern is with heat as a result of the above water activities.

When the body temperature rises, weather from a rise due to the exposure suit, or to the fact that the sun is out, or a combination of those, the body goes through several cooling mechanisms to protect the core temperature.

Initially, skin capillaries dilate, allowing heat from the blood to radiate to the skin. Perspiration follows, which cool the skin. If the core temperature remains high, the pulse races, to help circulate more blood to help cool the body. These responses continue until the core temperature returns to normal.


A diver's physiology also reacts the same to a temp drop to protect the core temperature. Water conducts heat more than 20 times faster than in air and requires much more heat to raise its temperature. This means temperature that seems just right in the air, may be considered cold underwater.

With out the proper exposure protection, the average diver will be dangerously cold in half an hour in 40 deg water. For the majority of divers, water must be warmer than 80 deg to dive with out a suit.

By insulating the diver, the suit will extend dive times by slowing the cooling process, and making the body efforts more effective.

Divers with more fat tissue tends to loose heat more slowly than those that are thinner.

As the body cools, temperature centers in the hands, feet and head trigger heat conserving response that begin a change in circulation. Blood flow to the extremities slows through vasoconstriction to reduce heat loss from the blood through the skin. If vasoconstriction does not sufficiently maintain the core temp then the body reacts by triggering shivering. Shivering signals a losing battle with the cold. Once this starts, you need to get out of the water and begin the warming process.

A diver extends the bodys ability to maintain the core temperature through proper use of exposure suits and diving techniques. The head loses heat because the body can not reduce blood flow to the brain. Therefore a wet suit hood makes a huge difference in reducing heat loss.

Now lets talk about wet suit compression. As you dive, the suit which has large air cells begin to shrink. Meaning that the deeper you go the less protection you have to the cold. And if the suit is old than the protection is lost to a greater extent.

Divers Alert Network (DAN)

If you are an active diver, you need what I am going to bring up next. Divers Alert Network (DAN) is an organization that offers dive insurance, and a multitude of training classes. It is not associated with any one dive organization, but to diving in general. At the present time there are at least 14 different classes offered. I am going to touch on a few of them here. If you ever have a chance to get to Durham, NC, stop in, they will give you a tour. In fact, they can also arrange for you to see the Chambers at Duke University Hospital.

Oxygen First Aid for Scuba Diving Injuries
As a recreational diver, you can receive training to provide vital first aid that can make a difference to a scuba diver with decompression illness. The DAN Oxygen Provider Course provides entry-level training in the recognition and management of possible diving-related injuries using emergency oxygen first aid.

Advanced Oxygen First Aid for Scuba Diving Injuries
This advanced-level program is designed to train existing DAN Oxygen Providers to use the MTV-100 or a Bag Valve Mask while providing care for a non-breathing injured diver.

First Aid for Hazardous Marine Life Injuries
Serious hazardous marine life injuries are rare, but most divers experience minor discomfort from unintentional encounters with fire coral, jellyfish and other marine creatures. This course teaches divers to minimize these injuries and reduce diver discomfort and pain.

On-site Neurological Assessment for Divers
Learn how to conduct a neurological assessment on a potentially injured diver in this course. The information gained in this assessment can help convince a diver of the need for oxygen first aid, and help a dive physician determine the proper treatment.

Diving Emergency Management Provider Program
Learn the knowledge and skills from several courses into one single approach to dive emergency management.

Diving Emergency Specialist (DES)
Learn about DAN’s new recognition program for divers who are interested in dive safety.

Diving Medical Technician
Take the next step in diving education. Become a DMT and learn about providing care for divers involved in dive accidents.

Click on this picture above to be taken directly to the Duke University Hyperbaric Chambers and Medicine Department. There is also a link to see the complete layout of the 7 chambers. Check out the photo album on the site for more pictures - (past and present).

Layout of Hyperbaric Chambers Check this out, you will be amazed.

Click on these two pictures to see an enlarged view of the control panels. Click on the above small pictures to go to DAN Specialty Courses.
There is more to DAN then I can cover here in this short time. You need to go to the web site and check it out. Divers Alert Network

Better Watch Out If You Hold Your Breath Underwater

There are 4 types of injuries that can occur to the lungs by holding your breath on ascent.
Most body air spaces respond to pressure decrease with neither complications nor voluntary action by the diver. The Lungs respond to this as well, provided the diver breathes continuously to them keep equalized to the declining pressures. If the diver holds their breath or air traps within a section of the lungs, and as pressure declines expanding air will almost always cause an over-expansion injury.

