Dec 2019

The Diving Bell

By Ollie 

One human trait that has existed since the beginning of time, is that of curiosity. Our curiosity to explore the lofty skies, the insides of the earth and the depths of the oceans. This curiosity for exploration resulted in something that is now known as “The Diving Bell”.

The diving bell was the world’s first submarine, the first instrument that allowed mankind to venture into the unknown deep blue sea and it is the first piece of equipment that helped us on our way to develop advanced marine technology. The diving bell is most definitely a milestone in the maritime history books.

So, What Exactly is a Diving Bell?

A diving bell is essentially a heavy, solid watertight chamber that is used to transport divers from the surface to a certain depth underwater and allow them to stay there for a period of time before re-surfacing. The diving bell is usually used to perform underwater commerical work, salvage wrecks and submarine rescues.

How is a Diving Bell Made?

In the earlier days, the bells were cast in all kinds of shapes and tried with all types of materials. There were wooden bells and cast-iron bells too. Some were bottle-shaped, while others resembled wine glasses. The only thing that each bell had in common was that they were all very, very, very heavy. This is why iron was commonly used to make these little underwater chariots. The reason it needs to be so heavy is because of the immense pressure exerted from the engulfing water. Nowadays they are made much differently and obviously the quality of the bell is far superior.

Here’s the process of how a modern-day diving bell is made:

  • The main part shape and design of the diving bell is created from very strong steel usually all in one piece.
  •  The bell is then cut and shaped with 3 primary sections: The body, the sides and the bottom.
  • The 3 separate sections are hand-welded together by certified experts to ensure the welding is strong enough the endure extremely high pressures as well as being completely watertight.
  • 2-3 windows or viewports are fitted, these are commonly made from cast acrylic.
  • After all of the 3 sections have been welded together, the bell is inspected by undertaking ultrasound and visual checks, then proof testing is started. Proof testing is to ensure that the bell can withstand pressures that it has been created for.
  • The bell is then sprayed with a specialist paint called a marine epoxy
  • Lights, CO2 pumps, heaters and fans are all added to the diving bell interior along with wiring, pipes to ensure the bell is fit for use.

How Does a Diving Bell Work?

The concept of a diving bell is quite simple, which makes it believable that an early version of it was being used in the 4th century. The concept is so simple that you can try it in your kitchen sink! Here’s how:

  • Fill your sink with water
  • Get an empty cup
  • Push the open end of it vertically into the water
  • Remove the cup

The water will not enter the cup. Why is that? Well, the pressure of the water creates an air pocket within the cup, which is the concept behind the diving bell.

The force of the water pushes the air upwards: as air is lighter than water, which makes an air pocket.

This air pocket is used by divers to enable them to breathe underwater from within the diving bell. However, this has its limitations. The diving bell could be submerged only so deep and still have a breathable pocket of air. It took a lot of research, trial and error, prototype development and the minds of some great inventors to create a version of the diving bell that allows the bell to enter greater depths and the person inside to be safe.

What Is The Diving Bell Pressure Equation?

The pressure equation is not so simple and to understand the diving bell pressure equation, we’ll need to refer to Boyle’s Law. Unfortunately, we don’t have any physicians that work at divecompare.com so we thought we’ leave this one to the experts and refer you to page 10 of the University of California’s document on scuba diving physics for the full explanation.

“For any gas at a constant temperature, the volume of the gas will vary inversely with the pressure.”

If an inverted bucket is filled with air at the surface where the pressure is one atmosphere (14.7 psi), and then taken under water to a depth of 33 fsw (10.1 msw), or two atmospheres (29.4 psi), it will be only half full of air.

 Any compressible air space, whether it is in a diver’s body or in a flexible container, will change its volume during descent and ascent. Ear and sinus-clearing, diving mask volume, changes in buoyancy, the functioning of a scuba regulator, descent or ascent, air consumption, decompression—all are governed by Boyle’s Law (see Figure 2.6).

Examples of Boyle’s Law An open-bottom diving bell with a volume of 24 cubic feet is lowered into the water from a surface support ship.

No air is supplied to or lost from the bell. Calculate the volume of the air space in the bell at depths of 33, 66, and 99 fsw (10.1, 20.3, and 30.4 msw, respectively).

Boyle’s Equation: P1 V1 = P2 V2 P1 = initial pressure surface absolute

V1 = initial volume in cubic feet (ft3)

P2 = final pressure absolute

V2 = final volume in cubic feet (ft3)

Example 1 – Boyle’s Law Transposing to determine the volume (V2) at 33 ft.: V2 = P1 V1 P2 P1 = 1 ata P2 = 2 ata V1 = 24 ft3 V2 = 1 ata × 24 ft3 2 ata V2 = 12 ft3  

NOTE: The volume of air in the open bell has been compressed from 24 to 12 ft3 in the first 33 ft. of water.

