We've all heard the epic stories of people being shot in the head, falling from the 10th floor, or being lost at sea for months. But it is enough to place a person anywhere in the known universe except for a thin layer of space extending a couple of miles above or below sea level on Earth, and the death of a person is inevitable. No matter how strong and elastic our body may seem in some situations, in the context of the cosmos as a whole, it is frighteningly fragile.
Many of the limits within which the average person can survive are fairly well defined. An example is the famous “rule of threes,” which determines how long we can go without air, water, and food (approximately three minutes, three days, and three weeks, respectively). Other limits are more controversial because people rarely test them (or don't test them at all). For example, how long can you stay awake before you die? How high can you rise before you suffocate? How much acceleration can your body withstand before it breaks apart?
Experiments conducted over decades have helped define the boundaries within which we live. Some of them were purposeful, some were accidental.
How long can we remain awake?
It is known that Air Force pilots, after three or four days of being awake, fell into such an uncontrollable state that they crashed their planes (falling asleep at the controls). Even one night without sleep affects a driver's ability in the same way as intoxication. The absolute limit of voluntary sleep resistance is 264 hours (about 11 days). This record was set by 17-year-old Randy Gardner for a high school science fair in 1965. Before he fell asleep on the 11th day, he was actually a plant with his eyes open.
But how long would it take for him to die?
In June this year, a 26-year-old Chinese man died after 11 days spent without sleep trying to watch all the games of the European Championship. At the same time, he consumed alcohol and smoked, which makes it difficult to accurately establish the cause of death. But definitely not a single person died due to lack of sleep. And for obvious ethical reasons, scientists cannot determine this period in laboratory conditions.
But they were able to do it in rats. In 1999, sleep researchers at the University of Chicago placed rats on a spinning disk placed over a pool of water. They continuously recorded the rats' behavior using a computer program that could detect the onset of sleep. When the rat began to fall asleep, the disc would suddenly turn, waking it up, throwing it against the wall and threatening to throw it into the water. The rats typically died after two weeks of this treatment. Before death, the rodents showed symptoms of hypermetabolism, a condition in which the body's resting metabolic rate increases so much that all excess calories are burned, even when the body is completely immobile. Hypermetabolism is associated with lack of sleep.
How much radiation can we withstand?
Radiation is a long-term danger because it causes DNA mutations, changing the genetic code in a way that leads to cancerous cell growth. But what dose of radiation will kill you immediately? According to Peter Caracappa, a nuclear engineer and radiation safety specialist at Rensler Polytechnic Institute, a dose of 5-6 sieverts (Sv) within a few minutes will destroy too many cells for the body to cope with. “The longer the dose accumulation period, the higher the chances of survival, as the body tries to repair itself during this time,” Caracappa explained.
By comparison, some workers at Japan's Fukushima nuclear power plant received between 0.4 and 1 Sv of radiation in an hour while confronting the accident last March. Although they survived, their risk of cancer was significantly increased, scientists say.
Even if nuclear accidents and supernova explosions are avoided, natural background radiation on Earth (from sources such as uranium in the soil, cosmic rays and medical devices) increases our chances of getting cancer in any year by 0.025 percent, Caracappa says. This sets a somewhat strange limit on human lifespan.
"The average person... exposed to an average dose of background radiation every year for 4,000 years, in the absence of other factors, will inevitably develop radiation-induced cancer," Caracappa says. In other words, even if we could defeat all diseases and turn off the genetic commands that control the aging process, we still would not live more than 4,000 years.
How much acceleration can we handle?
The ribcage protects our heart from strong impacts, but it is not a reliable protection against the jerks that have become possible today thanks to the development of technology. What acceleration can this organ of ours withstand?
NASA and military researchers have conducted a series of tests in an attempt to answer this question. The purpose of these tests was the safety of space and aircraft structures. (We don't want astronauts to lose consciousness when the rocket takes off.) Horizontal acceleration - a jerk to the side - has a negative effect on our insides, due to the asymmetry of the acting forces. According to a recent article published in the journal Popular Science, horizontal acceleration of 14 g can tear our organs apart from each other. Acceleration along the body towards the head can shift all the blood to the legs. Such a vertical acceleration of 4 to 8 g will render you unconscious. (1 g is the force of gravity that we feel on the earth's surface; 14 g is the force of gravity on a planet 14 times more massive than ours.)
Acceleration directed forward or backward is most beneficial for the body, since it accelerates the head and heart equally. The military's "human braking" experiments in the 1940s and 1950s (which essentially involved a rocket sled moving around Edwards Air Force Base in California) showed that we could brake at an acceleration of 45 g, and still be alive to tell the tale. With this kind of braking, when traveling at speeds above 600 mph, you can stop in a split second after traveling a few hundred feet. At 50 g of braking, experts estimate that we will probably turn into a bag of separate organs.
What environmental changes can we withstand?
