In this study, we will first learn about the physiological consequences of breathing gases at higher partial pressure than at the surface. To fully understand these effects we must have a firm understanding of these phenomena. The first thing we need to do is identify the substance within the blood that aids in the transport of oxygen and in what component of the blood is this substance contained? To answer this we must know that oxygen is efficiently transported throughout the body because of a substance called hemoglobin, which is contained in the red blood cells. If the blood did not contain this hemoglobin, our blood would have to circulate 15 to 20 times faster to keep up with our bodies demand for oxygen. We also should know that large amounts of carbon dioxide can be carried by our circulatory system back to our lungs for expiration primarily because carbon dioxide can be converted in bicarbonate. For the body to efficiently transport carbon dioxide to the lungs, the carbon dioxide is converted into bicarbonate. Once back in the lungs the bicarbonate is converted back into carbon dioxide and released through respiration. Next, we need to explain how proper diving techniques and equipment can help avoid exhaustion and build up of carbon dioxide. We should breath deeply while scuba diving to compensate for the increased dead-air space resulting from the regulator, the reduced lung volume resulting from compression of the chest and the increased amount of alveolar carbon dioxide. The practice of breathing slowly is important also to minimize resistance caused by turbelence in the airways. Once we understand this we are ready to learn the physiological mechanism by which voluntary hyperventilation enables a diver to extend breath holding time.
Example: When a breath holding diver submerges in cold water, his heart rate will? His heart rate will decrease due to the mammalian diving reflex.
A breath holding diver must move slowly and deliberately through the water in order to reduce the demand for oxygen. The same diver should also take a few rapid, deep breaths before submerging to reduce his alveolar carbon dioxide level. Moving on, we now need to explain the physiological mechanism that cause a "shallow water black out" and why this condition usually occurs on ascent rather than descent. To understand this we must know that the factor controlling our urge to breathe is not primarily the lack of oxygen in our blood but rather the elevated level of carbon dioxide. Hypoxia is the mechanism that causes a shallow water black out and results when the carbon dioxide level cannot accumulate to a level high enough to stimulate breathing before the tissues consume the oxygen. This black out normally occurs on ascent because the partial pressure of the alveolor oxygen rapidly decreases.
Example: If a diver is down to his last breath at 33 ft of depth what will happen when it ascents to the surface? If this diver barely had enough oxygen at depth to remain conscious and functional, he will black out as he ascends to the surface due to the abrupt decrease in the oxygen partial pressure.
We are now ready to explain the physiological mechanism that causes a "carotid sinus reflex" and how this affects the diver. To understand this phenomenon we must understand a few things. The first is we should know that our carotid sinus receptors stimulate the cardioinhibitory center which is located in the brain. This reflex occurs when the heart rate slows down to a point where it is unable to maintain sufficient blood flow to the brain and this is typically caused by an excessively too tight wetsuit or hood that constricts the neck. Once we understand this mechanism we are ready to understand the physiological effect of increased carbon monoxide levels on the diver and how they can be avoided. We should know that carbon dioxide is difficult to detect because it is odorless and tasteless. We should also know that carbon monoxide bonds with hemoglobin 200 times more readily than oxygen and this bond is so strong that it takes 8 - 12 hours for the circulatory system to eliminate it.
Now we need to explain the physiological mechanism of Decompression sickness and list the common factors that can contribute to its occurence. To understand this we should know that our tissues dont absorb and eliminate nitrogen at the same rate due to different densities in our tissues as well as our blood supply differs among tissues. So those tissues receiving more blood supply will have more gas delivered and eliminated. We should also know that DCS occurs to divers upon surfacing because of bubble formation. This phenomenon does not occur until the ambient pressure is reduced upon ascent. As humans we can tolerate some degree of supersaturation. Now we should define the terms "silent bubbles" as it relates to DCS. The term "silent bubbles" refers to bubbles that are so small they do not cause signs and symptoms of DCS. Silent bubbles cannot be detected by the human eye usually but rather by a Doppler Ultrasound Flowmeter which enables scientists to hear the bubbles as they travel through circulation. Next we should understand why oxygen is given to individuals with signs and symptoms of DCS as a first aid measure. Breathing pure oxygen aids the individual with DCS because it increases the pressure gradient between the nitrogen pressure in the tissues and the alveolar nitrogen pressure. Thus resulting in a significant increase in the driving force of the tissue nitrogen, thus aiding in its elimination. We should also explain the cause of nitrogen narcosis, state the approximate depth at which the disorder occurs and list three common sign/ symptoms. Nitrogen narcosis results from disruptions in the transmissions between nerve cells. Narcosis is usually experienced at a depth of 100 feet but differs highly on an individual basis. Three sign/symptoms of narcosis is poor judgement, decreased coordination, and a feeling of false security. Other signs/ symptoms include foolish behavior, anxious or uncomfortable feelings and a general disregard for safety.
Next we should define the term "barotrauma" and explain how it can occur to the lungs, sinuses and ears of the diver during both ascent and descent. The term barotrauma means pressure injury.
Example of a pressure injury would be a round window rupture. This can be caused an excessively forceful valsalva manuever. This is a primary reason why divers are warned to be cautious when clearing their ears under pressure using the valsalva manuever.
We should also know that vertigo refers to dizziness that a diver may experience while diving. To complete this lesson we should review the basic functions of the ear as well as understand the signs/ symptoms of DCS as well as air embolism.
The Ear: Sound vibrations are transferred from the outer to the inner ear via the ossicles. The ossicles are the series of bones that are attached at one end to the tympanic membrane or the outer ear, and are connected to the oval window of the inner ear. The vestibular canals are located in the inner ear and are responsible for balance and the portion of the ear that is most affected by changes in pressure in the middle ear.
Sign/ Symptoms of DCS and air embolism:
DCS: pain in the joints or fatigue
Air embolism: sudden unconsciousness
The most serious form of lung-expansion injury is an air embolism because air bubbles enter the arterial circulation.
We hope you have enjoyed our lesson on Scuba physiology and have benefited from this knowledge. Please return often for our latest blog.
