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BSAC releases gas density tables – sign up to FREE webinar this Sunday

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BSAC has released three sets of gas density tables for its members.

Considered an important source of safety information based on empirical research, the tables are intended to inform planning for safer deeper diving (>40m). In recent years there has been an increased understanding of the importance of gas density in gases breathed under pressure. BSAC has now released tables that recommend breathing mixes for open and closed-circuit divers.

The tables were specifically developed for mixed gas divers but gas density values also have implications for informing safe depth parameters for air and nitrox divers. The new tables align with findings from research conducted by Gavin Anthony and Professor Simon Mitchell that were presented in 2015 in a paper entitled Respiratory physiology of rebreather diving. Gavin is a BSAC member and Advanced Instructor, as well as the principal scientific advisor for BSAC National Diving Committee (NDC) Technical Group. He has been involved in the development of these tables from inception through to publication. The tables were then formulated by BSAC Technical Instructors Trevor Davies and Mike Rowley.

Mike Rowley said: “I’m thrilled to be able to release this really important safety support for our members. Gavin and Simon made the research freely available online but the point of developing look-up tables was so divers can see at a glance what the optimum gas mixture is for any given depth and application.”

BSAC members can access and download the gas density tables online.

So, what is gas density and why is it important for divers?

Gas density is a measure of mass per unit volume, measured in grams per litre (g/l). The deeper you go the density of the air you breathe increases. A high gas density means a given volume of gas weighs more and takes more effort to move, resulting in increased work of breathing (WOB).

Gas density is why WOB increases as we go deeper, and increased WOB, in turn, predisposes divers to CO2 retention. It is increasingly accepted that elevated breathing gas densities are dangerous and may well be implicated in exacerbating a range of diving ailments including not only CO2 retention but also O2 toxicity, nitrogen narcosis, decompression illness and immersion pulmonary oedema. Furthermore, elevated gas densities can impair the performance of breathing equipment such as regulators and rebreathers.

Mike Rowley said, “The role of gas density and its relevance has not been universally addressed in diving education. However, BSAC is now assisting divers in factoring this into diving planning with these new tables. The tables allow the diver to readily see optimum gas mixtures based upon gas density therefore they are a proactive planning tool.

In relation to BSAC diver training and safety recommendations:

  • žThis update has already been included in BSAC’s Safe Diving guidance.
  • žGas density is to become the basis for gas planning in all of the BSAC mixed gas courses.
  • žGas density also has implications to inform Dive Leader, Advanced Diver and First Class Diver safe diving parameters.

The National Diving Committee (NDC) will be working on and considering the above in its ongoing developments.

What are the tables exactly?

The BSAC gas density tables show in tabular form:

  • žBreathing gas densities for a variety of gas mixtures including air, nitrox, trimix and heliox at depths of 5m increments from 35 metres to 130 metres.
  • žEquivalent narcotic depths (END) for each gas mixture and depth increment.

There are three tables in total. Two tables are for open circuit gas mixtures. One is based upon a partial pressure of oxygen (PO2) of 1.4 bar. This table is for use by open-circuit divers choosing safe dive gas. The other open-circuit table is based on a PO2 of 1.6 bar and is intended for use by open-circuit divers choosing accelerated decompression gases and rebreather divers choosing open-circuit bailout gases.

Each table shows a range of breathing gas mixtures for each depth increment that come within the safe gas density parameters for that depth. Each table also has a much smaller table of “ideal” gas mixtures for the depth increments.

Further information and support

A webinar entitled The lowdown on gas density tables is scheduled for Sunday 21 June from 19:30-20:30. To be held by BSAC’s highly-experienced technical instructor, Mike Rowley, this webinar will help you understand more and give you the opportunity to have your questions answered.

Find out more and sign up online.

Please contact BSAC’s Diver Resources Team with any questions, comments or feedback. They are available at drt@bsac.com or on 0151 350 6203.

Marine Life & Conservation Blogs

Sharks the Ocean’s Greatest Mystery – Part 2

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Sharks are an incredibly significant animal in human culture of both the past and present, they are an animal that have been embodied in our culture for millennia. They are represented in formats such as books and clothing, but most notably in our TV and films, which is where a large portion of their negative reputation stems from. A popular TV representation of sharks comes from Discovery Channel’s ‘Shark Week’, and I believe sharks are possibly the only animal on our planet to have an entire week dedicated to them every year. However, despite this, we still know more collectively about the surface of the Moon and Mars, about Galaxies outside of our own, and even about animals that have been extinct for millions of years, than we do about sharks.

Sharks are our Ocean’s top predator, and they represent just how little we know about our blue planet. We have put more money into exploring outer space than we have exploring our seas and whilst many people call space the final frontier, I believe the final frontier is our Oceans. There are people that have lived in space for over a year, yet we aren’t able to stay underwater for more than a few short hours, and with each dive, scientists are discovering something new in the deep sea, giving us a better understanding of our oceans and the top predator that lives within them.

What we do not know

It is easier to talk about what we do not know and the implications of not knowing it, we still don’t know where most shark species mate or give birth, knowing this would accelerate conservation efforts for sharks in a huge way as these areas could then have realistic protections placed on them, allowing us to preserve key stages of the Sharks life cycle.

Marine Biologists have stated that the discovery of a White Shark breeding ground would be the holy grail of Ocean Science, but the only reports of White Sharks mating come from a handful of sightings from Fisherman and Sailors, so these cannot be used as an official record.

We know that Sharks mature late in the same way as us humans, it is estimated that some species are estimated to not be sexually mature until their late 30’s and 40’s, which means that these species are at extreme risk of disappearing due to fishing, as they aren’t able to replenish their numbers fast enough when put under extreme fishing pressure. There is a lot of debate over whether Sharks mature at a certain age or a certain size, for example it was estimated that White Sharks mature at four metres in length, however, in South Africa in 2017 a female White Shark was killed by Orcas, and it was determined that she was either immature or hadn’t mated, as there was the presence of a Hymen.

