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Recent Blogs
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HAIGH QUARRY OPENING FOR THE 2012 SEASON IN jANUARY?
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Capt. Darrick
Lorenzen
1/7/2012
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No, the season at Haigh Quarry is not opening this weekend! It will open for the 2012 season on Saturday April 7th, but because of our unusually warm weather Tina has decided to give Midwest divers a chance to scratch th...
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SCUBA DIVERS LEFT BEHIND IN FLORIDA
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Capt. Darrick
Lorenzen
10/6/2011
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The U.S. Coast Guard said Tuesday that it was investigating RJ Diving Ventures of Miami Florida. The investigation was initiated because the dive operator left behind two tourists while they were scuba diving.
D...
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Recent Posts
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Forum: BASIC SCUBA DISCUSSIONS
Topic:
Newbie Equipment Question
By: rosalind
Posted: 5/16/2012 7:41:35 AM
Despite the several benefits of the game, diving is very expensive. It's a excellent option to lease equipment before making any allergy choices. Besides providing excellent starting costs for newbies, lease locations us...
Forum: BASIC SCUBA DISCUSSIONS
Topic:
Newbie Equipment Question
By: rosalind
Posted: 5/16/2012 7:41:31 AM
Despite the several benefits of the game, diving is very expensive. It's a excellent option to lease equipment before making any allergy choices. Besides providing excellent starting costs for newbies, lease locations us...
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Midwest Scuba Diving
“Oxygen Toxicity”
In a world where more divers are starting to integrate technical elements into their standard diving regimens, it has become increasingly important for divers to understand the physiology of oxygen toxicity and how to decrease its risk and maximize their safety.
What is Oxygen Toxicity?
When you breathe oxygen, it reacts with the body’s naturally-occurring chemicals to create high-energy “free radicals” that can disrupt normal functions. Free radicals are atoms or molecules that have at least one unpaired electron, making them highly reactive. Free radicals can have damaging effects at the cellular level. The body has antioxidants, which act as protective agents, and can combine with the free radicals to reconvert them into water and oxygen molecules. When diving, a diver breathes oxygen at an increased partial pressure. This is most significant when diving on gas mixes with elevated oxygen content like nitrox or when using a closed or semi-closed circuit rebreather. As a result of breathing oxygen at an increased partial pressure, more free radicals are generated. If the quantity of free radicals is greater than the capacity of antioxidants to deactivate them, a diver is at increased risk for oxygen toxicity.
The risk of oxygen toxicity is determined by partial pressure and time. In a gas mix used for diving, the partial pressure of oxygen (PO2) is calculated by multiplying the fraction of oxygen in the gas mixture by the total pressure of the mixture, which is a function of the depth (PO2= volume fraction of oxygen × total pressure). When a diver is exposed to high partial pressures for a period of time, he may be susceptible to oxygen toxicity. As the partial pressure of oxygen increases, a diver should decrease his exposure times to attempt to reduce his risk for oxygen toxicity. It is important to note there are upper limits beyond which no period of time is considered safe (commonly regarded as any oxygen partial pressure in excess of 1.6 atmospheres absolute).
There is no definitive point at which a diver is absolutely susceptible to oxygen toxicity because many factors may influence risk, making it a highly unpredictable phenomenon. One diver may experience greater susceptibility to oxygen toxicity than his dive buddy; an individual may even experience varying degrees of susceptibility from dive to dive.
CNS Oxygen Toxicity
Oxygen toxicity can manifest in different body systems. Toxicity of the central nervous system (CNS) is the most relevant manifestation for divers. CNS oxygen toxicity is a concern for deep and technical divers, as well as divers using high-oxygen mixes such as nitrox. Safety guidelines generally advise divers using high-oxygen gas mixes that an oxygen partial pressure of up to 1.4 atmospheres absolute (ata) is within the range of acceptable risk for CNS oxygen toxicity (estimates vary from 1.4 to 1.6 ata). During decompression, when divers are most likely at rest, up to 1.6 ata is also often deemed tolerable; however, a PO2 in excess of 1.6 ata is generally considered hazardous and should be avoided. As mentioned, a diver’s susceptibility to oxygen toxicity is highly variable, and while these guidelines will preclude most cases of oxygen toxicity, the risk is still present; to minimize risk, divers should follow these safety guidelines conservatively.