Scuba or Snorkel San Diego with S.E.Adventures at www.GetWetSanDiego.com
619 962 9306
Thursday, September 4, 2008
Scuba Physics by www.GetWetSanDiego.com
First, when we are concerned with scuba diving physics, we need to address why water is able dissipate body heat faster than air, at what rate this occurs and what effect it has on the diver. To answer these questions we conclude that water conducts heat far more efficiently than heat because water is more dense than air and conducts heat 20 times faster than air. Next we need to know the behavior of light as it passes from an air/water interface and what effect this has on the diver. To answer this we have to know that this behavior of light is called refraction. Refraction is caused by the process of light traveling at different speeds as it passes through different substances. Also, objects tend to look larger underwater by a ratio of 4:3 and cause objects to appear magnified by 33%. Now we need to look at the visual reversal phenomenon and explain its effect. This phenomenom refers to an objects tendency to appear further away than its actual distance. The single most important factor affecting this phenomenom is turbidity. Once this is understand we need to know why sound travels faster underwater than in air, by how much and what effect this has on the diver. To answer this we need to know that light waves contain electromagnetic energy while sound waves are comprised of mechanical energy. We also know that sound travels 4x faster in water than it does in air and this effects divers because divers have a difficulty determining the direction of sound underwater due to an insufficient delay between the sound striking one ear before the other. With this information understood we get to Archimedes Principle, the principles of Buoyancy- "Any object wholly or partially immersed in a fluid bouyed up by a force equal to the weight of the fluid displaced by the object." (From this principle we can see whether or not an object floats or sinks according to the weight of the fluid. When working with the scuba diving we recognize Saltwater to weigh 64 lbs per cubic foot and freshwater to weigh 62.4 lbs per cubic foot and we also need to know pure water has a specific gravity of 1.0)
Example: Approximatley how much water must be displaced to bring a 900 lb object to the surface if the object displaces 10 cubic ft and lies in 132 of seawater.
To solve this we disregard the depth and focus on the weight of the object along with the displacement. To begin we must multiply the cubic ft of 10 by the weight of the water 64. We arrive at 640. Now we must subtract 640 from the weight of 900.
This equals 260. The final step is divide 260 by the weight of the water (64) to arrive at our answer of 4.06.
Once we master the concept of Archimedes prinicple we move on to Boyles Law.
To deal with Boyles Law we must know that for every 33 feet of descent in seawater add the pressure of 1 atm or 14.7. If you take a full breath at 33 feet your inhaling twice the number of air molecules as a full breath at the surface. Note this when accounting for the surface pressure when finding absolute values.
Example: What is the ambient pressure at 50 ft of Seawater? to solve this we multiply the number of ft (50) by the pressure exerted (.445 for seawater). We arrive at the answer of 22.25. To finish the answer we must apply 1 atm for surface pressure and add 14.7 to 22.25. The completed answer is 36.95.
If we fully understand this, we realize that 1 atmosphere weighs 14.7 lbs and exerts .432 lbs for freshwater and .445 lbs for seawater. Absolute and Ambient pressures require that we add 1 atm or 14.7 to our gauge pressure. Gauge pressure ignores the atmospheric pressure.
Now we are ready for Boyles Law. Boyles Law describes pressure volume relationships and states that "If the temperature remains constant, the volume of a given mass of gas is inversely proportional to the absolute pressure". The mathematical equation for Boyles Law is P1 x V1 = P2 x V2.
We will use Boyles Law to explain the relationship between pressure and volume on a flexible gas-filled container (Balloon or our lungs) as well as in-flexible container and calculate the changes that will occur to that container as it is raised and lowered in the water column.
You may find this chart useful:
Depth Pressure Volume
0 1 ata Full
33' 2 ata 1/2
66' 3 ata 1/3
99' 4 ata 1/4 .........
Example: A balloon (our lungs) containing 10 cubic feet of air at 25 ft of seawater is taken to a depth of 85 ft. What will be the exact volume of the balloon (our lungs) upon reaching 85 ft.
To solve this we will use the formula Boyles Law Formula:
P1 X V1 = P2 X V2.
P1 = 25 ft x .445 = 11.125 + 14.7 = 25.82
V1 = 10 ( # of cubic ft)
P2 = 85 ft x .445 = 37.82 + 14.7 = 52.53
V2 = x
Plug in variables
(P1)25.82 X (V1)10 = (P2)52.53 X (V2)x
258.2 = 52.53 X x
258.2 / 52.53 = 4.91
x = 4.91
Still dealing with Boyles Law we now need to explain the relationship between depth and the density of the air a diver breathes and calculate this relationship in increments of whole atmospheres. To determine this relationship we must determine the type of container being used being a balloon or lift bag or an inflexible container such as a scuba tank. When dealing with an inflexible container we know if pressure increases the volume must decrease and if pressure decreases volume must increase and the opposite when dealing with a balloon or flexible container. A flexible container will expand upon ascent, and reach the surface with the original quantity of gas times the number of atmospheres from which it was released. And we also know that a scuba tank or inflexible container is unaffected by the surrounding water pressure. Next we need to determine a divers air consumption rate at one depth and calculate how that consumption rate changes when depth changes.
Example: A diver has an air consumption rate of 3 cubic ft. per mintue at 66 ft of seawater. If all other factors but depth remain unchanged, what will his consumption rate be at 200 ft?
To answer this we must first determine the surface consumption rate. Which in this case the diver will consume one third the amount of air at the surface then he would at 66 ft (3ata).
Example: How much water is exerted at a depth of 200 ft? By dividing 33 feet into 200 ft we determine that 200 ft is 7 ata. (200/33 = 6.06. When accounting for atmospheric pressure we must add 1 to the gauge pressure. In this case the gauge pressure is 6.06. 6.06 + 1 = 7.06) We now know that the air consumption rate will increase to slightly more than 7 fold at 200 ft.
With all of this understood we now understand the Law and principles of Sir Robert Boyle and what happens to a volume of air when the pressure changes.
