# Why Don't Pencils Explode (Air Pressure)? **URL:** \ **Category:** Factual Questions\ **Created:** [October 17, 2018, 5:54am UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086 "2018-10-17T05:54:35Z")\ **Posts on this page:** 14\ **Page:** 2
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [October 17, 2018, 5:58pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/21 "2018-10-17T17:58:57Z")
While less dramatic, many solids will suffer from out-gassing under high vacuum. Cadmium, Zinc and Magnesium cause problems with a bit of heat and I had lots of problems with my home made vacuum depisiton chambers at below 10^-9 torr. Graphite which makes up most of pencil lead is great once properly degassed. The wood and paint would not fair so well under extended exposure to ultra high vacuum and will degrade over a period of time. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [October 17, 2018, 6:07pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/22 "2018-10-17T18:07:37Z")
> [@DSYoungEsq](#): > > Where, exactly, is this “air” in the apple? Are you talking in the core around the seeds? or are you asserting that an apple has lots of air just floating around inside the apple flesh? Cellulosic materials also contain a lot of water vapor and apples will also out-gas oil and grease vapor, solvents, and organic material. Even most stainless steels will out-gas some carbon monoxide and hydrogen. It all comes down to vapor pressure and chemical potential. ---
**Author:** ![Channing\_Idaho\_Banks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/channing_idaho_banks/32/250_2.png) [@Channing\_Idaho\_Banks](https://boards.straightdope.com/u/Channing_Idaho_Banks)\ **Post date:** [October 17, 2018, 6:19pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/23 "2018-10-17T18:19:45Z")
I’m still waiting to find out what it’s going to take to make this pencil explode. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 17, 2018, 6:32pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/24 "2018-10-17T18:32:15Z")
To be clear, **Riemann** , I posted my guess about air in apples before I saw your definitive cite. I wasn’t doubting you. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [October 17, 2018, 6:40pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/25 "2018-10-17T18:40:43Z")
> [@Channing\_Idaho\_Banks](#): > > I’m still waiting to find out what it’s going to take to make this pencil explode. Well, I don’t think anything is going to make a pencil explode. But it’s a quantitative difference, rather than a qualitative one. Wood does contain a considerable amount of air, and it would experience the same _kind_ of forces from the pressure differential as a milk carton upon rapid decompression. But it’s much stronger than a milk carton and wouldn’t collapse while the air escaped. Is there any kind of very soft wood with high air content (balsa?) that might be marginal? Probably not, but there’s a continuum of various other organic materials with varying air content, permeability and rigidity. As we’ve said, an apple is probably a marginal case, I don’t think we can say with confidence what would happen to an apple upon rapid decompression without experimentation. It might just shrink, it might rupture. ---
**Author:** ![rat\_avatar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rat_avatar/32/255_2.png) [@rat\_avatar](https://boards.straightdope.com/u/rat_avatar)\ **Post date:** [October 17, 2018, 6:41pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/26 "2018-10-17T18:41:15Z")
> [@Channing\_Idaho\_Banks](#): > > I’m still waiting to find out what it’s going to take to make this pencil explode. Sorry but the _Pressure \* Volume per Area per Time_ formula is going to lead to disappointment without serious changes to what is called a pencil. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [October 17, 2018, 6:44pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/27 "2018-10-17T18:44:15Z")
> [@Chronos](#): > > To be clear, **Riemann** , I posted my guess about air in apples before I saw your definitive cite. I wasn’t doubting you. …no worries, actually I posted the extract from that cite without seeing _your_ comment! I had found the cite just within the edit window of my prior post, and was adding an extract in a new comment. ---
**Author:** ![Projammer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/projammer/32/559_2.png) [@Projammer](https://boards.straightdope.com/u/Projammer)\ **Post date:** [October 17, 2018, 7:19pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/28 "2018-10-17T19:19:23Z")
> [@bob\_2](#): > > It works the other way around too. Let all the liquid out of a container without letting air in and unless the container is very strong, it will collapse - [sometimes spectacularly.](https://www.youtube.com/watch?v=Zz95_VvTxZM) That was a planned demonstration. [This one wasn’t.](https://www.youtube.com/watch?v=R_f4MXL4AFo) ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [October 17, 2018, 7:23pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/29 "2018-10-17T19:23:45Z")
