How much psi can a human body withstand?

Answer 1

Depends whether it is sustained force or not.

Note1: In this answer 'g' is used to refer to g-force not grams

Note2: The g-force of an object is its equal to its acceleration relative to free-fall. This means that an object on earth that is not falling or rising (relative to gravity) is experiencing 1g (0g being weightless). This in turn also means that 1g is equal to your weight etc

Human tolerances depend on the magnitude of the g-force, the length of time it is applied, the direction it acts, the location of application, and the posture of the body. The human body is flexible and deformable, particularly the softer tissues. A hard slap on the face may briefly impose hundreds of g locally but not produce any real damage; a constant 16 g for a minute, however, may be deadly.

Vertical axis g-force

Aircraft, in particular, exert g-force along the axis aligned with the spine. This causes significant variation in blood pressure along the length of the subject's body, which limits the maximum g-forces that can be tolerated.

In aircraft, g-forces are often towards the feet, which forces blood away from the head; this causes problems with the eyes and brain in particular. As g-forces increase a Brownout can occur, where the vision loses hue. If g-force is increased further tunnel vision will appear, and then at still higher g, loss of vision, while consciousness is maintained. This is termed "blacking out". Beyond this point loss of consciousness will occur, sometimes known as "G-LOC" ("loc" stands for "loss of consciousness"). Beyond G-LOC, if g-forces are not quickly reduced, death can occur.

While tolerance varies, with g-forces towards the feet, a typical person can handle about 5 g (49m/s²) before g-loc, but through the combination of special g-suits and efforts to strain muscles-both of which act to force blood back into the brain-modern pilots can typically handle 9 g (88 m/s²) sustained (for a period of time) or more.

Resistance to "negative" or upward g's, which drive blood to the head, is much lower. This limit is typically in the −2 to −3 g (−20 m/s² to −30 m/s²) range. The subject's vision turns red, referred to as a red out. This is probably because capillaries in the eyes swell or burst under the increased blood pressure.

Horizontal axis g-force

The human body is better at surviving g-forces that are perpendicular to the spine. In general when the acceleration is forwards, so that the g-force pushes the body backwards (colloquially known as "eyeballs in") a much higher tolerance is shown than when the acceleration is backwards, and the g-force is pushing the body forwards ("eyeballs out") since blood vessels in the retina appear more sensitive in the latter direction.

Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.

Answer 2

The first limit is oxygen toxicity.

Partial pressures of oxygen more than 1 atm are toxic

so breathing air, the limit is 1 atm/20% O2 = 5 atm = 75 psi = water depth of ~ 150 feet

However all you have to do is reduce the concentration of oxygen in whatever gas you are breathing.

The next limit is nitrogen narcosis.

Under high pressure nitrogen acts like nitrous oxide.

Too high a pressure and it will stop your breathing.

Partial pressures more than 10 atm are lethal.

So the limit would be ~ 10 atm = 150 psi = water depth of ~ 300 feet

However all you have to do is reduce the concentration of nitrogen in whatever gas you are breathing

(for example replace it with helium).

Helium-oxygen mixtures have been used to ~1000 foot depth.

(interesting side note, too little nitrogen is also annoying, causes headache and neurological problems

in short we require a bit of nitrogen narcosis in our everyday lives, so a small amount of nitrogen

in the mix significantly improves comfort)

The human body is essentially water and almost incompressible.

In theory helium-oxygen-nitrogen mixtures can be used to the deepest depths of the ocean (~30,000 feet = 1000 atm = 15000 psi).

In practice, mildly annoying things happen at depths > 3000 feet (100 atm, 1500 psi).

1) evaporation slows down, in particular the saliva does not evaporate from your lips and you begin to drool a lot.

2) exceeding 1000 atm, air exceeds the density of water and it starts to become a bit of effort to breath. A practical upper limit

due to air density in the lungs is about 2000 atm = 30,000 psi = 60,000 feet water depth (deeper than any ocean on earth).

A fix for this would be a heart/lung machine to inject oxygen/nitrogen directly into the bloodstream.

PS, a practical application of this would be to have the person connected to the heart/lung machine floating in water.

In this condition they could withstand an incredible 1,000 g! (the upper limit due to sedimentation of cellular organelles),

A final limit is the point in which barochemistry (changing reaction rates due to pressure) become important.

The "chemical energy density" of matter is an equivalent pressure of about 1.5 million atmospheres.

Pressures from 1-10% of this would be expected to alter metabolism significantly. So the absolute upper limit

is somewhere between 15,000 and 150,000 atm.

Answer 3

The quick answer is: we don't know, because we have not tried it, yet. But Probably, spending too much time at two or three thousand atmospheres would do you some serious harm. Six thousand atmospheres would probably kill one rather fast. But in any case death would only be caused by mechanical chemical-denaturation of some of your more fragile proteins. So, you would feel real sick and then die, but you would not perceive any sense of a crushing pressure.

This is because typical earthly pressures on solids and liquids cause little or no measurable compression -- they do not appreciably change their density, unlike with gases.

The current record for human tolerance is 2300 feet of simulated sea water (68 atmospheres) by persons in a hyperbolic chamber. See also http://en.wikipedia.org/wiki/Saturation_diving

High Pressure Processing (HPP) is a method of food processing where food is subjected to elevated pressures (up to 87,000 pounds per square inch or approximately 6,000 atmospheres or 39 miles of water). Pressure inactivates most vegetative bacteria at pressures above 60,000 pounds per square inch or 4,083 atmospheres - or 26 miles of water.

The deepest slot in the deepest trench of the ocean is less than seven miles deep. That's 36,200 feet, compared to the 2,300 foot current record. It's no where near the 26 miles needed to kill most bacteria, but could it kill people? Maybe.

So, in the movie "The Abyss" they did a pretty good job with the science of deep diving.

Answer 4

The average Human body can withstand about 50 PSI blast pressure meaning sudden impact. As far as sustained pressure the human body can withstand as much as 400 PSI providing it is gradually increased to this amount.

Answer 5

Pulmonary system may be fully working till a pressure of 697 hPa (typical sea level pressure is 1013 hPa) which is at a standard altitude of 10,000 feet. At or over this altitude, you may suffer of hypoxia because of the partial pressure of oxygen in your lungs which is too low to fix the haemoglobin in your blood. This may occur at a lower altitude for smokers. Symptoms are getting worse as you get higher.

An explosive depressurisation of the cabin in a typical jetliner flying at an altitude of 40,000 feet will give you less than 5 seconds of consciousness.

The body may withstand pressure up to 30 ATM when diving, again because of the pressure against your lungs which prevents you from breathing normally with an oxygen bottle.

Ears should resist at such a pressure thanks to different techniques.

Organs should as well resist as far as I know.

The most dangerous is cavitation, when swimming up to the surface. Nitrogen (70% of the atmosphere) is also present in your blood and saturated. As pressure decrease, bubbles may create and cause pain and injuries.

Answer 6

There is no air pressure, as such, in the human body. We are at an equilibrium with the atmospheric pressure, which is a little under 15psi. This is why astronauts need space suits when performing a space walk. Their suit maintains the internal pressure of the suit at about 15psi. If the human body were directly exposed to space (near vacuum), the fluids in the body would boil and out-gas into space.

Answer 7

Around 1 Amp of electricity can kill a person instantly any thing less than that can cause fatal heart rhythm's (ventricular fibrillation or ventricular tachycardia), voiding of the bowels and the batter, loss of consciousness etc.

Answer 8

it is said that the pressure exerted by atmosphere on the body is same as the pressure exerted when 2 baby elephant stands on your head