Moving on, we arrive at Charles Law which states, "the amount of change in volume of gas is directly proportional to the change in the absolute temperature at a constant pressure." Boyle's Law only dealt with the effects of pressure and volume. Charles Law deals with Temperature. Charles Law says that the amount of change in either volume or pressure of a given gas volume is directly proportional to the change in the absolute temperature.
The general guideline for Charles Law is the scuba tank pressure will change 5 psi for every 1 degree change. We may also combine the formula for Boyles Law:
P1/T1 = P2/T2
We also need to know that a flexible container such as a balloon or lift bag when placed in a freezer will decrease in volume because of less pressure in the balloon. As temperature decreases, the motion of the molecules decreases. As the motion decreases, the force of the impact of their collisions with each other decreases and since "the amount of change in volume of gas is directly proportional to the amount of change in the absolute temperature" we know that when pressure decreases volume decreases and when pressure increases volume increases. On the flip side when dealing with an in-flexible container such as a scuba tank the volume remains unchanged regardless of changes to the external pressure.
Example: A 80 cubic foot scuba tank is filled to 3225 psig at an ambient temperature of 78 degrees F. If the tank is then used in water temperature of 44 degreees F, what would the approximate tank pressure be?
To solve this we will need to remember the scuba tank pressure will change 5 psi for every 1 degree change. We will also need to use the formula, P1/T1 = P2/T2. Next we must determine what we know from this problem. The pressure the tank is filled to is 3225 and it asks us to determine what the pressure will become(P2). To predict the behavior of gases we must work in absolute terms, so we must add 15 (14.7) to the 3225 psig to arrive at 3240 psia or P1. The temperature of the tank is 78 degrees F and it will be used in 44 degrees F. When working in absolute terms we must convert degrees F into degrees Rankin. For this conversion we just add 460 degrees to the temperature of 78 degrees arriving at 538 degrees Rankin and 44 degrees F now becomes 504 degrees Rankin. Now we can plug these values into the equation.
3240/538 = x/504
504x3240/538 = x
x = 3035
3035 - 15 (14.7) = 3020.
If we understand the principles so far then we have a basic understanding of Charles Law and the principles in which apply including Boyle's Law.
Now we are ready to move on to Daltons Law which states, "the total pressure exerted by a mixture of gases is equal to the sum of the pressure of each of the different gases making up the mixture - each gas acts as if it alone were present and occupied the total volume." In essence, this means that each gas within a gas mixture acts independently of the others. This independent pressure is referred to as the partial pressure. When dealing with Dalton's Law we are referring to partial pressures and when dealing with partial pressures we are explaining the effects of breathing contaminated air mixtures at depth and calculating the equivalent effect such contamination would have upon the diver at the surface. We also must remember once the tank is filled, the percentages of gases within it cannot change.
Example:
Breathing from a contaminated air source with 1.5% carbon monoxide at a depth of 300 feet of seawater would have the same effect as breathing approximately what percentage of carbon monoxide at the surface?
We must first determine that 300 feet is 10 ata. We then multiply 1.5% by the ata of 10 to arrive at 15%.
Dalton's Law is important for divers because it deals with individual gases as well as surface equivalency which concerns us when we deal with toxic contaminates in our breathing gases.
Example: On the surface 0.5% of carbon monoxide is not toxic but at 5 ata, it is.
Once we understand Daltons Law and partial pressures we are ready for Henrys Law. The most common example of Henry's Law is a carbonated beverage such as a coke. When you open the beverage it foams and fizzes as carbon dioxide, dissolved in the liquid, comes out of solution. This demonstrates that liquids dissolve gases, and that if conditions change, the amount of gas that can stay in solution changes. This is true when dealing with gas in our bodies, such as nitrogen. Also, we should note that the pressure exerted from inside a liquid by a particular gas in solution is called gas tension. The difference between the partial pressure of gases in contact with a liquid and the gas tension within the liquid is referred to as the pressure gradient. When the gas tension within a liquid reaches equilibrium with the partial pressure of the gas in contact with the liquid, no more net exchange of the gas occurs. At this point the liquid is said to be saturated with that gas. Henry's Law describes supersaturation and the effects it has on a diver. Without Henry's Law we wouldn't have the dive tables and computers that allow us to minimize the risk of decompression sickness by providing no stop limits and/ or decompression stops. Now we need to explain what will occur to a liquid saturated with a gas at high pressure when the pressure of the gas in contact with the liquid is quickly reduced. To understand this we must know there is a tendency for a state of equilibrium to exist between the pressure within the liquid (gas tension), and the pressure of the gas in contact with that liquid. This equilibrium will be maintained until the pressure in contact with the liquid changes. Thus concluded, "the amount of gas that will dissolve into a liquid is almost directly proportional to the partial pressure of that gas."
Example: If a glass of water is placed in a vacuum for several days , no longer containing any gases, if it is then placed in a pressure pot and pressurized to 2 ata for several days what will be the gas pressure within the liquid? And if this vacuum is created, how will pressure of the gas, inside the liquid, change?
Since the amount of gas that will dissolve into a liquid is almost directly proportional to the partial pressure of that gas, the gas pressure within the liquid is 2. If the vacuum is created the pressure will decrease. A vacuum would represent zero pressure in contact with the liquid. Therefore, the tendency would be for any gas contained in the liquid to come out. So, the pressure will decrease.
Once we understand how a saturated liquid at high pressure will react when the pressure of a gas in contact with the liquid is quickly reduced, we are ready to learn about "supersaturation" and what conditions are necessary for gas bubbles to form in a supersaturated liquid. We use supersaturation to predict decompression outcomes with very high reliability. While diving, nitrogen gets absorbed in our tissues. Although at different rates, our tissues become saturated with nitrogen and when we surface our tissues become supersaturated with nitrogen. While diving we plan for no stop limits and decompression stops so that we don't end up with an excessive pressure gradient that results in decompression sickness. During these stops nitrogen is released out of solution (our tissues) and when the pressure gradient has declined enough you may move on the next stop.
To learn more about how our body deals with dissolved gases please see our blog on Diver Physiology.
I hope you have enjoyed our lesson on Scuba physics and hope you will visit us in San Diego. Thank you for visiting www.GetWetSanDiego.com and we hope you check back often for our latest blogs.