> [@Projammer](#): > > That was a planned demonstration. > > [This one wasn’t.](https://www.youtube.com/watch?v=R_f4MXL4AFo) I have a friend who’s car had a defective vacuum release valve in the gas tank, and ended up collapsing the tank as the gas was pumped out of it. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [October 17, 2018, 7:33pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/30 "2018-10-17T19:33:19Z")
Somewhat relevant is the Byford Dolphin decompression tank accident, in which several divers were killed. This involved an explosive decompression from equalized high pressure down to atmospheric pressure, but it’s somewhat analogous. > **[Byford Dolphin](https://en.wikipedia.org/wiki/Byford_Dolphin)** > > Byford Dolphin was a semi-submersible, column-stabilised drilling rig operated by Dolphin Drilling, a Fred Olsen Energy subsidiary. It drilled seasonally for various companies in the United Kingdom, Danish and Norwegian sectors of the North Sea. It was registered in Hamilton, Bermuda. > The rig suffered some serious accidents, most notably an explosive decompression in 1983 that killed four divers and one dive tender, as well as badly injured another dive tender. > As of March 2023, the Byford Do... If an experiment aims to test _rapid_ pressure drop, on Earth it’s much easier to set up a drop from high so standard than from standard to vacuum. This event involved a drop from 9 atmospheres to 1, a much greater difference than from 1 to zero. If we wanted to test an apple, I think the simplest way would be to raise the pressure slowly to 2 atm, then rapidly decompress to 1 atm. That should simulate what happens to an apple on a spaceship if it ruptures to vacuum. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [October 17, 2018, 10:03pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/31 "2018-10-17T22:03:42Z")
> [@Riemann](#): > > … > > If we wanted to test an apple, I think the simplest way would be to raise the pressure slowly to 2 atm, then rapidly decompress to 1 atm. That should simulate what happens to an apple on a spaceship if it ruptures to vacuum. The problem is - that might hint what happens from 1 to 0 psi; but ignores the secondary effect, where the water in the apple will vaporise at close to 0psi at room temperature. There are some pretty spectacular results that can be obtained by converting liquid to gas without allowing an escape mechanism. Or, if the item is flexible, it expands like a balloon. (An offhand comment in the old movie “My Bodyguard”, kid in ceramics class… “What are you making?” “A hand grenade. A thick lump of clay. When the stuff is fired, the outer skin will hold in the steam until it explodes…” Much later in the movie - teacher says “Unfortunately, one of the items in the kiln exploded and wrecked all the ceramics pieces…” ) ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [October 17, 2018, 10:17pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/32 "2018-10-17T22:17:06Z")
> [@md2000](#): > > The problem is - that might hint what happens from 1 to 0 psi; but ignores the secondary effect, where the water in the apple will vaporise at close to 0psi at room temperature… Point taken. From an engineering perspective, presumably the way to simulate rapid decompression to vacuum would be to enclose a small chamber at 1 atmostphere inside a much larger evacuated chamber, and open the small chamber? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 17, 2018, 10:31pm UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/33 "2018-10-17T22:31:59Z")
> [@](#): > > Quoth **md2000** : > > There are some pretty spectacular results that can be obtained by converting liquid to gas without allowing an escape mechanism. Yup. Some of those spectacular results are good with salt and melted butter. ---
**Author:** ![Colophon](https://avatars.discourse-cdn.com/v4/letter/c/f05b48/32.png) [@Colophon](https://boards.straightdope.com/u/Colophon)\ **Post date:** [October 18, 2018, 11:02am UTC](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086/34 "2018-10-18T11:02:09Z")
> [@Projammer](#): > > That was a planned demonstration. > > [This one wasn’t.](https://www.youtube.com/watch?v=R_f4MXL4AFo) For a video entitled “Septic Vacuum Tank Truck Implosion”, that was kind of disappointingly lacking in poop. [Previous page](https://boards.straightdope.com/t/why-dont-pencils-explode-air-pressure/823086.md?page=1)