Different people are able to withstand different changes in the usual atmospheric conditions, regardless of whether it is a change in temperature, pressure, or oxygen content in the air. The limits of survival are also related to how slowly environmental changes occur, since our bodies are able to gradually adjust oxygen consumption and alter metabolism in response to extreme conditions. But, nevertheless, we can roughly estimate what we are able to withstand.
Most people begin to suffer from overheating after 10 minutes of being in an extremely humid and hot environment (60 degrees Celsius). Establishing limits on death from chilling is more difficult. A person usually dies when their body temperature drops to 21 degrees Celsius. But how long this takes depends on how “used to the cold” a person is, and whether the mysterious, latent form of “hibernation” that is known to sometimes occur has manifested itself.
Survival boundaries are much better set for long-term comfort. According to a 1958 NASA report, humans can live indefinitely in environments whose temperatures range from 4 to 35 degrees Celsius, as long as the latter temperature is at a relative humidity of no more than 50 percent. With lower humidity, the maximum temperature increases, since less moisture in the air facilitates the process of sweating, and thereby cooling the body.
As can be seen from science fiction films in which the astronaut's helmet is opened outside the spacecraft, we cannot survive for long at very low levels of pressure or oxygen. At normal atmospheric pressure, air contains 21 percent oxygen. We will die from suffocation if the oxygen concentration drops below 11 percent. Too much oxygen also kills, gradually causing pneumonia over several days.
We lose consciousness when the pressure drops below 57 percent of atmospheric pressure, which corresponds to an altitude of 4,500 meters. Climbers are able to climb higher mountains as their bodies gradually adapt to the reduced amount of oxygen, but no one can survive long enough without oxygen tanks at altitudes above 7,900 meters.
It's about 8 kilometers up. And there are still almost 46 billion light years left to the edge of the known universe.
Natalie Wolchover
"Life's Little Mysteries"
August 2012
Translation: Gusev Alexander Vladimirovich
In aviation and space medicine, overload is considered an indicator of the magnitude of acceleration affecting a person when moving. It represents the ratio of the resultant moving forces to the mass of the human body.
Overload is measured in units of multiple body weight under terrestrial conditions. For a person located on the earth's surface, the overload is equal to one. The human body is adapted to it, so it is invisible to people.
If an external force imparts an acceleration of 5 g to any body, then the overload will be equal to 5. This means that the weight of the body under these conditions has increased five times compared to the original one.
When a conventional airliner takes off, passengers in the cabin experience a g-force of 1.5 g. According to international standards, the maximum permissible overload value for civil aircraft is 2.5 g.
At the moment the parachute opens, a person is exposed to inertial forces that cause an overload reaching 4 g. In this case, the overload indicator depends on the airspeed. For military parachutists, it can range from 4.3 g at a speed of 195 kilometers per hour to 6.8 g at a speed of 275 kilometers per hour.
The reaction to overloads depends on their magnitude, the rate of increase and the initial state of the body. Therefore, both minor functional changes (a feeling of heaviness in the body, difficulty moving, etc.) and very serious conditions can occur. These include complete loss of vision, dysfunction of the cardiovascular, respiratory and nervous systems, as well as loss of consciousness and the occurrence of pronounced morphological changes in tissues.
In order to increase the resistance of the pilots' body to acceleration in flight, anti-g and altitude-compensating suits are used, which, during overloads, create pressure on the abdominal wall and lower extremities, which leads to a delay in the outflow of blood to the lower half of the body and improves blood supply to the brain.
To increase resistance to acceleration, training is carried out in a centrifuge, hardening the body, and breathing oxygen under high pressure.
When ejecting, rough landing of an airplane or landing by parachute, significant overloads occur, which can also cause organic changes in the internal organs and spine. To increase resistance to them, special chairs are used that have in-depth headrests and secure the body with belts that limit the displacement of the limbs.
Overload is also a manifestation of gravity on board a spacecraft. If under terrestrial conditions the characteristic of gravity is the acceleration of free fall of bodies, then on board a spacecraft the characteristics of overload also include the acceleration of gravity, equal in magnitude to the reactive acceleration in the opposite direction. The ratio of this quantity to magnitude is called the "overload factor" or "overload".
In the acceleration section of the launch vehicle, the overload is determined by the resultant of non-gravitational forces - the thrust force and the aerodynamic drag force, which consists of the drag force directed opposite to the speed and the lift force perpendicular to it. This resultant creates non-gravitational acceleration, which determines the overload.
Its coefficient in the acceleration section is several units.
If a space rocket, under Earth conditions, moves with acceleration under the influence of engines or experiencing environmental resistance, then the pressure on the support will increase, causing an overload. If the movement occurs with the engines turned off in a vacuum, then the pressure on the support will disappear and a state of weightlessness will occur.
When a spacecraft is launched, the astronaut's magnitude varies from 1 to 7 g. According to statistics, astronauts rarely experience overloads exceeding 4 g.
The ability to withstand overloads depends on the ambient temperature, the oxygen content in the inhaled air, the length of time the astronaut spent in weightlessness before acceleration, etc. There are other more complex or less subtle factors whose influence is not yet fully understood.
