What Is The Most Important Rule In Scuba Diving? (Never Hold Your Breath)

What is the most important rule in scuba diving - Never hold your breath

The most important rule to follow over anything in scuba diving is to never hold your breath

Of all the rules in scuba diving, you may be wondering what is the most important rule to remember. When I taught beginner scuba divers I would highlight the most important rules of scuba diving. I always encourage safe diving practices, which is why it’s important to know what is the most important rule in scuba diving.

The most important rule to remember scuba diving is to breathe continuously and never hold your breath. If you hold your breath on an ascent you could rupture your lungs, which in the worst case scenario could be fatal. But if you follow the rule and never hold your breath and you’ll be okay.

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It was difficult to choose the most important rule, as there is another very important rule of scuba diving too. I cover this later in this article.

The deeper you dive the higher the pressure

If you didn’t know this already, water is nearly 800 times more dense than air. For example, at sea level you experience what is known as atmospheric pressure. Atmospheric pressure is also known as barometric pressure and is one bar of pressure.

One ‘bar‘ is a unit of pressure defined as 100 kilopascals and is about equal to the atmospheric pressure on Earth at sea level

But if you dive to 10 metres (33 feet) underwater, the pressure you experience at that depth doubles. So at 10 metres you are experience two bar. Or twice that of atmospheric pressure.

For each additional 10 metres (33 feet) you dive underwater the water pressure you experience increases by one bar. So for example:

  • 10 metres (33 feet), the pressure is two bar;
  • 20 metres (66 feet), the pressure is three bar;
  • 30 metres (98 feet), the pressure is four bar;
  • 40 metres (131 feet), the pressure is five bar.
  • 50 metres (164 feet), the water pressure is six bar.
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Why is pressure key to the most important rule in scuba diving?

Why are these pressure changes are important to scuba divers. Changes in pressure are important because in the same way that pressure increases as you go deeper, the reverse is true as you ascend and get shallower. The biggest pressure change is the first 10 metres.

From the surface to 10 metres the pressure doubles, but in reverse the pressure halves.

But why is this important you may ask? Plus why are scuba divers told not to hold their breath when ascending as a result of these pressure changes?

The answer to these questions can be demonstrated using a balloon filled with air.

The balloon experiment with water pressure underwater

This video explains the concept very well:

What happens If you hold your breath while scuba diving and freediving
In this video I will show you why it is dangerous to hold your breath while scuba diving. And what you should not do when diving

To demonstrate the importance of why should you never hold your breath while scuba diving can be explained using the simple balloon experiment.

You can try this ballon experiment, but please never experiment holding your breath when scuba diving!

If you fill a balloon with air at the surface and then take it down to 10 metres (33 feet), the volume of this balloon would halve in size. If you bring the same balloon back to the surface, it would return to the same size it was before it was submerged.

This is why it’s okay to hold your breath snorkelling. When you’re snorkelling the air in your lungs reduces as you dive down. But the same amount of air returns to the same volume it was when to come back to the surface.

The phenomenon that is demonstrated with a balloon is explained by Boyle’s Law.

What is Boyle’s Law in scuba diving?

Boyle’s Law in scuba diving explains how the volume of gas varies with the surrounding water pressure. For the purpose of scuba diving, the gas that varies is air.

Boyle’s Law is explained as follows; as the water pressure increases, ‘air spaces‘ decrease in size in direct proportion to the pressure increase, but only when the temperature is held constant.

Noting that as already explained, the deeper you dive the greater the water pressure. Similarly as water pressure decreases the, ‘air spaces‘ increases in size in direct proportion to the pressure decrease.

Understanding this simple ‘gas law‘ is key to staying safe when scuba diving. Take a moment to grasp this basic concept.

What happens if you fill the same balloon with air at 10 metres (33 feet) underwater

If you take an empty balloon down 10 metres and fully inflate it at this depth using compressed air and brig the balloon back to the surface you would get a completely different outcome. It’s likely the balloon will rupture.

The air inside the balloon will double in size. But because the balloon gets to its capacity size this is when it bursts.

Think of your lungs as similar to balloons

Perhaps you’ve never thought of your lungs this way before, but essentially your lungs are like balloons. They inflate in the same way as balloons and are made from flexible material like a balloon.

But the important difference with your lungs when compared to a balloon is that your lungs are surrounded by your rib-cage.

This means that even without the limitations of the expandability of the flexible material your lungs are made from, your lungs will not be able to expand any further than the restriction of your rib-cage.

This means that if you did a similar experiment as the balloon one above, but with you lungs instead, what do you think might happen?

But I can’t stress this enough, please do not try this experiment…this is only a hypothetical question.

Why should scuba divers not hold their breath?

If you fill your lungs with air at 10 metres (33 feet) and hold your breath and come to the surface, the air in your lungs want to expand to twice the volume by the time you reach the surface.

You may have already worked this out…

If your lungs are fully inflated already, there’s no way they could double in size without injury. Even if your lungs were able to double in size, your rib-cage would prevent this amount of expansion.

This would result in a lung rupture or what’s known medically as a Pulmonary Barotrauma.

Pulmonary barotrauma is the most life-threatening form of barotrauma. The classic example of pulmonary barotrauma occurs when a diver takes a breath at depth and then rapidly ascends while holding his or her breath.

John P. Santamaria MD on Science Direct

A lung rupture or pulmonary barotrauma of this nature is extremely serious and dangerous and should be avoided at all costs.

Lung over expansion can result in injuries such as a pneumothorax, also referred to as a collapsed lung. It can also lead to an arterial gas embolism or AGE.

Air or gas embolism in scuba divers: Air can escape from the lungs into the blood vessels (arterial gas embolism) or nitrogen bubbles can form in the blood vessels (decompression sickness or “the bends”). Air or gas embolisms can cause serious and potentially fatal conditions, such as a stroke or heart attack.

NHS UK – Air or gas embolism

The above dangers are the reasons why this is the most important rule in scuba diving.

What is the second most important rule to remember scuba diving?

The second important rule to remember of scuba diving is to used controlled slow ascents at the end of your dive finished off with a safety stop at 5-6 metres (16-20 feet). Use a dive computer to control your ascent to prevent any problems of decompression sickness.

A fast uncontrolled accent risks decompression sickness and should be avoided at all costs. You should take a read about the decompression sickness risk factors.

I hope you enjoyed this article about what is the most important rule in scuba diving

I’d love to hear from you. Tell us about your adventures of diving and snorkeling, in the comments below. Please also share your photos. Either from your underwater cameras or videos from your waterproof Gopro’s!

If this article hasn’t answered all of your questions. If you have more questions either about snorkeling or types of scuba diving (or specifically about what is the most important rule in scuba diving), please comment below with your questions.

There will also be many more articles about scuba diving (and snorkeling) for you to read and learn about these fabulous sports.

Have fun and be safe!

What Is The Most Important Rule In Scuba Diving? (Never Hold Your Breath)

Article written by Russell Bowyer who has been a scuba diver since diving on the Great Barrier Reef in Australia in 1989. After his first dive he trained as a BSAC diver in the UK. He attained his Diver Leader certification with BSAC. He then went on to become a scuba diving instructor, teaching others how to dive and was voted as Diving Officer and Treasurer for the Saffron Walden BSAC club too. Russell has dived all over the world, including the UK, on liveaboards in the Red Sea, the Caribbean, South Africa and the USA. Russell is experienced in all dive types, including drift diving, deep dives that involved decompression stops and recreational dives too.

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