Example: Approximatley how much water must be displaced to bring a 900 lb object to the surface if the object displaces 10 cubic ft and lies in 132 of seawater.
To solve this we disregard the depth and focus on the weight of the object along with the displacement. To begin we must multiply the cubic ft of 10 by the weight of the water 64. We arrive at 640. Now we must subtract 640 from the weight of 900.
This equals 260. The final step is divide 260 by the weight of the water (64) to arrive at our answer of 4.06.
Once we master the concept of Archimedes prinicple we move on to Boyles Law.
To deal with Boyles Law we must know that for every 33 feet of descent in seawater add the pressure of 1 atm or 14.7. If you take a full breath at 33 feet your inhaling twice the number of air molecules as a full breath at the surface. Note this when accounting for the surface pressure when finding absolute values.
Example: What is the ambient pressure at 50 ft of Seawater? to solve this we multiply the number of ft (50) by the pressure exerted (.445 for seawater). We arrive at the answer of 22.25. To finish the answer we must apply 1 atm for surface pressure and add 14.7 to 22.25. The completed answer is 36.95.
If we fully understand this, we realize that 1 atmosphere weighs 14.7 lbs and exerts .432 lbs for freshwater and .445 lbs for seawater. Absolute and Ambient pressures require that we add 1 atm or 14.7 to our gauge pressure. Gauge pressure ignores the atmospheric pressure.
Now we are ready for Boyles Law. Boyles Law describes pressure volume relationships and states that "If the temperature remains constant, the volume of a given mass of gas is inversely proportional to the absolute pressure". The mathematical equation for Boyles Law is P1 x V1 = P2 x V2.
We will use Boyles Law to explain the relationship between pressure and volume on a flexible gas-filled container (Balloon or our lungs) as well as in-flexible container and calculate the changes that will occur to that container as it is raised and lowered in the water column.
You may find this chart useful:
Depth Pressure Volume
0 1 ata Full
33' 2 ata 1/2
66' 3 ata 1/3
99' 4 ata 1/4 .........
Example: A balloon (our lungs) containing 10 cubic feet of air at 25 ft of seawater is taken to a depth of 85 ft. What will be the exact volume of the balloon (our lungs) upon reaching 85 ft.
To solve this we will use the formula Boyles Law Formula:
P1 X V1 = P2 X V2.
P1 = 25 ft x .445 = 11.125 + 14.7 = 25.82
V1 = 10 ( # of cubic ft)
P2 = 85 ft x .445 = 37.82 + 14.7 = 52.53
V2 = x
Plug in variables
(P1)25.82 X (V1)10 = (P2)52.53 X (V2)x
258.2 = 52.53 X x
258.2 / 52.53 = 4.91
x = 4.91
Still dealing with Boyles Law we now need to explain the relationship between depth and the density of the air a diver breathes and calculate this relationship in increments of whole atmospheres. To determine this relationship we must determine the type of container being used being a balloon or lift bag or an inflexible container such as a scuba tank. When dealing with an inflexible container we know if pressure increases the volume must decrease and if pressure decreases volume must increase and the opposite when dealing with a balloon or flexible container. A flexible container will expand upon ascent, and reach the surface with the original quantity of gas times the number of atmospheres from which it was released. And we also know that a scuba tank or inflexible container is unaffected by the surrounding water pressure. Next we need to determine a divers air consumption rate at one depth and calculate how that consumption rate changes when depth changes.
Example: A diver has an air consumption rate of 3 cubic ft. per mintue at 66 ft of seawater. If all other factors but depth remain unchanged, what will his consumption rate be at 200 ft?
To answer this we must first determine the surface consumption rate. Which in this case the diver will consume one third the amount of air at the surface then he would at 66 ft (3ata).
Example: How much water is exerted at a depth of 200 ft? By dividing 33 feet into 200 ft we determine that 200 ft is 7 ata. (200/33 = 6.06. When accounting for atmospheric pressure we must add 1 to the gauge pressure. In this case the gauge pressure is 6.06. 6.06 + 1 = 7.06) We now know that the air consumption rate will increase to slightly more than 7 fold at 200 ft.
With all of this understood we now understand the Law and principles of Sir Robert Boyle and what happens to a volume of air when the pressure changes.
Moving on, we arrive at Charles Law which states, "the amount of change in volume of gas is directly proportional to the change in the absolute temperature at a constant pressure." Boyle's Law only dealt with the effects of pressure and volume. Charles Law deals with Temperature. Charles Law says that the amount of change in either volume or pressure of a given gas volume is directly proportional to the change in the absolute temperature.
The general guideline for Charles Law is the scuba tank pressure will change 5 psi for every 1 degree change. We may also combine the formula for Boyles Law:
P1/T1 = P2/T2
We also need to know that a flexible container such as a balloon or lift bag when placed in a freezer will decrease in volume because of less pressure in the balloon. As temperature decreases, the motion of the molecules decreases. As the motion decreases, the force of the impact of their collisions with each other decreases and since "the amount of change in volume of gas is directly proportional to the amount of change in the absolute temperature" we know that when pressure decreases volume decreases and when pressure increases volume increases. On the flip side when dealing with an in-flexible container such as a scuba tank the volume remains unchanged regardless of changes to the external pressure.
Example: A 80 cubic foot scuba tank is filled to 3225 psig at an ambient temperature of 78 degrees F. If the tank is then used in water temperature of 44 degreees F, what would the approximate tank pressure be?
To solve this we will need to remember the scuba tank pressure will change 5 psi for every 1 degree change. We will also need to use the formula, P1/T1 = P2/T2. Next we must determine what we know from this problem. The pressure the tank is filled to is 3225 and it asks us to determine what the pressure will become(P2). To predict the behavior of gases we must work in absolute terms, so we must add 15 (14.7) to the 3225 psig to arrive at 3240 psia or P1. The temperature of the tank is 78 degrees F and it will be used in 44 degrees F. When working in absolute terms we must convert degrees F into degrees Rankin. For this conversion we just add 460 degrees to the temperature of 78 degrees arriving at 538 degrees Rankin and 44 degrees F now becomes 504 degrees Rankin. Now we can plug these values into the equation.
