Saturday, April 11, 2020

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Physics Applied to Diving; Henry's law

Physics Applied to Diving 6.- Henry's law

Henry's law shows the relationship between the pressure of a gas and the amount of substance inside a body. In SCUBA diving this law gives reason to the increase in nitrogen gas inside the body which could produce a Decompression Sickness.

This law enunciates that: The quantity of gas dissolved in a liquid is directly proportional to the partial pressure of the gas it's in contact with. [1]

The mathematical way to show this law is:

C=P*k

Where C is the concentration of the gas inside a body, P is the partial pressure of the gas and k is a constant value. This law tells us that a when a body is in contact with a gaseous system at equilibrium it has an amount of gas dissolved inside it proportional to the pressure of the gas. The constant "k" in the equation depends on several variables like the temperature, the liquid molecules, etc. In the table shown next we can see how the nitrogen concentration changes in human blood depending of the pressure of common air.

Table extracted from [2]


[1] M. B. King, Phase Equilibrium in Mixtures, Pergamon Press, 1969, page 203
[2] Tosun Ismail, The Thermodynamics of Phase and Reaction Equilibria, Elsevier, 2013, page 470 

Friday, April 10, 2020

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Air consumption calculation; SAC Rate and RMV

Air consumption calculation; SAC Rate and RMV

With some simple mathematical operations, you can know approximately how much air you will consume at a certain dive. Boyle's Law tells us that whenever we go deeper in a dive, the ambient pressure increases and the volume of the gas decreases, so to inhale the same volume of gas when we go deeper we need to inhale more amount of gas following Avogadro's Law. This is the reason why you consume your air faster in a deep dive than in a shallow one. In order to calculate how much air, you consume at a certain dive you need a reference value of your air consumption; that's when the SAC rate or/and the RMV comes in. 

Sunday, April 5, 2020

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Physics Applied to Diving 5.- Ideal Gas Model

Physics Applied to Diving 5.- Ideal Gas Model

The ideal gas model shows the relationships between the pressure, volume, amount of substance, and temperature of a gaseous system. This model is commonly express by the next equation:

Friday, April 3, 2020

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Top 4 pieces of gear you should buy first

Top 4 pieces of gear you should buy first

When you get into the diving world, you'll notice there's quite a big amount of gear you can/should buy. ¿Where to start? Well, while you should have some pieces of gear of your own, others you don't really until you start to become a more advance diver. Next I list the top 5 pieces of gear you should buy first.

1.- Mask


The mask is the most personal item you are going to have in your diving career. A mask that fits your unique face may not fit another person's face correctly and vice versa. So, if you rent a mask every time, chances are you are not going to have a perfect fit and have leak problems. Buying a good mask is a great investment.

2.- Fins


The second thing you should buy is a good pair of fins that fit you. People don't notice the importance of a good pair until they use them. Most of the work you do while diving depends on your fins so, if you don't have a good pair, chances are you are going to hurt your feet or at least have a bad propulsion technique and all the problems that come with it.

3.- Dive computer/watch


To prevent a decompression sickness (DS) scenario, you need to know your time and depth throughout the dive. For this you’ll need a depth meter and a watch or a dive computer that measures both. This may appear that if you buy a watch you should also buy a depth meter, but that's not the case. Depth meters normally come in a console with the pressure gauge which is part of your regulator. Don’t get me wrong, the best thing you can do it to buy a computer, but, if you are in a budget, at list buy a proper watch. 

4.- Wetsuit/drysuit


You should have the proper external protection for the dives you do. This way your air consumption will decrease and you will enjoy more your underwater experience. Having your own external protection like a wetsuit or a dry suit will secure you are comfortable underwater and that it won't squeeze you or smell like pee.



Wednesday, April 1, 2020

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Top 10 Mistakes Beginners Do

Top 10 Mistakes most Beginners do

The training to become a certified SCUBA diver can vary between a couple of days and several weeks. If you are a new diver first of all cogratulations; and also you may be doing one or several of the next mistakes. 

1.- Confusing the "OK" sign and the "ascend" sign

This mistake is not dangerous, and sometimes it can be funny. This happens when the new diver isn't complete used to communicate in sign language underwater and s/he gets confused between the "thumbs up" sign which means ascend and the "OK" sign which means everything is going fine. This could end in a shorter dive with no real intention of doing so. 

2.- Not being aware of the Dunning-Kruger effect


Not being aware of the Dunning-Kruger effect is not a dangerous mistake per se, but can produce many dangerous scenarios.  Like it’s shown in the graph, when you start learning about something you may become overconfident, but that's only because you ignore how much you don’t know. When you get to the pick of unskilled and unaware a lot of dangerous scenarios, like exceeding your limits, are more likely to happen.

3.- Forget to turn on air


This happens not only to beginners, but also to some more advance divers. Not turning your tank on before putting your gear on can become quite dangerous, but most of the time you notice it’s of while doing your check up.

4.- Not noticing about their buoyancy


When a diver is starting s/he normally doesn't manage to have a good breathing rhythm and, in consequence, ends going up and down apparently with no control. Most of the time the new diver doesn’t even notice s/he is at a different depth from his/her teammates.

5.- Not noticing their position


The position you have underwater, which must mainly be horizontal, is one of the must important thing you have to notice. Sometimes, because of bad training or an inappropriate weight test the diver has a diagonal position, either head down or head up. This diver will consume a lot of air and it’s likely to damage the dive site. This is the main reason people damage coral all around the world. 

6.- Make extra movements


When you are underwater the less unnecessary movements you do, the better. It is common that beginners use their hands and move their whole body trying to be comfortable underwater, and, in consequence,  damage the dive site and consume a lot of the air. Stay calm and remember your buoyancy depends on your breathing and your propulsion on you legs and feet. 

7.- Have stuff floating around


The closer you have your gear and gadgets to your body the best. If you have stuff floating around, they can get hurt as well as the dive site. Clip everything in the right place and try to be as compact at it’s possible. 

8.- Multitasking


When something happens underwater the first thing you must do is to calm down and think. When the problem you are solving is complex you may need to do more than one task so remember to do them one by one so you can focus on doing them right. Most of the time the problem is much more simply than it appears and trying to do several thing at the same time can worsen it.

9.- Forget to check air consumption


Mostly beginners and people that haven't dive in a long time don't really know what's their air consumption and they forget to check it every several minutes. This can be the cause of an emergency exit and/or other emergency procedures.

10.- Taking extra stuff


When you start in this sport you may get existed and start buying stuff you don't really need for every dive. Remember to take only the essential things, because if you take something you aren’t going to use it can easily get hurt or lost.


[1] Mohammadali M. Shoja et al. A Guide to the Scientific Career: Virtues, Communication, Research, and Academic Writing, Wiley, Fisrt edition, 2020, page 37

Monday, March 30, 2020

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Physics Applied to Diving 4.- Avogadro's Law

Physics Applied to Diving 4.- Avogadro's Law


Avogadro's law shows the relationship between the volume of a gas and the amount of substance in the Ideal Gas Model. In SCUBA diving this law gives reason to why when you fill your BCD it's volume is proportional to how much air you get in.