This article is from WeChat official account:span class=”text-remarks”>bring home science , author: seven Jun, the original title: “let diver afraid of physical phenomenaElephant, killed two-thirds of the divers who died on duty”, the title picture comes from: Visual China
You may go diving in the summer. Many recreational diving projects do not require players to actually dive, or even swim. Many people go into the water after a few minutes of temporary training on site, so many people are not aware of the real dangers of diving. Known.
Today, let’s take a look at the most dangerous conditions during diving. It is also the cause of death for most professional divers who died on duty-differential pressure(delta P).
Differential pressure means the difference in pressure. In fact, according to the data of the International Association of Diving Contractors (ADCI), the creator of the Internationally Recognized Standards for Commercial Diving and Underwater Operations, Two-thirds of professional divers who died on duty died of differential pressure.
As we learned in middle school, the pressure at any point underwater is proportional to the water depth, so if the water depth on both sides of the connector is different, there will be a differential pressure at the connection. However, as long as enough time is given to the communicating device, the water pressure around the small middle connecting place will eventually tend to balance, and the differential pressure will be 0 at this time.
Nitrogen, if the small water pipe is blocked, the small water pipe in the middle will be Alexander, and you need to see the urology department.
If there happens to be a diver in the small water pipe, the TA will feel an invisible hand holding him and not letting go. Because the connection cannot be balanced and the differential pressure is always not 0, the diver becomes a bottle stopper, and his breathing gradually disappears.
Because the differential pressure is invisible to the naked eye, it is quick to kill the killer without leaving a trace. Therefore, even professional divers and even fish living in the water have no counterattack in the face of differential pressure.
You may think this is a bit of a pull, is the differential pressure really so powerful, will it feel nothing nearby? Let’s find a crab boss who is rampant in the water and an empty pipe cut in the water to try.
Look, the crab boss turned into cardboard in an instant——
Brother Shark, who was not aware of the danger at all, was instantly sucked away by the dredging pump that sucked silt—-
According to the records of the International Association of Diving Contractors, in January 1989, an accident caused by differential pressure occurred when cleaning the drainage pipe of the dam.
A diver dived under the reservoir to clean the strainer of the drainage pipe. Unexpectedly, the debris was cleanedAfter the treatment, the differential pressure was released at once, and the diver was sucked in. The second diver stepped forward to rescue, but was also attracted.
The third diver went to rescue them. It took 40 minutes to get out of the water, but unfortunately both of them died.
A similar accident happened in May 1993 when a diver was repairing a swimming pool.
At that time, the diver was repairing the bottom of a swimming pool with a depth of 3 meters and was sucked by a drain pipe. His body locked the pipe, so the differential pressure could not be reduced to zero. He was also firmly pressed to the bottom of the water by the differential pressure, and unfortunately died.
For deep-water divers, even if they are not absorbed by the differential pressure, the differential pressure inside and outside the diving suit is fatal. In 2003, the rumor-stopper once had a show about the coming of Death.
They put the pork-made divers into diving suits and sank into the water at a depth of 90 meters. Next, they simulated the failure of the diving suit and the sudden drop in internal pressure.
Because of the huge pressure difference between the inside and outside of the diving suit, McDull was directly squeezed out of watermelon juice.
Differential pressure is not only the number one enemy of professional divers, it can also threaten unsuspecting ordinary people.
Such an accident happened in Brisbane, Australia, and it was recorded by the TV camera. At that time, the high-speed road was blocked by drainage ditch and water accumulated, and a maintenance worker in Brisbane went to drain the silt.
After he cleared the debris blocking the drain, he became a human manhole cover in full view, and his leg was sucked by the differential pressure.
Even if 7 people came forward to rescue, the poor worker’s face was soaked underwater for more than 1 minute. Finally, the teammate turned on the pump directly to pump the sewage clean, and the worker was saved. The danger of dredging after the flood is evident.