3240/538 = x/504
504x3240/538 = x
x = 3035
3035 - 15 (14.7) = 3020.
If we understand the principles so far then we have a basic understanding of Charles Law and the principles in which apply including Boyle's Law.
Now we are ready to move on to Daltons Law which states, "the total pressure exerted by a mixture of gases is equal to the sum of the pressure of each of the different gases making up the mixture - each gas acts as if it alone were present and occupied the total volume." In essence, this means that each gas within a gas mixture acts independently of the others. This independent pressure is referred to as the partial pressure. When dealing with Dalton's Law we are referring to partial pressures and when dealing with partial pressures we are explaining the effects of breathing contaminated air mixtures at depth and calculating the equivalent effect such contamination would have upon the diver at the surface. We also must remember once the tank is filled, the percentages of gases within it cannot change.
Example:
Breathing from a contaminated air source with 1.5% carbon monoxide at a depth of 300 feet of seawater would have the same effect as breathing approximately what percentage of carbon monoxide at the surface?
We must first determine that 300 feet is 10 ata. We then multiply 1.5% by the ata of 10 to arrive at 15%.
Dalton's Law is important for divers because it deals with individual gases as well as surface equivalency which concerns us when we deal with toxic contaminates in our breathing gases.
Example: On the surface 0.5% of carbon monoxide is not toxic but at 5 ata, it is.
Once we understand Daltons Law and partial pressures we are ready for Henrys Law. The most common example of Henry's Law is a carbonated beverage such as a coke. When you open the beverage it foams and fizzes as carbon dioxide, dissolved in the liquid, comes out of solution. This demonstrates that liquids dissolve gases, and that if conditions change, the amount of gas that can stay in solution changes. This is true when dealing with gas in our bodies, such as nitrogen. Also, we should note that the pressure exerted from inside a liquid by a particular gas in solution is called gas tension. The difference between the partial pressure of gases in contact with a liquid and the gas tension within the liquid is referred to as the pressure gradient. When the gas tension within a liquid reaches equilibrium with the partial pressure of the gas in contact with the liquid, no more net exchange of the gas occurs. At this point the liquid is said to be saturated with that gas. Henry's Law describes supersaturation and the effects it has on a diver. Without Henry's Law we wouldn't have the dive tables and computers that allow us to minimize the risk of decompression sickness by providing no stop limits and/ or decompression stops. Now we need to explain what will occur to a liquid saturated with a gas at high pressure when the pressure of the gas in contact with the liquid is quickly reduced. To understand this we must know there is a tendency for a state of equilibrium to exist between the pressure within the liquid (gas tension), and the pressure of the gas in contact with that liquid. This equilibrium will be maintained until the pressure in contact with the liquid changes. Thus concluded, "the amount of gas that will dissolve into a liquid is almost directly proportional to the partial pressure of that gas."
Example: If a glass of water is placed in a vacuum for several days , no longer containing any gases, if it is then placed in a pressure pot and pressurized to 2 ata for several days what will be the gas pressure within the liquid? And if this vacuum is created, how will pressure of the gas, inside the liquid, change?
Since the amount of gas that will dissolve into a liquid is almost directly proportional to the partial pressure of that gas, the gas pressure within the liquid is 2. If the vacuum is created the pressure will decrease. A vacuum would represent zero pressure in contact with the liquid. Therefore, the tendency would be for any gas contained in the liquid to come out. So, the pressure will decrease.
Once we understand how a saturated liquid at high pressure will react when the pressure of a gas in contact with the liquid is quickly reduced, we are ready to learn about "supersaturation" and what conditions are necessary for gas bubbles to form in a supersaturated liquid. We use supersaturation to predict decompression outcomes with very high reliability. While diving, nitrogen gets absorbed in our tissues. Although at different rates, our tissues become saturated with nitrogen and when we surface our tissues become supersaturated with nitrogen. While diving we plan for no stop limits and decompression stops so that we don't end up with an excessive pressure gradient that results in decompression sickness. During these stops nitrogen is released out of solution (our tissues) and when the pressure gradient has declined enough you may move on the next stop.
To learn more about how our body deals with dissolved gases please see our blog on Diver Physiology.
I hope you have enjoyed our lesson on Scuba physics and hope you will visit us in San Diego. Thank you for visiting www.GetWetSanDiego.com and we hope you check back often for our latest blogs.
Saturday, August 30, 2008
Scuba diving and Decompression Sickness
Decompression sickness or the bends is a name given to a variety of symptoms suffered by a person exposed to a decrease in pressure around the body. When inert gases, such as nitrogen, are forced to come out of physical solution as the pressure reduces gas bubbles are formed within the body resulting in signs and symptoms of decompression sickness. Lung Over-expansion injury's also involve gas entering the body. The mechanism for bubble formation differs from DCS but the ultimate problem is the same: bubbles blocking blood flow and causing other forms of tissue damage. An air embolism, caused by other processes, can have many of the same symptoms of DCS. DCS and air embolism are grouped together under the term DCI or Decompression Illness.
Henry's Law and how gases work in our bodies
According to Henry's Law, when the pressure of a gas over a liquid is decreased, the amount of gas dissolved in that liquid will also decrease. When your subjected to pressure by diving nitrogen and other physiologically inert gases dissolve into your tissues as a direct consequence of Henry's Law. Henry's Law states that the quantity of gas dissolved is proportional to the partial pressure of the gas. Henry's law also states that the human body will dissolve inert gas in proportion to the surrounding pressure.
"At the surface before a dive your body is saturated with nitrogen, meaning the tissues of your body are holding as much nitrogen in solution as possible at surface pressure. When you descend and the pressure increases, your body is no longer saturated because at the higher pressure, more nitrogen from your breathing gas goes in to solution. In your body, gases enter solution via your respiratory and circulatory systems. As you descend, nitrogen partial pressure in alveolar air increases, dissolves into alveolar blood and is carried throughout the body by circulation. Arterial nitrogen diffuses into the tissues since it has a higher pressure. The higher the pressure difference between the nitrogen in the alveolar air and the nitrogen in solutio in the blood, the faster nitrogen dissolves in the blood."