The "GOLDEN RULE" in diving - never hold your breath while on scuba and while underwater. Panic and ignorance have been the causes of divers holding their breath. Nausea, choking and carelessness have also been causes to this as well.

Obstruction in the lungs may also trap air in certain parts and in effect "hold its breath." A chest cold, or respiratory infection can cause mucus accumulation and cause an obstruction. Smoking has also been implicated in these injuries.

Lung injuries can occur from even a small amount of over-pressurization. Research has shown that starting with full lungs, holding ones breath and surfacing can have an injury in as little as a 3 to 4 feet distance.

Rather than the lungs bursting like a balloon, an over-pressurization tears the lungs. The injury does not occur from the tear to the lungs, but from the air escaping and entering the tissues and / or the bloodstream. Lung injuries can result in 1 of 4 ways: Air embolism, Pneumothorax, mediastinal emphysema, and subcutaneous emphysema.

Any lung injury causes pulmonary capillaries and alveoli to rupture, mixing blood and air in the lungs. This results, often times, to the victim coughing up blood.

This is the most serious type of lung over-pressurization injury. This results was the air enters the blood stream from a rupture of the alveoli into the pulmonary capillaries, causing an air embolism or arterial gas embolism. Click on image for larger view.

An embolism is any foreign object that enters the bloodstream that blocks its flow. An air embolism is the same but now it is an air bubble that blocks the flow of blood. So as you ascend the once small bubbles become larger and larger due to the expanding nature of the ascent. This is a bubble on the arterial side of the circulation.

Air enters the bloodstream in the lungs flows through the pulmonary vein into the heart, to the left side of the heart into the aorta and then the arterial system. This air bubble can lodge almost anywhere in the circulatory system - can cause severe damage by blocking blood flow to the tissue.
The first main branch off the aorta which include the carotids. The carotids supply the majority of blood to the brain. If bubbles travel into the carotids, which is likely, they will go to the brain and cause cerebral air embolism.

The bubbles deny the brain of oxygenated blood, which causes a stroke. The symptoms include dizziness, confusion, shock, personality changes, unconsiouness, and death. Compared to DCS, the effects of cerebral air embolism and other lung injuries tends to be rapid and dramatic. DCS tends to be delayed.

If the bubbles were to miss the carotids and block the coronary arteries, the result would be a heart attack.

If the overpresurized lung tears at it surface, the expanding air leaks between the lungs and the pleural lining (chest wall), causing the lung to collapse, either partially or entirely. This collapsed lung is called a pneumothorax.

This is not nearly as life threatening as an AGE because the victim, in most cases, still has a working lung to breathe from. This collapse lung causes severe chest pain, and may cause the victim to cough up blood.

There is another form of this condition called spontaneous pneumothorax. This occurs with out the expansion of the lungs but through a weakness in the lung itself. This causes a sudden tearing and collapse of the lung.

This condition is uncommon, but can be more serious than the standard pneumothorax. especially if it happens underwater. This type can be aggravated on ascent, when the air pressing on the collapsed lung expands, increasing the pressure of the injured lung.

Since spontanous pneumothorax tends to recur, it inhibits further diving till surgery is performed to correct the problem. Since out a physician who specializes in pulmonary dive medicine. CLICK ON THE PICTURE FOR A BETTER VIEW


Mediastinal means center of the chest.. This is sometimes called pneumomediastinum, is far less serious that air gas embolism and pneumothorax

This condition, air accumulating in the mediastinum presses on the heart and major blood vessels interfering with circulation. A victim may feel faint and short of breath due to impaired circulation. CLICK ON THE PICTURE TO SEE THE AIR BUBBLES IN THE MIDDLE OF THE CHEST.


This occurs frequently with mediastinal emphysema as air seek its way from the mediastinum, and folowing the path of least resistence, into the soft tissues at the base of the neck.

Air accumulates under the skin in this area. This causes the victim to feel a fullness in the neck and to experience a voice change. The skin may crakle if touched. CLICK ON THE PICTURE TO SEE THE AIR RISE TO THE NECK REGION.


The first aid for both the decompression sickness and lung overexpansion injuries are the same. You can say that the first aid for the Decompression illess injuries are the same. In fact you do not have to determine on site which you are dealing with to start giving aid to the diver.

