Tag Archive
Nitrox and Other Gases
A reader of Britain’s Diver Magazine recently wrote to me complaining that I had admitted in print to using independent twin tanks, one tank with air (MOD 182 feet at 1.4 bar ppO2) and one tank with nitrox 32 (MOD 108 feet) for a dive to 165 feet. He congratulates me on effectively using a single tank of air at 165 feet and asks what I would have done had my regulator failed? Well, I would have used the one on the other tank! Bear in mind, regulators and other equipment subject to high gas pressures usually fail when that pressure is at its highest. That is to say at the very beginning of a dive, not half way through it, unless it's caused by icing. In a history of a great many dives I have yet to experience a true failure in seawater other than within the first moments of turning a tank on. He goes on to ask what I should tell newly trained divers about going to 165 feet with only one tank. I answer that newly trained divers should stick to the depth limits of their certification and that if a PADI Open Water diver can go to 60 feet on a single tank, I believe a suitably trained and experienced diver with a twinset can go 60 feet below the MOD of the gas in his second tank providing he is breathing a suitable supply of gas in his first. Even then, the ppO2 limit of 1.4 bar is a limit currently set by training agencies with an eye on litigation. When we started using nitrox around fifteen years ago, we all used at least 1.6 bar as a limit. A limit of 1.6 bar ppO2 gives an MOD for nitrox 32 of 130 feet, so at 165... More »
Dive Accident Symptoms Delayed 6 Months?
(Q) 06.09.11 “Is it possible to suffer any problems from diving 6 months AFTER the dive? I had what I would consider a fairly normal dive experience. We were in Fiji and we dove to a max of 100ft. We flew home to New Zealand 2 days later. I had a panic attack (had only ever had one before in my life) where I felt like I couldn't breath about 3 weeks later but that was the only "odd" thing that happened. I've since flown to the States and back and when I returned from the States (it was almost 5 months post dive) was when I started noticing severe shortness of breath. (tests at the doc confirmed that I am only using 56% of my lung capacity and that my lungs are "restricted"). I never mentioned my diving because it never crossed my mind... especially since it was several months before the symptoms came on. I've had a lung x-ray and it showed no abnormalities. They haven't found a cause yet and the shortness of breath and chest tightness seems to be getting worse. A barium swallow and upper GI found some looping the bowel, but a chest x-ray, physical exam and EKG and exercise stress testing with echo were negative. Is there ANY chance it could be dive related??” (A) 06.14.11 “Hi m…., Given report that there was nothing abnormal in the dives, e.g., uncontrolled ascent, breath holding on ascent, chest discomfort, coughing up blood in the sputum; the first signs or symptoms of any medical problem weren't until about 3 weeks after the last dive ("panic attack," not further described); no pulmonary complaints (shortness of breath (SOB)) until about 5 months after ... More »
Fizzy drinks and DCS.
Not all IDC students are created equal. (Q) 04.11.10 Hey DocV, During my girlfriend's IDC, a candidate talked about the dangers of drinking fizzy drink (like coca cola) and then diving. He was specifically saying that the bubbles in the drink would increase the chances of a DCS hit. For me, the bubbles are in the stomach which is enclosed and away from the blood stream so apart from the possible changes to metabolism due to the caffeine and sugars, it shouldn't be a factor? Any thoughts? JB (A) 04.12.10 Hi JB, Yes, I think one of the IDC candidates in your g/f's class still has some important concepts to master. For openers, with the exception of a very small number of nitrogenated beers, mostly European, the bubbles in carbonated drinks, including all sodas, are composed of carbon dioxide (CO2), not nitrogen (N2). And of course it is the latter that’s the gaseous culprit in DCS in recreational divers. And you are right –- gas bubbles cannot enter the circulatory system from the GI system under anything resembling normal circumstances. It is theoretically possible that bubbles could enter blood circulation as a result of gastric or intestinal barotrauma, but it would be an extraordinary situation where expanding bubbles would tear the GI wall rather than be expelled from one or the other ends of the alimentary tract (i.e., flatulence or belching). Small amounts of gas from swallowed CO2 bubbles might pass into venous circulation in a dissolved state. However, if this occurred the gas would be rapidly dispersed in the blood coursing to the heart and off-gassed without issue. C02 readily binds to the hemoglobin in venous red blood cells and is then transported to the lungs where it is exhaled. You also mention the caffeine common to carbonated cola drinks. While that chemical does mildly increase the excretion of urine, this... More »
Submersible Stress!
There is really nothing new about deep diving submersible vehicles. Ed Link and other innovators dreamed up models back in the 1960s that seemed like they were excerpted from the pages of a Jules Verne novel. Originally, these subs were employed in pioneering oceanographic and scientific projects and were responsible for opening doors to the oceans' depths that had previously been considered unexplorable. As submersible technology became more affordable and diversified, the expanding commercial diving market quickly adopted such applications for survey and inspection work. In many instances, this proved far more cost effective than subjecting a diver to such an exposure. I had firsthand experience with exactly this same scenario while working with Navy diving teams in early 1971. Our project was based in St. Croix, the largest of the U. S. Virgin Islands, giving us close proximity to the 11,000-foot depths of the Virgin Islands Trench only an hour's steaming time from the Fredericksted pier where our support ship docked next to our operations partners, the sleek "fast attack" Navy submarines. Our job was to film these submarines and we had already passed the 300-foot depth mark several times as our work gradually moved deeper. This posed obvious risks including oxygen toxicity, narcosis, prolonged decompression some 10-15 miles offshore, and a rather overwhelming population of oceanic white tip sharks that liked to try to chew on us with unabated enthusiasm. Our unit had been sent a small Kittridge one-man submersible but it was accumulating mostly dust and rust as it sat stored in a Quonset hut warehouse waiting for a suitable mission to justify its use. This sub was decidedly small: about 10 feet in length overall with barely enough interior space for a single operator to squeeze in. Most of the contraption was taken up with compressed air ballast,... More »
Demystifying Recompression Chambers
Many divers have seen a chamber either in photographs or in real life, but very few have ever had occasion to be in one unless they were being treated. As a result a certain "mystique" has developed about chambers and many divers regard them as hostile and menacing environments. Briefly, we would like to acquaint our readers with the realities of these important devices. Generally, chambers are divided into two categories: recompression chambers (used for the treatment of diving related injuries and other ailments) and decompression chambers (used for surface or deck decompression facilities so the working diver can be removed from the water and complete the decompression obligation in a dry and controlled situation) Both of these units are also properly referred to as "hyperbaric chambers", meaning that the pressure inside will be higher than normal atmospheric pressure. These elevated pressures are usually expressed in feet of seawater (fsw) just as if we were diving in the ocean. Air pressure is introduced to the chamber to raise its internal pressure and begin the "dive". We can then use these chambers to treat DCS (decompression sickness) or AGE (arterial gas embolism) cases, conduct "dry" surface decompression schedules, or simulate dives for research purposes. In hospital situations, the role of hyperbaric medicine has been recognized as a specialty wherein victims of such injuries as crush wounds, burns, skin grafts, gangrene and carbon monoxide poisoning are treated with oxygen in large climate-controlled chambers. These typically are able to accommodate as many as 18 patients at once, have hatches shaped and sized like conventional doors, are equipped with air conditioning and humidity controls and even piped-in music. In the "field", things are just a little bit different. Forget the creature comforts and get prepared for close quarters. Although a well set up field chamber can provide the same... More »
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