What is the real meaning of a pressure between 0 and 1 bar?

[ZdMh]

When we increase the pressure value to for ex 3, 5, ...100 bars the pressure increases. When the pressure is 1 we called it atmospheric pressure. My question is what's happening when the pressure is between 0 and 1; at 0 it's a vacuum. The idea is that I can't imagine it: if I am in a room between with pressure between 0 and 1, will I feel anything strange(and maybe dangerous) when it decreases under 1 or let me ask in an example more clearly if I have 10^6 atom of hydrogen in volume V. If I increase the pressure to 3 bars, it becomes V'<V right? therefore if the pressure is between 0 and 1 it will expand into a volume V'>V, meaning will expand faster, and how is that make a Vacuum on 0 bar.

 

[Baluncore]

https://en.wikipedia.org/wiki/Atmospheric_pressure

 

[Chestermiller]

A pressure between 0 and 1 bar is called a "partial vacuum." You have already experienced pressures < 1 bar, when, for example, there is a low pressure in the atmosphere (such as when there is a rain storm present). However, if the pressure becomes very low, such as in space, you need to wear a space suit to avoid detrimental effects.

 

[jbriggs444]

I am in a room between with pressure between 0 and 1, will I feel anything strange

I've hiked altitudes of up to 12,000 feet (a bit under 4000 meters) in Rocky Mountain National Park as a child. It did not feel like anything special. At those altitudes, atmospheric pressure dips to about 0.67 bar.

No sensation of shortness of breath. No tendency to breathe rapidly. No excessive cooling from sweat. Just an ordinary day.

One of the benefits of having parents who were both school teachers was long camping trips to various parts of the country every summer growing up.

 

[sophiecentaur]

I've hiked altitudes of up to 12,000 feet (a bit under 4000 meters) in Rocky Mountain National Park as a child. It did not feel like anything special. At those altitudes, atmospheric pressure dips to about 0.67 bar.

No sensation of shortness of breath. No tendency to breathe rapidly. No excessive cooling from sweat. Just an ordinary day.

One of the benefits of having parents who were both school teachers was long camping trips to various parts of the country every summer growing up.

“One of the benefits” of being young is you probably have stamina. Sport parachuting is limited to 10k feet (3km) because that’s high enough to start to affect brain function.

(No reason not to be posting on PF, folks.)
Spending long periods at altitude [Edit: alters causes ] blood composition, tho and you can deal with it.

 

[JT Smith]

Walking around at 12K seems fine to many people, not just young ones. If you actually measure breathing rate and heart rate you'd find that they are both higher. And if you tried running up hill or doing something strenuous, even as a little kid, you'd notice the difference.

 

[JT Smith]

“Sport parachuting is limited to 10k feet (3km) because that’s high enough to start to affect brain function."

Reference?

I used to be a skydiver. The two drop zones I visited had normal exit altitudes of 12,500' and 13,500'. I think the highest I jumped was from 14,000'. Above 15K I think you have to have oxygen on board for the skydivers. I think there is a limit for sport skydiving but it's somewhere approaching 20K.

 

[Baluncore]

Above about 60,000 feet (18 km) you dehydrate rapidly because the pressure is only 0.062 bar, so the water in your body boils at body temperature.
https://en.wikipedia.org/wiki/Armstrong_limit

 

[anorlunda]

No sensation of shortness of breath. No tendency to breathe rapidly. No excessive cooling from sweat.

Not even ear popping?

 

[jbriggs444]

Not even ear popping?

You get ear popping from changes of altitude. Staying at 12,000 feet does nothing to make ears pop. As you know, ear popping is the result of the inner ear venting suddenly through the Eustachian tubes so that pressure is equalized.

On the way up the mountains (by automobile) and on the way back down, my ears popped multiple times, yes. One quickly learns to dry-swallow to get this to happen.

 

[anorlunda]

On the way up the mountains (by automobile) and on the way back down, my ears popped multiple times, yes

That was the OP's question I think. What will I feel when the pressure goes down?

 

[jbriggs444]

That was the OP's question I think. What will I feel when the pressure goes down?

Ahh, "what will I feel while pressure is decreasing?" rather than "what will I feel after pressure has decreased?". I had read it the latter way. But perhaps you are right.

For me, the sensation in the ears and the accompanying loss of auditory acuity is identical regardless of whether the pressure change is an increase or a decrease. Once both ears pop, everything returns to normal. I assume the relevant feature is tension on the eardrum. The direction of the net pressure responsible for the increased tension is not very relevant.

 

[sophiecentaur]

I used to be a skydiver.

I did a course in the early 70's. The instructor was Army Parachute Association and jumped with the Red Devils, I remember. The British Sport Parachute Association limited sports jumping to 10K fair. What I have read this morning suggests 10 to 15k is recent practice. Over 15k requires skydivers to use Oxygen, apparently.

I wonder if you skydived in the US. They had much easier rules there when I looked into it. People used to take US holidays and come back fully certificated after a short time but it could take months and months here. I dropped out because of so many abortive trips to remote jump sites.