The human body absorbs nitrogen at different rates in different tissues. The amount of nitrogen absorbed into your tissues directly relates to the dive's depth and duration. The deeper you ascend, the greater the pressure gradient between the nitrogen pressure in your lungs and the nitrogen pressure in your tissues. The higher gradient, the more rapidly nitrogen diffuses from your lungs into your blood stream and tissues. Also, the longer you remain uder pressure, the more time your body has to absorb nitrogen.
In conclusion, always make the recommended safety stop that is required for your dive and outlined on your RDP. A 3 minute safety stop is not mandatory after all dives but it is a good idea to get the happen of stopping at 15ft for 3 minutes after every dive you complete.
Signs and symptoms of DCS an DCI
Decompression sickness tends to be delayed after a dive and may take as long as 36 hours to manifest. DCS can worsen over the first few hours after onset. Based on these facts, a physician would know that a symptom appearing 48 hours after a dive, or one that appears shortly after a dive but quickly improves without any first aid or treatment, ls likely not DCS.
Physiologists have traditionally designated DCS as either Type 1 (non-serious, pain only) or Type II (serious, involving central nervous system) based on the symptoms present in a patient.
Type I DCS (pain only)
Cutaneous Decompression Sickness (skin bends); red rash in patches, usually on the shoulder and upper chest.
Type II DCS (relate to the nervous system)
Neurological DCS (effects on the nerve system); peripheral tingling and numbness, unconsciousness, respiratory affrest and paralysis.
Pulmonary DSC (manifest in lung capillaries)
Cerebral DSC (bubbles passing through pulmonary capillaries)
Henry's Law and how gases work in our bodies
According to Henry's Law, when the pressure of a gas over a liquid is decreased, the amount of gas dissolved in that liquid will also decrease. When your subjected to pressure by diving nitrogen and other physiologically inert gases dissolve into your tissues as a direct consequence of Henry's Law. Henry's Law states that the quantity of gas dissolved is proportional to the partial pressure of the gas. Henry's law also states that the human body will dissolve inert gas in proportion to the surrounding pressure.
"At the surface before a dive your body is saturated with nitrogen, meaning the tissues of your body are holding as much nitrogen in solution as possible at surface pressure. When you descend and the pressure increases, your body is no longer saturated because at the higher pressure, more nitrogen from your breathing gas goes in to solution. In your body, gases enter solution via your respiratory and circulatory systems. As you descend, nitrogen partial pressure in alveolar air increases, dissolves into alveolar blood and is carried throughout the body by circulation. Arterial nitrogen diffuses into the tissues since it has a higher pressure. The higher the pressure difference between the nitrogen in the alveolar air and the nitrogen in solutio in the blood, the faster nitrogen dissolves in the blood."
The human body absorbs nitrogen at different rates in different tissues. The amount of nitrogen absorbed into your tissues directly relates to the dive's depth and duration. The deeper you ascend, the greater the pressure gradient between the nitrogen pressure in your lungs and the nitrogen pressure in your tissues. The higher gradient, the more rapidly nitrogen diffuses from your lungs into your blood stream and tissues. Also, the longer you remain uder pressure, the more time your body has to absorb nitrogen.
In conclusion, always make the recommended safety stop that is required for your dive and outlined on your RDP. A 3 minute safety stop is not mandatory after all dives but it is a good idea to get the happen of stopping at 15ft for 3 minutes after every dive you complete.
Signs and symptoms of DCS an DCI
Decompression sickness tends to be delayed after a dive and may take as long as 36 hours to manifest. DCS can worsen over the first few hours after onset. Based on these facts, a physician would know that a symptom appearing 48 hours after a dive, or one that appears shortly after a dive but quickly improves without any first aid or treatment, ls likely not DCS.
Physiologists have traditionally designated DCS as either Type 1 (non-serious, pain only) or Type II (serious, involving central nervous system) based on the symptoms present in a patient.
Type I DCS (pain only)
Cutaneous Decompression Sickness (skin bends); red rash in patches, usually on the shoulder and upper chest.
Type II DCS (relate to the nervous system)
Neurological DCS (effects on the nerve system); peripheral tingling and numbness, unconsciousness, respiratory affrest and paralysis.
Pulmonary DSC (manifest in lung capillaries)
Cerebral DSC (bubbles passing through pulmonary capillaries)
Friday, August 29, 2008
Scuba diving shipwrecks in San Diego
Wreck Alley in San Diego
The premiere diving attraction of San Diego. This wonderful underwater adventure consists of a group of artifical reefs less than one mile off the San Diego coast. These sites are home to thousands of anemone and other sea life. The sites remain buoyed throughout the year for your safety and convenience, thanks to local Dive Boat Operators, San Diego Oceans Foundation and the Department of Fish and Game.
Wreck Alley is for the skilled and experienced divers only. Please keep in mind the rating system for determining the proper destinations for your skill level. If we do not have a trip that meets your experience, we do have DM's for hire for your adventure pleasures. Please be aware that we do not allow any hunting or removal of any artifacts in wreck alley.
The Yukon
Coordinates:
32 46.80N 117 17.12W
Skill Rating – Novice in calm, clear conditions.
The YukonThe YukonThe newest addition to San Diego's Wreck Alley. A 366' Canadian Destroyer Escort lieing in 105 feet of water off Mission Beach in the Northern Tip of Wreck Alley. The HMCS Yukon is San Diego's latest and most popular wreck. It is different from nearly all other wrecks as it is completely intact, which also makes it one of California's harderst wrecks to dive. Lieing on her port side, this amazing attraction has a minimum depth from bow to stern of about 75 feet along the starboard side. In year 2000, she was intentionally sunk by the San Diego Oceans Foundation as part of an artificial reef project. She was prepared for divers with an abundance of entry/exit holes to increase accessibility and diver safety. Penetration is readily available for those with the proper skill level.
Plumose AnemoneThis underwater reef is home to no less than 1000 Plumose anenome (Metridium senile). Growing Predominantly in the 70 – 100 feet depth range, this spectacular anemone with its feathery branched tentacles exists in white, brown and orange forms.
