# What did I see?

**URL:** <https://boards.straightdope.com/t/what-did-i-see/372850>\
**Category:** Factual Questions\
**Created:** [September 15, 2006, 4:11pm UTC](https://boards.straightdope.com/t/what-did-i-see/372850 "2006-09-15T16:11:19Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![FlyingRamenMonster](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@FlyingRamenMonster](https://boards.straightdope.com/u/FlyingRamenMonster)\
**Post date:** [September 15, 2006, 4:11pm UTC](https://boards.straightdope.com/t/what-did-i-see/372850/1 "2006-09-15T16:11:19Z")

</div>

There’s a petrol station on my bus route that’s being built. The other day I saw a large crane lowering something into the station (I couldn’t tell if it was going into the ground or into a building). It was kind of bulbous, like an egg but more like a [fat man](http://en.wikipedia.org/wiki/Fat_Man) bomb. What is it?

---

<div class="post-metadata">

**Author:** ![Leaffan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/leaffan/32/299_2.png) [@Leaffan](https://boards.straightdope.com/u/Leaffan)\
**Post date:** [September 15, 2006, 4:22pm UTC](https://boards.straightdope.com/t/what-did-i-see/372850/2 "2006-09-15T16:22:50Z")

</div>

An underground holding tank for the petrol?

---

<div class="post-metadata">

**Author:** ![The\_Eater\_in\_the\_Round](https://avatars.discourse-cdn.com/v4/letter/t/71c47a/32.png) [@The\_Eater\_in\_the\_Round](https://boards.straightdope.com/u/The_Eater_in_the_Round)\
**Post date:** [September 15, 2006, 4:23pm UTC](https://boards.straightdope.com/t/what-did-i-see/372850/3 "2006-09-15T16:23:24Z")

</div>

The tank(s) that will hold the fuel that the station pumps draw from. When the petrol delivery driver shows up you can watch him take off the “lid” to these tanks, a circular metal cap in the cement driveway, and drop a long pole into those tanks to measure how empty they are.

---

<div class="post-metadata">

**Author:** ![FlyingRamenMonster](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@FlyingRamenMonster](https://boards.straightdope.com/u/FlyingRamenMonster)\
**Post date:** [September 15, 2006, 4:33pm UTC](https://boards.straightdope.com/t/what-did-i-see/372850/4 "2006-09-15T16:33:05Z")

</div>

Oh, right. I always assumed those were rectangular for some reason.

---

<div class="post-metadata">

**Author:** ![Airman\_Doors\_USAF](https://avatars.discourse-cdn.com/v4/letter/a/e36b37/32.png) [@Airman\_Doors\_USAF](https://boards.straightdope.com/u/Airman_Doors_USAF)\
**Post date:** [September 15, 2006, 4:48pm UTC](https://boards.straightdope.com/t/what-did-i-see/372850/5 "2006-09-15T16:48:50Z")

</div>

> [@FlyingRamenMonster](#):
>
> Oh, right. I always assumed those were rectangular for some reason.

A rectangle would be the worst shape for that sort of thing. Tanks that either hold pressure or may have to resist changes in pressure are always round or cylindrical, a sphere being the best shape to resist such pressure and a cylinder simply being an elongated sphere. If it were some sort of square it would be more likely to rupture where the faces meet because while they may handle external loads well the joints will face considerable loads under internal (outward) pressure. Submarines, fire bottles, propane tanks, airplanes, soda cans, all of them are cylindrical for that reason.