Day 5

Today we started the day looking at US Navy diving tables, working out how much decompression you need depending on the depth, length of time and pressure. Initially it looks impossible but after a few exercises it is quick to pick up. Here is an example of a question:

A diver dives to 100 feet for 20 minutes. How long must he wait on surface before he can do the same dive again with no stops?

After this we looked at Divers Physics based on:

Archimedes Principle - When an object is immersed in a liquid it experiences an upthrust which is equal to the weight of the liquid that it displaces (When you put a object in water it does not weigh as much as it does in air. The difference in apparent weight loss is the same as the weight of the water displaced)

U = V x D (Upthrust = Volume x Density)

Boyle’s Law – For a given mass of gas, if the temperature is constant, the absolute pressure varies inversely with the volume (If you double the pressure you half the volume)

P x V = C (Pressure x Volume = Consumption or Content)

How long will a 12L cylinder filled to 220 bar last a diver at 25 meters if he breathes 35L on surface? He wishes to leave 50 bar in reserve.

220 bar - 50 bar = 170 bar

170 x 12L = 2040L
(25m) 3.5 Bar x 35L = 122.5L
2040L ÷ 122.5L = 16.65minutes

Charles’s Law - For a given mass of gas the absolute temperature varies directly as either the pressure or the volume (If you double the absolute temperature you double the pressure).

P1 / T1 = P2 / T2

A cylinder is filled to 200 bar & the temperature is 40º C. What will the pressure be when it cools to 12 ºC?

40º C = 313º Kelvin 12 ºC = 285 ºKelvin

200 / 313 = 179.55 / 285

Following lunch we learned the ins & outs of giving oxygen to a casualty (by the way all oxygen bottles have a white neck) and the different types of masks. This did not take too long and we all were given our first examination on First Aid. Having read over the book a few times and studying the main Acronyms I achieved 92%. There were 40 multiple choice questions all of which were fairly straight forward.

Before the end of the day we were given homework to do over the weekend (Reminded me of how I use to set a lot to my pupils / students), so this weekend I decided to return to Aberdeen to get my laundry done and complete all my work. It was a four hour long trip but this time I did a tour of the north of Scotland. Needless to say it was a long trip but beautiful. Rachel, you would have loved it. I drove through Fort Augusta, Loch Ness (stopped to see Urquhart Castle), Inverness, Elgin and finally Aberdeen.