Symptoms
CNS oxygen toxicity is rare but very dangerous, as it can result in a grand mal seizure (full body convulsions). The seizure itself is generally not the significant risk, but the event occurring underwater could result in drowning, pulmonary barotrauma or head trauma. It is important to know this event may occur without any prior warning, but there are some signs that can be indicators of CNS oxygen toxicity.
There are a wide range of symptoms commonly associated with CNS oxygen toxicity, including:
· Flashing lights in front of the eyes
· Tunnel vision
· Tinnitus (ringing or roaring sounds)
· Confusion
· Lethargy
· Dizziness
· Nausea or vertigo
· Numbness or tingling
· Muscular twitching (in the hands and particularly in the lips)
· Pallor
· Sweating
· Vomiting
· Hallucination
· Bradycardia (diminished heart rate)
Whenever a diver’s PO2 approaches or exceeds 1.4 ata, any symptoms should be considered suspect; aborting the dive is generally the best option, but this could be problematic if there is a decompression obligation. Should a diver notice any symptoms that could be indicators of oxygen toxicity, he should immediately notify his buddy and reduce the inspired oxygen partial pressure by either making a safe, controlled ascent or by switching to a gas with a lower percentage of oxygen. If on a closed-circuit rebreather, a diver should ascend, flush the breathing loop with a low partial pressure gas if possible, and lower his setpoint.
If your buddy is incapacitated underwater and has not lost his mouthpiece, you might be able to hold it in during ascent. If the incapacitated diver has lost his mouthpiece, disregard it, safely ascend and get the diver out of the water. In this situation, there is a small chance of embolism, but the risk of drowning is very high if the diver is unable to use his air supply while underwater.
It is recommended that all injured divers be given first aid oxygen on the surface, even if they are suspected of having experienced oxygen toxicity. When divers return to the surface, symptoms of oxygen toxicity will begin to resolve; therefore, first aid oxygen does not present a risk of causing additional symptoms.
Risk Factors
In addition to exposure time and depth, there are several factors that may influence oxygen toxicity risk; a diver should be aware of them and assess each throughout the course of his dive and adjust his PO2 to accommodate. For instance, water temperature, either very cold (less than 49°F) or very warm (in excess of 87°F), physical exertion and stress can all decrease a diver’s resistance to oxygen toxicity. Other contributing factors may include fever, vitamin E deficiency, carbon dioxide retention, cerebral blood flow (which refers to the rate at which oxygen is delivered to the brain), certain medications and medical conditions, among others.
Over the last several years, there has been a great deal of speculation as to whether certain medications, including Sudafed, could lower the oxygen-induced seizure threshold for divers using high-oxygen blends or diving deep. DAN is currently conducting a prospective research study to address questions regarding Sudafed use in the context of diving with nitrox and other special gas mixes.
Mitigate Your Risk
Oxygen toxicity has a degree of unpredictability, and the consequences of a seizure underwater can be fatal. As such, you should take every possible precaution to reduce your risk.
· Discuss any medications and medical conditions you have with your doctor to manage your risk of oxygen toxicity. If you or your doctor have any questions or would like a referral, call the DAN Medical Information Line at +1-919-684-2948 or contact us via email.
· Adhere to conservative limits on PO2 and exposure duration.
· Be aware of early warning signs and respond accordingly.
· Comprehend all relevant curriculum and training.
· Maintain your equipment.
· Analyze your gas prior to each dive.
· Stick to the buddy system, and always maintain clear visual contact.
· If an incident does occur, seek medical care.
For more information read, “OXTOX: If You Dive Nitrox You Should Know About OXTOX” and the 2008 DAN Technical Diving Conference Proceedings.
Divers Alert Network ® (DAN®) is a nonprofit organization dedicated to the safety and health of scuba divers. DAN operates a 24-hour emergency hotline (+1-919-684-9111) to help divers in need of medical emergency assistance for diving or non-diving incidents.
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