Day Four

Today we concentrated on Pressure and how it affects the body. This was really interesting and some of what was being said reminded me of my father-in-law. Initially we looked at Barotrauma and Boyle's Law which means more pressure = less volume. After going through the different types of 'squeezes' (Nips, Facial, Sinus, Tooth cavities, Thoracic and Aural) that affects you on descent we then looked at those that affect you on ascent (Stomach and Bowel, Dental, Sinus, Ears and Pulmonary).

What I did not know is that car sickness is brought on by the semicircular canals in your ears as your eyes process information that does not correspond with what your ears are feeling (pressure & hearing) The best method to combat Car Motion Sickness is to take either pills that will stop the signals in your ears or take anything that contains Ginger.

At the same time we looked at decompression and how air travels through the body. This is important as it could mean life or death if you do not know how your body operates (Do not worry Rachel I know it really well). We looked at collapsed lungs, holes in lungs and alveoli ruptures, all caused by improper decompression.

After a short break we were presented with decompression illnesses and Henry's law. Basically, the more you descend, the more pressure your body takes and the more gas is absorbed by the tissues. The Bends, a common diver problem is basically formed by bad decompression. At more depths gas bubbles are smaller as they are compressed and take up less volume. As you surface you need to decompress slowly to allow these bubbles to escape slowly out of your body. If you come to the surface too fast, you body is under less pressure which means bubbles expand and take up more volume. This can mean pains in joints, lungs and even the brain. However nowadays, with advances in technology and studies by the US navy, most dives are bend-free.

Finally we looked at Dalton's Law:

PP=AP x %
Partial Pressure = Absolute Pressure x %

Basically all gasses make up an Absolute Pressure. At sea level this is 1 bar Absolute (21% Oxygen and 79% Nitrogen - these are Partial Pressures) Going down 10m we are a 2 bar Absolute (2 x 0.21 Oxygen and 2 x 0.79 Nitrogen - or 0.42 + 1.58 = 2 bar) It is very straight forward although many of the guys in the class did not get it right away.

A short video by the Royal Navy on Diving tables and a short lesson afterwards was enough to put half the class asleep and luckily enough that was us finished for the day. Tomorrow I have my divers medical and due to some loud snoring last night I only managed to get 5 hours sleep... so I will leave this blog and get on with my studies. Wish me luck for tomorrow.