DEPTH Blog

The most useful snippets from our authors, all in one place. DEPTH discusses topics of diving, equipment and environment, physics and physiology, technique and technology, and hyperbarics.

Lobster and Lionfish

Lobster and Lionfish

Today marks the start of the annual two-day spiny lobster sport season in Florida, known as "mini-season," and it got us thinking (about more than just dinner) . . .

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Interview with Technical Diver, Asser Salama, Author of Deep Into Deco: The Diver's Decompression Textbook

We recently caught up with Asser Salama, author of the new release, Deep Into Deco: The Diver's Decompression Textbook. Asser is a technical diver and instructor, is founder of Tech Diving Mag and developer of Ultimate Planner decompression planning software. He has a bachelor’s degree in engineering and a master’s degree in business administration. A software developer with an interest in decompression modeling, Salama plans to implement computational algorithms based on credible research papers to prevent some pioneering work from fading into academic obscurity. 

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Video #2 (Preventing Diver Fatalities Series): Preventing Dive Site Entrance and Boat Related Injuries

Last week we released the first video in a new series on preventing diver fatalities. The second video in the series is now available! In the second video, we discuss two types of common surface related injuries to divers - those that occur during the entrance to a dive site, and boat related injuries.

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Preventing Diver Fatalities Video Series: Video 1, Defining Fitness to Dive

This month we are discussing how to prevent diver fatalities. As part of that discussion, we are launching a free three-part video series.

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Basic Underwater Navigation

Basic Underwater Navigation

Basic underwater navigation by means of simple observation or use of a compass and depth gauge remains a fundamental and essential skill for all divers. For most short excursions, these are the only instruments needed. Even when using advanced navigation instruments, basic navigation skills provide an important backup.

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Sinuses and Diving

Sinuses and Diving

The term “sinus” can mean any channel, hollow space, or cavity in a bone, or a dilated area in a blood vessel or soft tissue; most often sinus refers to the four, paired, mucus-lined air cavities in the facial bones of the head. The same kind of membrane lines the sinuses and nose, so nasal infections spread easily to the sinuses. In sinusitis, mucous membranes inflame and swell, closing sinus openings and preventing infected material from draining. If nasal inflammation, congestion, deformities, or masses block sinus openings, the sinus lining swells and inflames, absorbing pre-existing gas that forms negative pressure. When blockage occurs during descent, the relative vacuum in the sinus increases the risk of damage. Hemorrhage into the sinus and then into the divers mask may occur.

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Pick a Gauge, any Gauge! Case study of an open circuit diver.

Pick a Gauge, any Gauge! Case study of an open circuit diver.

An experienced open-circuit diver was trying the “latest, greatest” rebreather during an introductory dive experience. After a few minutes of cursory instruction, she entered the water and began her grand adventure. Descending gradually to 15 fsw (5 msw), she kept close watch on her gauges.

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Safety Considerations for Diving Around Sharks

Safety Considerations for Diving Around Sharks

The danger from sharks to humans is a combination of size, aggression, and dentition. Any shark over 3 ft (0.9 m) long should be regarded cautiously, and if over 8 ft (2.4 m) long, should be avoided even if this requires that the diver leave the water. For example, grey reef sharks (Carcharhinus amblyrhynchos) that range between 3–7 ft (0.9–2.1 m) in length are numerous in shallow tropical waters, and diving operations often cannot be performed unless the presence of sharks in the area is tolerated. When such sharks are in the vicinity, divers should avoid making sudden or erratic movements. Common sense dictates that no injured or distressed animals should be in the water because these are known to precipitate shark attacks. When operations are conducted in the presence of sharks, each group of divers should include one diver who keeps the sharks in view and is alert for changes in their behavior. The chances of trouble are minimal as long as the sharks swim slowly and move naturally. The situation may become dangerous, however, if the sharks assume agitated postures, such as pointing their pectoral fins downward, arching their backs, or elevating their heads. If feeding in a group, sharks may become highly agitated and bite at anything and everything, including each other. Most victims are attacked violently and without warning by single sharks. The first contact may be a “bumping” or an attempt by the shark to wound the victim prior to the definitive strike. Severe skin abrasions and lacerations can be caused in this manner due to the abrasiveness of shark skin, which is covered with denticles, small tooth-like projections which are modified placoid scales.

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Nitrox Breathing Mixtures

Nitrox Breathing Mixtures

Divers have used air as a breathing gas since the beginning of diving. Its principal advantages are that it is readily available and inexpensive to compress into cylinders or use directly from compressors with surface-supplied diving equipment. Air is not the “ideal” breathing mixture for diving because of the decompression liability it imposes. Since decompression obligation is dependent on exposure to inspired PN2 (nitrogen partial pressure), this obligation can be reduced by replacing a portion of the nitrogen content of the diver’s breathing gas with oxygen, which is metabolized by the body. This is the fundamental benefit of enriched air nitrox (Nx) diving (Wells 1989). Historically, the two most commonly used nitrox mixtures in NOAA have been 32% and 36% oxygen. Once called NOAA Nitrox 32 (NN32) and NOAA Nitrox 36 (NN36), such mixtures are now identified using a more general nomenclature as Nx32 and Nx36. The remaining gas in nitrox mixes is considered to be nitrogen, even though it may contain other inert gases like argon. “Nitrox” is a generic term that can be used for any gaseous mixture of nitrogen and oxygen, but in the context of this chapter, the implication is that nitrox is a mixture with a higher concentration of oxygen than that of air. Using such oxygen enhanced mixtures can significantly increase the amount of time a diver can spend at depth without incurring additional decompression when compared to air diving.

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Contingency Planning

Contingency Planning

Performing repetitive dives requires a the use of a dive plan. The diver must know what the no-stop dive time limits will be for the dives prior to descending so as not to incur additional decompression obligations. A planned dive schedule will work assuming the diver adheres to the maximum depth and time parameters defined before descending; however, this does not always occur. There are many reasons why divers may find themselves deeper than planned. Some of these might include: higher than normal tides while working on a specific site, down-welling currents, the need to descend deeper to pick up tools or experimental apparatus that may have been dropped, the unexpected need to provide assistance to divers who are working at deeper depths (either on a routine or emergency basis), or perhaps just plain inattention of the divers.

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Thermal Stress Irrespective of Ambient Temperature

Thermal Stress Irrespective of Ambient Temperature

Thermal Stress Irrespective of Ambient TemperatureHypothermia is not a problem exclusive to frigid environments—it can occur irrespective of ambient temperature. Similarly, divers may also suffer extremes of hot and cold thermal stress simultaneously during the same dive. There have been documented cases of severe heat exhaustion in arctic waters by commercial divers as a result of wearing thick, occlusive drysuits, aggravated by dehydration from breathing dry compressed gas and perspiring from prolonged underwater swimming or heavy underwater work. Perspiration from excessive or from pre-dive overheating can also cause the diver’s drysuit underwear to lose insulation, thus predisposing him to hypothermia.

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Divers Should Never Leave Home Without It...

When you prepare for a dive trip, there are things you pack that are on the "must have" list, such as mask, fins, BCD, and regulator. Then there are the things that you "should have" such as wetsuit, defog, and sunscreen. All of the other items typically fall onto the "it would be nice to have" list, such as snacks, sunglasses, and a camera. The question we have for you today is, onto which list do your dive rescue and dive accident management skills fall?

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