Humans are designed for terra firma. So taking the plunge and going diving exposes the body to some foreign (and potentially frightening) sensations.

Here’s what happens when you sink below the surface . . .

On the way down

10 m Under pressure
Water is much heavier than air, so for every 10 m descent the pressure on your body doubles. This increasing load on the eardrums and sinuses can some- times have scary side-effects, such as burst eardrums.

The protective pop To prevent burst eardrums you have to keep the pressure in your ears and sinuses the same as the water around you.

The handy Valsalva manoeuvre involves closing the mouth, pinching the nose and forcing air through the nose to “pop” the ears and equalise the pressure.

15 m Getting Tipsy
Every 15 m you descend hits you like a Martini on an empty stomach.

30 m Drunk diving
Once you drop below 30 m, nitrogen in the blood becomes toxic and leads to nitrogen narcosis, a mental state similar to alcohol intoxication.

Don’t be surprised if you descend into laughing fits or even hallucinations.

40 m Too heavy to Handle
Divers shouldn’t venture down further than 40 m. At this dangerous depth the pressure equals 90 metric tons!

50 m Lights out
Light from the surface simply can’t make it to this watery underworld, where it’s darker than the middle of the night!

On the way up

Decompress less
Swimming quickly to the surface causes masses of nitrogen bubbles to form in the bloodstream – it’s like shaking a fizzy cooldrink can before cracking it open.

The leads to decompression sickness: your skin itches, your head aches and you feel nauseous and dizzy. These symptoms get worse by the hour once you’re back on dry land.

Deadly bubbles
Decompression sickness, also known as “the bends”, can be life-threatening. If just one large nitrogen bubble reaches the brain or heart, it can cause a stroke or heart attack. These bubbles can also damage tissue, nerves and organs.

Do it right
When ascending, breathe rhythmically and correctly as you swim slowly to the surface. Also, whether you’re going up or diving down, make sure you swallow often to prevent pressure building up in the middle ear.

Don’t wait to exhale
Holding a deep breath before surfacing quickly is a recipe for disaster. Because air expands dramatically as you ascend it could even cause your lungs to burst. Large bubbles can also stream straight to the heart and brain, resulting in loss of consciousness or death.

Pressure cooker
Divers with “the bends” have to spend hours in a decompression chamber. The air pressure in the chamber is lowered slowly to allow nitrogen to gradually leave the diver’s body until normal surface pressure is reached.

Take it slow
Divers should never surface faster than the tiny bubbles around them.

How fast is that? Surfacing at about 9 m a minute or slower allows nitrogen bubbles to seep out of the bloodstream slowly and be exhaled safely.

Remember
Never dive alone. Always dive in a group or with a friend so that oxygen can be shared if one person’s tank fails.

Did you know?
The average person can hold his breath for 30 to 90 seconds.

All you need to know about diving

10 Tips for diving survival