## Sunday, December 2, 2012

### Scuba Diving Physics: Why people suffering from hearing loss cannot dive?

Written by Xinke Liu

Ever since Jacques-Yves Cousteau made the Great Blue Hole of Belize famous in 1971, this amazing wonder has lured thousands of scuba diving fans to explore it. The Great Blue Hole is said to be the largest blue hole in the world and has a perfect circular shape. This site is a great place to have a prehistoric journey to see remnants preserved from millions of years ago. You will have fascinating experience of swimming with SHARKS and freaky fish in the crystal clear water!!!! Myths say that the charming blue in the Great Blue Hole entices some divers to stay there FOREVER…. FOREVER…FOREVER…

Sadly, people suffering from ear diseases and hearing loss like me cannot dive. What’s keeping us away from this fascinating activity? One reason is that some of them may also have problem in balance that is controlled by the vestibular system in inner ear. But the major reason is, not surprisingly, pressure.

The Great Blue Hole is 412 feet deep. Most divers dive down to between 110 and 130 feet. How much pressure does the water exert on the eardrum when people are 130 feet deep into the sea?

The pressure P due to the weight of liquid is:

P = pgh.

We need to find out the density (p) for the water in the Great Blue Hole since density of seawater varies due to temperature, pressure, and salinity. Since the salinity of the seawater in the Great Blue hole is not as unusal as that of the seawater in Dead Sea, we would take the average value of density of surface surface seawater that is 1.025 *103  kg·m3.

130 feet  39.6m.

g = 9.8 m/s2.

P = (1.025 *103  kg·m3) * (9.8 m/s2) *(39.6m)  397782 N/m2.

≈ 3.98*105 Pa.

1 atm = 1.013 ×105 Pa.

P/ 1 atm = (3.98*105 Pa) / 1.013 ×105 Pa  3.9 atm .

When people are 130 feet down in the Great Deep Hole, the water exerts 3.9 atm of pressure on the eardrum, almost 4 times of the average atm level on sea level. And this could be a disaster to people with hearing problem. And when diving, eardrum is in direct contact with the water.

Some people may wonder why not divers just use earplugs to protect eardrum. However, in fact, earplugs are not recommended when diving. The graph below shows that fluids exert pressure on object from every direction. This means the seawater would push the earplug inside the ear.