# Vacu-sealing People **URL:** \ **Category:** Factual Questions\ **Created:** [April 9, 2003, 2:54am UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476 "2003-04-09T02:54:39Z")\ **Posts on this page:** 10\ **Page:** 2
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [April 10, 2003, 2:46pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/21 "2003-04-10T14:46:57Z")
> [@](#): > > \*Originally posted by Padeye \* > A pressure difference of as little as 1psi would put a load of several hundred pounds on a person’s abdomen making it impossible to breathe. I think you are overlooking the point in the OP that the person would have a channel to outside air into their lungs, causing the internal pressure of the person’s body to be equal to the ambient air pressure. Although I’m not sure–I’m open to hearing further reasoning on this. > [@](#): > > There is another way to try this experiment that several foolhardy people do; they try to breathe with a garden hose while at the bottom of a swimming pool and find it impossible to doe so due to water pressuer at even a shallow depth I believe the claim but not sure I understand why this is so. Is it because the water pressure at that depth overwhelms the air pressure in the hose, and your lungs can’t push out against the water pressure sufficiently to draw in the air? I have seen photos of “mermaid shows” where swimmers underwater breath from hoses, but I presume that the air is delivered under pressure. And lastly–for the purposes of the physics of it, is being in an evacuated bag with a straw in your mouth really the equivalent of being subjected to the pressure of, for example, being deep underwater? (I think not, note my earlier post, but I welcome corrections.) ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 10, 2003, 3:07pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/22 "2003-04-10T15:07:24Z")
I don’t think it is equivalent; normally, air pressure (~14psi) is balanced by an equal pressure from inside the body, when you dive underwater, but breathe through a (non-pumped) hose to the surface, your body is subjected to ~14psi **plus** the weight of the water above you, but the air you are breathing isn’t. Evacuating the spare air in the space between an effectively non-porous object and the plastic bag in which it resides cannot create any new pressure on the body (aside from the elasticity of the plastic) - it just enables the natural air pressure to push the plastic snugly against the skin; the balance of pressure is maintained. ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [April 10, 2003, 4:03pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/23 "2003-04-10T16:03:07Z")
Exactly, which is what I said at the outset. Divers have absolutely no problem breathing underwater with scuba equipment because the gas mixture they’re breathing is higher than the water perssure exerted on them. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [April 10, 2003, 5:45pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/24 "2003-04-10T17:45:46Z")
I stand corrected on the vacuum packed Gimp being able to breathe. After some thought I realize the error in my logic. I still think it may not be easy to breathe if there is significant vacuum but this may be more to trying to stretch the membrane holding him down. Someone needs to do some research on this. > [@](#): > > \*Originally posted by Mangetout \* > \*\*Are you sure that this effect isn’t at least partly due to the porous nature of the wood - properly dried wood contains air between the fibres, this can be evacuated, causing a much greater pressure differential. > > for example, I’m certain that you could vacuum-pack an inflated balloon and it would not shrink because you are not pumping out the air _from inside it_, however, if you were to take a sphere made of thin (but rigid) plastic and drill some holes in it, it would become possible to evacuate the gaseous contents of the sphere and vacuum-packing it would crush it. \*\* It may seem like a paradox but I don’t think the porosity of wood has anything to do with it. I think the perception comes from how we’re used to atmopheric pressure. Try this on for size. Take three slabs of non-pourus rigid material. Leave one bare, cover one with a sealing coat of polyurethane and put one in a vaccum bag and evacuate all the air. All three have 1 atmophere of pressure exerted on the surface. What’s the difference between the painted on coating and the vacuum bag? None really aside from the fact that the polyurethane probably has a molecule level bond to the slab. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 10, 2003, 6:53pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/25 "2003-04-10T18:53:29Z")
Certainly it does seem a stretch that the air from within the structure of the wood could be easily vented, but I suppose over time it would; this wouldn’t make the outdie pressure any greater, but the bag would try to ‘push’ into the minute cracks in the surface, which in itself would mean that the bag is ‘tighter’. I am certain though that if you took (say) two metal cans with airtight lids, drilled holes in one of them and vacuum-packed them both (individually), the one with holes in would be crushed, the one without would not. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [April 10, 2003, 7:11pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/26 "2003-04-10T19:11:11Z")
> [@](#): > > _Originally posted by Rusalka_ > I worry why you would want to do something like this? Sealing someone in a bag like this would definitely KILL them, even with an “air straw”. I assumed it was for freshness. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [April 10, 2003, 7:15pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/27 "2003-04-10T19:15:26Z")
I don’t know about wood for composite construction, vacuum bagging is done to squeeze the epoxy from the cloth. You apply layers of carbon or fiberglass cloth soaked in epoxy onto a mold, and cover the whole thing with a plastic bag. When you connect a vacuum pump (you need a real pump, not a vacuum cleaner) the lowered air pressure pulls the epoxy out of the cloth. It isn’t the plastic sheet pushing on the mold - there is no force acting on the mold itself. With wood, I think **Mangetout** is correct in saying that it’s the porous nature that makes it work. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [April 10, 2003, 7:21pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/28 "2003-04-10T19:21:03Z")
Er, that should have been “I don’t know about wood, but for compsite…” Also I should clarify that the goal is not to remove all the epoxy, but to remove the excess and leave just enough to keep the fiber together. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 10, 2003, 7:31pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/29 "2003-04-10T19:31:50Z")
> [@](#): > > \*Originally posted by scr4 \* > **When you connect a vacuum pump (you need a real pump, not a vacuum cleaner) the lowered air pressure pulls the epoxy out of the cloth. It isn’t the plastic sheet pushing on the mold - there is no force acting on the mold itself.** I don’t think that is correct; there is no such thing as ‘suck’\* - what is happening is that the lowered air pressure inside the system allows the normal atmospheric pressure _outside_ to press down on it and squeeze it - the plastic sheet really is pushing, because the atmosphere is pushing it. Someone will link to Cecil’s spaghetti article now, I’m sure. ---
**Author:** ![Padeye](https://avatars.discourse-cdn.com/v4/letter/p/a9a28c/32.png) [@Padeye](https://boards.straightdope.com/u/Padeye)\ **Post date:** [April 10, 2003, 9:47pm UTC](https://boards.straightdope.com/t/vacu-sealing-people/167476/30 "2003-04-10T21:47:39Z")
A difficult concept to grasp. Vacuum is not a thing but lack of a thing. Vacuum can no more exert a force than can “dark” or “cold.” Dark should be pretty obvious. No one believes the old gag of a flashlight (torch for UK dopers) works by sucking up dark. “Cold” doesn’t do anything but heat going from a hot place to a colder place can. This is why the second law of thermodynamics is far harder to understand than it appears. [Previous page](https://boards.straightdope.com/t/vacu-sealing-people/167476.md?page=1)