 

[JT Smith]

I wonder if you skydived in the US. They had much easier rules there when I looked into it.

Yes, in California in the 1990s. Things were pretty relaxed. We used to pack into a DC-3, forty of us layered in there on the floor like sardines. That old plane would blow an engine every so often. Good thing it had two.

My ears always pop easily going up, whether in a car or a plane. But going down they stick and I have to yawn or swallow to get them to pop.

Once I was a little congested and one of my ears didn't pop on a skydive. It only takes a minute to fall 10,000 feet and the rising pressure in my ear was really painful. It didn't pop after I landed either, not for days. After that experience I often used a nasal decongestant spray before a jump.

 

[russ_watters]

Reference?

I used to be a skydiver. The two drop zones I visited had normal exit altitudes of 12,500' and 13,500'. I think the highest I jumped was from 14,000'. Above 15K I think you have to have oxygen on board for the skydivers. I think there is a limit for sport skydiving but it's somewhere approaching 20K.

I've done exactly one skydive, from 12,500 ft. At altitude, before the jump, the instructors said I was white (I'm always white?) and gave me oxygen. Oxygen is required at that altitude for the pilots if they are going to be there over 30min. https://www.aopa.org/training-and-s...and-technique/operations/high-altitude-flying

It does matter how fast you go up in elevation. If you have a chance to acclimatize, people fare better. I skied at Keystone (summit 12,400) without issue.

 

[A.T.]

I've hiked altitudes of up to 12,000 feet (a bit under 4000 meters) in Rocky Mountain National Park as a child. It did not feel like anything special. At those altitudes, atmospheric pressure dips to about 0.67 bar.

No sensation of shortness of breath. No tendency to breathe rapidly. No excessive cooling from sweat. Just an ordinary day.

Also: The capitol of Bolivia is at 3600-3800m. And there are many smaller settlements with permanent inhabitants even higher than that. People have climbed the Mount Everest (8,848.86 m / 29,031.7 ft) without oxygen support.

 

[sophiecentaur]

Also: The capitol of Bolivia is at 3600-3800m. And there are many smaller settlements with permanent inhabitants even higher than that. People have climbed the Mount Everest (8,848.86 m / 29,031.7 ft) without oxygen support.

It all goes to show how adaptable humans can be. Spending time and training at high altitude is a technique used by competitive runners. The temporary high concentration of red blood cells tends to give them an advantage in races near sea level.
People who have climbed Mt Everest without oxygen must be serious outliers. You can easily die of 'Mountain Sickness' if you are not extremely fit. High altitude flying is much more common than mountaineering and even passengers, sitting in their seats and taking it easy, need pressurised cabins to be sure of remaining fit and well on their journey.

At the other extremes of pressure, divers have to 'decompress' after spending time at lower than 10m (+1Bar). Compression sickness and Caisson disease present serious problems after extended times (working hard) at only moderate depths. Special gas mixes are needed for working under 'saturation diving' conditions.

I read that even operating theatre staff can suffer from the effects of long term exposure to positive pressure ventilation. I looked for a link but SARS and Covid 19 seem to dominate all the google hits I could find just now.

Time is a big factor at depth. Submarine crews have escaped from depths up to 200m with escape suits which allow them to surface at a safe rate and have no serious ill effects after the relatively short time at depth. (You just have to keep breathing out as the air is expanding all the time and never try to hold your breath.)

 

[JT Smith]

Human adaptation has a limit. There is an elevation above which you don't find people living for extended periods. And those who live close to that limit tend to be adapted in an evolutionary way: bigger chests, higher lung capacity, and other genetic advantages.

An interesting high altitude effect is periodic breathing during sleep. Apparently the human body has two sensors to control breathing rate. One measures pH, basically the CO2 content, and the other oxygen saturation. At altitude your respiration rate increases because of the reduced oxygen content of the air. But breathing faster blows out more CO2. So the pH sensor tells your brain to stop breathing. Then the oxygen level falls and the other sensor tells the brain to breath.

It's very common to notice that your sleeping tent mate's breathing at altitude speeds up and slows down, sometimes even stopping. Most of the time it's no problem. But for some people the oscillations are extreme enough to result in repeated bouts of apnea and gasping. Then it disturbs the person's sleep.

 

[sophiecentaur]

But breathing faster blows out more CO2. So the pH sensor tells your brain to stop breathing.

A great post, overall and this quote reminds me of the dangers of hyperventilating to achieve long times under water. You can get hypoxia at the end of a free dive but by that time it's often too late and you just die without realising you actually needed to breathe.

 

[A.T.]

It all goes to show how adaptable humans can be. Spending time and training at high altitude is a technique used by competitive runners. The temporary high concentration of red blood cells tends to give them an advantage in races near sea level.

People from those high altitude areas have actually developed genetic modifications over time. And interestingly it's different adaptation mechanisms in different regions:

 

[sophiecentaur]

I'm not sure where the OP hoped this thread would take us but there have be a useful number of informative posts on the way.