Give 100% oxygen to the diver

Simply put, breathing 100% O2 accelerates diffusion of nitrogen from the body to slow and reverse bubble growth, and help bubble elimination. Breathing oxygen also raises the blood oxygen levels and maximizes the effectiveness of the blood that does reach the affected areas. Make sure the air ways are clear and treat for CPR if needed. The best first aid is to get them to a medical facility for proper care.

Now to the lung injuries FIRST AID

Three out of the four conditions are not immediately life threatening, the presence of any of these conditions indicates a lung over-expansion injury has occured. The AGE is the most life threatening and therefore when first aid is given, they treat any of these conditions as though they have AGE.

AGE needs immediate compression to diminish the bubbles in the bloodstream and force them into solution. This restores blood flow to the tissues. None of the other conditions require decompression, provided there is no AGE.

Pneumothorax requires surgical removal of the air from between the collapsed lung and the pleural lining, followed by a lung reinflation.

Mediastinum and subcutaneous emphysema will dissipate on their own as the blood slowly reabsorbs the trapped air. Breathing oxygen can speed up the reaborbtion process.


Regulators and the Environmental Seal

Regulators or regulator systems are really composed of many parts. The stage that attaches to the tank is known as the first stage, then comes the long air hose. This in turn is followed by the 2Nd stage, the part that actually goes into your mouth so you can breath the air.

First stage role is to accept the 3000 psi cylinder pressure coming from the tank and reduces it to an ambient pressure plus a preset intermediate pressure. It is here at second stage that its role is to reduce this ambient-plus-intermediate pressure to simply an ambient pressure so you can breathe off it. At this point we will not go into great detail on the exact mechanisms involve with this reduction.

Some first stages offer environmental sealing. This is where the first stage is completely sealed off from the water and air. Where as non-environmentally sealed regulators are open to the water temps and debris.

There are many ways to group regulators: piston vs diaphragm first stages, balanced vs unbalanced, downstream vs pivot valves, open vs closed. Even on these listed there are many combinations. Just understand there are many variations.

Still another way is what I will call non-sealed and sealed regulators. You can see on the non-sealed there are small holes on the sides, where as on the sealed the holes are missing. This is the easliest way to tell the difference.

In the sealed regulators, the water pressure doesn't act directly on the piston or diaphragm. Instead it acts on the silicone or alcohol based fluid inside a watertight, yet pressure-sensitive, barrier. This fluid then transmits to the piston or diaphragm.

Why is this important in diving ? First, it prevents salt, sediments and other contaminates from entering the first stage. This reduces internal corrosion and contaminant buildup. Second, it helps isolate the valve mechanism from freezing. This is important if you dive in extreme cold water, like in ice diving. If the first stage does freeze while diving it will seize to work.

Boyle's Law - How Depth Affects Air Volume

Sir Robert Boyle was a 17th Century Irish scientist. He wanted to know what happens to a quantity of air if the pressure on it changes. Boyle was greatly influenced by Torricelli. Torricelli determined the pressure exerted by the atmosphere. He determined that the atmosphere pressure equals about 30 inches of mercury.
(Click his picture for more information on GAS laws.)

Boyle has a famous experiment involving a U-shaped glass tube. Here he placed equal amounts of mercury in the tube. One end of the tube was open and the other closed. Under atmosphere pressure the mercury was level and equal. Boyle then started to add mercury to reduce the volume in the closed end. He found that to reduce the volume in the closed end by half, he had to add 30 inches more of mercury. Thus it proved to him that to half the volume in the closed end, a doubling of the atmosphere was needed. In other words, if temperature remains constant, the volume of the gas is inversely proportional to the absolute pressure. If you raise the pressure the volume will decrease proportionately.

Click on pictures to see it better.

Why do I need to know this as a diver ?
The deeper you dive the less volume of air you have in your tank Look at the chart here. Go from 1 ATA( Atmosphere) to 2 ATA you double the ATA but now the tank if 1/2 full. Go to 130 feet or 5 ATA -- 5 times the ATA, but now 1/5 the air volume. Another way. 5 breaths at the surface = to 1 breath at 130 feet. That is pressure and volume relationship. Increase pressure = decrease volume by that amount. This is why your stay at depth is shortened. Click on his picture above for more information on this principle.