The Ruby 'E'
Coordinates:
117 16'36' W 32 46'02' N
Skill Rating – Novice in calm, clear conditions.
The RubyThe Ruby 'E' began her life as the Coast Guard Cutter named "Cyane". Built in 1934, the 165' vessel was designed to intercept 'Rum Runners' during the Prohibition period. After Prohibition, she served dutifully in Alaska for 16 years and was officicaly decomissioned in 1950. Her career included Bering Sea and Alaskan Anti-Submarine Patrols during WWII. Before her last years of topside service as a salvage vessel, she was renamed Ruby 'E'. On June 18, 1989, she began her new life as an artificial reef thanks to Al Bruton and the local diving community convincing the Tug and Barge Company to donate the stripped ship to wreck alley. She now sits in 85 feet of water in an upright position. All the hatches have been made larger and most rooms have an exit to the outside. Penetration is availaible for those with the proper training.
Strawberry AnemoneThe wreck is in great condition and completely covered with strawberry anemonies (Corynactis californica) and other marine encrustations. Opportunitys for photography are endless with the wreck itself and the amount of marine life living on or around the wreck. The Ruby 'E' has truly become an oasis in the sand flats of Wreck Alley.
*It is recommended that divers have at least 10 cold water dives within the last 18 months to do this dive.
The El Rey
Coordinates:
32"45'51" N 117"16'36" W
Skill Rating – Novice in calm, clear conditions.
The El ReySan Diego's first site as part of the Artificial Reef Project. As one of Kelco's kelp cutters she harvested three feet of the kelp canopy from Point Conception to Mexico. During her 35 year career, she was also used to study marine life, assist other vessels in need, and occassionaly recover bodies. After some 3600 voyages and traveling 810,000 miles, the aginguctors and the California Department of Fish and game developed an Artificial Reef Program. In 1987, she was lowered into the sea to begin her new life as an artificial reef in San Diego's Wreck Alley.
The El Rey sits upright at the bottom of the ocean floor at a 90 foot depth. Over the years, heavy swells and currents have taken their toll and many areas of the superstructure and hull have collapsed. A few areas of the wreck can be penetrated but the wooden superstructure has badly deteriorated. The wreck is home to an abundance of marine swimming around and living inside the wreck and offers a great opportunity for photographs.
*It is recommended that divers have at least 10 cold water dives within the last 18 months to do this dive.
N.O.S.C Tower
Coordinates:
32"46'21" N 117"16'03" W
Skill Rating – Novice to beginner. With a maximum depth of 60 foot, this is a good site for new and beginner divers. Entanglement hazards do exist, so be advised of the conditions and ask your DM aboard for further guidance.
A research platfrom built by the Naval Ocean Systems Center in 1959. Knocked over by an El Nino strom in 1988, the NOSC (Naval Ocean Systems Center) Tower once sttod over 100 feet tall and was used for research of internal waves, swell, wave propagation and numerous other areas. Consisting of four stories, the tower had a dive platform, and above that labs that have parts missing that still haven't been found. Today it's a tangle of girders and beams from 30 to 60 feet. The wonderful underwater "jungle gym" is thickly covered with filter feeders like strawberry and yellow anemones, purple and brown gorgonians, hydrocorals, mussels, sponges and urchins. The "Tower" is a must see for divers exploring the underwater world of Wreck Alley and makes for a wonderful photo opportunity.
Point Loma Kelp Beds
Coordinates:
32' 42.50" N 117' 16.30" W
Kelp Beds, or kelp forests, are cold water marine habitats that feature a bounty of marine organims. Kelps are restricted to cold water climates because warmer waters tend to lack the rich supply of nutrients that kelp need to flourish. Many different types of kelp are found in kelp forests, among them are giant kelp, bullwhip kelp, the palm kelp and the feather boa kelp. Underwater kelp forests shelter snails, crabs, shrimp, starfish, sea anenomes, sea cucumbers, brittle, sea squirts and many other marine creatures. This kelp can grow up to 200 foot in ocean waters. Inside the Bulbous float at the end of the kelp is gas containing carbon monoxide.
Kelp BedsThis is a must see for divers visiting San Diego. This amazing adventure has an annual temperature averaging 60 degrees, the kelp is very healthy and supports an enormous amount of plant and fish life. A series of unique pinnacles and shelves along the bottom, interspersed among the kelp, give the feeling of truly being in a primeval forest. Only New Zealand comes close to matching this underwater forest haven.
Los Coronado Islands, Mexico
Coordinates:
32.43' N 117.27' W
Skill Rating – Beginner to Novice, this is a good site for new divers and often used for OW training.
Lying just 15 miles south of San Diego's Point Loma, "The Coronados" have fast become a favorite amongst the diving community due to the large Sea Lian and Horbor Seal Colonies. Although close to San Diego, they are just enough offshore to be bathed in very clear water. Coronado Del Norte (north island) is the northernmost island and the most frequented by San Diego Dive Boats. With diving visibility averaging between 50' – 150', and common encounters with Sea Lions, Harbor Seals, octopus, Horn Sharks, Moray Eels, Garibaldis and purple coral – this is diving you won't soon forget. The most popular spots at North Island are The Keyhole and The Lobster Shack. With depths ranging 10 – 130 feet, and even a small wreck near The Lobster Shack, the "Coronados" are an excellent place for any skill level and a must see attraction.
Thursday, August 28, 2008
Shore diving San Diego
www.GetWetSanDiego.com
La Jolla Shores
La Jolla Shores is located in beautiful La Jolla, California. This beach is a popular destination for tourists, surfers and divers. Two main features of this beach make it one of the most frequented dive locations in San Diego. The facilities, generally good conditions and relatively easy surf entries make the shores a good spot for diver training. For advanced divers, there is easy access to La Jolla Submarine Canyon. Submarine Canyon begins nearly 100 yards offshore, starting at about 50 feet and continuing in a series of ledges down to 800+ feet. The main drop off into Submarine Canyon contains most of the sea life, including but not limited too, small fish, lobster, octopus and anemone. On your way to the canyon, you should find numerous leopard sharks, turbot, sea stars, sting rays, surf perch, sand dollars, stone crab, halibut and bat ray. Also at La Jolla Shores is Kellogg Park, a grassy park that provides ample space to conduct dive briefings and surface intervals. La Jolla Shores is a beach, so a beach entry/ exit is required. The waves are usually mild here, which makes for easy access. A restroom and showers are nearby for added convenience. Let our experienced staff guide you along the sand flats and into the depths of Submarine Canyon for an experience you won't soon forget. La Jolla Shores is a great dive location for any skill level.
