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An Unforgettable Evening
with
David Doubilet, Michael Aw
and
Leandro Blanco
.

Monday 25 October 2010 at 7.00 for 7.15 p.m.

Further details


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Keith Lyall
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Epson Red Sea 2010
Monthly Online Competition

Epson Red Sea 2010 Monthly Competition

View the August entries


The Deep

The Deep - an exhibition at the Natural History Museum
Natural History Museum
28 May - 5 September 2010


Scottish Nature Photography Fair

Scottish Nature Fair
4th & 5th September 2010
Battleby Centre, Redgorton, Perth


Festival de'Image Sous-Marine

Festival de'Image Sous-Marine
27-31 October 2010 – Palais du Pharo, Marseille
Deadline 27th September


WildPhotos 2010

WildPhotos 2010
22 & 23 October, 2010
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SUPS Exhibition
A Global Walk Underwater

SUPS A Global Walk Underwater Exhibtiion
Throughout December 2010 Boxfield Gallery, Stevenage

 



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Sponsors

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Sport Diver - Sponsors of the annual Best of British Portfolio Competition & the British Splash-in Competition 2008, 2009, 2010

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New Holland - Sponsors of the British Splash-in Competition 2010

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Calumnet Photographic - Sponsors of the BSoUP/DIVER Print Cometition 2010

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Diver Magazine - Sponsors of the Annual Beginners Portfolio Competition and  the BSoUP/DIVER Print Competition 2009, 2010

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Ultimate Sports

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As heavy as . . . Air?

by Mike Russell

Reproduced from in focus 78 (Sping 2004)

 

 

Protection of the underwater environment is a prime consideration when diving, particularly when taking photographs. Major diving agencies teach buoyancy skills and posture. Numerous articles for photographers on how to approach and leave a coral reef without causing damage are quite rightly a regular feature in magazines, books and web sites. Achieving these skills is ultimately a matter of practice.

However, the most important time to achieve neutral is when? For one's own safety it must be prior to surfacing, when undertaking asafety stop or a decompression stop. Againall a matter of practice. Well is it? Perhaps just a little bit of knowledge may help.

We know at the start of a dive our cylinder, hopefully full of nitrox at between 20.9% to 40.0% oxygen, weighs more then at the end of a dive. Hence neutral buoyancy and the art of remaining at a decompression stop, which may be at a depth of no more than 3 metres, relies on us having the correct amount of overall weight just prior to surfacing. I've used e fairly rough and ready rule of thumb that a 12 litre cylinder is approximately 2 kg heavier when filled to 232 bar than it is at 50 bar. A 15 litre cylinder circa 2.5 kg heavier. However, what I didn't know was how accurate this was.

Recently a non?diving colleague asked me about air density. In order to help him with a demonstration he was preparing for a school I did some approximations based on the above f igures, but how close was I? So I tried to f ind a ref erence to air density and found it wasn't too easy to track down a f igure. By chance I was off to the Science Museum and decided to quiz them on the subject.


After much searching an enthusiastic chap come up with the answer.

Air density
At 200 °C and 760 mm of mercury, i.e. I atmosphere, the density of air is 1.204 mg/cu cm. Put in another way 1 litre of air weighs 1.204 gms

Not a lot of people know that.

So to see what that means in the real world look at the Table below:

Size - Litres Start - Pressure End - Pressure Weight Difference
15.0 l 232 bar 50 bar 3.2869 kg
12.0 l 232 bar 50 bar 2.6295 kg
10.0 l 232 bar 50 bar 2.1913 kg
03.0 l 232 bar 50 bar 0.6574 kg


Reproduced from in focus 78 (Sping 2004)






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