Now lets talk about density and pressure. While pressure and volume of a gas are inversely proportional, the pressure and density of a gas are directly proportional. If the gas volume is reduced, the space where the gas molecules are must also be reduced, therefore, the same number of molecules in now a smaller space become compact or denser. Let's get this principle. You reduce the volume (space) by pressure, which reduced the air volume you have to breath. But now the space is smaller for the same number of molecules making them more dense. The relationship is the same as before. If you double the ATA you will double the density because now it is a direct relationship. See chart to help with this relationship. So at depth, you have less air to breath, but the quality of molecules would be increased.

Divers take with them gas-filled containers -Tanks, BCDs, dry suits, mask, - and have have gas filled spaces in their bodies - sinuses, ears, and lungs. Even the tiny bubbles that comprise wet suits continually expand and contract as pressure changes as described by Boyle's Law.

Ascents - 5 Point Procedure

A few blogs ago I covered how to do a 5 point and comfortable descents. Now I will cover how to make a 5 point ascent, followed by Part 2 which will be how to ascend safely.

The five points are as follows:

As always you and your buddy are diving close to each other. After looking at your SPG (Submersible Pressure Gauge) you have determined that it is time to start to head up. You signal your buddy using your pre-determined signals that you want to go up or need to go up. Your buddy in turns returns the "up" signal. Again, you do this as a buddy team, and only when you are both agreed and facing each other do you start with the next step.

If you remember from the five point descent, you looked at you watch for the start time of the dive. Now you must again look at your watch for the end bottom time or BT. This is not really your end dive time but for calculating your dive profile using standard dive tables, this is the time that you use. A little confusing ? Let me try to clear it up. The actual dive time for a profile is the start of your descent till the time you start up again. This is of course considered a straight line profile. In other words you are using a standard table and not the PADI wheel. The PADI wheel is used to help calculate multi-level stops along the way up. I may cover this in more details, if I get a question on it.

Once you have the time you locate with your left hand the BCD controls, ie, where you will release air. And with your right hand you raise it up over your head. This may seem obvious, but I have seen many divers who do not do this step. You need to have your hand up to make clear the approach to the top.

Step 4: LOOK UP
As you raise your hand up you look up to see where you are going. You want to make sure that you are noting going to hit a boat, or a boat hits you. Although boatings are required to stay a certain distance from divers. Each state has a different distance, so check with the local dive shop to find out. Bare in mind that you are required to dive with a dive flag, so boaters will know where you are. Just a thought for safety. This flag says, "Divers down, stay away". But to be safe, still reach up and look up.

Last step is to swim up slowly while turning in a 360 deg rotation. Again, this lets you see all around so if anything is coming from another angle, you will be able to see it.

You are doing all of this while staying as close to your buddy as possible. These are the 5 basic steps to a ascent. On my next blog, I will cover how to make this 5 steps comfortable and how to ascend in a safe manner. I made mention to some of it already.

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Carotid - Sinus Reflex
Is this Harmful to Me as a Diver ?

How many of you as divers wear tight hoods, or extra tight wet suits, or even tight necks on your dry suit ? If so, have you ever came out of a dive not feeling quite right ? Did you get light headed, or dizzy as a result of it ? I have the answer to why this has happened ?

It is called Carotid-Sinus Reflex. Let's review, as you may know the carotids are the large arteries that run from your heart up the middle part of the neck to the brain.
In fact, these arteries are the major arteries to supply blood, nutrients, and oxygen to the brain. You might remember these as the ones that you check while doing CPR. Oh yea. Thats right. Normally you will sense a pulse while checking during CPR.

Now on to what this reflex is all about. Carotid Sinus receptors monitor blood pressure within these carotid arteries and send impulses to the cardioinhibitory center within the brain to regulate the heart.

So if these sensors senses high blood pressure, it stimulates this center in the brain to slow down the heart. At least till the blood pressure comes down. On the other hand, if these carotid receptors detect low blood pressure, it stops stimulating the cardioinjibitory center, which now in turn stops sending signals to the heart. The heart rate in this case increases.

Now, if a diver wears an excessively tight hood, neck in the wet suit or dry suit that constricts the neck, the carotid sinus receptors incorrectly interprets the excess local pressure as high blood pressure. Which then stimulates the cardioinhibitory center and then slows the heart in responses to it. This slow heart rate slows blood flow to the brain. If the pressure on the neck and receptors continues, causes an even greater high blood pressure, and a continued slow blood flow to the brain. Eventually, a diver may lose consciousness due to the reduced blood supply reaching the brain. In most cases, a diver feels discomfort and light-headedness before the constriction leads to a serious problem.

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Saturday, March 2, 2013

Buddy System - What Are The Benefits ?