We are also still unsure about the impacts of human activities on Sharks and how losing Sharks, or their habitat, would affect the habitats and environments on land, environments in which we depend on for our survival.

What we do know

New Shark discoveries are made every year, and scientists are predicting that in the next 15-20 years we will be entering the golden age of ocean and shark discoveries. We already know that sharks are the oceans top predator and we have determined that they affect the very mechanics and functions of the Ocean, if we were to remove them, we would be putting the worlds ecosystems at risk of collapsing. Sharks are an integral part of the balance of the oceans, they help by controlling populations of other species, if we were to lose sharks, species such as turtles would have an increase in population, therefore leading to more seagrass being eaten, which is a prime food source for many animals. Thus, other smaller animals would not be able to feed, and their population would decrease, also the decrease of sea grass would affect us humans on earth as the oceans plant life helps to absorb carbon dioxide and create oxygen, and actually up to 75% of the oxygen we breathe is created from the oceans.

We know that some Shark species have complex social relationships that aid in their survival, although this has only been observed in a handful of species. Lemon Sharks form bonds as pups and hunt together in the shallow mangrove swamps of the Bimini Atoll, and will learn and hunt together and learn vital skills needed in their future survival. Hammerheads are possibly the most famous for social interactions as they form huge schools off places such as the Galapagos Islands and it has been observed that the more dominant females swim in the centre of the school and display for the males.

Some shark species, such as the Zebra Shark, have been known to mimic other animals. Zebra sharks are born with stripes (which fade as they get older) and they have the second longest tail (after the Thresher Shark), this helps them to mimic the highly venomous, White-Banded Sea Snake in order to trick predators into avoiding them, they have even been reported to mimic taking a breath at the surface like a sea snake would do.

It has recently been discovered that Greenland Sharks are now the longest lived Vertebrate on our Planet, they are believed to be able to exceed the age of 500, with females not reaching sexual maturity until they are around 150 years old. This was discovered by examining special proteins in their eyes that do not degrade with age. Determining age and sexual maturity are crucial for understanding and managing shark populations as knowing what age a Shark can breed will allow us to gauge what protections a species needs.

It has recently been discovered that female Whale Sharks are able to store sperm to use over a period of time, this is in order to ensure their chance of reproducing, even without recently mating. This is a huge advantage for conserving the species, as Whale Sharks are classed as an endangered species and so, with the number of whale sharks declining, this ensures the species can continue. Along with this, Whale Sharks have also been found to be pregnant with up to 300 pups, and these pups can be at different stages of development due to the staggered use of stored sperm.

Of all things we know there is one thing that is certain, a Shark, no matter the species, is unique and worth more to our world alive than dead. In the next blog we will explore the threats that Sharks face and how we can help Sharks through the tough times ahead.


Follow Donovan on Instagram at www.instagram.com/donovans_reefs

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Nauticam NA-α1 Housing for Sony α1 Camera now shipping

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The Sony α1 is the company’s flagship full-frame interchangeable lens camera.  Designed around the new 50.1MP Exmor RS BSI CMOS sensor and the BIONZ XR processor, the α1 is truly a camera which can do it all.  It’s 759 point Fast Hybrid Autofocus system offers advanced subject tracking and real-time eye autofocus on both humans and animals.  The optimized processing within the α1 allows it to achieve 30fps continuous shooting at full resolution along with 8K 30p and 4K 120p 10-bit video recording.

Nauticam has supported the Sony Alpha full-frame line since the original a7 with professional grade aluminum housings that offer intuitive access to all the controls and functions of the cameras. As the cameras have evolved, so have the Nauticam housings. The NA-α1 underwater housing provides fingertip access to all key camera controls in a rugged and reliable aluminum underwater housing. Ergonomic camera control access is one of the defining strengths of a Nauticam housing, and the NA-α1 continues this tradition.

Integrated DSLR-housing styled handles with ergonomic rubberized grips and stainless steel stiffening brackets add stability and accessory mounting points. The NA-a1 also features dual rear thumb-levers that are easily reached from the handle that access three of the most-used controls on the rear of the camera. The right lever actuates the AF-ON and RECORD buttons while the left lever is mapped to the PLAY button.

Atop the housing on the left side are controls in the form of a MODE dial and FOCUS mode lever. The C1, C2 buttons as well as the EV compensation dial also have direct access from the top of the housing. The C3, which is typically assigned to control switching between the EVF and the LCD screen is easily reachable on the rear of the housing from the left handle.

For more information visit the UK Nauticam website by clicking here 

or to visit the USA Nauticam website click here.

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Explore the amazing triangle of Red Sea Reefs - The Brothers, Daedalus and Elphinstone on board the brand new liveaboard Big Blue.  With an option to add on a week at Roots Red Sea before or after. 

Strong currents and deep blue water are the catalysts that bring the pelagic species flocking to these reefs. The reefs themselves provide exquisite homes for a multitude of marine life.  The wafting soft corals are adorned with thousands of colourful fish. The gorgonian fans and hard corals provide magnificent back drops, all being patrolled by the reef’s predatory species.

£1475 per person based on double occupancy.  Soft all inclusive board basis, buffet meals with snacks, tea and coffee always available.  Add a week on at Roots Red Sea Resort before or after the liveaboard for just £725pp.  Flights and transfers are included.  See our brochure linked above for the full itinerary.

This trip will be hosted by The Scuba Place.  Come Dive with Us!

Call 020 3515 9955 or email john@thescubaplace.co.uk

www.thescubaplace.co.uk

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