Under the influence of acceleration exceeding 1 g, an astronaut may experience visual impairment. Acceleration of 3 g in the vertical direction that lasts more than three seconds can cause severe impairment of peripheral vision. Therefore, it is necessary to increase the level of illumination in the compartments of the spacecraft.
During longitudinal acceleration, the astronaut experiences visual illusions. It seems to him that the object he is looking at is moving in the direction of the resulting vector of acceleration and gravity. With angular accelerations, an apparent movement of the object of vision occurs in the plane of rotation. This illusion is called circumgyral and is a consequence of the effects of overload on the organs of the inner ear.
Numerous experimental studies, which were started by the scientist Konstantin Tsiolkovsky, have shown that the physiological effects of overload depend not only on its duration, but also on the position of the body. When a person is in an upright position, a significant part of the blood shifts to the lower half of the body, which leads to a disruption in the blood supply to the brain. Due to the increase in their weight, the internal organs move downwards and cause severe tension on the ligaments.
To weaken the effect of high accelerations, the astronaut is placed in the spacecraft in such a way that the overloads are directed along the horizontal axis, from the back to the chest. This position ensures effective blood supply to the astronaut’s brain at accelerations of up to 10 g, and for a short time even up to 25 g.
When a spacecraft returns to Earth, when it enters the dense layers of the atmosphere, the astronaut experiences braking overloads, that is, negative acceleration. In terms of integral value, braking corresponds to acceleration at start.
A spacecraft entering the dense layers of the atmosphere is oriented so that the braking overloads have a horizontal direction. Thus, their impact on the astronaut is minimized, as during the launch of the spacecraft.
The material was prepared based on information from RIA Novosti and open sources
For some special reason, much attention is paid in the world to the speed of acceleration of a car from 0 to 100 km/h (in the USA from 0 to 60 mph). Experts, engineers, fans of sports cars, as well as ordinary car enthusiasts, with some kind of obsession, constantly monitor the technical characteristics of cars, which usually reveal the dynamics of a car’s acceleration from 0 to 100 km/h. Moreover, all this interest is observed not only in sports cars for which the dynamics of acceleration from a standstill is very important, but also in completely ordinary economy class cars.
Nowadays, the greatest interest in acceleration dynamics is directed towards modern electric cars, which have begun to slowly displace sports supercars with their incredible acceleration speeds from the car niche. For example, just a few years ago it seemed simply fantastic that a car could accelerate to 100 km/h in just over 2 seconds. But today some modern ones have already come close to this indicator.
This naturally makes you wonder: What speed of acceleration of a car from 0 to 100 km/h is dangerous to human health? After all, the faster the car accelerates, the more load the driver who is (sitting) behind the wheel experiences.
Agree with us that the human body has its own certain limits and cannot withstand the endless increasing loads that act and have a certain impact on it during rapid acceleration of the vehicle. Let us find out together what the maximum acceleration of a car can theoretically and practically be withstood by a person.
Acceleration, as we all probably know, is a simple change in the speed of movement of a body per unit of time. The acceleration of any object on the ground depends, as a rule, on gravity. Gravity is a force acting on any material body that is close to the surface of the earth. The force of gravity on the surface of the earth consists of gravity and the centrifugal force of inertia, which arises due to the rotation of our planet.
If we want to be absolutely precise, then 1g human overload sitting behind the wheel of a car is formed when the car accelerates from 0 to 100 km/h in 2.83254504 seconds.
And so, we know that when overloaded in 1g the person does not experience any problems. For example, a production Tesla Model S car (an expensive special version) can accelerate from 0 to 100 km/h in 2.5 seconds (according to the specification). Accordingly, the driver behind the wheel of this car will experience an overload of 1.13g.
This, as we see, is more than the overload that a person experiences in ordinary life and which arises due to gravity and also due to the movement of the planet in space. But this is quite a bit and the overload does not pose any danger to humans. But, if we get behind the wheel of a powerful dragster (sports car), then the picture here is completely different, since we are already seeing different overload figures.
For example, the fastest one can accelerate from 0 to 100 km/h in just 0.4 seconds. As a result, it turns out that this acceleration causes overload inside the car in 7.08g. This is already, as you can see, a lot. Driving such a crazy vehicle you will not feel very comfortable, and all due to the fact that your weight will increase almost seven times compared to before. But despite this not very comfortable state with such acceleration dynamics, this (this) overload is not capable of killing you.
So how then does a car have to accelerate to kill a person (the driver)? In fact, it is impossible to answer this question unambiguously. The point here is the following. Each organism of any person is purely individual and it is natural that the consequences of exposure to certain forces on a person will also be completely different. Overload for some at 4-6g even for a few seconds it will already be (is) critical. Such an overload can lead to loss of consciousness and even death of that person. But usually such overload is not dangerous for many categories of people. There are known cases when overload in 100g allowed a person to survive. But the truth is, this is very rare.