La Jolla Cove
La Jolla Cove is a very small beach, tucked between adjacent sandstone cliffs. Due to its extraordinary beauty, La Jolla Cove is one of the most photographed beaches in Southern California. Visibility at the Cove can sometimes exceed 30 feet, making it a must see for SCUBA divers and snorkelers. "When the visibility is good here, its like swimming in an aquarium". "Simply amazing". La Jolla Cove lies within the San Diego/ La Jolla Underwater Park Ecological Reserve, which helps to ensure that marine life is abundant and plentiful. The average depth is 15 - 30 feet and can get deeper as you travel towards the outer cove. Seals and Sea Lions are very common around this area and are known to play with the divers and maybe give a tug to your fins. Close encounters with these playful creatures are not only amazing but also a great photo opportunity. Come join us for the day and experience the amazing beauty of this underwater haven. A public restroom building with showers are available for your convenience. This a look but dont touch area and the possession of game is unlawful.
La Jolla Kelp Beds
32" 48.373° N x 117" 16.725° W
The La Jolla kelp Beds are about a 300 yard swim from La Jolla Cove. Visibility averages 15 - 20 feet. It can be surgy and the color on the reef is limited. The best rock piles are in 40 - 60 feet of water. The average depth is 30 - 60 feet in the area. Much of the La Jolla Kelp forest is flat rock bottom and currents are rarely a problem. The only risk is thick kelp. Experience with kelp here is a plus, if tangled up slowly back out the way you came. It is suggested that you bring a knife with you on any kelp forest diving to allow you to free yourself should you become entangled. Depending on the season, current climate mode and storms, this forest can reach over two miles in length and a mile wide. To get to the kelp forest by shore, it requires a nice swim, about 300 yards, but absolutely worth every second you spend getting there. Let S.E.A. Adventures guide you on an unforgettable experience to the La Jolla Kelp Forest and experience this amazing underwater ecosystem.
Casa Cove / Childrens Pool
Casa Cove, or the Childrens Pool, is a popular dive location among underwater hunters due to the fact that right outside the jetty is a large reef where you can find tons of lobster. Casa Cove is also a beaching grounds for seals/ sea lions year round. Often while diving or snorkeling in Casa Cove you will encounter seals and sea lions as they tug on your fin or investigate your catch as you come in from a hunt. There is a barrier which protects the seals, the Marine Mammal Protection Act, and it is actively enforced there. There is often a large rip current throughout the Childrens Pool which is good if your heading out. There are bathrooms and showers for your added convenience. This shore dive is recommended for advanced/ or experienced divers only, due to strong currents and large swells. S.E.A Adventures has World-Class Dive Masters with years of experience at this site and are ready to guide you through an experience of a lifetime.
Marine Room
The Marine Room is a common location for divers and snorkelers in the La Jolla area. It is best known as a good place to see leopard sharks in the early summer months. The Marine Room has really neat shallow reef diving, and conditions similiar to La Jolla Shores area-relatively small waves, good visibility and less surge. Divers also use this location as an entry point to the La Jolla Submarine Canyon. Parking in the area is limited, so it is often desirable to arrive early in the morning. There are no public restrooms, showers or lifeguard services at the Marine Room. The beach at the marine Room is named after the World-Class restaurant that was built on its shore. The building was originally built in 1916 as a small inn and restaurant called the Spindrift Inn. The Inn was removed as part of a renovation and the site was reopened as the Marine Room on May 29, 1941.
Scuba diving Los Coronados Islands
Explorer Juan Cabrillo first described these islands in 1542 as "islas desiertas" (desert islands). In 1602, Vizcaino's priest named them Los Cuatro Coronados (the four crowns) to honor the four martyrs that fisherman saw amid the ancient rocks (Old Stone Face, The Sarcophagi, Dead Man's Island and Corpus Cristi). During the gold rush of the 1840's, high seas smugglers used the fog shrouded islands as a place to hide Chinese slaves bound for mining camps, before heading ashore. Later, hundereds of ships laden with treasures fell victim to the "Pirates of the Coronados" who made the islands their base of operations. The most bloodthirsty Gold Rush Pirate of Los Coronados was Jose Arvaez, called "The Pirate King". Nearly 400 hundred years after the islands' discovery, the first successful entrepreneurs arrived, during the Prohibition. Eventually, so many speedboats were rendezvousing among the foggy islands to pick up loads of Mexican rum, then trying to dodge the U.S. Coast Guard or outrun them in the dark, that Pirate Flagfatal fiery collisions occurred on a regular basis. Gambling and Hollywood followed the rumrunners. During the Great Depression, California lumber baron Fred Hamilton and Tijuana businessman Mariano Escobeda built a lavish restreat called Coronado Islands Yacht Club inside Smugglers Cove, but it was actually a cabaret casino frequented by Hollywood stars wanting to escape the public eye and by powerful producers holding tryouts for their hottest starlets. Errol Flynn, Al Capone and Harry Warner all made headlines with their adventures at the "Yacht Club". And perhaps because Hollywood had discovered Los Coronados for other reasons, the Pitcairn Island scenes from the movie "Mutiny on the Bounty" ended up being filmed at Coronado del sur. In 1935, Mexico's President, Lazardo Cardenas, abolished gambling in Mexico and the Yacht Club casino was abandoned. Things have been fairly quiet on Los Coronados since then. Only a lighthouse keeper and a Mexican Navy patrol crew live on the islands today. The Islands are now forbidden from anyone even stepping foot ashore.
Monday, August 25, 2008
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