Example 2 – Boyle’s Law Using the method illustrated above to determine the air volume at 66 ft.: V3 = P1 V1 P3 P3 = 3 ata V3 = 1 ata × 24 ft3 3 ata V3 = 8 ft3 NOTE: The volume of air in the open bell has been compressed from 24 to 8 ft3 at 66 ft.”

Content Reference: https://www.ehs.ucsb.edu/

When Was The Diving Bell Invented?

It is believed that the first diving bell was invented sometime around the 4th century BC: according to Greek philosopher Aristotle. Aristotle’s famous student Alexander the Great is often depicted in paintings sitting inside a glass cauldron at the bottom of the ocean, which suggests that the diving bell was in use.  The foundation of what the modern world would come to know as “scuba diving” centuries later, was laid. Other diving bells were invented and used in various places in Europe, mostly to salvage treasure.

The modern diving bell was invented by Englishman Edmund Halley (who is also known for the comet bearing his name). In 1690 Halley built a diving bell that used leather tubes and lead barrels to supply fresh air underwater. His diving bell was wooden, weighted with lead and fitted with a glass viewport. Inside, Halley hung a platform for the diver to rest and with the help of weighted barrels, when the diver pulled on them, water pressure from below forced the barrels to release fresh air into the bell. Helpers on the surface refilled the barrels with fresh air continually and Halley and a team of divers managed to stay underwater at a depth of around 60 ft (18.3 m) for as long as an hour and a half using his bell.

The Modern Diving Bell

Today we find the diving bell to be a modified version of its predecessor. It is a simple transport-bell, used to transfer divers from the deck of the diving-vessel to the area where they have to do their work and back again. This has proved to be a safe vehicle for travel to the limit of up to 100 meters on breathing mixtures. Despite the use of saturation diving techniques, decompression still is critical. A diver can reach a depth of 65 meters in 3 minutes, but it can take him more than 2.5 hours to return to the surface because of his decompression stops (off-loading nitrogen that has crept into the body). It is very dangerous not to obey the laws of decompression.

How Deep Can a Diving Bell Go?

Modern-day diving bells are made to reach depths of most and commercial diving is conducted between 65 (20 metres) and 1,000 feet (304 metres). However, some diving bells are made to only have a working depth of around 33 feet (10 metres).

What is a Diving Bell Depth Record?

Thanks to the advances made in technology especially the saturation diving industry, the diving bell depth record had been reached with the deepest dive to 2,300 feet (701 meters) by a human under the pressure of 71.1 atmospheres. Now that is one deep dive.

What is a Wet Bell?  

It is essentially a platform for divers use to descend and ascend from an underwater work area, the platform includes an air-filled space, open at the bottom, where the divers can stand or rest without their heads being submerged.

What is a Closed Bell?

A closed or dry bell is a pressurised chamber for human transport which is lowered underwater to a workplace, equalised in pressure to the environment, and opened to allow the divers in and out, keeping this pressure equal without flooding the interiors. The internal pressure requires a strong structure, and a spherical ended cylinder is usually the most efficient.

Closed bells are used in the commercial diving industry regularly and require the inhabitants to have a strong technical background. Closed bells once back on the surface attach to decompression chambers to aid with diver decompression once the underwater work is completed. They are used for submarine rescues and similar operations like it.

Diving Bell Accidents

In the nineteenth century and before scientists discovered the effects of pressure on the human body, decompression sickness and casualties because of “the bends” had become a common theme among deep-sea explorers.

One diving bell accident occurred when a drilling rig called the Byford Dolphin, in 1983. Five crew members passed away and a sixth was seriously injured. The platform was drilling in a gas field when four divers were in two connected chambers. One of these chambers was also connected to a diving bell. Due to human error, the clamp of the bell was opened earlier than required and the higher pressure chamber rushed into the lower pressure of the bell. As a result, there was an explosion and the bell was blown away with unfortunate casualties.

Newer bells have much more enhanced safety and security systems in place to prevent catastrophes such as these accidents.

Diving Bell Submarine Rescue

During the earlier days of the United States Navy Submarine Force, there were several accidents in which submarines sank with the loss of life. These experiences led submariner Charles Momsen to think of alternatives for rescuing survivors from sunken submarines, which at that time was still a virtual impossibility. Momsen soon conceived a submarine rescue chamber that could be lowered from the surface to mate with a submarine’s escape hatch. Since then, great advancements have been made to the chambers which have led to hundreds of successful rescue operations.

That concludes our thoughts on the diving bell, I hope you enjoyed the article. If you have anything to add or would like to share your thoughts, please do so in the comments below and don’t forget to share with your friends on social media.

Happy Diving!

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Ollie