During the confined water and through out your training, using the buddy system is a high priority when you dive. No matter how advanced or skilled you are in diving, you should dive with a buddy. During this topic we will center on why it is important to dive with a buddy.

There are three general reasons to dive with a buddy; they are 1)practicality, 2)safety, and 3) fun. I will talk about each one of these in detail.

As mentioned in a previous lesson, having a buddy will help get your gear on. This not only pertains to the BCD, but also the fins, if you are getting them on in the water. They can help stabilize your footing. On the surface you need to conduct the BWRAF procedure. Your buddy helps remind you of your depth, time, to check your air supply.

If while diving you do go to deep and begin to 'act" funny, then your buddy and help you up. If you panic and start to breathe fast, they can be there to help calm you down. If you get tired on the surface, they will be able to get you to shore with the tired diver tow. From a safety standpoint, diving with a buddy is a must.

3) FUN
Diving is a social activity. It is something that when a dive is completed, you will be able to talk about for a long time. Together, you and your buddy share experiences and underwater adventures. If you see a "big" fish and tell about it, your dive buddy will agree. Diving with buddies will introduce you to a whole new circle of friends.

Good buddies avoid problems in the following ways:
1) Agree on an entry, exit points, and dive objectives
You need to talk about where you want to go, and what you are trying to accomplish in the dive. Are you going to do a out and back pattern, a square pattern, or random. Talk about who will lead and follow etc. Both buddies show use their compass and track the patterns, so it one is off the other can help.

2) Agree on depth limits and how long the dive will be
This goes along with 1 above. Depends on where you are going.

3) Establish and review communications
Are there different dive signs yo will use. Some common ones are up, down, low on air, directions, check you air, I have ?? psi left. Just go over the signs prior to any dive,

4) Discuss how to stay together, and what to do if separated
If separated, search for 5 minutes and then ascend to the surface, rejoin at the surface, continue dive it air supply warrants it. This is a good practice no matter how deep your dive is.

5) Discuss emergency procedures
Tired diver tows, out of air problems, sharing air. etc.

You and your buddy have a responsibility to each other. For this system to work both of you need to take it serious, but still have fun, while working on staying together. So every dive develop the habit of diving with buddy.

How to Pick the Correct Mask

Choosing the right mask is easy. As with most pieces of equipment getting the correct fit is vitally important. A mask that does not fit properly will leak and be uncomfortable, both of these are a constant distraction will diving.

To determine whether a mask will fit or not divers take the following steps.

1. Remove the strap or place it in front of the lens, so it is out of the way.

2. Place the mask lightly against the face while looking up. Make sure the shirt is not tucked under and that the mask is sitting flush to your face.

3. Inhale slightly through your nose. The mask at this point will feel like it is sucking against your face.

4. While inhaling, lightly tuck on the mask and look down. If the mask fits properly, it will remain on you face. If it is loose or falls, then it does not fit your face.

5. Make sure the mask you choose feels comfortable to you. And for all the female divers, it is all about the colors. I know, you need a mask that says something about you, and the color does just that.

Now you need to compare other features. Does the mask have one large lens, or 2 smaller ones? Does it have side lens ? How are the straps, are they easy to use ?

Are you a diver that has glasses. Then you need to get a mask that has 2 lens so that you can buy presciption lens to replace them. Seeing underwater is a good thing.

Friday, March 1, 2013

Why is A Burst Disk Important ?

All Scuba cylinders have a maximum working pressure
past which the tank should not be filled too. To help to make certain that the tank doesn't accidentally go beyond this point, some cylinder valves have a device known as a burst disk. This is an industry requirement in North America.

A burst disk consist of a thin copper disk held in place with a gasket and a vented plug. If the pressure inside the tanks rises to 140% of the working pressure, the disk ruptures, and the air escapes thought the vented plug. They are designed to rupture at pressures between 125% and 166%.

Burst disk protect against damage that may occur when the tank is over filled. Burst disk usually rupture when full if they are left to sit in the hot sun. In the hot sun tank pressures have been known to rise to several hundred psi. If the burst disk is old - or the burst disk has the wrong pressure rating - this rise in pressure may be sufficient to cause rupture.

In newer burst disk assemblies the vented plug directs the escaping air to both sides of the valves instead of straight out. This safer because the air escapes won't cause the tank to spin.

Keep in mind, when a tank goes through it's normal yearly Visual Inspection, the burst disk is changed at that time.