The Byford Dolphin Incident: How do you get sucked into something so strongly by a change of air from 9 atmospheres of pressure to 1?



Please somebody know what I’m talking about. If not, then please see the diving bell incident in the link provided below. I just don’t see how you are killed by air.

In: Physics

The best way to think of it is to think of the “weight” of air. 1 atm is how heavy all the air molecules are above you at sea level. It doesn’t seem like a lot but it is actually just under 15 lbs. So multiply that by 9 and you get 135 lbs. That’s 135lbs of force being applied to every square inch of a person.

This is essentially the same as an explosion. Which is why these events are known as explosive decompression.

Well one atmosphere of pressure is equal to 14.69 pounds per square inch. (Nice)

So 9 atm would be 132 pounds per square inch. Average person has a surface area of around 3,000 square inches. So that’s nearly 400,00 pounds of force

So…what part of a force equal to the weight of several fully loaded semis doing damage to a person is confusing?

Basically, liquids at higher pressures are able to take in higher quantities of dissolved gasses. ‘Liquids’ includes blood. So as a body goes to a higher pressure, it ends up having more dissolved gasses (like nitrogen) in the blood.

That gas isn’t able to stay dissolved in the blood as a body goes to a lower pressure. Under normal, slow decompression, we’re able to exhale that excess gas as we breathe. But when it’s all at once, blood will let all that gas go instantly, all over the body. Mild cases of decompression sickness make people quite ill. This was an extreme case, they probably had blood vessels burst all across their body; aneurisms and internal bleeding, at the same time as their lungs trying to expand to 9x their volume, at the same time as what basically was an explosion.

To truly explain it to a 5 year old, imagine the body as a balloon. It’s able to regulate itself slowly so that it stays the same size as air pressure changes going up and down a mountain. It can also slowly regulate to go to higher pressures. As pressure increases, it lets a little more air in to stay the same size. So long as it’s slow, you can get to several times the normal air pressure without deflating the balloon. And the process is reversible. But if all the outside pressure is released at once, the balloon will then want to expand to several times its ideal size, and pop.

You know how when you crack a can of soda suddenly it starts bubbling? under pressure the bubbles stay in the soda, when you release the pressure the bubbles come out. basically same thing happens to human blood under pressure, we absorb nitrogen gas in our bloodstream.

instantly going from 9 to 1 likely “boiled” their blood instantly.

They were inside a high-pressure environment that gained a small opening to a much, much lower-pressure environment.

Have you ever seen what happens when you put some dry ice in a water bottle and seal the lid? It builds up internal pressure as the frozen CO² sublimates into gas, then the thing violently explodes because the pressure differential between the bottle and the atmosphere is so great. It’s like that, but in a much larger, rigid bottle, where just the cap blows off, and there’s a balloon full of meat inside.

Gas is always trying to equalise pressure. That means that when something is pressurised to 9 bars (atmospheres) in a 1 bar environment, it’s pressing against its container with 8 bars of force. And unlike a liquid, it’s pressing in all directions at once. Gas under pressure will find the weakest point in its container; it’s why gas explosions are so dramatic. Note that scientifically, both liquids and gases are considered ‘fluids’ because both have some common behaviours they both display; under certain conditions, gases can behave like liquids, and vice versa. When highly compressed, gases suddenly start looking a lot like liquids.

1 bar is equivalent to 14.7psi. So every square inch basically has a weight of 14.7 pounds applied to it. At 9 bars, it’s 132.3 pounds on every square inch of exposed surface. The outside is pushing back with 1 bar, hence the 8 bar difference. So the air inside the chamber was pressing against the entire surface with 117.6 pounds per square inch.

Because the gas is always pushing, the instant a hole opens, it’ll find that hole and escape. What happened in the Byford Dolphin was, the trunk where the diving bell connected formed a bottleneck. You know how if you’re spraying water through a hose and pinch it, the water shoots further? Same principle. Less air flows through a bottleneck, but at higher speed. So you have a lot of high pressure air, which is already pressing outwards with a huge amount of force, suddenly being released. It’s just like shaking up a bottle of soda and then pulling the cap off – the higher pressure inside the bottle escapes explosively. And that’s only a small pressure difference. As air equalises pressure, it expands, (pressure is inversely proportional to volume) so again, pushing in all directions, it creates a shockwave.

The very unfortunate diver who was closing the trunk reduced the bottleneck even further, adding more pinch to the hose. So the high-pressure air behind him instantly escaped through the hole, applying all that pressure to whatever is in the way. Like a battering ram, force is mass multiplied by acceleration. And air does have mass; at 9 bars, the same cube of air weighs 9 times what it does at sea level. The air has been squashed into a smaller box.

And because there was already air in his lungs at 9 bar, it immediately escaped as well. The human body is not designed to handle rapid changes in pressure; very gradual, controlled changes are possible, but rapid changes will cause horrific damage. That’s why divers have the diving chamber in the first place. The human body isn’t strong enough to withstand huge pressure differences, so the high-pressure air within his body, when exposed to the lower outside pressure… well, it chose the quickest way out to equalise, it doesn’t care what’s in the way. Really nasty.

The other resting divers were killed by the same thing – the diving chamber suddenly went from 9 bars to 1 bar, causing horrific internal injuries as the air inside them expanded.

Compressed air is incredibly dangerous. For something so vital to life, it has been the cause of unexpected injuries, deaths and damage. A great illustration is an exploding tyre – something so everyday and benign? If air escapes a pressurised container suddenly, the damage it can do is staggering.

Explosive decompression only requires a difference of one atmosphere of pressure. And a difference of one is what happens when you get sucked into space.