Seeing this, many people may not dare to go swimming. But did you know that the differential pressure that can suffocate you also exists in your body. The reason why you can breathe happily is also because the delicate design of your body helps you hold up the differential pressure.
That’s it, the lungs are a bit like blowing up balloons. The balloon is very elastic and has a high surface tension. The surface tension of the balloon must be able to withstand the differential pressure between the inside and the outside, so that the balloon will not explode or leak, and be in a balanced state, right?
However, the human lung is not a balloon. It is made up of many interconnected balloons-alveoli. The size of the alveoli is different, and big things can happen if they connect.
Alveoli
What’s the big deal?
Look at the experiment where two balloons of different sizes are connected together. If you guess blindly, after two balloons of different sizes are connected, should they become the same size in the end?
No, the big balloon will suck the air out of the small balloon. You can also try it yourself to verify it——
What determines this phenomenon is the Yang-Laplace formula (Laplace-Young Equation).
The Yang-Laplace formula. Deltap is the pressure difference between the two sides of the membrane. γ is the surface tension of the film. R is the radius of the sphere.
According to the Yang-Laplace formula, the larger the bubble, the smaller the differential pressure inside and outside the bubble. Because everyone is at atmospheric pressure outside, the smaller the balloon, the higher the pressure inside, and the gas inside wants to be released.
The gas will diffuse from the place where the pressure is high to the place where the pressure is low, so if two balloons are connected, the air in the small balloon will blow to the big balloon, causing the big balloon to grow bigger. This is why the hardest time to blow a balloon is when you first blow the balloon. It is easier to blow the balloon after it is bigger.
So the problem is here: as long as one alveolar is bigger than others, it will suck the gas from other small alveoli. The big alveoli become bigger and bigger and finally burst, the small alveoli are all inhaled and the lungs are still How to breathe? This condition does exist, and it is medically called atelectasis(atelectasis).
In 1929, the German physiologist Kurt von Neergaard (Kurt von Neergaard) was studying Yang Rapp Lars first noticed the relationship between it and atelectasis during the formula, and accurately guessed the solution to the lungs.
He believes that the lungs must have a mechanism to prevent the destruction of alveolar masses, and this mechanism exists in the fluid on the surface of the alveoli.
The water strider stands on the surface of the water because of the surface tension of the water
OriginalNow, there is a liquid film on the alveoli. Similar to a balloon, this liquid film has surface tension.
According to the Young-Laplace formula, the differential pressure is proportional to the surface tension of the liquid, and is proportional to the size of the alveoli(diameter radius) is inversely proportional. Therefore, von Niergarde boldly guessed that if the differential pressure of the small alveoli is to be reduced to prevent the gas inside the small alveoli from being sucked away by the large alveoli, it is enough to reduce the surface tension of the liquid film on the surface of the alveoli.
Alveoli expand and contract with breathing
At the time, however, he only guessed the function of the liquid film on the alveolar surface, but did not discover what exactly changed the surface tension of this liquid film.
It took more than 30 years before the medical community really realized that von Nilgard was right, and the alveoli can really secrete substances that regulate surface tension.
In fact, this substance is similar to soap liquid. It is a surfactant-lung surfactant, the main ingredient is dipalmitoylphosphatidylcholine. In the case of different alveolar differential pressures, as long as the lung surfactant is added, the surface tension of the liquid film can be effectively reduced, so that the small alveoli will not collapse.
The discovery of surfactants in the lungs perfectly explains why premature babies often have difficulty breathing.
It turned out that at the 24th week of embryonic development, the lung cells of the fetus began to produce a small amount of lung surfactant. At the 34th week, the secretion of surfactants in the lungs began to increase suddenly. At this time, the alveoli of children born are not easy to collapse.
Conversely, premature babies less than 34 weeks old are prone to alveolar collapse due to insufficient lung surfactants.situation. This is the neonatal respiratory distress syndrome (infant respiratory distress syndrome), which is why we see premature babies often wear ventilators.
This article is from WeChat official account: science home (ID: steamforkids) , Author: Seven Jun